Jeong-Yeol Yoon

Interests

Research

Biosensor, Food Safety, Lab-on-a-Chip, Organ-on-a-Chip

Teaching

Biosensor, Biomaterial, Nanotechnology

Courses

Scholarly Contributions

Books

• Yoon, J. (2022). Tissue Engineering: A Primer with Laboratory Demonstrations. Cham: Springer. doi:https://doi.org/10.1007/978-3-030-83696-2
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  Tissue Engineering: A Primer with Laboratory Demonstrations concisely covers the fundamental basics of tissue engineering. A series of simple, low-cost, and easy-to-implement laboratory modules are included in each chapter, along with experimental results with actual images and data, and a set of questions and discussion topics for each laboratory exercise. The textbook is appropriate for upper-undergraduate and graduate-level courses in cell and tissue engineering. The inclusion of images and data for all laboratory exercises also makes the book a valuable tool for scientists and engineers to learn the concepts in a hands-on and visual manner and lay a foundation to build their experiments towards their research and commercial development. ​Concisely covers the most up-to-date aspects of tissue engineering; Provides step-by-step learning of all necessary concepts; Includes simple, low-cost, and easy-to-implement laboratory exercises.
• Yoon, J., & Yoon, J. (2020). Smartphone Based Medical Diagnostics. London, San Diego, Cambridge, Oxford: Elsevier.
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  Editor and author of first three chapters (out of eleven).Smartphone Based Medical Diagnostics provides the theoretical background and practical applications for leveraging the strengths of smartphones toward a host of different diagnostics, including, but not limited to, optical sensing, electrochemical detection, integration with other devices, data processing, data sharing and storage. The book also explores the translational, regulatory and commercialization challenges of smartphone incorporation into point-of-care medical diagnostics and food safety settings.
• Yoon, J. (2016). Introduction to Biosensors: From Electric Circuits to Immunosensors, Second Edition. Springer. doi:10.1007/978-3-319-27413-3
• Yoon, J. (2013). Introduction to Biosensors: From Electric Circuits to Immunosensors. New York, NY: Springer.
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  Whole book is written by Jeong-Yeol Yoon.ISBN: 978-1-4419-6021-4

Chapters

• Kaarj, K., & Yoon, J. (2023). Loop-Mediated Isothermal Amplification on Paper Microfluidic Chips for Highly Sensitive and Specific Zika Virus Detection Using Smartphone. In Clinical Applications of Nucleic Acid Amplification(pp 307-323). Humana Press. doi:https://doi.org/10.1007/978-1-0716-2950-5_18
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  Zika virus (ZIKV) infection may cause serious birth defects and is a critical concern for women of child-bearing age in affected regions. A simple, portable, and easy-to-use ZIKV detection method would enable point-of-care testing, which may aid in prevention of the spread of the virus. Herein, we describe a reverse transcription isothermal loop-mediated amplification (RT-LAMP) method that detects the presence of ZIKV RNA in complex samples (e.g., blood, urine, and tap water). Phenol red is the colorimetric indicator of successful amplification. Color changes based on the amplified RT-LAMP product from the presence of viral target are monitored using a smartphone camera under ambient light conditions. A single viral RNA molecule per μL can be detected in as quickly as 15 min using this method with 100% sensitivity and 100% specificity in blood and tap water, while 100% sensitivity and 67% specificity in urine. This platform can also be used to identify other viruses including SARS-CoV-2 and improve the current state of field-based diagnostics.
• Dieckhaus, L., Park, T. S., & Yoon, J. (2021). Smartphone Based Paper Microfluidic Immunoassay of Salmonella and E. coli. In Salmonella: Methods and Protocols, Third Edition(pp 83-101). New York: Springer. doi:https://doi.org/10.1007/978-1-0716-0791-6_9
• Fronczek, C. F., & Yoon, J. (2016). Detection of Foodborne Pathogens Using Biosensors. In Antimicrobial Food Packaging(pp 153-166). Academic Press (Elsevier). doi:10.1016/B978-0-12-800723-5.00012-7
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  To prevent the outbreaks of foodborne diseases, early detection of common pathogens is necessary, using field deployable biosensors. In this chapter, traditional laboratory-based assays are discussed: culture plating and colony counting, enzyme-linked immunosorbent assay (ELISA), and polymerase chain reaction (PCR). Subsequent efforts in making these laboratory assays into field deployable biosensors are discussed, specifically using the lab-on-a-chip (LOC) platforms, paper microfluidics, as well as the use of smartphones.
• Harshman, D. K., & Yoon, J. (2016). Wire-Guided Droplet Manipulation for Molecular Biology. In Microfluidic Methods for Molecular Biology(pp 235-252). Springer. doi:10.1007/978-3-319-30019-1_12
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  Wire-guided droplet manipulation (WDM) is a simple method of manipulating liquid droplets in a hydrophobic environment to conduct experiments, reactions, and assays. In WDM, a wire (or needle tip) manipulates microliter-sized liquid droplets within an immiscible liquid or on a hydrophobic surface. The attributes of this format for liquid handling address some of the challenges facing the use of conventional techniques. Specifically, WDM provides solutions for development of automated, sample-to-answer, point-of-care systems with potential applications in medicine, life science research, forensics, veterinary diagnostics, and disease control. The widespread applicability of this technique is due to its inherent simplicity, stemming from the attractive force between the droplet and the wire. The physics of this interaction will be explained in this chapter. WDM can be applied to standard protocols and is easily reprogrammable for different liquid handling applications. Dilution, mixing, centrifugation, and thermocycling have all be automated by WDM [1]. If desired, the principles of droplet manipulation can be easily integrated into the common scientific automation strategy, using commercially available robotic pipetting systems. WDM is automatable, reprogrammable, easy to use, and robust. These are essential features of rapid, all-in-one, sample-to-answer systems to be used at the point-of-care. The applications of WDM within molecular biology that have been demonstrated include DNA extraction (lysing, precipitation, washing and rehydration), nanoparticle surface deposition for fabrication of a protein nanoarray, immunoassay, PCR thermocycling, and real-time PCR.
• Liang, P., Park, T. S., & Yoon, J. (2016). Light Scattering Based Detection of Food Pathogens. In Light Scattering Technology for Food Property, Quality and Safety Assessment(pp 429-444). Taylor & Francis. doi:10.1201/b20220-17

Journals/Publications

• Kim, S., Sosnowski, K., Hwang, D. S., & Yoon, J. (2024). Smartphone-Based Microalgae Monitoring Platform Using Machine Learning. ACS ES&T Engineering, 4(1), 186-195. doi:https://doi.org/10.1021/acsestengg.3c00261
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  There is a growing demand for microalgae monitoring techniques since microalgae are one of the most influential underwater organisms in aquatic environments. Specifically, such a technique should be hand-held, rapid, and easily accessible in the field since current methods (benchtop microscopy, flow cytometry, or satellite imaging) require high equipment costs and well-trained personnel. This study’s main objective was to develop a field-deployable microalgae monitoring platform using only a single smartphone and inexpensive acrylic color films. It aimed to evaluate the morphological states of microalgae including stress, cell concentration, and dominant species. Using a smartphone’s white LED flash and camera, the platform detected fluorescence and reflectance intensities from microalgal samples in various excitation and emission color combinations. Multidimensional intensity data were evaluated from the smartphone images and used to train a support vector machine (SVM) based machine learning model to classify various morphological states. The SVM classification accuracies were 0.84–0.96 in classifying four- to five-tier stress types, cell concentration, and dominant species and 0.99–1.00 in classifying two-tier stress types and cell concentrations. Additional field samples were collected from the local pond and independently tested using the laboratory-collected training set, showing two-tier classification accuracies of 0.90–1.00. This platform enables accessible and on-site microalgae monitoring for nonexperts and can be potentially applied to monitoring harmful algal blooms (HABs).
• Breshears, L. E., Mata-Robles, S., Tang, Y., Baker, J. C., Reynolds, K. A., & Yoon, J. (2023). Rapid, sensitive detection of PFOA with smartphone-based flow rate analysis utilizing competitive molecular interactions during capillary action. Journal of Hazardous Materials, 446, 130699. doi:https://doi.org/10.1016/j.jhazmat.2022.130699
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  Perfluorinated-alkyl substances (PFAS) pose an unmet threat to the public because they are not strictly monitored and regulated. Perfluorinated-carbon alkyl chains (PFOA), a type of PFAS, at 70 fg/μL is the current health and safety recommendation. Current testing methods for PFOA and PFAS chemicals include HPLC-MS/MS and molecularly imprinted polymers, which are expensive, time-consuming, and require training. In this work, PFOA and PFOS detection was performed on a paper microfluidic chip using competitive interactions between PFOA/PFOS, cellulose fibers, and various reagents (L-lysine, casein, and albumin). Such interactions altered the surface tension at the wetting front and, subsequently, the capillary flow rate. A smartphone captured the videos of this capillary action. The samples flowed through the channel in less than 2 min. Albumin worked the best in detecting PFOA, followed by casein. The detection limit was 10 ag/μL in DI water and 1 fg/μL in effluent (processed) wastewater. Specificity to other non-fluorocarbon surfactants was also tested, using anionic sodium dodecyl sulfate (SDS), non-ionic Tween 20, and cationic cetrimonium bromide (CTAB). A combination of the reagents successfully distinguished PFOA from all three surfactants at 100% accuracy. This low-cost, handheld assay can be an accessible alternative for rapid in situ estimation of PFOA concentration.
• Chung, S., Loh, A., Jennings, C. M., Sosnowski, K., Ha, S. Y., Yim, U. H., & Yoon, J. (2023). Capillary flow velocity profile analysis on paper-based microfluidic chips for screening oil types using machine learning. Journal of Hazardous Materials, 447, 130806. doi:https://doi.org/10.1016/j.jhazmat.2023.130806
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  We conceived a novel approach to screen oil types on a wax-printed paper-based microfluidic platform. Various oil samples spontaneously flowed through a micrometer-scale channel via capillary action while their components were filtered and partitioned. The resulting capillary flow velocity profile fluctuated during the flow, which was used to screen oil types. Raspberry Pi camera captured the video clips, and a custom Python code analyzed them to obtain the capillary flow velocity profiles. 106 velocity profiles (each with 125 frames for 5 s) were recorded from various oil samples to build a training database. Principal component analysis (PCA), support vector machine (SVM), and linear discriminant analysis (LDA) were used to classify the oil types into heavy-to-medium crude, light crude, marine fuel, lubricant, and diesel oils. The second-order polynomial SVM model with PCA as a pre-processing step showed the highest accuracy: 90% in classifying crude oils and 81% in classifying non-crude oils. The assay took less than 30 s from the sample to answer, with 5 s of the capillary action-driven flow. This simple and effective assay will allow rapid preliminary screening of oil types, enable early tracking, and reduce the number of suspect samples to be analyzed by laboratory fingerprinting analysis.
• Hertenstein, T., Tang, Y., Day, A. S., Reynolds, J., Viboolmate, P. V., & Yoon, J. (2023). Rapid and sensitive detection of miRNA via light scatter-aided emulsion-based isothermal amplification using a custom low-cost device. Biosensors and Bioelectronics, 237, 115444. doi:https://doi.org/10.1016/j.bios.2023.115444
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  MicroRNAs are likely to be a next-generation clinical biomarker for many diseases. While gold-standard technologies, e.g., reverse transcription-quantitative polymerase chain reaction (RT-qPCR), exist for microRNA detection, there is a need for rapid and low-cost testing. Here, an emulsion loop-mediated isothermal amplification (eLAMP) assay was developed for miRNA that compartmentalizes a LAMP reaction and shortens the time-to-detection. The miRNA was a primer to facilitate the overall amplification rate of template DNA. Light scatter intensity decreased when the emulsion droplet got smaller during the ongoing amplification, which was utilized to moitor the amplification non-invasively. A custom low-cost device was designed and fabricated using a computer cooling fan, a Peltier heater, an LED, a photoresistor, and a temperature controller. It allowed more stable vortexing and accurate light scatter detection. Three miRNAs, miR-21, miR-16, and miR-192, were successfully detected using the custom device. Specifically, new template and primer sequences were developed for miR-16 and miR-192. Zeta potential measurements and microscopic observations confirmed emulsion size reduction and amplicon adsorption. The detection limit was 0.01 fM, corresponding to 2.4 copies per reaction, and the detection could be made in 5 min. Since the assays were rapid and both template and miRNA + template could eventually be amplified, we introduced the success rate (compared to the 95% confidence interval of the template result) as a new measure, which worked well with lower concentrations and inefficient amplifications. This assay brings us one step closer to allowing circulating miRNA biomarker detection to become commonplace in the clinical world.
• Khanthaphixay, B., Wu, L., & Yoon, J. (2023). Microparticle-Based Detection of Viruses. Biosensors, 13(8), 820. doi:https://doi.org/10.3390/bios13080820
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  Surveillance of viral pathogens in both point-of-care and clinical settings is imperative to preventing the widespread propagation of disease—undetected viral outbreaks can pose dire health risks on a large scale. Thus, portable, accessible, and reliable biosensors are necessary for proactive measures. Polymeric microparticles have recently gained popularity for their size, surface area, and versatility, which make them ideal biosensing tools. This review cataloged recent investigations on polymeric microparticle-based detection platforms across eight virus families. These microparticles were used as labels for detection (often with fluorescent microparticles) and for capturing viruses for isolation or purification (often with magnetic microparticles). We also categorized all methods by the characteristics, materials, conjugated receptors, and size of microparticles. Current approaches were compared, addressing strengths and weaknesses in the context of virus detection. In-depth analyses were conducted for each virus family, categorizing whether the polymeric microparticles were used as labels, for capturing, or both. We also summarized the types of receptors conjugated to polymeric microparticles for each virus family.
• Kim, S., Samanta, K., Nguyen, B. T., Mata-Robles, S., Richer, L., Yoon, J., & Gomes-Solecki, M. (2023). A portable immunosensor provides sensitive and rapid detection of Borrelia burgdorferi antigen in spiked blood. Scientific Reports, 13, 7546. doi:https://doi.org/10.1038/s41598-023-34108-9
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  There are no assays for detecting B. burgdorferi antigen in blood of infected Lyme disease individuals. Here, we provide proof-of-principle evidence that we can quantify B. burgdorferi antigen in spiked blood using a portable smartphone-based fluorescence microscope that measures immunoagglutination on a paper microfluidic chip. We targeted B. burgdorferi OspA to develop a working prototype and added examples of two antigens (OspC and VlsE) that have diagnostic value for discrimination of Lyme disease stage. Using an extensively validated monoclonal antibody to OspA (LA-2), detection of OspA antigen had a broad linear range up to 100 pg/mL in 1% blood and the limit of detection (LOD) was 100 fg/mL (= 10 pg/mL in undiluted blood), which was 1000 times lower than our target of 10 ng/mL. Analysis of the two other targets was done using polyclonal and monoclonal antibodies. OspC antigen was detected at LOD 100 pg/mL (= 10 ng/mL of undiluted blood) and VlsE antigen was detected at LOD 1–10 pg/mL (= 0.1–1 ng/mL of undiluted blood). The method is accurate and was performed in 20 min from sample to answer. When optimized for detecting several B. burgdorferi antigens, this assay may differentiate active from past infections and facilitate diagnosis of Lyme disease in the initial weeks of infection, when antibody presence is typically below the threshold to be detected by serologic methods.
• Liang, Y., Buchanan, B. C., Khanthaphixay, B., Zhou, A., Quirk, G., Worobey, M., & Yoon, J. (2023). Sensitive SARS-CoV-2 salivary antibody assays for clinical saline gargle samples using smartphone-based competitive particle immunoassay platforms. Biosensors and Bioelectronics, 229, 115221. doi:https://doi.org/10.1016/j.bios.2023.115221
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  Antibody assay for SARS-CoV-2 has become increasingly important to track latent and asymptomatic infections, check the individual's immune status, and confirm vaccine efficacy and durability. However, current SARS-CoV-2 antibody assays require invasive blood collection, requiring a remote laboratory and a trained phlebotomist. Direct detection of SARS-CoV-2 antibodies from clinical saline gargle samples has been considered challenging due to the smaller number of antibodies in such specimens and the high limit of detection of currently available rapid tests. This work demonstrates simple and non-invasive methods for detecting SARS-CoV-2 salivary antibodies. Competitive particle immunoassays were developed on a paper microfluidic chip using the receptor-binding domain (RBD) antigens on spike proteins. Using a smartphone, they were monitored by counting the captured fluorescent particles or evaluating the capillary flow velocities. The limit of detection (LOD), cross-binding between alpha- and omicron-strains, and the effect of angiotensin-converting enzyme 2 (ACE2) presence were investigated. LODs were 1–5 ng/mL in both 10% and 1% saliva. Clinical saline gargle samples were assayed using both methods, showing a statistical difference between virus-negative and virus-positive samples, although the assays targeted antibodies. Only a small number of virus-positive samples were antibody-negative. The high assay sensitivity detected a small number of antibodies developed even during the early phase of infections. Overall, this work demonstrates the ability to detect SARS-CoV-2 salivary IgG antibodies on simple, cost-effective, portable platforms towards mitigating SARS-CoV-2 and potentially other respiratory viruses.
• Liang, Y., Lee, M. H., Zhou, A., Khanthaphixay, B., Hwang, D. S., & Yoon, J. (2023). eXtreme gradient boosting-based classification of bacterial mixtures in water and milk using wireless microscopic imaging of quorum sensing peptide-conjugated particles. Biosensors and Bioelectronics, 227, 115144. doi:https://doi.org/10.1016/j.bios.2023.115144
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  Numerous bacteria can cause water- and foodborne diseases and are often found in bacterial mixtures, making their detection challenging. Specific bioreceptors or selective growth media are necessary for most bacterial detection methods. In this work, we collectively used five quorum sensing-based peptides identified from bacterial biofilms to identify 10 different bacterial species (Bacillus subtilis, Campylobacter jejuni, Enterococcus faecium, Escherichia coli, Legionella pneumophila, Listeria monocytogenes, Pseudomonas aeruginosa, Salmonella Typhimurium, Staphylococcus aureus, Vibrio parahaemolyticus) and their mixtures in water and milk. Four different machine learning classification methods were used: k-nearest neighbors (k-NN), decision tree (DT), support vector machine (SVM), and eXtreme Gradient Boosting (XGBoost). Peptides were crosslinked to submicron particles, and peptide-bacteria interactions on paper microfluidic chips caused the particle aggregation. A wireless, pocket fluorescence microscope (interfaced with a smartphone) counted such particle aggregations. XGBoost showed the best accuracy of 83.75% in identifying bacterial species from water samples using 320 different datasets and 91.67% from milk samples using 140 different datasets (5 peptide features per dataset). Each peptide's contribution to correct classification was evaluated. The results were concentration-dependent, allowing the identification of a dominant species from bacterial mixtures. Using XGBoost and the previous milk database, we tested 14 blind samples of various bacterial mixtures in milk samples, with an accuracy of 81.55% to predict the dominant species. The entire process could be completed within a half hour. The demonstrated system can provide a handheld, low-cost, easy-to-operate tool for potential hygiene spot-checks, public health, or personal healthcare.
• Reynolds, J., Loeffler, R. S., Leigh, P. J., Lopez, H. A., & Yoon, J. (2023). Recent Uses of Paper Microfluidics in Isothermal Nucleic Acid Amplification Tests. Biosensors, 13(9), 885. doi:https://doi.org/10.3390/bios13090885
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  Isothermal nucleic acid amplification tests have recently gained popularity over polymerase chain reaction (PCR), as they only require a constant temperature and significantly simplify nucleic acid amplification. Recently, numerous attempts have been made to incorporate paper microfluidics into these isothermal amplification tests. Paper microfluidics (including lateral flow strips) have been used to extract nucleic acids, amplify the target gene, and detect amplified products, all toward automating the process. We investigated the literature from 2020 to the present, i.e., since the onset of the COVID-19 pandemic, during which a significant surge in isothermal amplification tests has been observed. Paper microfluidic detection has been used extensively for recombinase polymerase amplification (RPA) and its related methods, along with loop-mediated isothermal amplification (LAMP) and rolling circle amplification (RCA). Detection was conducted primarily with colorimetric and fluorometric methods, although a few publications demonstrated flow distance- and surface-enhanced Raman spectroscopic (SERS)-based detection. A good number of publications could be found that demonstrated both amplification and detection on paper microfluidic platforms. A small number of publications could be found that showed extraction or all three procedures (i.e., fully integrated systems) on paper microfluidic platforms, necessitating the need for future work.
• Akarapipad, P., Kaarj, K., Breshears, L. E., Sosnowski, K., Baker, J., Nguyen, B. T., Eades, C., Uhrlaub, J. L., Quirk, G., Nikolich-Zugich, J., Worobey, M., & Yoon, J. (2022). Smartphone-based sensitive detection of SARS-CoV-2 from saline gargle samples via flow profile analysis on a paper microfluidic chip. Biosensors and Bioelectronics, 207, 114192. doi:https://doi.org/10.1016/j.bios.2022.114192
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  Respiratory viruses, especially coronaviruses, have resulted in worldwide pandemics in the past couple of decades. Saliva-based paper microfluidic assays represent an opportunity for noninvasive and rapid screening, yet both the sample matrix and test method come with unique challenges. In this work, we demonstrated the rapid and sensitive detection of SARS-CoV-2 from saliva samples, which could be simpler and more comfortable for patients than existing methods. Furthermore, we systematically investigated the components of saliva samples that affected assay performance. Using only a smartphone, an antibody-conjugated particle suspension, and a paper microfluidic chip, we made the assay user-friendly with minimal processing. Unlike the previously established flow rate assays that depended solely on the flow rate or distance, this unique assay analyzes the flow profile to determine infection status. Particle-target immunoagglutination changed the surface tension and subsequently the capillary flow velocity profile. A smartphone camera automatically measured the flow profile using a Python script, which was not affected by ambient light variations. The limit of detection (LOD) was 1 fg/μL SARS-CoV-2 from 1% saliva samples and 10 fg/μL from simulated saline gargle samples (15% saliva and 0.9% saline). This method was highly specific as demonstrated using influenza A/H1N1. The sample-to-answer assay time was
• Breshears, L. E., Nguyen, B. T., Akarapipad, P., Sosnowski, K., Kaarj, K., Quirk, G., Uhrlaub, J. L., Nikolich-Zugich, J., Worobey, M., & Yoon, J. (2022). Sensitive, smartphone-based SARS-CoV-2 detection from clinical saline gargle samples. PNAS Nexus, pgac028. doi:https://doi.org/10.1093/pnasnexus/pgac028
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  Saliva specimens have drawn interest for diagnosing respiratory viral infections due to their ease of collection and decreased risk to healthcare providers. However, rapid and sensitive immunoassays have not yet been satisfactorily demonstrated for such specimens due to their viscosity and low viral loads. Using paper microfluidic chips and a smartphone-based fluorescence microscope, we developed a highly sensitive, low-cost immunofluorescence particulometric SARS-CoV-2 assay from clinical saline gargle samples. We demonstrated the limit of detection of 10 ag/μL. With easy-to-collect saline gargle samples, our clinical sensitivity, specificity, and accuracy were 100%, 86%, and 93%, respectively, for n = 27 human subjects with n = 13 RT-qPCR positives.
• Breshears, L. E., Nguyen, B. T., Mata-Robles, S., Wu, L., & Yoon, J. (2022). Biosensor Detection of Airborne Respiratory Viruses Such As SARS-CoV-2. SLAS Technology, 27, 4-17. doi:https://doi.org/10.1016/j.slast.2021.12.004
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  Airborne SARS-CoV-2 transmission represents a significant route for possible human infection that is not yet fully understood. Viruses in droplets and aerosols are difficult to detect because they are typically present in low amounts. In addition, the current techniques used, such as RT-PCR and virus culturing, require large amounts of time to get results. Biosensor technology can provide rapid, handheld, and point-of-care systems that can identify virus presence quickly and accurately. This paper reviews the background of airborne virus transmission and the characteristics of SARS-CoV-2, its relative risk for transmission even at distances greater than the currently suggested 6 feet (or 2 m) physical distancing. Publications on biosensor technology that may be applied to the detection of airborne SARS-CoV-2 and other respiratory viruses are also summarized. Based on the current research we believe that there is a pressing need for continued research into handheld and rapid methods for sensitive collection and detection of airborne viruses. We propose a paper-based microfluidic chip and immunofluorescence assay as one method that could be investigated as a low-cost and portable option.
• Buchanan, B. C., & Yoon, J. (2022). Microscopic Imaging Methods for Organ-on-a-Chip Platforms. Micromachines, 13, 328. doi:https://doi.org/10.3390/mi13020328
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  Microscopic imaging is essential and the most popular method for in situ monitoring and evaluating the outcome of various organ-on-a-chip (OOC) platforms, including the number and morphology of mammalian cells, gene expression, protein secretions, etc. This review presents an overview of how various imaging methods can be used to image organ-on-a-chip platforms, including transillumination imaging (including brightfield, phase-contrast, and holographic optofluidic imaging), fluorescence imaging (including confocal fluorescence and light-sheet fluorescence imaging), and smartphone-based imaging (including microscope attachment-based, quantitative phase, and lens-free imaging). While various microscopic imaging methods have been demonstrated for conventional microfluidic devices, a relatively small number of microscopic imaging methods have been demonstrated for OOC platforms. Some methods have rarely been used to image OOCs. Specific requirements for imaging OOCs will be discussed in comparison to the conventional microfluidic devices and future directions will be introduced in this review.
• Buchanan, B. C., Safavinia, B., Wu, L., & Yoon, J. (2022). Smartphone-based autofluorescence imaging to detect bacterial species on laboratory surfaces. Analyst, 147, 2980-2987. doi:https://doi.org/10.1039/D2AN00358A
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  The potential of bacterial contamination is commonly seen in biological and clinical laboratory surfaces, creating a need to detect the presence of bacteria on a surface. Various bacterial species have been found to naturally exist on surfaces, including Escherichia coli, Salmonella Typhimurium, and Staphylococcus aureus that were investigated in this study. Bacterial presence was identified from laboratory surfaces using a smartphone and low-cost components without culturing or staining. Autofluorescence from bacteria was quantified using a 405 nm LED as an excitation light source. A low-cost acrylic film could isolate the autofluorescence emission. ImageJ was used to process and analyze the images and quantify the emitted autofluorescence signal. This imaging platform successfully detected the presence of all three bacterial species from the heavily used laboratory surfaces. A trend of decreasing fluorescence signal was observed with decreasing bacterial concentration, and the limit of detection was 104 CFU cm−2. It could also distinguish from tap water, protein (bovine serum albumin), and NaCl solutions. This preliminary work emphasizes the ability to detect autofluorescence signals of bacteria and non-microbial surface contaminants using a cost-effective and straightforward imaging platform.
• Kim, S., Akarapipad, P., Nguyen, B. T., Breshears, L. E., Sosnowski, K., Baker, J., Uhrlaub, J. L., Nikolich-Zugich, J., & Yoon, J. (2022). Direct Capture and Smartphone Quantification of Airborne SARS-CoV-2 on a Paper Microfluidic Chip. Biosensors and Bioelectronics, 200, 113912. doi:https://doi.org/10.1016/j.bios.2021.113912
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  SARS, a new type of respiratory disease caused by SARS-CoV, was identified in 2003 with significant levels of morbidity and mortality. The recent pandemic of COVID-19, caused by SARS-CoV-2, has generated even greater extents of morbidity and mortality across the entire world. Both SARS-CoV and SARS-CoV-2 spreads through the air in the form of droplets and potentially smaller droplets (aerosols) via exhaling, coughing, and sneezing. Direct detection from such airborne droplets would be ideal for protecting general public from potential exposure before they infect individuals. However, the number of viruses in such droplets and aerosols is too low to be detected directly. A separate air sampler and enough collection time (several hours) are necessary to capture a sufficient number of viruses. In this work, we have demonstrated the direct capture of the airborne droplets on the paper microfluidic chip without the need for any other equipment. 10% human saliva samples were spiked with the known concentration of SARS-CoV-2 and sprayed to generate liquid droplets and aerosols into the air. Antibody-conjugated submicron particle suspension is then added to the paper channel, and a smartphone-based fluorescence microscope isolated and counted the immunoagglutinated particles on the paper chip. The total capture-to-assay time was < 30 minutes, compared to several hours with the other methods. In this manner, SARS-CoV-2 could be detected directly from the air in a handheld and low-cost manner, contributing to slowing the spread of SARS-CoV-2. We can presumably adapt this technology to a wide range of other respiratory viruses.
• Kim, S., Day, A. S., & Yoon, J. (2022). Machine learning classification of bacterial species using mix-and-match reagents on paper microfluidic chips and smartphone-based capillary flow analysis. Analytical and Bioanalytical Chemistry, 414, 3895–3904. doi:https://doi.org/10.1007/s00216-022-04031-5
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  Traditionally, specific bioreceptors such as antibodies have rapidly identified bacterial species in environmental water samples. However, this method has the disadvantages of requiring an additional process to conjugate or immobilize bioreceptors on the assay platform, which becomes unstable at room temperature. Here, we demonstrate a novel mix-and-match method to identify bacteria species by loading the bacterial samples with simple bacteria interacting components (not bioreceptors), such as lipopolysaccharides, peptidoglycan, and bovine serum albumin, and carboxylated particles, all separately on multiple channels. Neither covalent conjugation nor surface immobilization was necessary. Interactions between bacteria and the above bacteria interacting components resulted in varied surface tension and viscosity, leading to various flow velocities of capillary action through the paper fibers. The smartphone camera and a custom Python code recorded multiple channel flow velocity, each loaded with different bacteria interacting components. A multi-dimensional data set was obtained for a given bacterial species and concentration and used as a machine learning training model. A support vector machine was applied to classify the six bacterial species: Escherichia coli, Salmonella Typhimurium, Pseudomonas aeruginosa, Staphylococcus aureus, Enterococcus faecium, and Bacillus subtilis. Under optimized conditions, the training model predicts the bacterial species with an accuracy of > 85% of the six bacteria species.
• Kim, S., Eades, C., & Yoon, J. (2022). COVID-19 variants’ cross-reactivity on the paper microfluidic particle counting immunoassay. Analytical and Bioanalytical Chemistry, 414, 7957–7965. doi:https://doi.org/10.1007/s00216-022-04333-8
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  SARS-CoV-2 has mutated many times since the onset of the COVID-19 pandemic, and the omicron is currently the most dominant variant. Determining the specific strain of the virus is beneficial in providing proper care and containment of the disease. We have previously reported a novel method of counting the number of particle immunoagglutination on a paper microfluidic chip using a smartphone-based fluorescence microscope. A single-copy-level detection was demonstrated from clinical saline gargle samples. In this work, we further evaluated two different SARS-CoV-2 monoclonal antibodies to spike vs. nucleocapsid antigens for detecting omicron vs. delta and spike vs. nucleocapsid proteins. The SARS-CoV-2 monoclonal antibody to nucleocapsid proteins could distinguish omicron from delta variants and nucleocapsid from spike proteins. However, such distinction could not be found with the monoclonal antibody to spike proteins, despite the numerous mutations found in spike proteins among variants. This result may suggest a clue to the role of nucleocapsid proteins in recognizing different variants.
• Liang, Y., Zhou, A., & Yoon, J. (2022). Machine Learning-Based Quantification of (−)-trans-Δ-Tetrahydrocannabinol from Human Saliva Samples on a Smartphone-Based Paper Microfluidic Platform. ACS Omega, 7, 30064-30073. doi:https://doi.org/10.1021/acsomega.2c03099
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  (−)-trans-Δ-Tetrahydrocannabinol (THC) is a major psychoactive component in cannabis. Despite the recent trends of THC legalization for medical or recreational use in some areas, many THC-driven impairments have been verified. Therefore, convenient, sensitive, quantitative detection of THC is highly needed to improve its regulation and legalization. We demonstrated a biosensor platform to detect and quantify THC with a paper microfluidic chip and a handheld smartphone-based fluorescence microscope. Microfluidic competitive immunoassay was applied with anti-THC-conjugated fluorescent nanoparticles. The smartphone-based fluorescence microscope counted the fluorescent nanoparticles in the test zone, achieving a 1 pg/mL limit of detection from human saliva samples. Specificity experiments were conducted with cannabidiol (CBD) and various mixtures of THC and CBD. No cross-reactivity to CBD was found. Machine learning techniques were also used to quantify the THC concentrations from multiple saliva samples. Multidimensional data were collected by diluting the saliva samples with saline at four different dilutions. A training database was established to estimate the THC concentration from multiple saliva samples, eliminating the sample-to-sample variations. The classification algorithms included k-nearest neighbor (k-NN), decision tree, and support vector machine (SVM), and the SVM showed the best accuracy of 88% in estimating six different THC concentrations. Additional validation experiments were conducted using independent validation sample sets, successfully identifying positive samples at 100% accuracy and quantifying the THC concentration at 80% accuracy. The platform provided a quick, low-cost, sensitive, and quantitative point-of-care saliva test for cannabis.
• Liang, Y., Zhou, A., Bever, C. S., Cheng, L. W., & Yoon, J. (2022). Smartphone-based paper microfluidic competitive immunoassay for the detection of α-amanitin from mushrooms. Microchimica Acta, 189, 322. doi:https://doi.org/10.1007/s00604-022-05407-1
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  α-Amanitin is often considered the most poisonous mushroom toxin produced by various mushroom species, which are hard to identify from edible, non-toxic mushrooms. Conventional detection methods require expensive and bulky equipment or fail to meet high analytical sensitivity. We developed a smartphone-based fluorescence microscope platform to detect α-amanitin from dry mushroom tissues. Antibody-nanoparticle conjugates were captured by immobilized antigen-hapten conjugates while competing with the free analytes in the sample. Captured fluorescent nanoparticles were excited at 460 nm and imaged at 500 nm. The pixel numbers of such nanoparticles in the test zone were counted, showing a decreasing trend with increasing analyte concentration. The detection method exhibited a low detection limit (1 pg/mL), high specificity, and selectivity, allowing us to utilize a simple rinsing for toxin extraction and avoiding the need for high-speed centrifugation. In addition, this assay’s short response time and portable features enable field detection of α-amanitin from amanitin-producing mushrooms.
• Mannier, C., & Yoon, J. (2022). Progression of LAMP as a Result of the COVID-19 Pandemic: Is PCR Finally Rivaled?. Biosensors, 12, 492. doi:https://doi.org/10.3390/bios12070492
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  Reflecting on the past three years and the coronavirus disease 19 (COVID-19) pandemic, varying global tactics offer insights into the most effective public-health responses. In the US, specifically, rapid and widespread testing was quickly prioritized to lower restrictions sooner. Essentially, only two types of COVID-19 diagnostic tests were publicly employed during the peak pandemic: the rapid antigen test and reverse transcription polymerase chain reaction (RT-PCR). However, neither test ideally suited the situation, as rapid antigen tests are far too inaccurate, and RT-PCR tests require skilled personnel and sophisticated equipment, leading to long wait times. Loop-mediated isothermal amplification (LAMP) is another exceptionally accurate nucleic acid amplification test (NAAT) that offers far quicker time to results. However, RT-LAMP COVID-19 tests have not been embraced as extensively as rapid antigen tests or RT-PCR. This review will investigate the performance of current RT-LAMP-based COVID-19 tests and summarize the reasons behind the hesitancy to embrace RT-LAMP instead of RT-PCR. We will also look at other LAMP platforms to explore possible improvements in the accuracy and portability of LAMP, which could be applied to COVID-19 diagnostics and future public-health outbreaks.
• Sosnowski, K., Loh, A., Zubler, A. V., Shir, H., Ha, S. Y., Yim, U. H., & Yoon, J. (2022). Machine learning techniques for chemical and type analysis of ocean oil samples via handheld spectrophotometer device. Biosensors and Bioelectronics: X, 10, 100128. doi:https://doi.org/10.1016/j.biosx.2022.100128
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  We designed and constructed a handheld, sturdy fluorescence spectrometry device for identifying samples from ocean oil spills. Two large training databases of autofluorescence spectra from raw oil samples (538 samples/1614 spectra and 767 samples/2301 spectra) were cross validated using support vector machine (SVM) to identify oil type and SARA (saturate, aromatic, resin, and asphaltene) contents. The device's performance was then validated on an independent set of 79 ocean oil samples, which were added to and then collected from ocean water during outdoor exposure to hot, humid weather to represent an actual oil spill. It successfully classified oil types with 92%–100% sensitivity and specificity and F1 scores of 85.7–100%. Further classification of light fuel oils into marine gas oil (MGO)-like and Bunker A (BA)-like categories was successful with the training set (raw oil samples), while less successful with the independent validation set (ocean oil samples). SARA content classification models performed well in training for the saturate (80.8% accuracy) and asphaltene (90.7%) contents. The developed training model was validated using ocean oil samples, and the resulting accuracies were 62.0% (saturate) and 93.7% (asphaltene). These results indicate the difficulties in classifying volatile light fuel oils with a low molecular weight that have experienced weathering effects, while high molecular weight compounds and general oil type can be analyzed.
• Yoon, J., & Chen, C. (2022). Microfluidic detection of viruses for human health. Biomicrofluidics, 16, 060401. doi:https://doi.org/10.1063/5.0130555
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  Given the pandemic of COVID-19, the need for field- and clinic-ready diagnostic kits is in high demand. Low-cost disposable devices for virus detections on the scale are critical to minimize infection spreading in a society. Many commercial testing kits based on antigen binding are available in the market (known as rapid antigen tests), while the challenges in rapid virus determination and quantification remain. Indeed, many lab-intensive protocols, such as virus extraction, lysis, antibody assay, and polymerase chain reaction (PCR), are required to precisely measure the virus from human specimens, including nasopharyngeal swabs, blood withdrawals, urine, or feces, while the conventional antigen binding assay with limited detection sensitivity can only be useful for certain scenarios. In the "Microfluidic Detection of Viruses for Human Health" Special Topic in Biomicrofluidics, a series of emerging microfluidic strategies are introduced to offer potential new advanced diagnostic kits to detect the virus in a more timely manner. For example, microfluidic PCR technology was investigated to quantify the virus with a high sensitivity to indicate infectious disease progress. In addition, many novel chemical materials and microfluidic components are introduced here to extract the virus and related biomarkers to convert a lab-based bio-chemical analysis to a rapid point of care assay by using a low-cost integrative device.
• Yu, C., Takhistov, P., Alocilja, E., Reyes de Corcuera, J., Frey, M. W., Gomes, C. L., Mao, Y. J., McLamore, E. S., Lin, M., Tsyusko, O. V., Tzeng, T. J., Yoon, J., & Zhou, A. (2022). Bioanalytical approaches for the detection, characterization, and risk assessment of micro/nanoplastics in agriculture and food systems. Analytical and Bioanalytical Chemistry, 414, 4591–4612. doi:https://doi.org/10.1007/s00216-022-04069-5
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  This review discusses the most recent literature (mostly since 2019) on the presence and impact of microplastics (MPs, particle size of 1 μm to 5 mm) and nanoplastics (NPs, particle size of 1 to 1000 nm) throughout the agricultural and food supply chain, focusing on the methods and technologies for the detection and characterization of these materials at key entry points. Methods for the detection of M/NPs include electron and atomic force microscopy, vibrational spectroscopy (FTIR and Raman), hyperspectral (bright field and dark field) and fluorescence imaging, and pyrolysis–gas chromatography coupled to mass spectrometry. Microfluidic biosensors and risk assessment assays of MP/NP for in vitro, in vivo, and in silico models have also been used. Advantages and limitations of each method or approach in specific application scenarios are discussed to highlight the scientific and technological obstacles to be overcome in future research. Although progress in recent years has increased our understanding of the mechanisms and the extent to which MP/NP affects health and the environment, many challenges remain largely due to the lack of standardized and reliable detection and characterization methods. Most of the methods available today are low-throughput, which limits their practical application to food and agricultural samples. Development of rapid and high-throughput field-deployable methods for onsite screening of MP/NPs is therefore a high priority. Based on the current literature, we conclude that detecting the presence and understanding the impact of MP/NP throughout the agricultural and food supply chain require the development of novel deployable analytical methods and sensors, the combination of high-precision lab analysis with rapid onsite screening, and a data hub(s) that hosts and curates data for future analysis.
• Zenhausern, R., Day, A. S., Safavinia, B., Han, S., Rudy, P. E., Won, Y., & Yoon, J. (2022). Natural Killer Cell Detection, Quantification, and Subpopulation Identification on Paper Microfluidic Cell Chromatography Using Smartphone-based Machine Learning Classification. Biosensors and Bioelectronics, 200, 113916. doi:https://doi.org/10.1016/j.bios.2021.113916
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  Natural killer (NK) cells are immune cells that defend against viral infections and cancer and are used in cancer immunotherapies. Subpopulations of NK cells include CD56dim and CD56bright which either produce cytokines or cytotoxically kill cells directly. The absolute number and proportion of these cells in peripheral blood are tied to proper immune function. Current methods of cytokine detection and proportion of NK cell subpopulations require fluorescent dyes and highly specialized equipment, e.g., flow cytometry, thus rapid cell quantification and subpopulation analysis are needed in the clinical setting. Here, a smartphone-based device and a two-component paper microfluidic chip were used towards identifying NK cell subpopulation and inflammatory markers. One unit measured flow velocity via smartphone-captured video, determining cytokine (IL-2) and total NK cell concentrations in undiluted buffy coat blood samples. The other, single flow lane unit performs spatial separation of CD56dim and CD56bright and cells over its length using differential binding of anti-CD56 nanoparticles. A smartphone microscope combined with cloud-based machine learning predictive modeling (utilizing a random forest classification algorithm) analyzed both flow data and NK cell subpopulation differentiation. Limits of detection for cytokine and cell concentrations were 98 IU/mL and 68 cells/mL, respectively, and cell subpopulation analysis showed 89% accuracy.
• Akarapipad, P., Kaarj, K., Liang, Y., & Yoon, J. (2021). Environmental Toxicology Assays Using Organ-on-Chip. Annual Reviews in Analytical Chemistry, 14, 155-183. doi:https://doi.org/10.1146/annurev-anchem-091620-091335
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  Adverse effects of environmental toxicants to human health have traditionally been assayed using in vitro assays. Organ-on-chip (OOC) is a new platform that can bridge the gaps between in vitro assays (or 3D cell culture) and animal tests. Microenvironments, physical and biochemical stimuli, and adequate sensing and biosensing systems can be integrated into OOC devices to better recapitulate the in vivo tissue and organ behavior and metabolism. While OOCs have extensively been studied for drug toxicity screening, their implementation in environmental toxicology assays is minimal and has limitations. In this review, recent attempts of environmental toxicology assays using OOCs, including multiple-organs-on-chip, are summarized and compared with OOC-based drug toxicity screening. Requirements for further improvements are identified and potential solutions are suggested.
• Chung, S., Breshears, L. E., Gonzales, A., Jennings, C. M., Morrison, C. M., Betancourt, W. Q., Reynolds, K. A., & Yoon, J. (2021). Norovirus Detection in Water Samples at the Level of Single Virus Copies per Microliter Using a Smartphone-based Fluorescence Microscope. Nature Protocols, 16, 1452-1475. doi:https://doi.org/10.1038/s41596-020-00460-7
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  Norovirus is a widespread public health threat and has a very low infectious dose. This protocol presents the extremely sensitive mobile detection of norovirus from water samples using a custom-built smartphone-based fluorescence microscope and a paper microfluidic chip. Antibody-conjugated fluorescent particles are immunoagglutinated and spread over the paper microfluidic chip by capillary action for individual counting using a smartphone-based fluorescence microscope. Smartphone images are analyzed using intensity- and size-based thresholding for the elimination of background noise and autofluorescence as well as for the isolation of immunoagglutinated particles. The resulting pixel counts of particles are correlated with the norovirus concentration of the tested sample. This protocol provides detailed guidelines for the construction and optimization of the smartphone- and paper-based assay. In addition, a 3D-printed enclosure is presented to incorporate all components in a dark environment. On-chip concentration and the assay of higher concentrations are presented to further broaden the assay range. This method is the first to be presented as a highly sensitive mobile platform for norovirus detection using low-cost materials. With all materials and reagents prepared, a single standard assay takes under 20 min. Although the method described is used for detection of norovirus, the same protocol could be adapted for detection of other pathogens by using different antibodies.
• Day, A. S., Ulep, T., Budiman, E., Dieckhaus, L., Safavinia, B., Hertenstein, T., & Yoon, J. (2021). Contamination-resistant, Rapid Emulsion-based Isothermal Nucleic Acid Amplification with Mie-scatter Inspired Light Scatter Analysis for Bacterial Identification. Scientific Reports, 11, 19933. doi:https://doi.org/10.1038/s41598-021-99200-4
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  An emulsion loop-mediated isothermal amplification (eLAMP) platform was developed to reduce the impact that contamination has on assay performance. Ongoing LAMP reactions within the emulsion droplets cause a decrease in interfacial tension, causing a decrease in droplet size, which results in decreased light scatter intensity due to Mie theory. Light scatter intensity was monitored via spectrophotometers and fiber optic cables placed at 30 degree and 60 degree. Light scatter intensities collected at 3 min, 30 degree were able to statistically differentiate 10^3 and 10^6 CFU/uL initial Escherichia coli O157:H7 concentrations compared to NTC (0 CFU/uL), while the intensity at 60 degree were able to statistically differentiate 10^6 CFU/uL initial concentrations and NTC. Control experiments were conducted to validate nucleic acid detection versus bacterial adsorption, finding that the light scatter intensities change is due specifically to ongoing LAMP amplification. After inducing contamination of bulk LAMP reagents, specificity lowered to 0% with conventional LAMP, while the eLAMP platform showed 87.5% specificity. We have demonstrated the use of angle-dependent light scatter intensity as a means of real-time monitoring of an emulsion LAMP platform and fabricated a smartphone-based monitoring system that showed similar trends as spectrophotometer light scatter data, validating the technology for a field deployable platform.
• Day, A. S., Ulep, T., Safavinia, B., Hertenstein, T., Budiman, E., Dieckhaus, L., & Yoon, J. (2021). Emulsion-based Isothermal Nucleic Acid Amplification for Rapid SARS-CoV-2 Detection via Angle-dependent Light Scatter Analysis. Biosensors and Bioelectronics, 179, 113099. doi:https://doi.org/10.1016/j.bios.2021.113099
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  The SARS-CoV-2 pandemic, an ongoing global health crisis, has revealed the need for new technologies that integrate the sensitivity and specificity of RT-PCR tests with a faster time-to-detection. Here, an emulsion loop-mediated isothermal amplification (eLAMP) platform was developed to allow for the compartmentalization of LAMP reactions, leading to faster changes in emulsion characteristics, and thus lowering time-to-detection. Within these droplets, ongoing LAMP reactions lead to adsorption of amplicons to the water-oil interface, causing a decrease in interfacial tension, resulting in smaller emulsion diameters. Changes in emulsion diameter allow for the monitoring of the reaction by use of angle-dependent light scatter (based off Mie scatter theory). Mie scatter simulations confirmed that light scatter intensity is diameter-dependent and smaller colloids have lower intensity values compared to larger colloids. Via spectrophotometers and fiber optic cables placed at 30° and 60°, light scatter intensity was monitored. Scatter intensities collected at 5 min, 30 degree could statistically differentiate 10, 10^3, and 10^5 copies/uL initial concentrations compared to NTC. Similarly, 5 min scatter intensities collected at 60 degree could statistically differentiate 10^5 copies/uL initial concentrations in comparison to NTC. The use of both angles during the eLAMP assay allows for distinction between high and low initial target concentrations. The efficacy of a smartphone-based platform was also tested and had a similar limit of detection and assay time of less than 10 min. Furthermore, fluorescence-labeled primers were used to validate target nucleic acid amplification. Compared to existing LAMP assays for SARS-CoV-2 detection, these times-to-detections are very rapid.
• Kim, S., Lee, M. H., Wiwasuku, T., Day, A. S., Youngme, S., Hwang, D. S., & Yoon, J. (2021). Human Sensor-inspired Supervised Machine Learning of Smartphone-based Paper Microfluidic Analysis for Bacterial Species Classification. Biosensors and Bioelectronics, 188, 113335. doi:https://doi.org/10.1016/j.bios.2021.113335
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  Bacteria identification has predominantly been conducted using specific bioreceptors such as antibodies or nucleic acid sequences. This approach may be inappropriate for environmental monitoring when the user does not know the target bacterial species and for screening complex water samples with many unknown bacterial species. In this work, we investigate the supervised machine learning of the bacteria-particle aggregation pattern induced by the peptide sets identified from the biofilm-bacteria interface. Each peptide is covalently conjugated to polystyrene particles and loaded together with bacterial suspensions onto paper microfluidic chips. Each peptide interacts with bacterial species to a different extent, leading to varying sizes of particle aggregation. This aggregation changes the surface tension and viscosity of the liquid flowing through the paper pores, altering the flow velocity at different extents. A smartphone camera captures this flow velocity without being affected by ambient and environmental conditions, towards a low-cost, rapid, and field-ready assay. A collection of such flow velocity data generates a unique fingerprinting profile for each bacterial species. Support vector machine is utilized to classify the species. At optimized conditions, the training model can predict the species at 93.3% accuracy out of five bacteria: Escherichia coli, Staphylococcus aureus, Salmonella Typhimurium, Enterococcus faecium, and Pseudomonas aeruginosa. Flow rates are monitored for less than 6 s and the sample-to-answer assay time is less than 10 min. The demonstrated method can open a new way of analyzing complex biological and environmental samples in a biomimetic manner with machine learning classification.
• Kim, S., Romero-Lozano, A., Hwang, D. S., & Yoon, J. (2021). A guanidinium-rich polymer as a new universal bioreceptor for multiplex detection of bacteria from environmental samples. Journal of Hazardous Materials, 413, 125338. doi:https://doi.org/10.1016/j.jhazmat.2021.125338
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  Protamine, a guanidinium rich polymer, is proposed as a universal bioreceptor for bacteria, towards rapid and handheld bacteria detection from complex environmental water samples without the need for specific antibodies or primers. Escherichia coli K12, Salmonella Typhimurium, and Staphylococcus aureus (MSSA) were assayed, representing gram-negative, gram-positive, rod- and round-shaped bacteria. Samples and the protamine conjugated fluorescent particles were sequentially loaded to the paper microfluidic chips and flowed through the channels spontaneously via capillary action. The particles were aggregated via protamine-bacteria membrane interactions and unbound particles were rinsed via capillary action. A low-cost smartphone fluorescence microscope was designed, fabricated, and imaged the paper channels. A unique image processing algorithm isolated only the aggregated particles to detect all three bacteria (p < 0.05) with a detection limit of 10^1−10^2 CFU/mL. Protamine did not induce any particle aggregation with a model protein, algae, and virus. Successful bacteria detection was also demonstrated with environmental field water samples. Total assay time was < 10 min with neither extraction nor enrichment steps. In summary, a guanidinium-rich polymer showed a promise as a universal bioreceptor for bacteria and can be used on a paper microfluidic chip and smartphone quantification towards rapid and handheld detection.
• Liang, Y., & Yoon, J. (2021). In situ sensors for blood-brain barrier (BBB) on a chip. Sensors and Actuators Reports, 3, 100031. doi:https://doi.org/10.1016/j.snr.2021.100031
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  The blood-brain barrier (BBB) is critical for the central nervous system, as its integrity protects neurons and other brain cells from harmful toxicants and disease-associated molecules, while it also blocks the delivery of therapeutic drugs to brain. Understanding the function and physiology of BBB have made slow progress due to the relative lack of effective models. Microfluidic BBB-on-a-chip models have gained attentions recently through recreating a more accessible, in vivo-like microenvironments. Although many fabrication and application methods have been demonstrated and improved for BBB-on-a-chip, the detection methods used in those systems seem to heavily reply on conventional analytical instruments, which are bulky, expensive, time-consuming, and not suitable for large-scale industrial operations. The TEER (transendothelial electrical resistance) measurement has become popular for identifying the integrity of BBB due to its compatibility, noninvasiveness, and rapid readings. While the TEER sensor has been a major success in BBB-on-a-chip, this may be the only major in situ sensor that have been successfully incorporated in BBB-on-a-chip models. In this review paper, we (1) compared the current BBB experimental models, (2) briefly summarized their fabrication considerations, (3) discussed the detection techniques used in such models, and (4) provided suggestions to incorporate various in situ biosensors/sensors into these models. The coming years will likely see the continued development of BBB-on-a-chip models, powerful detection techniques applied on these models will assist in improving our understanding of BBB function, providing new insights on neurological disease, as well as developing and screening novel therapeutic drugs.
• McLamore, E. S., Alocilja, E., Gomes, C., Gunasekaran, S., Jenkins, D., Datta, S. P., Li, Y., Mao, Y., Nugen, S. R., Reyes-De-Corcuera, J. I., Takhistov, P., Tsyusko, O., Cochran, J. P., Tzeng, T., Yu, C., Yoon, J., & Zhou, A. (2021). FEAST of Biosensors: Food, Environmental and Agricultural Sensing Technologies (FEAST) in North America. Biosensors and Bioelectronics, 178, 113011. doi:https://doi.org/10.1016/j.bios.2021.113011
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  We review the challenges and opportunities for biosensor research in North America aimed to accelerate translational research. We call for platform approaches based on: i) tools that can support interoperability between food, environment and agriculture, ii) open-source tools for analytics, iii) algorithms used for data and information arbitrage, and iv) use-inspired sensor design. We summarize select mobile devices and phone-based biosensors that couple analytical systems with biosensors for improving decision support. Over 100 biosensors developed by labs in North America were analyzed, including lab-based and portable devices. The results of this literature review show that nearly one quarter of the manuscripts focused on fundamental platform development or material characterization. Among the biosensors analyzed for food (post-harvest) or environmental applications, most devices were based on optical transduction (whether a lab assay or portable device). Most biosensors for agricultural applications were based on electrochemical transduction and few utilized a mobile platform. Presently, the FEAST of biosensors has produced a wealth of opportunity but faces a famine of actionable information without a platform for analytics.
• Schackart III, K. E., & Yoon, J. (2021). Machine Learning Enhances the Performance of Bioreceptor-Free Biosensors. Sensors, 21(16), 5519. doi:https://doi.org/10.3390/s21165519
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  Since their inception, biosensors have frequently employed simple regression models to calculate analyte composition based on the biosensor’s signal magnitude. Traditionally, bioreceptors provide excellent sensitivity and specificity to the biosensor. Increasingly, however, bioreceptor-free biosensors have been developed for a wide range of applications. Without a bioreceptor, maintaining strong specificity and a low limit of detection have become the major challenge. Machine learning (ML) has been introduced to improve the performance of these biosensors, effectively replacing the bioreceptor with modeling to gain specificity. Here, we present how ML has been used to enhance the performance of these bioreceptor-free biosensors. Particularly, we discuss how ML has been used for imaging, Enose and Etongue, and surface-enhanced Raman spectroscopy (SERS) biosensors. Notably, principal component analysis (PCA) combined with support vector machine (SVM) and various artificial neural network (ANN) algorithms have shown outstanding performance in a variety of tasks. We anticipate that ML will continue to improve the performance of bioreceptor-free biosensors, especially with the prospects of sharing trained models and cloud computing for mobile computation. To facilitate this, the biosensing community would benefit from increased contributions to open-access data repositories for biosensor data.
• Zenhausern, R., Chen, C., & Yoon, J. (2021). Microfluidic Sample Preparation for Respiratory Virus Detection: A Review. Biomicrofluidics, 15, 011503. doi:https://doi.org/10.1063/5.0041089
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  Techniques used to prepare clinical samples have been perfected for use in diagnostic testing in a variety of clinical situations, e.g., to extract, concentrate, and purify respiratory virus particles. These techniques offer a high level of purity and concentration of target samples but require significant equipment and highly trained personnel to conduct, which is difficult to achieve in resource-limited environments where rapid testing and diagnostics are crucial for proper handling of respiratory viruses. Microfluidics has popularly been utilized toward rapid virus detection in resource-limited environments, where most devices focused on detection rather than sample preparation. Initial microfluidic prototypes have been hindered by their reliance on several off-chip preprocessing steps and external laboratory equipment. Recently, sample preparation methods have also been incorporated into microfluidics to conduct the virus detection in an all-in-one, automated manner. Extraction, concentration, and purification of viruses have been demonstrated in smaller volumes of samples and reagents, with no need for specialized training or complex machinery. Recent devices show the ability to function independently and efficiently to provide rapid, automated sample preparation as well as the detection of viral samples with high efficiency. In this review, methods of microfluidic sample preparation for the isolation and purification of viral samples are discussed, limitations of current systems are summarized, and potential advances are identified.
• Bills, M. V., & Yoon, J. (2020). Label-free Mie Scattering Identification of Tumor Tissue Using an Angular Photodiode Array. IEEE Sensors Letters, 4(7), 4500704. doi:https://doi.org/10.1109/LSENS.2020.3001489
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  Tumors differ from normal tissues in several meaningful ways, including cellular size, morphology, and protein expression, which will accordingly change the refractive index and the size/morphology of cells. There are also important differences in the tissue organization and unique tissue-specific cell densities. Instead of the time-consuming and labor-intensive histology involving the use of a benchtop microscope, a plot of Mie scattering intensities at a fixed wavelength against the scattering angle, which we referred to as “Mie spectrum,” is suggested as an alternative to identify a tumor from normal tissues. An angular photodiode array is developed to measure this Mie spectrum with three different light-emitting diodes (blue, green, and red) as light sources. The resulting Mie spectra show the characteristic peaks for the rat colonic tissues, and substantial differences can be found between the tumor and normal tissues. Two peaks were identified at 120° and 150° scattering angles, potentially representing the capillaries and colon cells, respectively. Contributions from crypts and goblet cells, represented by the scattering at 140°, were minimal. Substantial differences between the tumor and normal tissues were found with 45°-70° light irradiation angles.
• Bills, M. V., Loh, A., Sosnowski, K., Nguyen, B. T., Ha, S. Y., Yim, U. H., & Yoon, J. (2020). Handheld UV Fluorescence Spectrophotometer Device for the Classification and Analysis of Petroleum Oil Samples. Biosensors and Bioelectronics, 159, 112193. doi:https://doi.org/10.1016/j.bios.2020.112193
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  Oil spills can be environmentally devastating and result in unintended economic and social consequences. An important element of the concerted effort to respond to spills includes the ability to rapidly classify and characterize oil spill samples, preferably on-site. An easy-to-use, handheld sensor is developed and demonstrated in this work, capable of classifying oil spills rapidly on-site. Our device uses the computational power and affordability of a Raspberry Pi microcontroller and a Pi camera, coupled with three ultraviolet light emitting diodes (UV-LEDs), a diffraction grating, and collimation slit, in order to collect a large data set of UV fluorescence fingerprints from various oil samples. Based on a 160-sample (in 5x replicates each with slightly varied dilutions) database this platform is able to classify oil samples into four broad categories: crude oil, heavy fuel oil, light fuel oil, and lubricating oil. The device uses principal component analysis (PCA) to reduce spectral dimensionality (1203 features) and support vector machine (SVM) for classification with 95% accuracy. The device is also able to predict some physiochemical properties, specifically saturate, aromatic, resin, and asphaltene percentages (SARA) based off linear relationships between different principal components (PCs) and the percentages of these residues. Sample preparation for our device is also straightforward and appropriate for field deployment, requiring little more than a Pasteur pipette and not being affected by dilution factors. These properties make our device a valuable field-deployable tool for oil sample analysis.
• Kaarj, K., Madias, M., Akarapipad, P., Cho, S., & Yoon, J. (2020). Paper-based In Vitro Tissue Chip for Delivering Programmed Mechanical Stimuli of Local Compression and Shear Flow. Journal of Biological Engineering, 14, 20. doi:https://doi.org/10.1186/s13036-020-00242-5
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  Mechanical stimuli play important roles on the growth, development, and behavior of tissue. A simple and novel paper-based in vitro tissue chip was developed that can deliver two types of mechanical stimuli—local compression and shear flow—in a programmed manner. Rat vascular endothelial cells (RVECs) were patterned on collagen-coated nitrocellulose paper to create a tissue chip. Localized compression and shear flow were introduced by simply tapping and bending the paper chip in a programmed manner, utilizing an inexpensive servo motor controlled by an Arduino microcontroller and powered by batteries. All electrical compartments and a paper-based tissue chip were enclosed in a single 3D-printed enclosure, allowing the whole device to be independently placed within an incubator. This simple device effectively simulated in vivo conditions and induced successful RVEC migration in as early as 5 h. The developed device provides an inexpensive and flexible alternative for delivering mechanical stimuli to other in vitro tissue models.
• Kaarj, K., Ngo, J., Loera, C., Akarapipad, P., Cho, S., & Yoon, J. (2020). Simple Paper-based Liver Cell Model for Drug Screening. BioChip Journal, 14, 218-229. doi:https://doi.org/10.1007/s13206-020-4211-6
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  Investigation of the potential adverse effects of chemicals and drugs is essential during the drug development process. In vitro cell model systems have been developed over the past years towards such toxicity investigation. 96-well plate is the common platform for screening drug toxicity due to its simplicity. However, this platform only offers 2D cell culture environment and lacks the flow of solutions, which fails to provide the suitable environment for the cells to adequately metabolize the drugs, for the media to replenish, and for the metabolites and wastes to be removed. Microfluidic chips populated with human or animal cells, known as organ-on-a-chip (OOC), can reconcile many issues of in vitro cell models, such as the lack of extracellular matrix and flow as well as the species difference. However, OOC can be complicated to fabricate and operate. To bridge this gap, we utilized paper as a primary substrate for OOC, considering its fibrous structure that can mimic natural extracellular matrix, as well as a syringe pump and filter that are commonly available in most laboratories. Paper microfluidic model was designed and fabricated by wax printing on nitrocellulose paper, seeded and proliferated with liver cells (primary rat hepatocytes and HepG2 cells), and two paper substrates were stacked together to complete the paper model. To this paper-based liver cell model, the following drugs were added: Phenacetin (pain reliever and fever reducer), Bupropion (antidepressant), Dextromethorphan (antidepressant), and phosphate-buffered saline (PBS) as a control, all under a physiologically relevant flow rate. The combination of these drugs with Fluconazole (antifungal drug) was also investigated. Cell count, cell morphology, protein production, and urea secretion after drug treatment confirmed that the model successfully predicted toxicity within 40 minutes. This simple, paper-based liver cell model provided enhanced and faster cell response to drug toxicity and showed comparable or better behavior than the cells cultured in conventional 2D in vitro models.
• Sadeghi, K., Yoon, J., & Seo, J. (2020). Chromogenic Polymers and Their Packaging Applications: A Review. Progress in Polymer Science, 60(3), 442-492. doi:https://doi.org/10.1080/15583724.2019.1676775
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  This review paper provides an overview of chromogenic polymers and their classifications, mechanisms, chemistry, synthesis procedures, and potential applications with a focus on packaging. Commonly and academically accepted classifications derived from chemical engineering, material science, and packaging science are used. Furthermore, recent progress and outputs aligned with chromogenic polymers for overcoming the common challenges are discussed. Finally, future prospects, market trends and academic investigations are described, including challenges related to chromogenic polymers.
• Sosnowski, K., Akarapipad, P., & Yoon, J. (2020). The Future of Microbiome Analysis: Biosensor Methods for Big Data Collection and Clinical Diagnostics. Medical Devices and Sensors, 3(5), e10085. doi:https://doi.org/10.1002/mds3.10085
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  The invisible realm of the human microbiota contains patterns that, when properly detected and interpreted, could indicate much about the health or disease of its host, the human body. Biosensing techniques for the detection of the human microbiota have the potential to transform clinical diagnostics, yet point‐of‐care (POC) biosensors for direct detection of disturbances in microbial communities are not presently available in clinical settings. The objective of this review paper is to explore the potential for biosensors to usher the study of the microbiome into the spaces of clinical diagnostics and big data collection. To achieve this goal, we first outline the types of biosensor methods that have been used to detect multiple targets from clinical and field samples, discuss the challenges inherent in multiplex detection from complex samples and examine the potential for biosensors to integrate microbiome analysis with the diagnostic process. We then consider the potential pitfalls of biosensor‐based microbiome analysis and highlight the anticipation for machine‐learning techniques to address the unique challenges associated with the large variability in microbiota composition between individuals. We finally conclude that biosensor technologies with integrated machine learning algorithms will shape the future of microbiome analysis by allowing for acquisition of vast amounts of microbiome data that can eventually be harnessed in clinical settings for more rapid and accurate diagnoses.
• Ulep, T., Zenhausern, R., Gonzales, A., Knoff, D. S., Lengerke Diaz, P., Castro, J. E., & Yoon, J. (2020). Smartphone based on-chip fluorescence imaging and capillary flow velocity measurement for detecting ROR1+ cancer cells from buffy coat blood samples on dual-layer paper microfluidic chip. Biosensors and Bioelectronics, 153, 112042. doi:https://doi.org/10.1016/j.bios.2020.112042
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  Diagnosis of hematological cancer requires complete white blood cell count, followed by flow cytometry with multiple markers, and cytology. It requires substantial time and specialized training. A dual-layer paper microfluidic chip was developed as a quicker, low-cost, and field-deployable alternative to detect ROR1+ (receptor tyrosine-like orphan receptor one) cancer cells from the undiluted and untreated buffy coat blood samples. The first capture layer consisted of a GF/D glass fiber substrate, preloaded with cancer specific anti-ROR1 conjugated fluorescent particles to its center for cancer cell capture and direct smartphone fluorescence imaging. The second flow layer was comprised of a grade 1 cellulose chromatography paper with wax-printed four channels for wicking and capillary flow-based detection. The flow velocity was used as measure of antigen concentration in the buffy coat sample. In this manner, intact cells and their antigens were separated and independently analyzed by both imaging and flow velocity analyses. A custom-made smartphone-based fluorescence microscope and automated image processing and particle counter software were developed to enumerate particles on paper, with the limit of detection of 1 cell/μL. Flow velocity analysis showed even greater sensitivity, with the limit of detection of 0.1 cells/μL in the first 6 s of assay. Comparison with capillary flow model revealed great alignment with experimental data and greater correlation to viscosity than interfacial tension. Our proposed device is able to capture and on-chip image ROR1+ cancer cells within a complex sample matrix (buffy coat) while simultaneously quantifying cell concentration in a point-of-care manner.
• Zubler, A. V., & Yoon, J. (2020). Proximal Methods for Plant Stress Detection Using Optical Sensors and Machine Learning. Biosensors, 10(12), 193. doi:https://doi.org/10.3390/bios10120193
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  Plant stresses have been monitored using the imaging or spectrometry of plant leaves in the visible (red-green-blue or RGB), near-infrared (NIR), infrared (IR), and ultraviolet (UV) wavebands, often augmented by fluorescence imaging or fluorescence spectrometry. Imaging at multiple specific wavelengths (multi-spectral imaging) or across a wide range of wavelengths (hyperspectral imaging) can provide exceptional information on plant stress and subsequent diseases. Digital cameras, thermal cameras, and optical filters have become available at a low cost in recent years, while hyperspectral cameras have become increasingly more compact and portable. Furthermore, smartphone cameras have dramatically improved in quality, making them a viable option for rapid, on-site stress detection. Due to these developments in imaging technology, plant stresses can be monitored more easily using handheld and field-deployable methods. Recent advances in machine learning algorithms have allowed for images and spectra to be analyzed and classified in a fully automated and reproducible manner, without the need for complicated image or spectrum analysis methods. This review will highlight recent advances in portable (including smartphone-based) detection methods for biotic and abiotic stresses, discuss data processing and machine learning techniques that can produce results for stress identification and classification, and suggest future directions towards the successful translation of these methods into practical use.
• Alouidor, B., Sweeney, R. E., Tat, T., Wong, R. K., & Yoon, J. (2019). Microfluidic Point-of-care Ecarin Based Clotting and Chromogenic Assays for Monitoring Direct Thrombin Inhibitors. Journal of ExtraCorporeal Technology, 51, 29-37.
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  Directthrombininhibitors(DTIs),suchasbivalirudin and dabigatran, have maintained steady inpatient and outpatientuseassubstitutesforheparinandwarfarin,respectively, because of their high bioavailability and relatively safe “ontherapy” range. Current clinical methods lack the capacity to directly quantify plasma DTI concentrations across wide ranges. At present, the gold standard is the ecarin clotting time (ECT), where ecarin maximizes thrombin activity and clotting time is evaluated to assess DTIs’ anticoagulation capability. This work focused on the development of a microfluidic paper analytic device (uPAD) that can quantify the extent of anticoagulation as well as DTI concentration within a patient’s whole blood sample. Capillary action propels a small blood sample to flow through the nitrocellulose paper channels. Digital images of whole blood migration are then captured by our self-coded Raspberry Pi and/or the Samsung Galaxy S8 smartphone camera. Both the flow length and the blue absorbance from the plasma front on the mPAD were measured, allowing simultaneous, dual assays: ecarin clotting test (ECT) and ecarin chromogenic assay (ECA). Statistically significant (p < .05) changes in flow and absorbance were observed within our translational research study. Currently, there are no quantitative, commercially available point-of-care tests for the ECT and ECA within the United States. Both the ECT and ECA assays could be instrumental to differentiate between supratherapeutic and subtherapeutic incidents during bridging anticoagulanttherapyandlimittheunwarranteduseofreversal agents.
• Bills, M. V., Nguyen, B. T., & Yoon, J. (2019). Simplified White Blood Cell Differential: An Inexpensive, Smartphone- and Paper-Based Blood Cell Count. IEEE Sensors Journal, 19(18), 7822-7828. doi:https://doi.org/10.1109/JSEN.2019.2920235
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  Sorting and measuring blood by cell type is extremely valuable clinically and provides physicians with key information for diagnosing many different disease states including: leukemia, autoimmune disorders, and bacterial infections. Despite the value, the present methods are unnecessarily costly and inhibitive particularly in resource poor settings, as they require multiple steps of reagent and/or dye additions and subsequent rinsing followed by manual counting using a hemocytometer, or they require a bulky, expensive equipment such as a flow cytometer. While direct on-paper imaging has been considered challenging, paper substrate offers a strong potential to simplify such reagent/dye addition and rinsing. In this paper, three-layer paper-based device is developed to automate such reagent/dye addition and rinsing via capillary action, and separating white blood cells (WBCs) from whole blood samples. Direct on-paper imaging is demonstrated using a commercial microscope attachment to a smartphone coupled with a blue LED and 500 nm long pass optical filter. Image analysis is accomplished using an original MATLAB code, to evaluate the total WBC count, and differential WBC count, i.e., granulocytes (primarily neutrophils) versus agranulocytes (primarily lymphocytes). Only a finger-prick of whole blood is required for this assay. The total assay time from finger-prick to data collection is under five minutes. Comparison with a hemocytometry-based manual counting corroborates the accuracy and effectiveness of the proposed method. This approach could be potentially used to help make blood cell counting technologies more readily available, especially in resource poor and point-of-care settings.
• Chung, S., Breshears, L. E., Perea, S., Morrison, C. M., Betancourt, W. Q., Reynolds, K. A., & Yoon, J. (2019). Smartphone-Based Paper Microfluidic Particulometry of Norovirus from Environmental Water Samples at the Single Copy Level. ACS Omega, 4(6), 11180-11188. doi:https://doi.org/10.1021/acsomega.9b00772
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  Human enteric viruses can be highly infectious and thus capable of causing disease upon ingestion of low doses ranging from 10^0 to 10^2 virions. Norovirus is a good example with a minimum infectious dose as low as a few tens of virions, that is, below femtogram scale. Norovirus detection from commonly implicated environmental matrices (water and food) involves complicated concentration of viruses and/or amplification of the norovirus genome, thus rendering detection approaches not feasible for field applications. In this work, norovirus detection was performed on a microfluidic paper analytic device without using any sample concentration or nucleic acid amplification steps by directly imaging and counting on-paper aggregation of antibody-conjugated, fluorescent submicron particles. An in-house developed smartphone-based fluorescence microscope and an image-processing algorithm isolated the particles aggregated by antibody–antigen binding, leading to an extremely low limit of norovirus detection, as low as 1 genome copy/μL in deionized water and 10 genome copies/μL in reclaimed wastewater.
• Chung, S., Jennings, C. M., & Yoon, J. (2019). Distance versus Capillary Flow Dynamics‐Based Detection Methods on a Microfluidic Paper‐Based Analytical Device (μPAD). Chemistry - A European Journal, 25(57), 13070-13077. doi:https://doi.org/10.1002/chem.201901514
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  In recent years, there has been high interest in paper‐based microfluidic sensors or microfluidic paper‐based analytical devices (μPADs) towards low‐cost, portable, and easy‐to‐use sensing for chemical and biological targets. μPAD allows spontaneous liquid flow without any external or internal pumping, as well as an innate filtration capability. Although both optical (colorimetric and fluorescent) and electrochemical detection have been demonstrated on μPADs, several limitations still remain, such as the need for additional equipment, vulnerability to ambient lighting perturbation, and inferior sensitivity. Herein, alternative detection methods on μPADs are reviewed to resolve these issues, including relatively well studied distance‐based measurements and the newer capillary flow dynamics‐based method. Detection principles, assay performance, strengths, and weaknesses are explained for these methods, along with their potential future applications towards point‐of‐care medical diagnostics and other field‐based applications.
• Kaarj, K., & Yoon, J. (2019). Methods of Delivering Mechanical Stimuli to Organ-on-a-Chip. Micromachines, 10(10), 700. doi:https://doi.org/10.3390/mi10100700
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  Recent advances in integrating microengineering and tissue engineering have enabled the creation of promising microengineered physiological models, known as organ-on-a-chip (OOC), for experimental medicine and pharmaceutical research. OOCs have been used to recapitulate the physiologically critical features of specific human tissues and organs and their interactions. Application of chemical and mechanical stimuli is critical for tissue development and behavior, and they were also applied to OOC systems. Mechanical stimuli applied to tissues and organs are quite complex in vivo, which have not adequately recapitulated in OOCs. Due to the recent advancement of microengineering, more complicated and physiologically relevant mechanical stimuli are being introduced to OOC systems, and this is the right time to assess the published literature on this topic, especially focusing on the technical details of device design and equipment used. We first discuss the different types of mechanical stimuli applied to OOC systems: shear flow, compression, and stretch/strain. This is followed by the examples of mechanical stimuli-incorporated OOC systems. Finally, we discuss the potential OOC systems where various types of mechanical stimuli can be applied to a single OOC device, as a better, physiologically relevant recapitulation model, towards studying and evaluating experimental medicine, human disease modeling, drug development, and toxicology.
• Klug, K. E., Jennings, C. M., Lytal, N., An, L., & Yoon, J. (2019). Mie Scattering and Microparticle-Based Characterization of Heavy Metal Ions and Classification by Statistical Inference Methods. Royal Society Open Science, 6(5), 190001. doi:https://doi.org/10.1098/rsos.190001
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  A straightforward method for classifying heavy metal ions in water is proposed using statistical classification and clustering techniques from non-specific microparticle scattering data. A set of carboxylated polystyrene microparticles of sizes 0.91, 0.75 and 0.40 µm was mixed with the solutions of nine heavy metal ions and two control cations, and scattering measurements were collected at two angles optimized for scattering from non-aggregated and aggregated particles. Classification of these observations was conducted and compared among several machine learning techniques, including linear discriminant analysis, support vector machine analysis, K-means clustering and K-medians clustering. This study found the highest classification accuracy using the linear discriminant and support vector machine analysis, each reporting high classification rates for heavy metal ions with respect to the model. This may be attributed to moderate correlation between detection angle and particle size. These classification models provide reasonable discrimination between most ion species, with the highest distinction seen for Pb(II), Cd(II), Ni(II) and Co(II), followed by Fe(II) and Fe(III), potentially due to its known sorption with carboxyl groups. The support vector machine analysis was also applied to three different mixture solutions representing leaching from pipes and mine tailings, and showed good correlation with single-species data, specifically with Pb(II) and Ni(II). With more expansive training data and further processing, this method shows promise for low-cost and portable heavy metal identification and sensing.
• Lee, K., Park, H., Baek, S., Han, S., Kim, D., Chung, S., Yoon, J., & Seo, J. (2019). Colorimetric Array Freshness Indicator and Digital Color Processing for Monitoring the Freshness of Packaged Chicken Breast. Food Packaging and Shelf Life, 22, 100408. doi:https://doi.org/10.1016/j.fpsl.2019.100408
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  A colorimetric array freshness indicator was developed to monitor chicken breast spoilage, consisting of an inner poly(ether-block-amide) (PEBA) film, a color-changing layer of eight polymer-immobilized pH dyes, and an outer poly(ethylene terephthalate) film. Simulated experiments with trimethyl amine (TMA) revealed the necessary color changes and the optimum dye concentration for the expected quality range for stored chicken breast was determined. The optimized colorimetric array freshness indicator was then applied to chicken breast packaging and digital images for its color response were acquired using a smartphone camera over storage time. The obtained data were analyzed by both the newly developed chromatic factor and principal component analysis. Chicken breast samples stored at 4 °C and 10 °C could be categorized into two groups, fresh and spoiled states over the storage time. The chromatic parameter X was well correlated with the microorganism counts as well as total volatile base nitrogen (TVBN) and CO2 from the chicken meat samples. Future implementation of the indicator in combination with a smartphone application could provide a low-cost, specific, and sensitive monitoring method for food product freshness.
• Sweeney, R. E., Nguyen, V., Alouidor, B., Budiman, E., Wong, R. K., & Yoon, J. (2019). Flow Rate and Raspberry Pi-based Paper Microfluidic Blood Coagulation Assay Device. IEEE Sensors Journal, 19(13), 4743-4751. doi:https://doi.org/10.1109/JSEN.2019.2902065
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  Monitoring blood coagulation in response to an anticoagulant (heparin) and its reversal agent (protamine) is essential during and after surgery, especially with cardiopulmonary bypass. A current clinical standard is the use of activated clotting time, where the mechanical movement of a plunger through a whole blood-filled channel is monitored to evaluate the endpoint time of coagulation. As a rapid, simple, low-volume, and cost-effective alternative, we have developed a paper microfluidic assay and Raspberry Pi-based device with the aim of quantifying the extent of blood coagulation in response to varying doses of heparin and protamine. The flow rate of blood through the paper microfluidic channel is automatically monitored using the Python-coded edge detection algorithm. For each set of the assay, 8-μL of fresh human whole blood (untreated and undiluted) from human subjects is loaded onto each of eight sample pads, which have been preloaded with varying amounts of heparin or protamine. The total assay time is 3-5 min including the time for sample loading and incubation.
• Ulep, T., Day, A. S., Sosnowski, K., Shumaker, A., & Yoon, J. (2019). Interfacial Effect-Based Quantification of Droplet Isothermal Nucleic Acid Amplification for Bacterial Infection. Scientific Reports, 9, 9629. doi:https://doi.org/10.1038/s41598-019-46028-8
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  Bacterial infection is a widespread problem in humans that can potentially lead to hospitalization and morbidity. The largest obstacle for physicians/clinicians is the time delay in accurately identifying infectious bacteria, especially their sub-species, in order to adequately treat and diagnose such infected patients. Loop-mediated amplification (LAMP) is a nucleic acid amplification method that has been widely used in diagnostic applications due to its simplicity of constant temperature, use of up to 4 to 6 primers (rendering it highly specific), and capability of amplifying low copies of target sequences. Use of interfacial effect-based monitoring is expected to dramatically shorten the time-to-results of nucleic acid amplification techniques. In this work, we developed a LAMP-based point-of-care platform for detection of bacterial infection, utilizing smartphone measurement of contact angle from oil-immersed droplet LAMP reactions. Whole bacteria (Escherichia coli O157:H7) were assayed in buffer as well as 5% diluted human whole blood. Monitoring of droplet LAMP reactions was demonstrated in a three-compartment, isothermal proportional-integrated-derived (PID)-controlled chip. Smartphone-captured images of droplet LAMP reactions, and their contact angles, were evaluated. Contact angle decreased substantially upon target amplification in both buffer and whole blood samples. In comparison, no-target control (NTC) droplets remained stable throughout the 30 min isothermal reactions. These results were explained by the pre-adsorption of plasma proteins to an oil-water interface (lowering contact angle), followed by time-dependent amplicon formation and their preferential adsorption to the plasma protein-occupied oil-water interface. Time-to-results was as fast as 5 min, allowing physicians to quickly make their decision for infected patients. The developed assay demonstrated quantification of bacteria concentration, with a limit-of-detection at 10^2 CFU/μL for buffer samples, and binary target or no-target identification with a limit-of-detection at 10 CFU/μL for 5% diluted whole blood samples.
• Baynes, C., & Yoon, J. (2018). μPAD Fluorescence Scattering Immunoagglutination Assay for Cancer Biomarkers from Blood and Serum. SLAS Technology, 23(1), 30-43. doi:10.1177/2472630317731891
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  A microfluidic paper analytical device (μPAD) was created for the sensitive quantification of cancer antigens, carcinoembryonic antigen (CEA) and carbohydrate antigen 19-9 (CA 19-9), from human whole blood and serum, toward diagnosis and prognosis of colorectal cancer. Anti-CEA and anti–CA 19-9 antibodies were covalently linked to submicron, fluorescent polystyrene particles, loaded, and then dried in the center of the μPAD channel. CEA- or CA 19-9–spiked blood or serum samples were loaded to the inlet of μPAD, and subsequent immunoagglutination changed the fluorescent scatter signals upon ultraviolet (UV) excitation. The total assay time was about 1 min. Detection limits were 1 pg/mL for CEA and 0.1 U/mL for CA 19-9 from both 10% diluted blood and undiluted serum. The use of UV excitation and subsequent fluorescence scattering enabled much higher double-normalized intensities (up to 1.28–3.51, compared with 1.067 with the elastic Mie scatter detection), successful detection in the presence of blood or serum, and distinct multiplex assays with minimum cross-reaction of antibodies. The results with undiluted serum showed the larger dynamic range and smaller standard errors, which can be attributed to the presence of serum proteins, functioning as a stabilizer or a passivating protein for the particles within paper fibers.
• Chung, S., Breshears, L. E., & Yoon, J. (2018). Smartphone Near Infrared Monitoring of Plant Stress. Computers and Electronics in Agriculture, 154, 93-98. doi:10.1016/j.compag.2018.08.046
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  The most widely used method for monitoring plant stress is the use of near infrared (NIR) spectrophotometry to calculate normalized difference vegetation index (NDVI), as defined by [NIR reflectance − red reflectance]/[NIR reflectance + red reflectance]. NDVI measures the chlorophyll absorption in the red spectrum relative to the scattering by cellular structure in NIR, and has been used to monitor vegetation health and subsequently its stress from aerial or satellite images. Rather than using an NIR spectrophotometer or an NIR camera that is rather expensive, we attempted to use a commercial smartphone, utilizing its (potentially unintended) ability in recognizing near infrared (NIR) color. Some of the most recent versions of smartphones have eliminated the NIR block filters on their cameras, and able to recognize NIR in their red pixels of CMOS array. Through attaching an inexpensive high pass filter at 800 nm to a smartphone camera, we were able to collect the NIR reflectance (with a high pass optical filter) and the red reflectance (without a filter), enabling NDVI assessments. This method was verified by measuring the NDVI values from a series of chlorophyll solutions, and showed a strong linear correlation with R^2 = 0.948, corroborating the smartphone’s ability in evaluating NDVI. Using the leaves from three different plant species, the NDVI values were evaluated using the smartphone and compared with the plants' chlorophyll contents using acetone extraction and subsequent spectrophotometry. A good linear relationship was found with R^2 = 0.88-0.92. We further evaluated the NDVI values against the plants’ water contents (measured by oven-drying), showing the non-linear relationship with the NDVI saturation above 50% water content. The assay time was almost instantaneous, requiring only a smartphone and a high pass filter, thus allowing inexpensive, easy-to-use, rapid, and early prediction of plant stress that can be used for field and household applications.
• Kaarj, K., Akarapipad, P., & Yoon, J. (2018). Simpler, Faster, and Sensitive Zika Virus Assay Using Smartphone Detection of Loop-Mediated Isothermal Amplification on Paper Microfluidic Chips. Scientific Reports, 8(12438). doi:10.1038/s41598-018-30797-9
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  The recent Zika virus (ZIKV) outbreak has prompted the need for field-ready diagnostics that are rapid, easy-to-use, handheld, and disposable while providing extreme sensitivity and specificity. To meet this demand, we developed a wax-printed paper microfluidic chip utilizing reverse transcription loop-mediated isothermal amplification (RT-LAMP). The developed simple and sensitive ZIKV assay was demonstrated using undiluted tap water, human urine, and diluted (10%) human blood plasma. Paper type, pore size, and channel dimension of various paper microfluidic chips were investigated and optimized to ensure proper filtration of direct-use biological samples (tap water, urine, and plasma) during capillary action-driven flow. Once ZIKV RNA has flowed and reached to a detection area of the paper microfluidic chip, it was excised for the addition of an RT-LAMP mixture with a pH indicator, then placed on a hot plate at 68 C. Visible color changes from successful amplification were observed in 15 minutes and quantified by smartphone imaging. The limit of detection was as low as 1 copy/uL. The developed platform can also be used for identifying other flaviviruses, such as Chikungunya virus (CHIKV) and Dengue virus (DENV), and potentially other quickly transmitted virus pathogens, towards field-based diagnostics.
• Klug, K. E., Reynolds, K. A., & Yoon, J. (2018). A Capillary Flow Dynamics-Based Sensing Modality for Direct Environmental Pathogen Monitoring. Chemistry - A European Journal, 24(23), 6025-6029. doi:10.1002/chem.201800085
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  Toward ultra‐simple and field‐ready biosensors, we demonstrate a novel assay transducer mechanism based on interfacial property changes and capillary flow dynamics in antibody‐conjugated submicron particle suspensions. Differential capillary flow is tunable, allowing pathogen quantification as a function of flow rate through a paper‐based microfluidic device. Flow models based on interfacial and rheological properties indicate a significant relationship between the flow rate and the interfacial effects caused by target‐particle aggregation. This mechanism is demonstrated for assays of Escherichia coli K12 in water samples and Zika virus (ZIKV) in blood serum. These assays achieved very low limits of detection compared with other demonstrated methods (1 log CFU/mL E. coli and 20 pg/mL ZIKV whole virus) with an operating time of 30 s, showing promise for environmental and health monitoring.
• Ulep, T., & Yoon, J. (2018). Challenges in Paper-Based Fluorogenic Optical Sensing with Smartphones. Nano Convergence, 5(14). doi:10.1186/s40580-018-0146-1
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  Application of optically superior, tunable fluorescent nanotechnologies have long been demonstrated throughout many chemical and biological sensing applications. Combined with microfluidics technologies, i.e. on lab-on-a-chip platforms, such fluorescent nanotechnologies have often enabled extreme sensitivity, sometimes down to single molecule level. Within recent years there has been a peak interest in translating fluorescent nanotechnology onto paper-based platforms for chemical and biological sensing, as a simple, low-cost, disposable alternative to conventional silicone-based microfluidic substrates. On the other hand, smartphone integration as an optical detection system as well as user interface and data processing component has been widely attempted, serving as a gateway to on-board quantitative processing, enhanced mobility, and interconnectivity with informational networks. Smartphone sensing can be integrated to these paper-based fluorogenic assays towards demonstrating extreme sensitivity as well as ease-of-use and low-cost. However, with these emerging technologies there are always technical limitations that must be addressed; for example, paper’s autofluorescence that perturbs fluorogenic sensing; smartphone flash’s limitations in fluorescent excitation; smartphone camera’s limitations in detecting narrow-band fluorescent emission, etc. In this review, physical optical setups, digital enhancement algorithms, and various fluorescent measurement techniques are discussed and pinpointed as areas of opportunities to further improve paper-based fluorogenic optical sensing with smartphones.
• Cho, S., & Yoon, J. (2017). Organ-on-a-Chip for Assessing Environmental Toxicants. Current Opinion in Biotechnology, 45, 34-42. doi:10.1016/j.copbio.2016.11.019
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  Man-made xenobiotics, whose potential toxicological effects are not fully understood, are oversaturating the already-contaminated environment. Due to the rate of toxicant accumulation, unmanaged disposal, and unknown adverse effects to the environment and the human population, there is a crucial need to screen for environmental toxicants. Animal models and in vitro models are ineffective models in predicting in vivo responses due to inter-species difference and/or lack of physiologically-relevant 3D tissue environment. Such conventional screening assays possess limitations that prevent dynamic understanding of toxicants and their metabolites produced in the human body. Organ-on-a-chip systems can recapitulate in vivo like environment and subsequently in vivo like responses generating a realistic mock-up of human organs of interest, which can potentially provide human physiology-relevant models for studying environmental toxicology. Feasibility, tunability, and low-maintenance features of organ-on-chips can also make possible to construct an interconnected network of multiple-organs-on-chip towards a realistic human-on-a-chip system. Such interconnected organ-on-a-chip network can be efficiently utilized for toxicological studies by enabling the study of metabolism, collective response, and fate of toxicants through its journey in the human body. Further advancements can address the challenges of this technology, which potentiates high predictive power for environmental toxicology studies.
• Cho, S., Park, T. S., Reynolds, K. A., & Yoon, J. (2017). Multi-Normalization and Interpolation Protocol to Improve Norovirus Immunoagglutination Assay from Paper Microfluidics with Smartphone Detection. SLAS Technology, 22(6), 609-615. doi:10.1177/2472630317724769
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  Norovirus (NoV) is one of the leading causes of acute gastroenteritis, affecting 685 million people per year around the world. The best preventive measure is to screen water for possible NoV contamination, not from infected humans, preferably using rapid and field-deployable diagnostic methods. While enzyme immunoassays (EIAs) can be used for such detection, the low infectious dose as well as the generally inferior sensitivity and low titer of available NoV antibodies render critical challenges in using EIAs toward NoV detection. In this work, we demonstrated smartphone-based Mie scatter detection of NoV with immunoagglutinated latex particles on paper microfluidic chips. Using only three different concentrations of anti-NoV-conjugated particles, we were able to construct a single standard curve that covered seven orders of magnitude of NoV antigen concentrations. Multiple normalization steps and interpolation procedures were developed to estimate the optimum amount of antibody-conjugated particles that matched to the target NoV concentration. A very low detection limit of 10 pg/mL was achieved without using any concentration or enrichment steps. This method can also be adapted for detection of any other virus pathogens whose antibodies possess low sensitivity and low antibody titer.
• McCracken, K. E., Tat, T., Paz, V., & Yoon, J. (2017). Smartphone-Based Fluorescence Detection of Bisphenol A from Water Samples. RSC Advances, 7(15), 9237-9243. doi:10.1039/C6RA27726H
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  Bisphenol A (BPA), an emerging environmental contaminant and endocrine disrupting compound, has been observed globally in surface waters and waste leachates at concentrations that are hazardous to aquatic life and potentially to humans. Limitations in field monitoring on account of the extensive laboratory infrastructure required for standard BPA detection warrants investigation into portable or handheld sensing platforms. In this work, we evaluated a standalone smartphone-based fluorescence sensing method for identifying BPA from water samples. Toward this goal, we demonstrated the novel application of 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS) as a fluorescent probe with suitable specificity to BPA compared to functionally and structurally similar hormone and endocrine disrupting compounds. Using this method, bisphenol A was quantifiable through both standard fluorescence spectroscopy and smartphone detection, with an empirical binding constant of K_SV = 2040 M^-1 and a direct, unfiltered detection limit of 4.4 μM from unprocessed samples, suitable for waste leachate and industrial samples. Implementation of further digital image processing and smartphone spectroscopy methods may help to lower this detection limit, bearing promise for future direct detection of bisphenol A from wastewater leachate and environmental samples via smartphones.
• Nicolini, A. M., McCracken, K. E., & Yoon, J. (2017). Future Developments in Biosensors for Field-Ready Zika Virus Diagnostics. Journal of Biological Engineering, 11, 7. doi:10.1186/s13036-016-0046-z
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  Since early reports of the ongoing Zika virus outbreak in May 2015, much has been learned and discussed regarding Zika virus infection and transmission. However, many opportunities still remain for translating these findings into field-ready sensors and diagnostics. In this brief review, we discuss current diagnostic methods, consider the prospects of translating other flavivirus biosensors directly to Zika virus sensing, and look toward the future developments needed for high-sensitivity and high-specificity biosensors to come.
• Nicolini, A. M., Toth, T. D., Kim, S. Y., Mandel, M. A., Galbraith, D. W., & Yoon, J. (2017). Mie Scatter and Interfacial Tension Based Real-Time Quantification of Colloidal Emulsion Nucleic Acid Amplification. Advanced Biosystems, 1(10), 1700098. doi:10.1002/adbi.201700098
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  This work demonstrates for the first time rapid, real-time Mie scatter sensing of colloidal emulsion nucleic acid amplification directly from emulsion droplets. Loop-mediated isothermal amplification is used in this study, and, to our knowledge, has not previously been used in a colloidal emulsion platform. Interfacial tension values (γ) associated with bulk protein adsorption and denaturation at the oil–water interface exhibit characteristic changes in the absence or presence of amplification. In the presence of target and amplicon, emulsions maintain a constant 300–400 nm diameter, whereas emulsions formed with no target control show a rapid decrease in droplet diameter to
• Park, T. S., Cho, S., Nahapetian, T. G., & Yoon, J. (2017). Smartphone Detection of UV LED Enhanced Particle Immunoassay on Paper Microfluidics. SLAS Technology, 22(1), 7-12. doi:10.1177/2211068216639566
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  Use of a smartphone as an optical detector for paper microfluidic devices has recently gained substantial attention due to its simplicity, ease-of-use, and handheld capability. Utilization of a UV light source enhances the optical signal intensities, especially for the particle immunoagglutination assay that has typically utilized visible or ambient light. Such enhancement is essential for true assimilation of assays to field deployable and point-of-care applications by greatly reducing the effects by independent environmental factors. This work is the first demonstration of utilizing a UV LED (UVA) to enhance the Mie scatter signals from the particle immunoagglutination assay on the paper microfluidic devices, and subsequent smartphone detection. Smartphone’s CMOS camera can recognize the UVA scatter from the paper microfluidic channels efficiently in its green channel. For Escherichia coli assay, the normalized signal intensities increased up to 50% from the negative signal with UV LED, compared to the 4-7% with ambient light. Detection limit was 10 CFU/mL. Similar results were obtained in the presence of 10% human whole blood.
• Sweeney, R. E., & Yoon, J. (2017). Angular Photodiode Array-Based Device to Detect Bacterial Pathogens in a Wound Model. IEEE Sensors Journal, 17(21), 6911-6917. doi:10.1109/JSEN.2017.2752155
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  We have developed a device that is able to rapidly and specifically diagnose bacterial pathogens in a wound model based on Mie scatter spectra from a tissue surface. The Mie scatter spectra collected is defined as the intensity of Mie scatter over the angle of detection from a tissue surface. A 650-nm LED perpendicular to the surface illuminates a tissue sample (90°) and photodiodes positioned in 10° increments from 10° to 80° of backscatter act as the detectors to collect these Mie scatter spectra. Through principal component analysis of the Mie scatter spectra collected, we have shown significant differences between Mie scatter spectra of tissues with bacterial pathogens versus those without, as well as significant differences between each species of bacteria tested. The device developed has been tested with a porcine dermis wound model, with samples inoculated with one of three bacterial species (Staphylococcus aureus, Escherichia coli, or Salmonella Typhimurium). Such a device could be critical in the monitoring of a wound for infection and rapid, specific diagnosis of a bacterial wound infection, which would significantly reduce the time and cost associated with specific diagnosis of a bacterial wound infection currently.
• Sweeney, R. E., Budiman, E., & Yoon, J. (2017). Mie Scatter Spectra-Based Device for Instant, Contact-Free, and Specific Diagnosis of Bacterial Skin Infection. Scientific Reports, 7, 4801. doi:10.1038/s41598-017-05061-1
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  Rapid and specific diagnostic techniques are needed to expedite specific treatment of bacterial skin infections with narrow-spectrum antibiotics, rather than broad-spectrum. Through this work a device was developed to determine the presence of and species responsible for a bacterial skin infection using differences in Mie scatter spectra created by different bacterial species. A 650 nm LED at five different incident angles is used to illuminate the tissue, with Mie scatter being detected by PIN photodiodes at eight different detection angles. Mie scatter patterns are collected at all photodiode angles for each of the incident light angles, resulting in a Mie scatter spectra. Detectable differences in Mie scatter spectra were found using the device developed between commensal bacteria (no infection) and bacteria inoculated (infection) on the surface of both porcine and human cadaveric epidermis. Detectable differences were found between species of infection, specifically Escherichia coli and Staphylococcus aureus, with differences summarized through principle component analysis. Mie scatter spectra can be detected within a few seconds without skin contact. This device is the first to rapidly and specifically diagnose bacterial skin infections in a contact-less manner, allowing for initial treatment with narrow spectrum antibiotics, and helping to reduce the likelihood of resistance.
• Yoon, J. (2017). Towards the 10-Year Milestone of Journal of Biological Engineering. Journal of Biological Engineering, 11, 3. doi:10.1186/s13036-016-0038-z
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  October 10th, 2016 marked the 9th anniversary for the Journal of Biological Engineering (JBE), the official journal of Institute of Biological Engineering (IBE), published by BioMed Central. We are entering into the 10th year of its exciting and productive history. In this editorial, a brief history of JBE is summarized, along with a series of analyses on average number of citations, breakdown of topical subjects, geographical representations and so forth for all published articles in JBE. Future prospects and new directions of JBE are also described in this editorial.
• Cho, S., Islas-Robles, A., Nicolini, A. M., Monks, T. J., & Yoon, J. (2016). In Situ, Dual-Mode Monitoring of Organ-on-a-Chip with Smartphone-Based Fluorescence Microscope. Biosensors and Bioelectronics, 86, 697-705. doi:10.1016/j.bios.2016.07.015
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  The use of organ-on-a-chip (OOC) platforms enables improved simulation of the human kidney’s response to nephrotoxic drugs. The standard method of analyzing nephrotoxicity from existing OOC has majorly consisted of invasively collecting samples (cells, lysates, media, etc.) from OOC. Such disruptive analyses potentiate contamination, disrupt the replicated in vivo environment, and require expertise to execute. Moreover, traditional analyses, including immunofluorescence microscopy, immunoblot, and microplate immunoassay are essentially not in situ and require substantial time, resources, and cost. In the present work, the incorporation of fluorescence nanoparticle immunocapture/immunoagglutination assay into an OOC enabled dual-mode monitoring of drug-induced nephrotoxicity in situ. A smartphone-based fluorescence microscope was fabricated as a handheld in situ monitoring device attached to an OOC. Both the presence of γ-glutamyl transpeptidase (GGT) on the apical brush-border membrane of 786-O proximal tubule cells within the OOC surface, and the release of GGT to the outflow of the OOC were evaluated with the fluorescence scatter detection of captured and immunoagglutinated anti-GGT conjugated nanoparticles. This dual-mode assay method provides a novel groundbreaking tool to enable the internal and external in situ monitoring of the OOC, which may be integrated into any existing OOCs to facilitate their subsequent analyses.
• McCracken, K. E., & Yoon, J. (2016). Recent Approaches for Optical Smartphone Sensing in Resource-Limited Settings: A Brief Review. Analytical Methods, 8, 6591-6601. doi:10.1039/C6AY01575A
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  Developments in the emerging fields of smartphone chemical and biosensing have dovetailed with increased interest in environmental and health monitoring for resource-limited environments, culminating in research toward field-ready smartphone sensors. Optical sensors have received particular focus, in which smartphone imaging and on-board analysis have been integrated into both existing and novel colorimetric, fluorescent, chemiluminescent, spectroscopy-based, and scattering-based assays. Research in recent years has shown promising progress, but substantial limitations still exist due to environmental lighting interference, reliance upon proprietary smartphone attachments, and the undefined sensitivity variations between different smartphones. In this review, recent research in smartphone chemical and biosensing is assessed, and discussion is made regarding the opportunities that new research methods have to improve the scope resource-limited sensing.
• McCracken, K. E., Angus, S. V., Reynolds, K. A., & Yoon, J. (2016). Multimodal Imaging and Lighting Bias Correction for Improved uPAD-based Water Quality Monitoring via Smartphones. Scientific Reports, 6(27529). doi:10.1038/srep27529
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  Smartphone image-based sensing of microfluidic paper analytical devices (μPADs) offers low-cost and mobile evaluation of water quality. However, consistent quantification is a challenge due to variable environmental, paper, and lighting conditions, especially across large multi-target μPADs. Compensations must be made for variations between images to achieve reproducible results without a separate lighting enclosure. We thus developed a simple method using triple-reference point normalization and a fast-Fourier transform (FFT)-based pre-processing scheme to quantify consistent reflected light intensity signals under variable lighting and channel conditions. This technique was evaluated using various angles/heights of light source, imaging backgrounds, and type/quality of light source. Further testing evaluated its handle of absorbance, quenching, and relative scattering intensity measurements from assays detecting four water contaminants – Cr(VI), total chlorine, caffeine, and E. coli K12 – at similar wavelengths using the green channel of RGB images. Between assays, this algorithm reduced error from μPAD surface inconsistencies and cross-image lighting gradients. Although the algorithm could not completely remove the anomalies arising from point shadows within channels or some non-uniform background reflections, it still afforded order-of-magnitude quantification and stable assay specificity under these conditions, offering one route toward improving smartphone quantification of μPAD assays for in-field water quality monitoring.
• Nicolini, A. M., Toth, T. D., & Yoon, J. (2016). Tuneable Nanoparticle-Nanofiber Composite Substrate for Improved Cellular Adhesion. Colloids and Surfaces B: Biointerfaces, 145, 830-838. doi:10.1016/j.colsurfb.2016.05.079
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  This work presents a novel technique using a reverse potential electrospinning mode for fabricating nanoparticle-embedded composites that can be tailored to represent various fiber diameters, surface morphologies, and functional groups necessary for improved cellular adhesion. Polycaprolactone (PCL) nanofibers were electrospun in both traditional positive (PP) and reverse potential (RP) electrical fields. The fibers were incorporated with 300 nm polystyrene (PS) fluorescent particles, which contained carboxyl, amine groups, and surfactants. In the unconventional RP, the charged colloidal particles and surfactants were shown to have an exaggerated effect on Taylor cone morphology and fiber diameter caused by the changes in charge density and surface tension of the bulk solution. The RP mode was shown to lead to a decrease in fiber diameter from 1200 ± 100 nm (diameter ± SE) for the nanofibers made with PCL alone to 440 ± 80 nm with the incorporation of colloidal particles, compared to the PP mode ranging from 530 ± 90 nm to 350 ± 50 nm, respectively. The nanoparticle-nanofiber composite substrates were cultured with human umbilical vein endothelial cells (HUVECs) and evaluated for cellular viability and adhesion for up to 5 days. Adhesion to the nanofibrous substrates was improved by 180 ± 10% with the addition of carboxylated particles and by 480 ± 60% with the functionalization of an RGD ligand compared to the PCL nanofibers. The novel approach of electrospinning in the RP mode with the addition of colloids in order to alter charge density and surface tension could be utilized towards many applications, one being implantable biomaterials and tissue engineered scaffolds as demonstrated in this work.
• Angus, S. V., Cho, S., Harshman, D. K., Song, J., & Yoon, J. (2015). A Portable, Shock-Proof, Surface-Heated Droplet PCR System for Escherichia coli Detection. Biosensors and Bioelectronics, 74, 360-368. doi:10.1016/j.bios.2015.06.026
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  A novel quantitative polymerase chain reaction (qPCR) device was developed based on wire-guided droplet manipulation (WDM) method, where the droplet is guided to move over three different heating chambers, and subsequent real-time quantification utilizing a smartphone. The device was initially tested to amplify GAPDH (glyceraldehyde-3-phosphate dehydrogenase) gene and further tested to identify 16S rRNA gene (V3 hypervariable region) from Escherichia coli. The lower limit of detection was 10^3 CFU (colony forming units) or genome copies per sample. The device is portable with real-time quantification and provides the assay results quickly (30-cycle amplification for 15 min) and accurately. The system is also shock and vibration resistant, due to the multiple points of contact using the thermocouple to guide the droplet and the Teflon film on the heater surfaces. The thermocouple is also used to provide real-time temperature feedback on the droplet to ensure it reaches the set temperature before moving to the next chamber/step in PCR. The device is equipped to use either silicone oil or coconut oil, while the latter provides additional portability (without spilling and easier transportation) with its high melting temperature (solid at room temperature).
• Cho, S., Park, T. S., Nahapetian, T. G., & Yoon, J. (2015). Smartphone-based, sensitive uPAD detection of urinary tract infection and gonorrhea. Biosensors and Bioelectronics, 74, 601-611. doi:10.1016/j.bios.2015.07.014
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  The presence of bacteria in urine can be used to monitor the onset or prognosis of urinary tract infection (UTI) and some sexually-transmitted diseases (STDs), such as gonorrhea. Typically, bacteria’s presence in urine is confirmed by culturing samples overnight on agar plates, followed by a microscopic examination. Additionally, the presence of E. coli in a urine sample can be indirectly confirmed through assaying for nitrite (generated by reducing nitrate in urine), however this is not sufficiently specific and sensitive. Species/strains identification of bacteria in a urine sample provides insight to appropriate antibiotic treatment options. In this work, a microfluidic paper analytic device (uPAD) was designed and fabricated for evaluating UTI (Escherichia coli) and STD (Neisseria gonorrhoeae) from human urine samples. Anti-E. coli or anti-N. gonorrhoeae antibodies were conjugated to submicron particles then pre-loaded and dried in the center of each paper microfluidic channel. Human urine samples (undiluted) spiked with E. coli or N. gonorrhoeae were incubated for 5 minutes with 1% Tween 80. The bacteria-spiked urine samples were then introduced to the inlet of paper microfluidic channel, which flowed through the channel by capillary force. Data confirms proteins were not filtered by uPAD, which is essential for this assay. Urobilin, the component responsible for the yellow appearance of urine and green fluorescence emission, was filtered by uPAD, resulting in significantly minimized false-positive signals. This filtration was simultaneously made during the uPAD assay and no pretreatment/purification step was necessary. Antibody-conjugated particles were immunoagglutinated at the center of the paper channel. The extent of immunoagglutination was quantified by angle-specific Mie scatter under ambient lighting conditions, utilizing a smartphone camera as a detector. The total uPAD assay time was less than 30 seconds. The detection limit was 10 CFU/mL for both E. coli and N. gonorrhoeae, while commercially available gonorrhea rapid kit showed a detection limit of 10^6 CFU/mL. A commercially available nitrite assay test strip also had a detection limit of 10^6 CFU/mL, but this method is not antibody-based and thus not sufficiently specific. By optimizing the particle concentration, we were also able to extend the linear range of the assay up to 10^7 CFU/mL. The proposed prototype will serve as a low-cost, point-of-care, sensitive urinalysis biosensor to monitor UTI and gonorrhea from human urine.
• Fronczek, C. F., & Yoon, J. (2015). Biosensors for Monitoring Airborne Pathogens. Journal of Laboratory Automation, 20(4), 309-410. doi:10.1177/2211068215580935
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  Airborne pathogens affect both humans and animals and are often highly and rapidly transmittable. Many problematic airborne pathogens, namely viral (influenza A/H1N1, rubella, and avian influenza/H5N1) and bacterial (Mycobacterium tuberculosis, Streptococcus pneumoniae, and Bacillus anthracis) have huge impacts on healthcare and agricultural applications and can potentially be used as bio-terrorism agents. Many different laboratory-based methods have been introduced and are currently being used. However, such detection is generally limited by sample collection, including nasal swabs and blood analysis. Direct identification from air (specifically aerosol samples) would be ideal, but such detection has not been very successful due to the difficulty in sample collection and the extremely low pathogen concentration found in aerosol samples. In this review, we will discuss the portable biosensors and/or micro total analysis system (μTAS) that can be used for monitoring such airborne pathogens, similar to smoke detectors. Current laboratory-based methods will be reviewed and the possible solutions to convert these lab-based methods into μTAS biosensor will be discussed.
• Harshman, D. K., Rao, B. M., Mclain, J. E., Watts, G. S., & Yoon, J. (2015). Interfacial effects revolutionize qPCR by low threshold cycle detection and inhibition relief. Science Advances, 1(8), e1400061. doi:10.1126/sciadv.1400061
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  Molecular diagnostics offer quick access to information but fail to operate at speeds required for clinical decision-making. Our novel methodology for droplet on thermocouple silhouette real-time PCR (DOTS qPCR) utilizes interfacial effects to achieve droplet actuation, inhibition relief and sensing, for a sample-to-answer time as short as 5 min. Towards diagnosis of infective endocarditis we demonstrate reproducibility, differentiation of antibiotic susceptibility, sub-picogram limit of detection, and thermocycling speeds of 28 s/cycle in the presence of tissue contaminants. Langmuir and Gibbs adsorption isotherms are used to describe interfacial tension decrease upon amplification, and a log-linear relationship is presented for real-time quantification at the fifth thermocycle, by imaging the droplet silhouette with a smartphone. Commercially available real-time PCR systems that rely on fluorescent detection have substantially higher threshold cycles and require expensive optical components and extensive sample preparation. Our work is the first demonstrated use of interfacial effects for sensing of reaction progress and will enable molecular diagnosis of infection at the point-of-care.
• Liang, P., Nicolini, A. M., Ogden, K. L., & Yoon, J. (2015). Use of biosensors in secondary education classroom. Transactions of the ASABE, 58(2), 181-190. doi:10.13031/trans.58.10631
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  The multidisciplinary and multi-application character of a biosensor makes it a very attractive topic to introduce science and engineering concepts into a secondary education classroom. Some of the techniques used in biosensors are easy to demonstrate and can be intriguing to students. We evaluated which application areas and techniques were more intriguing to the students through a survey, and developed a 60-90-min introductory lesson plan with hands-on experience. The survey was conducted to determine students’ greatest interest and motivation among four biosensor applications- medical diagnostics, food safety, biosecurity, and environmental monitoring- as well as seven techniques used in biosensors: genetic engineering, nanotechnology, circuit building, microfabrication, 3D printing, smartphone utilization, and computer programming. For the application areas, the middle school students showed the most interest in food safety, followed by environmental monitoring and medical diagnostics. The high school students showed the most interest in medical diagnostics. For the techniques used in biosensors, the middle school students showed the most interest in 3D printing, followed by circuit building and smartphone utilization, while the high school students showed the most interests in genetic engineering and nanotechnology. To capture the most interest early in the students’ education, we have designed a 60-90-min lesson plan for middle school students utilizing the application areas of food safety and environmental monitoring, as well as the techniques of 3D printing, circuit building, and smartphone utilization. Simplified sampling protocols are introduced for monitoring E. coli from lettuce, Salmonella from chicken packaging, and influenza A from aerosols. As an example of a biosensor, a commercial glucose assay kit is demonstrated using a simple photometric circuit (including an LED and a photodiode) as an optical transducer. As a second example, a commercial pregnancy test strip is demonstrated using a smartphone camera as an optical transducer. Finally, a plastic attachment to a smartphone, made with a 3D printer, is demonstrated to improve the sensitivity and reproducibility of the same pregnancy test. This lesson was carried out in a classroom, and the results exemplify the potential benefit of using biosensor research in a middle school classroom as well as the possibility of inspiring the students towards science and engineering fields of study or careers.
• Nicolini, A. M., Fronczek, C. F., & Yoon, J. (2015). Droplet-Based Immunoassay on a 'Sticky' Nanofibrous Surface for Multiplexed and Double Detection of Bacteria Using Smartphones. Biosensors and Bioelectronics, 67, 560-569.
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  We have developed a rapid, sensitive, and specific droplet-based immunoassay for the detection of E. coli and Salmonella within a single-pipetted sample. Polycaprolactone (PCL) electrospun fibers on indium-tin-oxide (ITO) glass provide a sufficient surface to render a non-slip droplet condition, and while the PCL fibers lend a local hydrophilicity (contact angle theta = 74 deg) for sufficient sub-micron particle adhesion, air pockets within the fibers lend an apparent hydrophobicity. Overall, the contact angle of water on this electrospun surface is 119 deg, and the air pockets cause the droplet to be completely immobile and resistant to movement, protecting it from external vibration. By using both anti-E. coli conjugated, 510 nm diameter green fluorescent particles (480 nm excitation and 520 nm emission) and anti-Salmonella conjugated, 400 nm diameter red fluorescent particles (640 nm excitation and 690 nm emission), we can detect multiple targets in a single droplet. Using appropriate light sources guided by fiber optics, we determined a detection limit of 10^2 CFU/mL. Immunoagglutination can be observed under a fluorescence microscope. Fluorescence detection (at the emission wavelength) of immunoagglutination was maximum at 90 degrees from the incident light, while light scattering (at the excitation wavelength) was still present and behaved similarly, indicating the ability of double detection, greatly improving credibility and reproducibility of the assay. A power function (light intensity) simulation of elastic Mie scatter confirmed that both fluorescence and light scattering were present. Due to the size of the fluorescent particles relative to their incident excitation wavelengths, Mie scatter conditions were observed, and fluorescence signals show a similar trend to light scattering signals. Smartphone detection was included for true portable detection, in which the high contact angle pinning of the droplet makes this format re-usable and re-configurable.
• Park, T. S., & Yoon, J. (2015). Smartphone Detection of Escherichia coli from Field Water Samples on Paper Microfluidics. IEEE Sensors Journal, 15(3), 1902-1907.
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  Smartphone detection of Escherichia coli from field water samples is successfully demonstrated using paper microfluidics. A three-channel paper chip is designed and fabricated, with a negative control channel pre-loaded with bovine serum albumin (BSA) conjugated beads and two E. coli detection channels pre-loaded with anti-E. coli conjugated beads, for low and high concentration detection. Field water samples are introduced to the paper chip by dipping or pipetting, and the antigens from E. coli travel through the paper fibers by capillary action while the dust/soil or algae particles are effectively filtered. Antibody-conjugated beads, confined within the paper fibers, immunoagglutinate in the presence of E. coli antigens, while BSA-conjugated beads do not. The extent of immunoagglutination is quantified by evaluating Mie scatter intensity from the digital images taken at an optimized angle and distance using a smartphone. The assay results show excellent agreement with the MacConkey plate results, i.e. the count of viable E. coli. The scatter simulation procedure is introduced to substitute for experimental optimization, such that the proposed method can be easily adapted to the other types of samples. A smartphone application is developed, incorporating the internal gyroscope of a smartphone, to allow the user to position the smartphone at an optimized angle of scatter detection. The detection limit is single-cell-level and the total assay time is 90 seconds.
• Fronczek, C. F., Park, T. S., Harshman, D. K., Nicolini, A. M., & Yoon, J. (2014). Paper microfluidic extraction and direct smartphone-based identification of pathogenic nucleic acids from field and clinical samples. RSC Advances, 4(22), 11103-11110.
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  Abstract: A rapid, paper microfluidic- and smartphone-based protocol was developed for the extraction and direct fluorescent identification of the nucleic acids of Salmonella Typhimurium from field and clinical samples. Initially, liquid samples (10% diluted) from fresh poultry packaging were loaded on the paper chips and were lysed with Tris-EDTA (TE) buffer. Nucleic acids from the lysed samples were eluted through the paper channel with TE buffer and the paper channel was excised into three pieces for the further polymerase chain reaction (PCR) assay. The extraction efficiency was determined by measuring fluorescence reflectance with either a benchtop optical detection system (consisting of an LED light source, a pair of optical fibers, and a miniature spectrophotometer, all built on micro-positioning stages) or a smartphone-based fluorescent microscope (in-house fabricated). The limit of detection of Salmonella Typhimurium in 10% poultry packaging liquid with cellulose paper was 10 3 CFU mL-1, while that extracted with nitrocellulose paper was 104 CFU mL-1 (as determined by both PCR and fluorescence reflectance). Cellulose channels proved more appropriate for measuring low and very high concentrations of pathogen DNA, while nitrocellulose proved better for analysing the mid-range concentrations. We observed that DNA migrated through nitrocellulose at a faster rate and further than through cellulose due to charge-charge repulsion between nitrocellulose and DNA (both negatively charged), thus contributing to consistent and efficient extraction. We tested the efficiency of Salmonella extraction from 10% poultry packaging liquid, 10% whole blood, and 10% fecal samples, and obtained comparable extraction efficiency, as confirmed by smartphone-based direct fluorescent detection. This protocol is suitable for the direct detection of total bacteria count in a dirty sample (when specificity is not necessary) as well as determining extraction efficiency. This protocol is compatible with PCR, to provide specific information about the type of pathogen present in sample. © 2014 The Royal Society of Chemistry.
• Harshman, D. K., Reyes, R., Park, T. S., You, D. J., Song, J., & Yoon, J. (2014). Enhanced nucleic acid amplification with blood in situ by wire-guided droplet manipulation (WDM). Biosensors and Bioelectronics, 53, 167-174.
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  PMID: 24140832;PMCID: PMC3868462;Abstract: There are many challenges facing the use of molecular biology to provide pertinent information in a timely, cost effective manner. Wire-guided droplet manipulation (WDM) is an emerging format for conducting molecular biology with unique characteristics to address these challenges. To demonstrate the use of WDM, an apparatus was designed and assembled to automate polymerase chain reaction (PCR) on a reprogrammable platform. WDM minimizes thermal resistance by convective heat transfer to a constantly moving droplet in direct contact with heated silicone oil. PCR amplification of the GAPDH gene was demonstrated at a speed of 8.67s/cycle. Conventional PCR was shown to be inhibited by the presence of blood. WDM PCR utilizes molecular partitioning of nucleic acids and other PCR reagents from blood components, within the water-in-oil droplet, to increase PCR reaction efficiency with blood in situ. The ability to amplify nucleic acids in the presence of blood simplifies pre-treatment protocols towards true point-of-care diagnostic use. The 16s rRNA hypervariable regions V3 and V6 were amplified from Klebsiella pneumoniae genomic DNA with blood in situ. The detection limit of WDM PCR was 1ng/μL or 105genomes/μL with blood in situ. The application of WDM for rapid, automated detection of bacterial DNA from whole blood may have an enormous impact on the clinical diagnosis of infections in bloodstream or chronic wound/ulcer, and patient safety and morbidity. © 2013 Elsevier B.V.
• Kwon, H., Fronczek, C. F., Angus, S. V., Nicolini, A. M., & Yoon, J. (2014). Rapid and Sensitive Detection of H1N1/2009 Virus from Aerosol Samples with a Microfluidic Immunosensor. Journal of Laboratory Automation, 19(3), 322-331.
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  Influenza A H1N1/2009 is a highly infectious, rapidly spreading airborne disease that needs to be monitored in near real time, preferably in a microfluidic format. However, such demonstration is difficult to find as H1N1 concentration in aerosol samples is extremely low, with interference from dust particles. In this work, we measured Mie scatter intensities from a microfluidic device with optical waveguide channels, where the antibody-conjugated latex beads immunoagglutinated with the target H1N1 antigens. Through careful optimizations of optical parameters, we were able to maximize the Mie scatter increase from the latex immunoagglutinations while minimizing the background scatter from the dust particles. The aerosol samples were collected from a 1:10 mock classroom using a button air sampler, where a nebulizer generated aerosols, simulating human coughing. The detection limits with real aerosol samples were 1 and 10 pg/mL, using a spectrometer or a cell phone camera as an optical detector, respectively. These are several orders of magnitudes more sensitive than the other methods. The microfluidic immunosensor readings are in concordance with the results of reverse transcription polymerase chain reaction. The assay time was 30 s for sampling and 5 min for the microfluidic assay.
• Liang, P., Park, T. S., & Yoon, J. (2014). Rapid and Reagentless Detection of Microbial Contamination within Meat Utilizing a Smartphone-Based Biosensor. Scientific Reports, 4(5953).
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  A smartphone-utilized biosensor was developed for detecting microbial spoilage on ground beef, without using antibodies, microbeads or any other reagents, towards a preliminary screening tool for microbial contamination on meat products, and potentially towards wound infection. Escherichia coli K12 solutions (10^1 - 10^8 CFU/mL) were added to ground beef products to simulate microbial spoilage. An 880 nm near infrared LED was irradiated perpendicular to the surface of ground beef, and the scatter signals at various angles were evaluated utilizing the gyro sensor and the digital camera of a smartphone. The angle that maximized the Mie scatter varied by the E. coli concentration: 15 deg for 10^8 CFU/mL, 30 deg for 10^4 CFU/mL, and 45 deg for 10 CFU/mL, etc. SEM and fluorescence microscopy experiments revealed that the antigens and cell fragments from E. coli bonded preferably to the fat particles within meat, and the size and morphologies of such aggregates varied by the E. coli concentration.
• Park, T. S., Baynes, C., Cho, S., & Yoon, J. (2014). Paper Microfluidics for Red Wine Tasting. RSC Advances, 4(46), 24356-24362.
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  A paper microfluidic chip was designed and fabricated to evaluate the taste of 4 different red wines using a set of chemical dyes. The digital camera of a smartphone captured the images, and its red-green-blue (RGB) pixel intensities were analyzed by principal component analysis (PCA). Using 8 dyes and 2 principal components (PCs), we were able to distinguish each wine by the grape variety and the oxidation status. Through comparing with the flavor map by human evaluations, PC1 seemed to represent the sweetness and PC2 the dryness of red wine. This superior performance is attributed to: 1) careful selection of commercially available dyes through a series of linear correlation study with the taste chemicals in red wines, 2) minimization of sample-to-sample variation by splitting a single sample into multiple wells on the paper microfluidics, and 3) filtration of particulate matter through paper fibers. The image processing and PCA procedure can eventually be implemented as a stand-alone smartphone application and can be adopted as an extremely low-cost, fully handheld, easy-to-use, yet sensitive and specific quality control method for appraising red wine or similar beverage products in resource-limited environments.
• Stemple, C. C., Angus, S. V., Park, T. S., & Yoon, J. (2014). Smartphone-Based Optofluidic Lab-on-a-Chip for Detecting Pathogens from Blood. Journal of Laboratory Automation, 19(1), 35-41.
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  Abstract: A novel smartphone-based detection device was created to detect infectious pathogens directly from diluted (10%) human whole blood. The model pathogen was histidine-rich protein 2 (HRP-2), an antigen specific to Plasmodium falciparum (malaria). Anti-HRP-2-conjugated submicrobeads were mixed with HRP-2-infused 10% blood in a lab-on-a-chip device. The white LED flash and the digital camera of the smartphone were used as light source and detector, which delivered light to and from the bead and blood mixture via optofluidic channels in the lab-on-a-chip. The optofluidic channels were angled at 45 degrees to capture the Mie scatter from the sample. Considering the absorption and scattering characteristics of blood (red/infrared preferred) and the Mie scatter simulations for microbead immunoagglutination (UV preferred), blue detection showed the best results. The detection limit was 1 pg/mL in 10% blood. The linear range was from 1 pg/mL to 10 ng/mL. A handheld device, easily attachable to a single smartphone, was finally designed and fabricated using optical mirrors and lenses and successfully detected the HRP-2 from 10% blood. The total assay time was approximately 10 min. The proposed device can potentially be used for detecting a wide range of blood infection with high sensitivity. © 2013 Society for Laboratory Automation and Screening.
• Yoon, J. (2014). Smartphone-Based lab-on-a-chip sensor for flu detection. Resource: Engineering and Technology for Sustainable World, 21(1), 20-22.
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  Abstract: It is desirable to conduct reverse transcription polymerase chain reaction (RT-PCR) or an immunoassay at the point-of-care level or in the field for early diagnosis of influenza. The lab-on-a-chip (LOC) is the perfect instrument to perform such a task. An LOC is a network of channels and wells that is etched onto a silicon or polymer substrate to build a miniature laboratory. The LOC enables sample handing, mixing, dilution, separation, staining, and detection within a single, integrated system and is perfectly suitable for chemical or biological assays. Final detections in an LOC can be made electrochemically or optically, but optical detection is gaining popularity due to its high sensitivity and better specificity. Optical detection in an LOC can be implemented through the use of an LED light source, a pair of optical fibers, and a miniature spectrometer.
• Fronczek, C. F., You, D. J., & Yoon, J. (2013). Single-pipetting microfluidic assay device for rapid detection of Salmonella from poultry package. Biosensors & bioelectronics, 40(1), 342-349.
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  A direct, sensitive, near-real-time, handheld optical immunoassay device was developed to detect Salmonella typhimurium in the naturally occurring liquid from fresh poultry packages (hereafter chicken matrix), with just single pipetting of sample (i.e., no filtration, culturing and/or isolation, thus reducing the assay time and the error associated with them). Carboxylated, polystyrene microparticles were covalently conjugated with anti-Salmonella, and the immunoagglutination due to the presence of Salmonella was detected by reading the Mie scatter signals from the microfluidic channels using a handheld device. The presence of chicken matrix did not affect the light scatter signal, since the optical parameters (particle size d, wavelength of incident light lambda; and scatter angle theta) were optimized to minimize the effect of sample matrix (animal tissues and blood proteins, etc.). The sample was loaded into a microfluidic chip that was split into two channels, one pre-loaded with vacuum-dried, antibody-conjugated particles and the other with vacuum-dried, bovine serum albumin-conjugated particles. This eliminated the need for a separate negative control, effectively minimizing chip-to-chip and sample-to-sample variations. Particles and the sample were diffused in-channel through chemical agitation by Tween 80, also vacuum-dried within the microchannels. Sequential mixing of the sample to the reagents under a strict laminar flow condition synergistically improved the reproducibility and linearity of the assay. In addition, dried particles were shown to successfully detect lower Salmonella concentrations for up to 8 weeks. The handheld device contains simplified circuitry eliminating unnecessary adjustment stages, providing a stable signal, thus maximizing sensitivity. Total assay time was 10 min, and the detection limit 10 CFU/mL was observed in all matrices, demonstrating the suitability of this device for field assays.
• Fronczek, C. F., You, D. J., & Yoon, J. (2013). Single-pipetting microfluidic assay device for rapid detection of Salmonella from poultry package. Biosensors and Bioelectronics, 40(1), 342-349.
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  PMID: 22939509;Abstract: A direct, sensitive, near-real-time, handheld optical immunoassay device was developed to detect Salmonella typhimurium in the naturally occurring liquid from fresh poultry packages (hereafter "chicken matrix"), with just single pipetting of sample (i.e., no filtration, culturing and/or isolation, thus reducing the assay time and the error associated with them). Carboxylated, polystyrene microparticles were covalently conjugated with anti-Salmonella, and the immunoagglutination due to the presence of Salmonella was detected by reading the Mie scatter signals from the microfluidic channels using a handheld device. The presence of chicken matrix did not affect the light scatter signal, since the optical parameters (particle size d, wavelength of incident light λ and scatter angle θ) were optimized to minimize the effect of sample matrix (animal tissues and blood proteins, etc.). The sample was loaded into a microfluidic chip that was split into two channels, one pre-loaded with vacuum-dried, antibody-conjugated particles and the other with vacuum-dried, bovine serum albumin-conjugated particles. This eliminated the need for a separate negative control, effectively minimizing chip-to-chip and sample-to-sample variations. Particles and the sample were diffused in-channel through chemical agitation by Tween 80, also vacuum-dried within the microchannels. Sequential mixing of the sample to the reagents under a strict laminar flow condition synergistically improved the reproducibility and linearity of the assay. In addition, dried particles were shown to successfully detect lower Salmonella concentrations for up to 8 weeks. The handheld device contains simplified circuitry eliminating unnecessary adjustment stages, providing a stable signal, thus maximizing sensitivity. Total assay time was 10min, and the detection limit 10CFUmL-1 was observed in all matrices, demonstrating the suitability of this device for field assays. © 2012 Elsevier B.V.
• Gamboa, J. R., Mohandes, S., Tran, P. L., Slepian, M. J., & Yoon, J. (2013). Linear fibroblast alignment on sinusoidal wave micropatterns. Colloids & surfaces. B, Biointerfaces, 104, 318-325.
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  Micrometer and nanometer grooved surfaces have been determined to influence cellular orientation, morphology, and migration through contact guidance. Cells typically elongate along the direction of an underlying groove and often migrate with guidance provided by constraints of the pattern. This phenomenon has been studied primarily using linear grooves, post, or well patterns. We investigated the behavior of mouse embryonic fibroblasts on non-linear, sinusoidal wave grooves created via electron beam lithography on a polymethyl methacrylate (PMMA) substrate that was spin-coated onto a positively charged glass surface. Three different wave patterns, with varying wavelengths and amplitudes, and two different line patterns were created. Cell orientation and adhesion was examined after 4, 24, and 48 h after cell seeding. Attachment strength was studied via subjecting cells on substrates to centrifugal force following a 24-h incubation period. For all wave patterns studied, it was noted that cells did not reside within the groove, rather they were observed to cross over each groove, residing both inside and outside of each wave pattern, aligning linearly along the long axis of the pattern. For the linear patterns, we observed that cells tended to reside within the grooves, consistent with previous observations. The ability to add texture to a surface to manipulate cell adhesion strength and growth with only localized attachment, maintaining free space in curvilinear microtopography underlying the cell, may be a useful addition for tissue engineering and the fabrication of novel biomedical devices.
• Gamboa, J. R., Mohandes, S., Tran, P. L., Slepian, M. J., & Yoon, J. (2013). Linear fibroblast alignment on sinusoidal wave micropatterns. Colloids and Surfaces B: Biointerfaces, 104, 318-325.
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  PMID: 23375052;PMCID: PMC3582717;Abstract: Micrometer and nanometer grooved surfaces have been determined to influence cellular orientation, morphology, and migration through contact guidance. Cells typically elongate along the direction of an underlying groove and often migrate with guidance provided by constraints of the pattern. This phenomenon has been studied primarily using linear grooves, post, or well patterns. We investigated the behavior of mouse embryonic fibroblasts on non-linear, sinusoidal wave grooves created via electron beam lithography on a polymethyl methacrylate (PMMA) substrate that was spin-coated onto a positively charged glass surface. Three different wave patterns, with varying wavelengths and amplitudes, and two different line patterns were created. Cell orientation and adhesion was examined after 4, 24, and 48. h after cell seeding. Attachment strength was studied via subjecting cells on substrates to centrifugal force following a 24-h incubation period. For all wave patterns studied, it was noted that cells did not reside within the groove, rather they were observed to cross over each groove, residing both inside and outside of each wave pattern, aligning linearly along the long axis of the pattern. For the linear patterns, we observed that cells tended to reside within the grooves, consistent with previous observations. The ability to add texture to a surface to manipulate cell adhesion strength and growth with only localized attachment, maintaining free space in curvilinear microtopography underlying the cell, may be a useful addition for tissue engineering and the fabrication of novel biomedical devices. © 2012 Elsevier B.V.
• Liang, P. -., & Yoon, J. -. (2013). Optofluidic lab-on-a-chip monitoring of subsurface bacterial transport. Biological Engineering Transactions, 6(1), 17-28.
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  Abstract: An optofluidic lab-on-a-chip system and subsequent sampling procedure were developed for detecting bacteria from soil samples utilizing light scattering detection of immunoagglutination assay. This system and protocol detected the presence of Escherichia coli K12 from soil particles in near real-time (10 min) with a detection limit down to 1 CFU mL-1, which is superior to the conventional methods, such as plate counting or polymerase chain reaction (PCR) assays. E. coli solutions were applied to the surface of a mock soil system and incubated overnight. The light scattering immunoagglutination assays using the optofluidic lab-on-a-chip showed two E. coli peaks over the soil depth, one at 1 cm and the other at 4 cm. Comparison with bacterial viability assay and Bradford protein assay revealed that smaller E. coli colonies were found at 1 cm depth and larger colonies at 4 cm, while free antigens adsorbed and desorbed more reversibly at both locations. The two peaks were explained by the two-step process of protein-surface interaction and gravitational force. The target molecules with small sizes (free antigens and single cells) arrived at the soil particle surface faster according to the diffusion model, and the larger E. coli colonies arrived later where the soil surface was already occupied. Because the free antigens adsorbed and desorbed in a more reversible manner, they could be found throughout the depth of the mock-up soil system, whereas the larger E. coli colonies traveled through the void space within soil particles via gravitational force and accumulated at the bottom of where the liquid reached. This work also demonstrates a device and procedure that could be potentially implemented in field studies. With proper soil sample handling protocol and light scattering detection of immunoagglutination assay in an optofluidic lab-on-a-chip, developing more complete bacteria subsurface transport models with actual field results can be achieved. © 2013 ASABE.
• Liang, P., & Yoon, J. (2013). Optofluidic Lab-on-a-chip Monitoring of Subsurface Bacterial Transport. Biological engineering transactions, 6(1), 17-28.
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  An optofluidic lab-on-a-chip system and subsequent sampling procedure were developed for detecting bacteria from soil samples utilizing light scattering detection of immunoagglutination assay. This system and protocol detected the presence of Escherichia coli K12 from soil particles in near real-time (10 min) with a detection limit down to 1 CFU/mL, which is superior to the conventional methods, such as plate counting or polymerase chain reaction (PCR) assays. E. coli solutions were applied to the surface of a mock soil system and incubated overnight. The light scattering immunoagglutination assays using the optofluidic lab-on-a-chip showed two E. coli peaks over the soil depth, one at 1 cm and the other at 4 cm. Comparison with bacterial viability assay and Bradford protein assay revealed that smaller E. coli colonies were found at 1 cm depth and larger colonies at 4 cm, while free antigens adsorbed and desorbed more reversibly at both locations. The two peaks were explained by the two-step process of protein-surface interaction and gravitational force. The target molecules with small sizes (free antigens and single cells) arrived at the soil particle surface faster according to the diffusion model, and the larger E. coli colonies arrived later where the soil surface was already occupied. Because the free antigens adsorbed and desorbed in a more reversible manner, they could be found throughout the depth of the mock-up soil system, whereas the larger E. coli colonies traveled through the void space within soil particles via gravitational force and accumulated at the bottom of where the liquid reached. This work also demonstrates a device and procedure that could be potentially implemented in field studies. With proper soil sample handling protocol and light scattering detection of immunoagglutination assay in an optofluidic lab-on-a-chip, developing more complete bacteria subsurface transport models with actual field results can be achieved.
• McCracken, K. E., Tran, P. L., You, D. J., Slepian, M. J., & Yoon, J. (2013). Shear- vs. nanotopography-guided control of growth of endothelial cells on RGD-nanoparticle-nanowell arrays. Journal of Biological Engineering, 7(1).
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  PMID: 23607894;PMCID: PMC3637365;Abstract: Endothelialization of therapeutic cardiovascular implants is essential for their intravascular hemocompatibility. We previously described a novel nanowell-RGD-nanoparticle ensemble, which when applied to surfaces led to enhanced endothelialization and retention under static conditions and low flow rates. In the present study we extend our work to determine the interrelated effects of flow rate and the orientation of ensemble-decorated surface arrays on the growth, adhesion and morphology of endothelial cells. Human umbilical vascular endothelial cells (HUVECs) were grown on array surfaces with either 1 μm × 5 μm spacing (" parallel to flow" ) and 5 μm × 1 μm spacing (" perpendicular to flow" ) and were exposed to a range of shear stress of (0 to 4.7 ± 0.2 dyn·cm-2 ), utilizing a pulsatile flow chamber. Under physiological flow (4.7 ± 0.2 dyn·cm-2), RGD-nanoparticle-nanowell array patterning significantly enhanced cell adhesion and spreading compared with control surfaces and with static conditions. Furthermore, improved adhesion coincided with higher alignment to surface patterning, intimating the importance of interaction and response to the array surface as a means of resisting flow detachment. Under sub-physiological condition (1.7 ± 0.3 dyn·cm-2; corresponding to early angiogenesis), nanowell-nanoparticle patterning did not provide enhanced cell growth and adhesion compared with control surfaces. However, it revealed increased alignment along the direction of flow, rather than the direction of the pattern, thus potentially indicating a threshold for cell guidance and related retention. These results could provide a cue for controlling cell growth and alignment under varying physiological conditions. © 2013 McCracken et al.; licensee BioMed Central Ltd.
• McCracken, K. E., Tran, P. L., You, D. J., Slepian, M. J., & Yoon, J. (2013). Shear- vs. nanotopography-guided control of growth of endothelial cells on RGD-nanoparticle-nanowell arrays. Journal of biological engineering, 7(11).
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  Endothelialization of therapeutic cardiovascular implants is essential for their intravascular hemocompatibility. We previously described a novel nanowell-RGD-nanoparticle ensemble, which when applied to surfaces led to enhanced endothelialization and retention under static conditions and low flow rates. In the present study we extend our work to determine the interrelated effects of flow rate and the orientation of ensemble-decorated surface arrays on the growth, adhesion and morphology of endothelial cells. Human umbilical vascular endothelial cells (HUVECs) were grown on array surfaces with either 1 um x 5 um spacing (parallel to flow) and 5 um x 1 um spacing (perpendicular to flow) and were exposed to a range of shear stress of (0 to 4.7 +/- 0.2 dyn cm(-2)), utilizing a pulsatile flow chamber. Under physiological flow (4.7 +/- 0.2 dyn cm(-2)), RGD-nanoparticle-nanowell array patterning significantly enhanced cell adhesion and spreading compared with control surfaces and with static conditions. Furthermore, improved adhesion coincided with higher alignment to surface patterning, intimating the importance of interaction and response to the array surface as a means of resisting flow detachment. Under sub-physiological condition (1.7 +/- 0.3 dyn cm(-2)); corresponding to early angiogenesis), nanowell-nanoparticle patterning did not provide enhanced cell growth and adhesion compared with control surfaces. However, it revealed increased alignment along the direction of flow, rather than the direction of the pattern, thus potentially indicating a threshold for cell guidance and related retention. These results could provide a cue for controlling cell growth and alignment under varying physiological conditions.
• Park, T. S., Li, W., McCracken, K. E., & Yoon, J. (2013). Smartphone quantifies Salmonella from paper microfluidics. Lab on a chip, 13(24), 4832-4840.
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  Smartphone-based optical detection is a potentially easy-to-use, handheld, true point-of-care diagnostic tool for the early and rapid detection of pathogens. Paper microfluidics is a low-cost, field-deployable, and easy-to-use alternative to conventional microfluidic devices. Most paper-based microfluidic assays typically utilize dyes or enzyme-substrate binding, while bacterial detection on paper microfluidics is rare. We demonstrate a novel application of smartphone-based detection of Salmonella on paper microfluidics. Each paper microfluidic channel was pre-loaded with anti-Salmonella Typhimurium and anti-Escherichia coli conjugated submicroparticles. Dipping the paper microfluidic device into the Salmonella solutions led to the antibody-conjugated particles that were still confined within the paper fibers to immunoagglutinate. The extent of immunoagglutination was quantified by evaluating Mie scattering from the digital images taken at an optimized angle and distance with a smartphone. A smartphone application was designed and programmed to allow the user to position the smartphone at an optimized angle and distance from the paper microfluidic device, and a simple image processing algorithm was implemented to calculate and display the bacterial concentration on the smartphone. The detection limit was single-cell-level and the total assay time was less than one minute.
• Park, T. S., Wenyue, L. i., McCracken, K. E., & Yoon, J. (2013). Smartphone quantifies Salmonella from paper microfluidics. Lab on a Chip - Miniaturisation for Chemistry and Biology, 13(24), 4832-4840.
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  PMID: 24162816;Abstract: Smartphone-based optical detection is a potentially easy-to-use, handheld, true point-of-care diagnostic tool for the early and rapid detection of pathogens. Paper microfluidics is a low-cost, field-deployable, and easy-to-use alternative to conventional microfluidic devices. Most paper-based microfluidic assays typically utilize dyes or enzyme-substrate binding, while bacterial detection on paper microfluidics is rare. We demonstrate a novel application of smartphone-based detection of Salmonella on paper microfluidics. Each paper microfluidic channel was pre-loaded with anti-Salmonella Typhimurium and anti-Escherichia coli conjugated submicroparticles. Dipping the paper microfluidic device into the Salmonella solutions led to the antibody-conjugated particles that were still confined within the paper fibers to immunoagglutinate. The extent of immunoagglutination was quantified by evaluating Mie scattering from the digital images taken at an optimized angle and distance with a smartphone. A smartphone application was designed and programmed to allow the user to position the smartphone at an optimized angle and distance from the paper microfluidic device, and a simple image processing algorithm was implemented to calculate and display the bacterial concentration on the smartphone. The detection limit was single-cell-level and the total assay time was less than one minute. © 2013 The Royal Society of Chemistry.
• Tran, P. L., Gamboa, J. R., McCracken, K. E., Riley, M. R., Slepian, M. J., & Yoon, J. (2013). Nanowell-trapped charged ligand-bearing nanoparticle surfaces: a novel method of enhancing flow-resistant cell adhesion. Advanced healthcare materials, 2(7), 1019-1027.
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  Assuring cell adhesion to an underlying biomaterial surface is vital in implant device design and tissue engineering, particularly under circumstances where cells are subjected to potential detachment from overriding fluid flow. Cell-substrate adhesion is a highly regulated process involving the interplay of mechanical properties, surface topographic features, electrostatic charge, and biochemical mechanisms. At the nanoscale level, the physical properties of the underlying substrate are of particular importance in cell adhesion. Conventionally, natural, pro-adhesive, and often thrombogenic, protein biomaterials are frequently utilized to facilitate adhesion. In the present study, nanofabrication techniques are utilized to enhance the biological functionality of a synthetic polymer surface, polymethymethacrylate, with respect to cell adhesion. Specifically we examine the effect on cell adhesion of combining: 1. optimized surface texturing, 2. electrostatic charge and 3. cell adhesive ligands, uniquely assembled on the substrata surface, as an ensemble of nanoparticles trapped in nanowells. Our results reveal that the ensemble strategy leads to enhanced, more than simply additive, endothelial cell adhesion under both static and flow conditions. This strategy may be of particular utility for enhancing flow-resistant endothelialization of blood-contacting surfaces of cardiovascular devices subjected to flow-mediated shear.
• Tran, P. L., Gamboa, J. R., Mccracken, K. E., Riley, M. R., Slepian, M. J., & Yoon, J. (2013). Nanowell-Trapped Charged Ligand-Bearing Nanoparticle Surfaces: A Novel Method of Enhancing Flow-Resistant Cell Adhesion. Advanced Healthcare Materials, 2(7), 1019-1027.
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  PMID: 23225491;Abstract: Assuring cell adhesion to an underlying biomaterial surface is vital in implant device design and tissue engineering, particularly under circumstances where cells are subjected to potential detachment from overriding fluid flow. Cell-substrate adhesion is a highly regulated process involving the interplay of mechanical properties, surface topographic features, electrostatic charge, and biochemical mechanisms. At the nanoscale level, the physical properties of the underlying substrate are of particular importance in cell adhesion. Conventionally, natural, pro-adhesive, and often thrombogenic, protein biomaterials are frequently utilized to facilitate adhesion. In the present study, nanofabrication techniques are utilized to enhance the biological functionality of a synthetic polymer surface, polymethymethacrylate, with respect to cell adhesion. Specifically we examine the effect on cell adhesion of combining: 1. optimized surface texturing, 2. electrostatic charge and 3. cell adhesive ligands, uniquely assembled on the substrata surface, as an ensemble of nanoparticles trapped in nanowells. Our results reveal that the ensemble strategy leads to enhanced, more than simply additive, endothelial cell adhesion under both static and flow conditions. This strategy may be of particular utility for enhancing flow-resistant endothelialization of blood-contacting surfaces of cardiovascular devices subjected to flow-mediated shear. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
• Tran, P. L., Gamboa, J. R., Mccracken, K. E., Yoon, J., & Slepian, M. J. (2013). Interaction with nanoscale topography: The use of nanowelltrapped charged ligand-bearing nanoparticle surfaces to modulate physiological focal adhesions in endothelial cells. ASME 2013 2nd Global Congress on NanoEngineering for Medicine and Biology, NEMB 2013.
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  Abstract: Achieving cell adhesion, growth and homeostasis on an underlying biomaterial surface may be a desirable feature in implant device design and tissue engineering. Insight has been gained from numerous cell patterning strategies where spatial cues and physical constraints have been shown to regulate the structure and function of cells. Despite significant advances in modifying substrates for cellular attachment, migration and proliferation, the achievement of confluent and aligned growth of functional endothelial cells on cardiovascular blood-contacting implants under physiologically significant wall shear stress has proven difficult. Recently we have reported on a method that enhances cellular adhesion under flow conditions on synthetic polymer surfaces, without reliance on pro-adhesive protein biomaterials, which are often thrombogenic. In this method we utilize electron beam lithography and size-dependent selfassembly to fabricate line arrays of nanowells allowing entrapment and retention of charged nanoparticles, covalently conjugated with a RGD adhesive ligand, GRGDSPK. This approach is an additive strategy of combining substrata topographic alteration, electrostatic charge and biochemical ligands, all uniquely incorporated as an ensemble of charged, ligand-bearing nanoparticles entrapped in arrays of nanowells. However, the modulation of endothelial cell physiologic mechanisms as a result of ensemble surface exposure remains to be characterized. In this report, we extend our studies and probe cell physiologic mechanisms altered as a result of nanofeatured surface exposure. We first examined the functional intactness or normalcy of endothelial cells adherent to the nanofeatured ensemble surface utilizing standard immunostaining and flow cytometry methods. We found β1-integrin expression dominated quiescent adherent endothelial cells while αVβ3-integrins expression was more common in migratory cells. Endothelial cells were noted to express high levels of PECAM-1 over time when exposed to nanofeatured surface and RGD peptides. For understanding the contribution of the nanofeatured surface (entrapped RGD conjugated nanoparticles) to cell adhesion, cytochalasin B was used to alter cell spreading. Confocal microscopy illustrated the uptake of nanoparticles in endothelial cells on composite surfaces, as well as the inhibition of this endocytosis by cytochalasin B. After prohibiting the cells from engulfing nanoparticles, we found an 80% reduction in cell adhesion; suggesting that an endocytic mechanism might play a role in maintaining cell adhesion. Nanofeatured ensemble surfaces appear to be good substrates for achieving a high level of EC adhesion, with maintained growth and stability. Copyright © 2013 by ASME.
• You, D. J., Park, T. S., & Yoon, J. (2013). Cell-phone-based measurement of TSH using Mie scatter optimized lateral flow assays. Biosensors & bioelectronics, 40(1), 180-185.
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  Semi-quantitative thyroid stimulating hormone (TSH) lateral flow immunochromatographic assays (LFA) are used to screen for serum TSH concentration higher than 5 mIU/L (hypothyroidism). The LFA format, however, is unable to measure TSH in the normal range or detect suppressed levels of TSH (less than 0.4 mIU/L; hyperthyroidism). In fact, it does not provide quantitative TSH values at all. Obtaining quantitative TSH results, especially in the low concentration range, has until now required the use of centralized clinical laboratories which require specimen transport, specialized equipment and personnel, and result in increased cost and delays in the timely reporting of important clinical results. We have conducted a series of experiments to develop and validate an optical system and image analysis algorithm based upon a cell phone platform. It is able to provide point-of-care quantitative TSH results with a high level of sensitivity and reproducibility comparable to that of a clinical laboratory-based third-generation TSH immunoassay. Our research approach uses the methodology of the optimized Rayleigh/Mie scatter detection by taking into consideration the optical characteristics of a nitrocellulose membrane and gold nanoparticles on an LFA for quantifying TSH levels. Using a miniature spectrometer, LED light source, and optical fibers on a rotating benchtop apparatus, the light intensity from different angles of incident light and angles of detection to the LFA were measured. The optimum angles were found that the minimized Mie scattering from nitrocellulose membrane, consequently maximizes the Rayleigh scatter detection from the gold nanoparticles in the LFA bands. Using the results from the benchtop apparatus, a cell-phone-based apparatus was designed which utilized the embedded flash in the cell phone camera as the light source, piped the light with an optical fiber from the flash through a collimating lens to illuminate the LFA. Quantification of TSH was performed in an iOS application directly on the phone and verified using the code written in MATLAB. The limit of detection of the system was determined to be 0.31 mIU/L (never achieved before on an LFA format), below the commonly accepted minimum concentration of 0.4 mIU/L indicating clinical significance of hyperthyroidism. The system was further evaluated using human serum showing an accurate and reproducible platform for rapid and point-of-care quantification of TSH using a cell phone.
• You, D. J., Park, T. S., & Yoon, J. (2013). Cell-phone-based measurement of TSH using Mie scatter optimized lateral flow assays. Biosensors and Bioelectronics, 40(1), 180-185.
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  PMID: 22863118;Abstract: Semi-quantitative thyroid stimulating hormone (TSH) lateral flow immunochromatographic assays (LFA) are used to screen for serum TSH concentration >5mIUL-1 (hypothyroidism). The LFA format, however, is unable to measure TSH in the normal range or detect suppressed levels of TSH (
• Angus, S. V., Kwon, H., & Yoon, J. (2012). Field-deployable and near-real-time optical microfluidic biosensors for single-oocyst-level detection of Cryptosporidium parvum from field water samples. Journal of Environmental Monitoring, 14(12), 3295-3304.
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  PMID: 23152174;Abstract: Cryptosporidium spp. is an obligate, parasitic protozoan that is difficult to detect and causes diarrhea in healthy adults while potentially causing death in the immunocompromised and children. Its treatment options are few and treat the symptoms, not the actual parasite. Current methods of detection are inefficient and rely too heavily upon laboratory sample preparations and technician skill, including differential staining, negative staining, and immunofluorescence methods [especially U.S. Environmental Protection Agency (EPA) Method 1623]. These assays can take from hours to days and require a laboratory environment. In this work, we demonstrated the microbead immunoagglutination assay combined with Mie scatter detection in a microfluidic device to provide a field-deployable and near-real-time alternative to the laboratory-based method (especially EPA Method 1623). Two main challenges were the relatively big diameter of Cryptosporidium oocysts (5-6 μm) and the contaminants in field water samples that negatively affected the immunoagglutination and its scatter detection. We used 4 min sonication to liberate Cryptosporidium oocyst wall proteins (COWP), which was previously used to inactivate Cryptosporidium oocysts. As for the contaminants, we optimized the microbead diameter (920 nm) and the wavelength of incident light (375 nm) to find the angle of scatter detection (45°) where the Mie scatter from immunoagglutinated microbeads was maximum and the background scatter from contaminants was minimum. This enabled the sub-single-oocyst-level detection despite the fact that only a very small volume of water sample (15 μL) was introduced to the microfluidic biosensor. When combined with filtration/concentration, this method is able to detect ≤1 oocyst per large volume of water, comparable to or potentially better than the EPA method 1623, while effectively reducing the time and labor necessary for staining and microscopic analysis. For faster, near-real-time assays, filtration/ concentration may not be used, where the detection limit was 1-10 oocysts per mL with the total assay time of 10 min including the 4 min sonication time. The linear range of assay was over 5 orders of magnitude. The final device was compact and had the potential to be used in field situations, and required less technical expertise and/or training compared to the other methods. © The Royal Society of Chemistry 2012.
• Angus, S. V., Kwon, H., & Yoon, J. (2012). Field-deployable and near-real-time optical microfluidic biosensors for single-oocyst-level detection of Cryptosporidium parvum from field water samples. Journal of environmental monitoring, 14(12), 3295-3304.
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  Cryptosporidium spp. is an obligate, parasitic protozoan that is difficult to detect and causes diarrhea in healthy adults while potentially causing death in the immunocompromised and children. Its treatment options are few and treat the symptoms, not the actual parasite. Current methods of detection are inefficient and rely too heavily upon laboratory sample preparations and technician skill, including differential staining, negative staining, and immunofluorescence methods [especially U.S. Environmental Protection Agency (EPA) Method 1623]. These assays can take from hours to days and require a laboratory environment. In this work, we demonstrated the microbead immunoagglutination assay combined with Mie scatter detection in a microfluidic device to provide a field-deployable and near-real-time alternative to the laboratory-based method (especially EPA Method 1623). Two main challenges were the relatively big diameter of Cryptosporidium oocysts (5-6 um) and the contaminants in field water samples that negatively affected the immunoagglutination and its scatter detection. We used 4 min sonication to liberate Cryptosporidium oocyst wall proteins (COWP), which was previously used to inactivate Cryptosporidium oocysts. As for the contaminants, we optimized the microbead diameter (920 nm) and the wavelength of incident light (375 nm) to find the angle of scatter detection (45 deg) where the Mie scatter from immunoagglutinated microbeads was maximum and the background scatter from contaminants was minimum. This enabled the sub-single-oocyst-level detection despite the fact that only a very small volume of water sample (15 uL) was introduced to the microfluidic biosensor. When combined with filtration/concentration, this method is able to detect
• Angus, S. V., Kwon, H., & Yoon, J. (2012). Low-level detection of Cryptosporidium parvum in field water using optical microfluidic biosensors. Progress in Biomedical Optics and Imaging - Proceedings of SPIE, 8229.
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  Abstract: Cryptosporidium parvum is a difficult-to-detect protozoan that causes diarrhea in the healthy adults and death in immunocompromised individuals. While it is easy to understand the transmission routes of Cryptosporidium, it is currently difficult to identify low concentrations of Cryptosporidium, especially when following EPA method 1623, which can easily require tens of liters of water to get a positive signal. The current detection method is unacceptable and severely inefficient when taking into account the time that goes into concentrating a sample, actual assays, and training associated with the assays. Using our method, it is possible to use only 15 μL of sample, which is an immunoagglutination assay that uses Mie scatter intensity changes to detect different Cryptosporidium concentrations. In addition to creating a standard curve using a clean sample matrix (i.e., phosphate buffered saline), field samples were collected from a chlorine treated swimming pool, a sump located on a farm, and a turtle pond. Each sample had different intensity changes but the trend represented within the data was the same. This assay has a detection limit of 100-101 oocysts/mL and can be done in as little as 10 minutes. © 2012 SPIE.
• Stemple, C. C., Kwon, H., & Yoon, J. (2012). Rapid and Sensitive Detection of Malaria Antigen in Human Blood with Lab-on-a-Chip. IEEE sensors journal, 12(9), 2735-2736.
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  A novel lab-on-a-chip detection device, based on the properties of immunoagglutination, was modified to detect malaria in the human blood through histidine-rich protein 2, an antigen expressed only by Plasmodium falciparum. Utilizing Mie scattering detection, which is angle- and size-dependent, the extent of immunoagglutination could be accurately measured while the optical disturbance from the human blood was minimized. The presence of human serum albumin in the blood is believed to further stabilize the antibody-conjugated submicron beads and/or break off the larger agglutinated beads. The lowest detection limit was 1 pg/mL in 10% of whole blood (equivalent to 10 pg/mL in undiluted whole blood), a few orders of magnitude lower than other assays. The final device is compact, with a fast assay time of approximately 8 min.
• Stemple, C. C., Kwon, H., & Yoon, J. (2012). Rapid and sensitive detection of malaria antigen in human blood with lab-on-a-chip. IEEE Sensors Journal, 12(9), 2735-2736.
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  Abstract: A novel lab-on-a-chip detection device, based on the properties of immunoagglutination, was modified to detect malaria in the human blood through histidine-rich protein 2, an antigen expressed only by Plasmodium falciparum. Utilizing Mie scattering detection, which is angle- and size-dependent, the extent of immunoagglutination could be accurately measured while the optical disturbance from the human blood was minimized. The presence of human serum albumin in the blood is believed to further stabilize the antibody-conjugated submicron beads and/or break off the larger agglutinated beads. The lowest detection limit was 1 pg/mL in 10% of whole blood (equivalent to 10 pg/mL in undiluted whole blood), a few orders of magnitude lower than other assays. The final device is compact, with a fast assay time of approximately 8 min. © 2001-2012 IEEE.
• Yoon, J. (2012). Who we are & what we can do. Resource: Engineering and Technology for Sustainable World, 19(3), 19-21.
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  Abstract: Many agricultural and biological engineers are aimed to claim exciting new research areas and pursue new industrial opportunities. Some argue that biomedical engineering should be included as a subset of biological engineering. The reality is that a substantial number of ABE departments retain the word 'agricultural' in their department name, even though their undergraduate programs do not. Many interdepartmental or interdisciplinary graduate programs in biomedical engineering are converting to stand-alone departments that offer undergraduate programs, and they are attracting large numbers of students. BMES, the governing society for biomedical engineering is thriving, with a rapid increase in membership. ASABE, a small engineering society, is aimed at works such as water recycling systems that include agricultural water use, drinking water, industrial uses, public health, sensor networks and remote sensing, food safety, and bioenergy.
• Yoon, J., & Kim, B. (2012). Lab-on-a-chip pathogen sensors for food safety. Sensors (Basel, Switzerland), 12(8), 10713-10741.
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  There have been a number of cases of foodborne illness among humans that are caused by pathogens such as Escherichia coli O157:H7, Salmonella typhimurium, etc. The current practices to detect such pathogenic agents are cell culturing, immunoassays, or polymerase chain reactions (PCRs). These methods are essentially laboratory-based methods that are not at all real-time and thus unavailable for early-monitoring of such pathogens. They are also very difficult to implement in the field. Lab-on-a-chip biosensors, however, have a strong potential to be used in the field since they can be miniaturized and automated; they are also potentially fast and very sensitive. These lab-on-a-chip biosensors can detect pathogens in farms, packaging/processing facilities, delivery/distribution systems, and at the consumer level. There are still several issues to be resolved before applying these lab-on-a-chip sensors to field applications, including the pre-treatment of a sample, proper storage of reagents, full integration into a battery-powered system, and demonstration of very high sensitivity, which are addressed in this review article. Several different types of lab-on-a-chip biosensors, including immunoassay- and PCR-based, have been developed and tested for detecting foodborne pathogens. Their assay performance, including detection limit and assay time, are also summarized. Finally, the use of optical fibers or optical waveguide is discussed as a means to improve the portability and sensitivity of lab-on-a-chip pathogen sensors.
• Yoon, J., & Kim, B. (2012). Lab-on-a-chip pathogen sensors for food safety. Sensors (Switzerland), 12(8), 10713-10741.
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  PMID: 23112625;PMCID: PMC3472853;Abstract: There have been a number of cases of foodborne illness among humans that are caused by pathogens such as Escherichia coli O157:H7, Salmonella typhimurium, etc. The current practices to detect such pathogenic agents are cell culturing, immunoassays, or polymerase chain reactions (PCRs). These methods are essentially laboratory-based methods that are not at all real-time and thus unavailable for early-monitoring of such pathogens. They are also very difficult to implement in the field. Lab-on-a-chip biosensors, however, have a strong potential to be used in the field since they can be miniaturized and automated; they are also potentially fast and very sensitive. These lab-on-a-chip biosensors can detect pathogens in farms, packaging/processing facilities, delivery/distribution systems, and at the consumer level. There are still several issues to be resolved before applying these lab-on-a-chip sensors to field applications, including the pre-treatment of a sample, proper storage of reagents, full integration into a battery-powered system, and demonstration of very high sensitivity, which are addressed in this review article. Several different types of lab-on-a-chip biosensors, including immunoassay- and PCR-based, have been developed and tested for detecting foodborne pathogens. Their assay performance, including detection limit and assay time, are also summarized. Finally, the use of optical fibers or optical waveguide is discussed as a means to improve the portability and sensitivity of lab-on-a-chip pathogen sensors. © 2012 by the authors; licensee MDPI, Basel, Switzerland.
• You, D. J., & Yoon, J. (2012). Droplet centrifugation, droplet DNA extraction, and rapid droplet thermocycling for simpler and faster PCR assay using wire-guided manipulations. Journal of Biological Engineering, 6.
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  PMID: 22947281;PMCID: PMC3526397;Abstract: A computer numerical control (CNC) apparatus was used to perform droplet centrifugation, droplet DNA extraction, and rapid droplet thermocycling on a single superhydrophobic surface and a multi-chambered PCB heater. Droplets were manipulated using " wire-guided" method (a pipette tip was used in this study). This methodology can be easily adapted to existing commercial robotic pipetting system, while demonstrated added capabilities such as vibrational mixing, high-speed centrifuging of droplets, simple DNA extraction utilizing the hydrophobicity difference between the tip and the superhydrophobic surface, and rapid thermocycling with a moving droplet, all with wire-guided droplet manipulations on a superhydrophobic surface and a multi-chambered PCB heater (i.e., not on a 96-well plate). Serial dilutions were demonstrated for diluting sample matrix. Centrifuging was demonstrated by rotating a 10 μL droplet at 2300 round per minute, concentrating E. coli by more than 3-fold within 3 min. DNA extraction was demonstrated from E. coli sample utilizing the disposable pipette tip to cleverly attract the extracted DNA from the droplet residing on a superhydrophobic surface, which took less than 10 min. Following extraction, the 1500 bp sequence of Peptidase D from E. coli was amplified using rapid droplet thermocycling, which took 10 min for 30 cycles. The total assay time was 23 min, including droplet centrifugation, droplet DNA extraction and rapid droplet thermocycling. Evaporation from of 10 μL droplets was not significant during these procedures, since the longest time exposure to air and the vibrations was less than 5 min (during DNA extraction). The results of these sequentially executed processes were analyzed using gel electrophoresis. Thus, this work demonstrates the adaptability of the system to replace many common laboratory tasks on a single platform (through re-programmability), in rapid succession (using droplets), and with a high level of accuracy and automation. © 2012 You and Yoon; licensee BioMed Central Ltd.
• You, D. J., & Yoon, J. (2012). Droplet centrifugation, droplet DNA extraction, and rapid droplet thermocycling for simpler and faster PCR assay using wire-guided manipulations. Journal of biological engineering, 6(15).
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  A computer numerical control (CNC) apparatus was used to perform droplet centrifugation, droplet DNA extraction, and rapid droplet thermocycling on a single superhydrophobic surface and a multi-chambered PCB heater. Droplets were manipulated using wire-guided method (a pipette tip was used in this study). This methodology can be easily adapted to existing commercial robotic pipetting system, while demonstrated added capabilities such as vibrational mixing, high-speed centrifuging of droplets, simple DNA extraction utilizing the hydrophobicity difference between the tip and the superhydrophobic surface, and rapid thermocycling with a moving droplet, all with wire-guided droplet manipulations on a superhydrophobic surface and a multi-chambered PCB heater (i.e., not on a 96-well plate). Serial dilutions were demonstrated for diluting sample matrix. Centrifuging was demonstrated by rotating a 10 uL droplet at 2300 round per minute, concentrating E. coli by more than 3-fold within 3 min. DNA extraction was demonstrated from E. coli sample utilizing the disposable pipette tip to cleverly attract the extracted DNA from the droplet residing on a superhydrophobic surface, which took less than 10 min. Following extraction, the 1500 bp sequence of Peptidase D from E. coli was amplified using rapid droplet thermocycling, which took 10 min for 30 cycles. The total assay time was 23 min, including droplet centrifugation, droplet DNA extraction and rapid droplet thermocycling. Evaporation from of 10 uL droplets was not significant during these procedures, since the longest time exposure to air and the vibrations was less than 5 min (during DNA extraction). The results of these sequentially executed processes were analyzed using gel electrophoresis. Thus, this work demonstrates the adaptability of the system to replace many common laboratory tasks on a single platform (through re-programmability), in rapid succession (using droplets), and with a high level of accuracy and automation.
• Heinze, B. C., & Yoon, J. (2011). Nanoparticle immunoagglutination Rayleigh scatter assay to complement microparticle immunoagglutination Mie scatter assay in a microfluidic device. Colloids & surfaces. B, Biointerfaces, 85(2), 168-173.
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  In this work, particle immunoagglutination assays for pathogen detection, utilizing light scattering measurements at a fixed angle from incident light delivery, are explored in both Rayleigh and Mie scatter regimes through scatter intensity simulations and compared to experimental results. The average size of immunoagglutinated particles obtained from microscope images correspond to the particle size parameter from simulations. Mie scatter measurements yield a greater signal increase with increasing pathogen concentration than Rayleigh scatter measurements, but with a non-monotonic relationship that is not observed in the Rayleigh scatter regime. These two similar yet distinctly different sources of information could easily be integrated into a single device through fabrication of a simple microfluidic device containing two y-channels, each for performing the respective light scattering measurement. Escherichia coli was used as a representative target, and detected in a microfluidic device down to a concentration of 1 colony forming units (CFU) per mL.
• Heinze, B. C., & Yoon, J. (2011). Nanoparticle immunoagglutination Rayleigh scatter assay to complement microparticle immunoagglutination Mie scatter assay in a microfluidic device. Colloids and Surfaces B: Biointerfaces, 85(2), 168-173.
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  PMID: 21411297;Abstract: In this work, particle immunoagglutination assays for pathogen detection, utilizing light scattering measurements at a fixed angle from incident light delivery, are explored in both Rayleigh and Mie scatter regimes through scatter intensity simulations and compared to experimental results. The average size of immunoagglutinated particles obtained from microscope images correspond to the particle size parameter from simulations. Mie scatter measurements yield a greater signal increase with increasing pathogen concentration than Rayleigh scatter measurements, but with a non-monotonic relationship that is not observed in the Rayleigh scatter regime. These two similar yet distinctly different sources of information could easily be integrated into a single device through fabrication of a simple microfluidic device containing two y-channels, each for performing the respective light scattering measurement. Escherichia coli was used as a representative target, and detected in a microfluidic device down to a concentration of 1 colony forming units (CFU) per mL. © 2011 Elsevier B.V.
• Kwon, H., Angus, S. V., You, D. J., Stemple, C. C., & Yoon, J. (2011). Development of a handheld optofluidic immunosensor to track the transport and distribution of H1N1/2009 virus in a mock classroom. 15th International Conference on Miniaturized Systems for Chemistry and Life Sciences 2011, MicroTAS 2011, 2, 1421-1423.
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  Abstract: A handheld lab-on-a-chip immunosensor was developed for rapid detection of H1N1/2009 virus inside a 1:10 scale mock classroom. The device detected Mie light scattering from immunoagglutination of antibody-conjugated submicron latex beads with H1N1/2009 target in a handheld optofluidic device. The lowest detectable amount was 55 pg of H1N1/2009 viruses in 0.1 m3 of a room with 2 min sampling time. A 3-D computational fluid dynamics simulation was utilized to track the transport and distribution of H1N1/09 within a mock classroom, and corresponded very well with immunosensor readings. The device and 3-D CFD model could serve as a good model for monitoring the viral pathogen within a human environment. Copyright © (2011) by the Chemical and Biological Microsystems Society.
• Song, J., Lee, C., Choi, E., Kim, K., & Yoon, J. (2011). Sensitive Mie scattering immunoagglutination assay of porcine reproductive and respiratory syndrome virus (PRRSV) from lung tissue samples in a microfluidic chip. Journal of Virological Methods, 178(1-2), 31-38.
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  PMID: 21871925;Abstract: A microfluidic immunosensor utilizing Mie scattering immunoaggultination assay was developed for rapid and sensitive detection of porcine reproductive and respiratory syndrome virus (PRRSV) from lung tissue samples of domesticated pigs. Antibodies against PRRSV were conjugated to the surface of highly carboxylated polystyrene microparticles (diameter=920nm) and mixed with the diluted PRRSV tissue samples in a Y-shaped microchannel. Antibody-antigen binding induced microparticle immunoagglutination, which was detected by measuring the forward 45° light scattering of 380nm incident beam using microcallipered, proximity fiber optics. For comparison, multi-well experiments were also performed using the same optical detection setup. The detection limit was determined to be 10 -3TCID 50ml -1 for PRRSV dissolved in PBS, while those of previous RT-PCR studies for PRRSV were 10 1TCID 50ml -1 (conventional assays) or
• Song, J., Lee, C., Choi, E., Kim, K., & Yoon, J. (2011). Sensitive Mie scattering immunoagglutination assay of porcine reproductive and respiratory syndrome virus (PRRSV) from lung tissue samples in a microfluidic chip. Journal of virological methods, 178(1-2), 31-38.
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  A microfluidic immunosensor utilizing Mie scattering immunoaggultination assay was developed for rapid and sensitive detection of porcine reproductive and respiratory syndrome virus (PRRSV) from lung tissue samples of domesticated pigs. Antibodies against PRRSV were conjugated to the surface of highly carboxylated polystyrene microparticles (diameter = 920 nm) and mixed with the diluted PRRSV tissue samples in a Y-shaped microchannel. Antibody-antigen binding induced microparticle immunoagglutination, which was detected by measuring the forward 45 degree light scattering of 380 nm incident beam using microcallipered, proximity fiber optics. For comparison, multi-well experiments were also performed using the same optical detection setup. The detection limit was determined to be 10(-3) TCID50/ml for PRRSV dissolved in PBS, while those of previous RT-PCR studies for PRRSV were 10(1) TCID50/ml (conventional assays) or 1 TCID50/ml (quantitative real-time assays). Mie scattering simulations were able to predict the shape of the PRRSV standard curve, indicating that any non-linearity of the standard curve can be interpreted purely as an optical phenomenon. Each assay took less than 5 min. A strong correlation could be found between RT-PCR and this method for the lung tissue samples, even though their respective detection mechanisms are different fundamentally (nucleic acids for RT-PCR and virus antigens for light scattering immunoagglutination assay). Several different dilution factors were also tested for tissue samples, and 1/10 and 1/100 were found to be usable. If the microfluidic chips are used only once (i.e. without re-using them), both superior sensitivity and satisfactory specificity can be demonstrated. Specificity studies revealed the presence of Type II PRRSV and non-presence of Type I PRRSV and that the microfluidic chip assay could detect Type II North American strain of PRRSV for the animals tested. This work demonstrates the potential of the Mie scattering immunoassay on a microfluidic chip towards real-time detection system for viral pathogens in domesticated animals.
• You, D. J., Geshell, K. J., & Yoon, J. (2011). Direct and sensitive detection of foodborne pathogens within fresh produce samples using a field-deployable handheld device. Biosensors & bioelectronics, 28(1), 399-406.
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  Direct and sensitive detection of foodborne pathogens from fresh produce samples was accomplished using a handheld lab-on-a-chip device, requiring little to no sample processing and enrichment steps for a near-real-time detection and truly field-deployable device. The detection of Escherichia coli K12 and O157:H7 in iceberg lettuce was achieved utilizing optimized Mie light scatter parameters with a latex particle immunoagglutination assay. The system exhibited good sensitivity, with a limit of detection of 10 CFU/mL and an assay time of <6 min. Minimal pretreatment with no detrimental effects on assay sensitivity and reproducibility was accomplished with a simple and cost-effective KimWipes filter and disposable syringe. Mie simulations were used to determine the optimal parameters (particle size d, wavelength lambda, and scatter angle theta) for the assay that maximize light scatter intensity of agglutinated latex microparticles and minimize light scatter intensity of the tissue fragments of iceberg lettuce, which were experimentally validated. This introduces a powerful method for detecting foodborne pathogens in fresh produce and other potential sample matrices. The integration of a multi-channel microfluidic chip allowed for differential detection of the agglutinated particles in the presence of the antigen, revealing a true field-deployable detection system with decreased assay time and improved robustness over comparable benchtop systems. Additionally, two sample preparation methods were evaluated through simulated field studies based on overall sensitivity, protocol complexity, and assay time. Preparation of the plant tissue sample by grinding resulted in a two-fold improvement in scatter intensity over washing, accompanied with a significant increase in assay time: 5 min (grinding) versus 1 min (washing). Specificity studies demonstrated binding of E. coli O157:H7 EDL933 to only O157:H7 antibody conjugated particles, with no cross-reactivity to K12. This suggests the adaptability of the system for use with a wide variety of pathogens, and the potential to detect in a variety of biological matrices with little to no sample pretreatment.
• You, D. J., Geshell, K. J., & Yoon, J. (2011). Direct and sensitive detection of foodborne pathogens within fresh produce samples using a field-deployable handheld device. Biosensors and Bioelectronics, 28(1), 399-406.
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  PMID: 21840701;Abstract: Direct and sensitive detection of foodborne pathogens from fresh produce samples was accomplished using a handheld lab-on-a-chip device, requiring little to no sample processing and enrichment steps for a near-real-time detection and truly field-deployable device. The detection of Escherichia coli K12 and O157:H7 in iceberg lettuce was achieved utilizing optimized Mie light scatter parameters with a latex particle immunoagglutination assay. The system exhibited good sensitivity, with a limit of detection of 10CFUmL -1 and an assay time of
• You, D. J., Tran, P. L., Kwon, H., Patel, D., & Yoon, J. (2011). Very quick reverse transcription polymerase chain reaction for detecting 2009 H1N1 influenza A using wire-guide droplet manipulations. Faraday Discussions, 149, 159-170.
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  PMID: 21413180;Abstract: Reverse transcription polymerase chain reaction (RT-PCR) is currently a gold standard in identifying influenza A virus, especially H1N1 flu. Typical RT-PCR assays take about 1-2 h for thermocycling, and there is a growing need to further speed up the thermocycling to less than 30 min. Additionally, the PCR assay system should be made portable as a point-of-care detection tool. There have been attempts to further speed up the PCR assays by reducing its volume. There have also been attempts to use droplet microfluidics technology to PCR, primarily to automate the PCR enrichment processes and take advantage of its small volume. In all these attempts, heating and cooling is made by conduction heat transfer. Rapid movements of droplets (immersed in oil) over three different temperature zones make very quick PCR possible, as heating/cooling will be made by convection heat transfer, whose heat transfer coefficients are much higher than that of conduction. We used our newly-invented method of wire-guide droplet manipulations towards very quick RT-PCR. Computational fluid dynamics (CFD) simulation of our system revealed that heating/cooling for each temperature change takes 1-4 s for a 10 μL droplet, as compared to >30 s in the other quick PCRs. Theoretically a 30-cycle process can take as short as 13 s × 30 cycles = 6 min 30 s. The entire system was made as a single instrument, with the components made by a milling machine and a rapid prototyping device. No additional equipment and external computers are required. With this newly developed system, 160 bp gene sequence was amplified from 2009 H1N1 influenza A (human origin). The 30-cycle process took as short as 6 min 50 s for a 10 μL droplet (with additional 4 min for reverse transcription). Its product was confirmed by traditional gel electrophoresis, subsequent imaging as well as gene sequencing, which has been very difficult with the other stationary droplet/nanodrop approaches. The proposed system has a potential to become an extremely rapid, portable, point-of-care tool for detecting influenza A. © 2011 The Royal Society of Chemistry.
• You, D. J., Tran, P. L., Kwon, H., Patel, D., & Yoon, J. (2011). Very quick reverse transcription polymerase chain reaction for detecting 2009 H1N1 influenza A using wire-guide droplet manipulationst. Faraday discussions, 149(1), 159-170.
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  Reverse transcription polymerase chain reaction (RT-PCR) is currently a gold standard in identifying influenza A virus, especially H1N1 flu. Typical RT-PCR assays take about 1-2 h for thermocycling, and there is a growing need to further speed up the thermocycling to less than 30 min. Additionally, the PCR assay system should be made portable as a point-of-care detection tool. There have been attempts to further speed up the PCR assays by reducing its volume. There have also been attempts to use droplet microfluidics technology to PCR, primarily to automate the PCR enrichment processes and take advantage of its small volume. In all these attempts, heating and cooling is made by conduction heat transfer. Rapid movements of droplets (immersed in oil) over three different temperature zones make very quick PCR possible, as heating/cooling will be made by convection heat transfer, whose heat transfer coefficients are much higher than that of conduction. We used our newly-invented method of wire-guide droplet manipulations towards very quick RT-PCR. Computational fluid dynamics (CFD) simulation of our system revealed that heating/cooling for each temperature change takes 1-4 s for a 10 uL droplet, as compared to 30 s in the other quick PCRs. Theoretically a 30-cycle process can take as short as 13 s x 30 cycles = 6 min 30 s. The entire system was made as a single instrument, with the components made by a milling machine and a rapid prototyping device. No additional equipment and external computers are required. With this newly developed system, 160 bp gene sequence was amplified from 2009 H1N1 influenza A (human origin). The 30-cycle process took as short as 6 min 50 s for a 10 uL droplet (with additional 4 min for reverse transcription). Its product was confirmed by traditional gel electrophoresis, subsequent imaging as well as gene sequencing, which has been very difficult with the other stationary droplet/nanodrop approaches. The proposed system has a potential to become an extremely rapid, portable, point-of-care tool for detecting influenza A.
• Heinze, B. C., Gamboa, J. R., Kim, K., Song, J., & Yoon, J. (2010). Microfluidic immunosensor with integrated liquid core waveguides for sensitive Mie scattering detection of avian influenza antigens in a real biological matrix. Analytical and Bioanalytical Chemistry, 398(6), 2693-2700.
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  PMID: 20859619;Abstract: This work presents the use of integrated, liquid core, optical waveguides for measuring immunoagglutinationinduced light scattering in a microfluidic device, towards rapid and sensitive detection of avian influenza (AI) viral antigens in a real biological matrix (chicken feces). Mie scattering simulations were performed and tested to optimize the scattering efficiency of the device through proper scatter angle waveguide geometry. The detection limit is demonstrated to be 1 pgmL-1 in both clean buffer and real biological matrix. This low detection limit is made possible through on-chip diffusional mixing of AI target antigens and high acid content microparticle assay reagents, coupledwith real-timemonitoring of immunoagglutination-induced forward Mie scattering via high refractive index liquid core optical waveguides in close proximity (100 μm) to the sample chamber. The detection time for the assay is
• Kwon, H., Dean, Z. S., Angus, S. V., & Yoon, J. (2010). Lab-on-a-Chip for Field Escherichia coli Assays: Long-Term Stability of Reagents and Automatic Sampling System. JALA - Journal of the Association for Laboratory Automation, 15(3), 216-223.
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  Abstract: A field lab-on-a-chip system was constructed to detect mouse immunoglobulin G (mIgG; model protein target) and . Escherichia coli (. E. coli; model microorganism target) by using light scattering detection of particle immunoagglutination. The antibodies to these targets were conjugated to the submicron particles by covalent binding, and their long-term stability was evaluated. Antibody-conjugated particles were able to be stored in a 4. °C refrigerator for at least 4 weeks and to be lyophilized as a powder form for the storage in room temperature. The optimum antibody coverage on the particles was 50% for mIgG and 100% for . E. coli in terms of assay sensitivity and long-term storage of reagents. Lab-on-a-chip device was fabricated from acrylic plate using an industrial-grade milling machine eliminating the need for photolithography and internal or external pumping. An automatic sampling system was constructed using drip emitters, such that the system can be connected to a pressurized water pipe for detecting . E. coli. The automatic sampling system generated the same volume of droplets (70. μL) regardless of pressure. The developed system was successfully tested for . E. coli presence in field water samples. The system can potentially be connected to pressurized pipe networks for drinking, processing, irrigation, and wastewater. © 2010.
• Kwon, H., Lee, C., Choi, E., Song, J., Heinze, B. C., & Yoon, J. (2010). Optofluidic device monitoring and fluid dynamics simulation for the spread of viral pathogens in a livestock environment. Journal of Environmental Monitoring, 12(11), 2138-2144.
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  PMID: 20886169;Abstract: Rapid monitoring of the spreads of porcine reproductive and respiratory syndrome virus (PRRSV) was attempted using samples collected from nasal swabs of pigs and air samplers within an experimental swine building. An optofluidic device containing liquid-core waveguides was used to detect forward Mie light scattering caused by the agglutination of anti-PRRSV-conjugated submicron particles, with enhanced sensitivity, signal reproducibility, and reusability (reusable up to 75 assays). These results were compared with reverse transcription polymerase chain reaction (RT-PCR) assays (35 cycles) and showed excellent agreements to them. Each assay took less than 10 min including all necessary sample pre-processing, while the RT-PCR assays took up to 4 h including sample pre-processing and gel imaging for PCR products. A 3-D computational fluid dynamics (CFD) simulation was utilized to track the transport and distribution of PRRSV (from the mouths of pigs to the exhaust fans) within a swine building, and compared with the readings from an optofluidic device. Simulation results corresponded well with the experimental data, validating our 3-D CFD model for the spread of viral pathogens in a livestock environment. The developed optofluidic device and 3-D CFD model can serve as a good model for monitoring the spread of influenza A (swine and avian) within animal and human environments. © 2010 The Royal Society of Chemistry.
• Tran, P. L., Gamboa, J. R., You, D. J., & Yoon, J. (2010). FRET detection of Octamer-4 on a protein nanoarray made by size-dependent self-assembly. Analytical and Bioanalytical Chemistry, 398(2), 759-768.
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  PMID: 20652550;PMCID: PMC2991207;Abstract: An alternative approach for fabricating a protein array at nanoscale is suggested with a capability of characterization and/or localization of multiple components on a nanoarray. Fluorescent micro- and nanobeads each conjugated with different antibodies are assembled by size-dependent self-assembly (SDSA) onto nanometer wells that were created on a polymethyl methacrylate (PMMA) substrate by electron beam lithography (EBL). Antibody-conjugated beads of different diameters are added serially and electrostatically attached to corresponding wells through electrostatic attraction between the charged beads (confirmed by zeta potential analysis) and exposed p-doped silicon substrate underneath the PMMA layer. This SDSA method is enhanced by vibrated-wire-guide manipulation of droplets on the PMMA surface containing nanometer wells. Saturation rates of antibody-conjugated beads to the nanometer patterns are up to 97% under one component and 58-70% under two components nanoarrays. High-density arrays (up to 40,000 wells) could be fabricated, which can also be multi-component. Target detection utilizes fluorescence resonance energy transfer (FRET) from fluorescent beads to fluorescent-tagged secondary antibodies to Octamer-4 (Oct4), which eliminates the need for multiple steps of rinsing. The 100 nm green beads are covalently conjugated with anti-Oct4 to capture Oct4 peptides (39 kDa); where the secondary anti-Oct4 and F(ab)2 fragment of anti-gIgG tagged with phycoerythrin are then added to function as an indicator of Oct4 detection. FRET signals are detected through confocal microscopes, and further confirmed by Fluorolog3 spectrofluorometer. The success rates of detecting Oct4 are 32% and 14% of the beads in right place under one and two component nanoarrays, respectively. Ratiometric FRET is used to quantify the amount of Oct4 peptides per each bead, which is estimated about 2 molecules per bead. © 2010 Springer-Verlag.
• Yoon, J., & Kwon, H. (2010). Biosensor detection CS of an airborne mystery disease. Resource: Engineering and Technology for Sustainable World, 17(5), 5-7.
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  Abstract: The use of a field-deployable biosensor device in a networked system in a real animal/human environment is important to monitor the spread of dangerous viral pathogens. Surrogate molecules have been used to perform experimental monitoring and/or computational fluid dynamics (CFD) studies, including smoke (for particulate movement) and CO2 (to simulate respiration). The current standard for detecting both porcine reproductive and respiratory syndrome (PRRSV) and influenza A is reverse transcription polymerase chain reaction (RT-PCR), which may take up to four hours to perform, including sample pre-processing, reverse transcription, thermocycling, and gel imaging for product identification. A lab-on-a-chip (LOC) is used to monitor airborne pathogens and enable to perform sample handling, mixing, dilution, electrophoresis, staining, and detection in a single integrated system. The three-dimensional CFD model would serve as a good model for monitoring the spread of many other viral pathogens within animal and human environments.
• Han, J., & Yoon, J. (2009). Reusable, polyethylene glycol-structured microfluidic channel for particle immunoassays. Journal of Biological Engineering, 3.
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  PMID: 19400962;PMCID: PMC2680825;Abstract: A microfluidic channel made entirely out of polyethylene glycol (PEG), not PEG coating to silicon or polydimethylsiloxane (PDMS) surface, was fabricated and tested for its reusability in particle immunoassays and passive protein fouling, at relatively high target concentrations (1 mg ml-1). The PEG devices were reusable up to ten times while the oxygen-plasma-treated polydimethyl siloxane (PDMS) device could be reused up to four times and plain PDMS were not reusable. Liquid was delivered spontaneously via capillary action and complicated bonding procedure was not necessary. The contact angle analysis revealed that the water contact angle on microchannel surface should be lower than ∼60°, which are comparable to those on dried protein films, to be reusable for particle immunoassays and passive protein fouling. © 2009 Han and Yoon; licensee BioMed Central Ltd.
• Han, J., Kwon, H., Yoon, J., Kim, K., Nam, S., & Son, J. E. (2009). Analysis of the thermal environment in a mushroom house using sensible heat balance and 3-D computational fluid dynamics. Biosystems Engineering, 104(3), 417-424.
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  Abstract: An environmental prediction model was developed for optimal ventilation in a mushroom house utilising a sensible heat balance and a three-dimensional (3-D) computational fluid dynamics (CFD) model. The respiration of the mushrooms and the use of a low-capacity cooler were considered. A mushroom-house-specific ventilation equation was developed to calculate the ventilation rate for a given environmental condition. Calculated ventilation rates were compared with the experimentally measured data for the indoor temperature set to the optimum for growing mushrooms (16.2 °C) with varying outdoor temperature. There was good agreement between the measured and predicted rates (0.2-5.1% error). Calculated ventilation rates (from the sensible heat balance) were used as an input parameter for 3-D CFD model, eliminating the need for experimental measurement of ventilation rate. 3-D CFD simulations were conducted using the same environmental condition to establish the local heat distribution in a mushroom house. The simulation results for temperature were compared with the experimental data at several different locations in a mushroom house and showed negligible errors. The CFD model was also used to improve heat distribution of a mushroom house. It was predicted that enhanced cooling and more uniform temperature distribution could be achieved just by changing the direction of airflow from air inlet ducts and/or installing small fans onto them, but not by changing the directions of airflow from a cooler. This would be a more economical than replacing a cooler or redesigning the entire structure. The model could be used to predict the environmental conditions over different locations in a mushroom house without the need for experimentally determining the ventilation rate. © 2009 IAgrE.
• Heinze, B. C., Song, J., Lee, C., Najam, A., & Yoon, J. (2009). Microfluidic immunosensor for rapid and sensitive detection of bovine viral diarrhea virus. Sensors and Actuators, B: Chemical, 138(2), 491-496.
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  Abstract: We have investigated the utilization of microparticle immunoagglutination assays using forward light scattering measurements in a microfluidic chip towards detecting viral particles. The model viral target was bovine viral diarrhea virus (BVDV). Highly carboxylated polystyrene microparticles (510 nm) were coated with anti-BVDV monoclonal antibodies. This solution was in turn used to detect BVDV in diluted tissue culture media and fetal calf serum. The assay was first performed in a two well slide format for proof of concept and particle stability experiments, then in a simple y-channel microfluidic chip with optical fibers arranged in a close proximity setup. Microparticle immunoagglutination was detected via static forward light scattering measurements taken at 45° to incident light. In the microfluidic chip, BVDV was detected down to a concentration of 10 TCID50 mL-1. For assay comparison purposes reverse transcriptase polymerase chain reaction (RT-PCR) was performed on serial dilutions of the BVDV sample used in the two well and microfluidic testing. RT-PCR was effective down to a concentration of 103 TCID50 mL-1 in detecting the identical BVDV used for microfluidic assays. © 2009 Elsevier B.V. All rights reserved.
• Powell, T. B., Tran, P. L., Kim, K., & Yoon, J. (2009). Size-dependent self-assembly of submicron/nano beads-protein conjugates for construction of a protein nanoarray. Materials Science and Engineering C, 29(8), 2459-2463.
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  Abstract: A protein nanoarray is created when submicro and nano beads, varying in their size and each conjugated with different proteins, self-assemble to specific locations depending on the diameter matching the surface electron beam patterns created. Protein binding is confirmed from the fluorescence attenuation of the beads upon antigen-antibody binding on the bead surface. This method, called size-dependent self-assembly, allows control of the location of each type of bead, and thus, control of the location of multiple proteins. It provides fast multi-component patterning with a high binding resolution, which can be detected using a fluorescent light microscope. This method is developed to be a simple stand-alone tool for analysis of protein interactions. In addition, it has the potential to be used in conjunction with other protein analysis methods, such as enzyme-linked immunosorbent assay (ELISA) and atomic force microscopy (AFM). © 2009 Elsevier B.V.
• Tran, P. L., Tchao, Y., & Yoon, J. (2009). Fluorescence resonance energy transfer detection of mouse immunoglobulin G and octamer-4 on protein nanoarray. 2009 ICME International Conference on Complex Medical Engineering, CME 2009.
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  Abstract: An alternative approach for fabricating a protein array at nanoscale (
• Tran, P. L., Tchao, Y., You, D. J., & Yoon, J. (2009). Protein nanoarray made by size-dependent self-assembly for detection of mouse immunoglobulin G and octamer-4. Progress in Biomedical Optics and Imaging - Proceedings of SPIE, 7313.
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  Abstract: An alternative approach for fabricating a protein array at nanoscale (
• Yoon, J. -., Han, J. -., Choi, C. Y., Bui, M., & Sinclair, R. G. (2009). Real-time detection of Escherichia coli in water pipe using a microfluidic device with one-step latex immunoagglutination assay. Transactions of the ASABE, 52(3), 1031-1039.
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  Abstract: The number of cases involving produce-associated illnesses has been increasing recently, especially those related to pathogen-contaminated irrigation water. Clearly, real-time and extremely sensitive detection of these pathogens is needed to ensure that produce-related farming procedures are safe. In our study, we demonstrated that the use of a microfluidic system can detect Escherichia coli in a water pipe at laminar and turbulent flow regimes. A one-step latex immunoagglutination assay was performed within a microfluidic device that uses fiber optics to detect pathogens. The results were then successfully validated by using cultured E. coli and a salt tracer. The detection of the E. coli was thus accomplished in real time (
• Yoon, J., & Riley, M. R. (2009). Grand challenges for biological engineering. Journal of Biological Engineering, 3.
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  PMID: 19772647;PMCID: PMC2754978;Abstract: Biological engineering will play a significant role in solving many of the world's problems in medicine, agriculture, and the environment. Recently the U.S. National Academy of Engineering (NAE) released a document "Grand Challenges in Engineering," covering broad realms of human concern from sustainability, health, vulnerability and the joy of living. Biological engineers, having tools and techniques at the interface between living and non-living entities, will play a prominent role in forging a better future. The 2010 Institute of Biological Engineering (IBE) conference in Cambridge, MA, USA will address, in part, the roles of biological engineering in solving the challenges presented by the NAE. This letter presents a brief outline of how biological engineers are working to solve these large scale and integrated problems of our society. © 2009 Yoon and Riley; licensee BioMed Central Ltd.
• Yoon, J., Heinze, B. C., Gamboa, J., & You, D. J. (2009). Detection of avian influenza antigens in proximity fiber, droplet and optical waveguide microfluidics. Progress in Biomedical Optics and Imaging - Proceedings of SPIE, 7313.
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  Abstract: Virus antigens of avian influenza subtype H3N2 were detected on two different microfluidic platforms: microchannel and droplet. Latex immunoagglutination assays were performed using 920-nm highly carboxylated polystyrene beads that are conjugated with antibody to avian influenza virus. The bead suspension was merged with the solutions of avian influenza virus antigens in a Y-junction of a microchannel made by polydimethylsiloxane soft lithography. The resulting latex immunoagglutinations were measured with two optical fibers in proximity setup to detect 45° forward light scattering. Alternatively, 10 μL droplets of a bead suspension and an antigen solution were merged on a superhydrophobic surface (water contact angle = 155°), whose movement was guided by a metal wire, and 180° back light scattering is measured with a backscattering optical probe. Detection limits were 0.1 pg mL-1 for both microchannel with proximity fibers and droplet microfluidics, thanks to the use of micro-positioning stages to help generate reproducible optical signals. Additionally, optical waveguide was tested by constructing optical waveguide channels (filled with mineral oil) within a microfluidic device to detect the same light scattering. Detection limit was 0.1 ng mL-1 for an optical waveguide device, with a strong potential of improvement in the near future. The use of optical waveguide enabled smaller device setup, easier operation, smaller standard deviations and broader linear range of assay than proximity fiber microchannel and droplet microfluidics. Total assay time was less than 10 min.© 2009 SPIE.
• Han, J., Heinze, B. C., & Yoon, J. (2008). Single cell level detection of Escherichia coli in microfluidic device. Biosensors and Bioelectronics, 23(8), 1303-1306.
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  PMID: 18182284;Abstract: Detection of Escherichia coli K-12 in phosphate buffered saline (PBS) was demonstrated in a Y-channel polydimethylsiloxane (PDMS) microfluidic device through optical fiber monitoring of latex immunoagglutination. The latex immunoagglutination assay was performed for serially diluted E. coli solutions using 0.92-μm highly carboxylated polystyrene particles conjugated with polyclonal anti-E. coli. Pre-treatments such as cell lysis or culturing to enhance the signal were not used. Proximity optical fibers around the view cell of the device were used to quantify the increase in 45° forward light scattering of the immunoagglutinated particles. In order to reduce false positive signals caused by antibodies binding to non-viable E. coli cells or free antigens in solution, target solutions were washed three times, and then the results were compared to non-washing treatments. The detection limit was found to be less than 10 cfu ml-1 (1 cfu per device) without PBS washing (thus detecting non-viable cells and free antigens), or less than 40 cfu ml-1 (4 cfu per device) with PBS washing (thus detecting viable E. coli cells only). © 2007 Elsevier B.V. All rights reserved.
• Heinze, B. C., Song, J., Han, J., & Yoon, J. (2008). Latex immunoagglutination assay for bovine viral diarrhea virus utilizing forward light scattering in a microfluidic device. Proceedings of SPIE - The International Society for Optical Engineering, 6886.
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  Abstract: We have investigated the utilization of particle agglutination assays using forward light scattering measurements in a microfluidic device towards detecting viral particles. The model viral target was bovine viral diarrhea virus (BVDV). Highly carboxylated polystyrene microspheres (510 nm) were coated with anti-BVDV monoclonal antibodies. This solution was in turn used to detect live modified BVDV. This assay was first performed in a two well slide for proof of concept and then in a simple y-channel microfluidic device with optical fibers arranged in a close proximity setup. Particle immunoagglutination was detected through static light scattering measurements taken at 45° to incident light. In the microfluidic device, modified live BVDV was detected with a detection limit of 0.5 TCID50 mL-1.
• Yoon, J., & You, D. J. (2008). Backscattering particle immunoassays in wire-guide droplet manipulations. Journal of Biological Engineering, 2.
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  PMID: 19014703;PMCID: PMC2596077;Abstract: A simpler way for manipulating droplets on a flat surface was demonstrated, eliminating the complications in the existing methods of open-surface digital microfluidics. Programmed and motorized movements of 10 μL droplets were demonstrated using stepper motors and microcontrollers, including merging, complicated movement along the programmed path, and rapid mixing. Latex immunoagglutination assays for mouse immunoglobulin G, bovine viral diarrhea virus and Escherichia coli were demonstrated by merging two droplets on a superhydrophobic surface (contact angle = 155 ± 2°) and using subsequent back light scattering detection, with detection limits of 50 pg mL-1, 2.5 TCID50 mL-1 and 85 CFU mL-1, respectively, all significantly lower than the other immunoassay demonstrations in conventional microfluidics (∼1 ng mL-1 for proteins, ∼100 TCID50 mL-1 for viruses and ∼100 CFU mL-1 for bacteria). Advantages of this system over conventional microfluidics or microwell plate assays include: (1) minimized biofouling and repeated use (>100 times) of a platform; (2) possibility of nanoliter droplet manipulation; (3) reprogrammability with a computer or a game pad interface. © 2008 Yoon and You; licensee BioMed Central Ltd.
• Han, J., Kim, K., & Yoon, J. (2007). The enhanced diffusional mixing for latex immunoagglutination assay in a microfluidic device. Analytica Chimica Acta, 584(2), 252-259.
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  PMID: 17386612;Abstract: Latex immunoagglutination assay in a microfluidic device is expected to be even easier than its large-sized, commercialized counterpart. However, such demonstration has had a limited success due to the difficulties in mixing in a microfluidic device, especially for the microparticles used in latex immunoagglutination assay. The primary goal of this work is to improve diffusional mixing towards the successful latex immunoagglutination in a microfluidic devices without any non-specific binding. To this end, SDS (sodium dodecyl sulfate, an ionic surfactant) or Tween 80 (polyethylene sorbitol ester, a non-ionic surfactant) was added to the antibody-conjugated polystyrene (PS) microparticle suspension. These surfactant-added particle suspensions were mixed with the target antigen solution at the Y-junction of a microfluidic device. The immunoagglutination and the diffusion behavior were visually identified with an inverted light microscope. Both surfactants showed some problems such as non-specific binding (with SDS) or very poor diffusion (with Tween 80). As an alternative approach, therefore, highly carboxylated PS microparticles, where the surface is saturated with carboxyl-terminated side chains, were evaluated without using any surfactants. These particles showed very low non-specific binding comparable to that with Tween 80 and good diffusional mixing equivalent to that with SDS. © 2006 Elsevier B.V. All rights reserved.
• Kim, K., Giacomelii, G. A., Yoon, J., Sase, S., Son, J., Nam, S., & Lee, I. (2007). CFD modeling to improve the design of a fog system for cooling greenhouses. Japan Agricultural Research Quarterly, 41(4), 283-290.
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  Abstract: A CFD model was developed to simulate the air temperature and relative humidity distribution in greenhouses adopting fog-cooling systems using FLUENT. The developed model was validated using the data from a fog-cooling experiment in a single-span greenhouse without plants. The measured and simulated air temperatures varied from 0.1 to 1.4°C and the differences of relative humidity varied 0.3-6.0%. The validated model was then used to evaluate the design of a fog-cooling system in a multi-span glasshouse. The optimal system design was determined in terms of the cooling efficiency and the special uniformity of air temperature and relative humidity. The simulations demonstrated that the best performance of the cooling system occurred when the fog nozzles were located at the height of 2.3 m above the floor and at a distance of 1.9 m from the sidewalls with uniform row-to-row spacing of 3.7 m. The most effective location of the nozzles was within the air entry from the sidewall ventilator inlets of the greenhouse. However, it was important not to wet the sidewalls with the fog. This study suggested that the CFD model developed could be a useful tool to design and evaluate the fog-cooling systems in greenhouses with various configurations.
• Lucas, L. J., Chesler, J. N., & Yoon, J. (2007). Lab-on-a-chip immunoassay for multiple antibodies using microsphere light scattering and quantum dot emission. Biosensors and Bioelectronics, 23(5), 675-681.
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  PMID: 17869502;Abstract: Double detection of microsphere light scattering and quantum dot emission was demonstrated for lab-on-a-chip immunoassay without using stationary support. We conjugated quantum dots (QDs) onto microspheres to enable multiplex assays as well as to enhance the limit of detection (LOD). We named this configuration "nano-on-micro" or "NOM". Upon radiation with UV light (380 nm), a stronger light scattering signal is observed with NOMs than QDs or microspheres alone. Additionally, NOMs are easier to handle than QDs. Since QDs also provide fluorescent emission, we are able to utilize an increase in light scattering for detecting antigen-antibody reaction and a decrease in QD emission to identify which antibody (or antigen) is present. Two types of NOM combinations were used. One batch of microspheres was coated with QDs emitting at 655 nm and mouse IgG (mIgG); the other with QDs emitting at 605 nm and bovine serum albumin (BSA). A mixture of these two NOMs was used to identify either anti-mIgG or anti-BSA. NOM particles and target solutions were mixed in a microfluidic device (using highly carboxylated microspheres as previously demonstrated by our group) and on-chip detection was performed using proximity optical fibers. Forward light scattering at 380 nm was collected. With the positive target, the scattering signal was increased. The LOD was as low as 50 ng ml-1 (330 pM) with p < 0.05. Fluorescent emission (655 or 605 nm) was simultaneously collected. With the positive target, the emission signal was attenuated. Therefore, we were able to detect two different antibodies simultaneously with two different detection protocols. We believe this NOM bioassay has the ability to screen for and detect multiple antibodies with minimal sample processing and handling (one-step lab-on-a-chip immunoassay). © 2007.
• Lucas, L. J., Chesler, J., & Yoon, J. (2007). Lab-on-a-chip immunoassay for multiple antibodies using microsphere light scattering and quantum dot emission. 2007 ASABE Annual International Meeting, Technical Papers, 15 BOOK.
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  Abstract: Detection of multiple biomarkers has recently received great interest from the biosensors community. These diagnostic methods must be rapid, specific, sensitive, and cost-effective. In 2006, our group demonstrated a successful lab-on-a-chip immunoassay using microsphere light scattering, which is essentially a one-step, automated protocol, on a reusable chip. In the past, this had been difficult due to the limitations of microfluidic mixing and false-positive readings of particle immunoassays in a chip environment. In this current study, we conjugated quantum dots (QDs) onto microspheres to enable multiplex assays as well as to enhance the limit of detection (LOD). We named this configuration "nano-on-micro" or "NOM." Upon radiation with UVlight (380 nm), a stronger light scattering signal is observed with NOMs than QDs or microspheres alone. Additionally, NOMs are easier to handle than QDs. Since QDs also provide fluorescent emission, we are able to utilize an increase in light scattering for detecting antigen-antibody reaction and a decrease in QD emission to identify which antibody (or antigen) is present. Two types of NOM combinations were used. One batch of microspheres was coated with QDs emitting at 655 nm and mouse IgG (mlgG); the other with QDs emitting at 605 nm and bovine serum albumin (BSA). A mixture of these two NOMs was used to identify either anti-mlgG or anti-BSA. NOM particles and target solutions were mixed in a microfluidic device and on-chip detection was performed using proximity optical fibers. Forward light scattering at 380 nm was collected. With the positive target, the scattering signal was increased. The LOD was 25 ng ml-1 (165 pM) with p
• Lucas, L. J., Han, J., Chesler, J., & Yoon, J. (2007). Latex immunoagglutination assay for a vasculitis marker in a microfluidic device using static light scattering detection. Biosensors and Bioelectronics, 22(9-10), 2216-2222.
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  PMID: 17141495;Abstract: We have developed a microfluidic immunoassay device using fiber optics to detect static light scattering (SLS) of latex microsphere agglutination. A 400-μm silica fiber was used to deliver blue light emitting diode (LED) or red laser light sources. A miniature, portable spectrometer was used to measure forward light scattering intensity collected by the same type of multi-mode fiber. To first show feasibility, anti-mouse IgG were used as target biomolecules and highly carboxylated polystyrene latex microspheres (510 nm) coated with mouse IgG were used as probes. Next, we tested for the vasculitis marker, anti-PR3, using the same type of microspheres coated with PR3 proteins. No false negatives or positives were observed. A limit of detection (LOD) of 50 ng mL-1 was demonstrated for the vasculitis marker, anti-PR3. (Plasma samples from patients with vasculitis exhibited anti-PR3 at a median level of 380 ng mL-1.) The optical detection system works without any fluorescence or chemiluminescence markers. The entire system proposed here is cost effective, small in size, and re-usable with simple rinsing. This may eventually lead to a portable, low-cost, re-useable, microfluidic, point of care immunoassay device. © 2006 Elsevier B.V. All rights reserved.
• Yoon, J., Han, J., Choi, C. Y., Heinze, B., & Lucas, L. J. (2007). Microfluidic device monitoring of waterborne pathogens in model water distribution systems. 2007 ASABE Annual International Meeting, Technical Papers, 15 BOOK.
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  Abstract: Microfluidic device detections of E. coli K12 in deionized (Dl) water and E. coli in field water sample were demonstrated through static light scattering of latex immunoagglutination using proximity optical fibers. This method is a fully-automated, one-step detection, and requires neither sample pre-treatment nor cell culturing often required in many on-chip detections. We have used highly carboxylated polystyrene submicron latex particles without surfactants to enhance diffusional mixing and prevent non-specific bindings towards successful demonstration of latex immunoagglutination in microfluidic device. Detection of E. coll was performed by taking microscopic images from the view cell of a microfluidic device and counting the fractions of non-agglutinated and agglutinated particles. The limit of detection (LOD) was ca. 150 CFU ml -1 with this method for both E. coli K12 in Dl water and E. coli in field water sample, indicating no non-specific bindings. Improved LOD of ca. 5 CFU ml-1 was achieved by measuring forward static light scattering from microfluidic device, using proximity optical fibers and a USB-powered miniature spectrometer. The total assay time for sample preparation (mostly dilutions) and on-chip assay (mostly injections and short incubation time) was
• Yoon, J., Han, J., Heinze, B., & Lucas, L. J. (2007). Microfluidic device detection of waterborne pathogens through static light scattering of latex immunoagglutination using proximity optical fibers. Proceedings of SPIE - The International Society for Optical Engineering, 6556.
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  Abstract: Microfluidic device detections of E. coli K12 in deionized (DI) water and E. coli in field water sample were demonstrated through static light scattering of latex immunoagglutination using proximity optical fibers. This method is a fully-automated, one-step detection, and requires neither sample pre-treatment nor cell culturing often required in many on-chip detections. We have used highly carboxylated polystyrene submicron latex particles without surfactants to enhance diffusional mixing and prevent non-specific bindings towards successful demonstration of latex immunoagglutination in microfluidic device. Detection of E. coli was performed by taking microscopic images from the view cell of a microfluidic device and counting the fractions of non-agglutinated and agglutinated particles. The limit of detection (LOD) was ca. 150 CFU ml -1 with this method for both E. coli K12 in DI water and E. coli in field water sample, indicating no non-specific bindings. Improved LOD of < 4.3 CFU ml-1 was achieved by measuring forward static light scattering from microfluidic device, using proximity optical fibers and a USB-powered miniature spectrometer. The total assay time for sample preparation (mostly dilutions) and on-chip assay (mostly injections and short incubation time) was < 10 min.
• Lucas, L. J., Han, J., & Yoon, J. (2006). Using highly carboxylated microspheres to simplify immunoassays and enhance diffusional mixing in a microfluidic device. Colloids and Surfaces B: Biointerfaces, 49(2), 106-111.
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  PMID: 16621472;Abstract: Manufacturers of latex immunoassays have typically added surfactants to improve detection sensitivity and prevent non-specific aggregation of microspheres, which may cause both false positives and negatives during diagnostic testing. There is also growing interest in conducting immunoassays in smaller volumes using microfluidic devices with minimum human effort. The first goal of our study was to simplify immunoassays by eliminating the use of surfactants. Our second objective was to determine if this strategy would also enhance diffusional mixing in a microfluidic channel, which has been one of the biggest barriers to using these devices. We first ran a series of cuvette experiments to document the performance of sodium dodecyl sulfate (SDS) and polysorbate 80 (Tween 80) surfactants in a mouse immunoglobulin G (IgG) immunoassay using plain polystyrene microspheres. Next, we tested highly carboxylated microspheres with no surfactants, to determine if the same levels of accuracy and specificity could be achieved. Finally, we evaluated the surfactants and highly carboxylated microspheres in a microfluidic device. Our results show that highly carboxylated microspheres can indeed be used to replace surfactants and to induce rapid mixing via diffusion in a microfluidic device. © 2006 Elsevier B.V. All rights reserved.
• Powell, T., & Yoon, J. (2006). Fluorescent biorecognition of gold nanoparticle-IgG conjugates self-assembled on E-beam patterns. Biotechnology Progress, 22(1), 106-110.
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  PMID: 16454499;Abstract: A new concept for line patterning of immunoglobulin G (IgG) in nanometer scale using gold nanoparticles (AuNPs) self-assembled in a nanochannel written with an electron beam is proposed and demonstrated. AuNPs are synthesized by reducing KAuCl4 with NaBH4, producing AuNPs 40-70 nm in size, where Cl- ions are capping AuNPs thus making them negatively charged and subsequently stabilized. IgG is conjugated to these AuNPs by simple adsorption. Single or multiple nanochannels are written with an electron beam using a scanning electron microscope (SEM) in a layer of poly(methyl methacrylate) (PMMA), which is spin-coated on a p-doped Si wafer. AuNPs bind into the etched nanochannel where the Si surface is exposed, while the relatively hydrophobic PMMA area repels the particles. The particles with a diameter larger than the channel width are not able to go inside of it. Anti-IgG, conjugated with fluorescein isothiocyanate (FITC), is then exposed to the patterned surface, binding specifically to the IgG-AuNP conjugates within the line patterns. These antibody-antigen bindings can be visualized with a fluorescent microscope, showing the fluorescent signal only along with the nanometer line pattern. These initial steps will lead to the formation of complex protein nanoarrays, based on the size-dependent self-assembly of AuNPs within variously sized nanopatterns. © 2006 American Chemical Society and American Institute of Chemical Engineers.
• Powell, T., & Yoon, J. (2005). Self-assembly of gold nanoparticles on e-beam nano-patterns towards protein nanoarray. 2005 NSTI Nanotechnology Conference and Trade Show - NSTI Nanotech 2005 Technical Proceedings, 351-354.
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  Abstract: As our understanding of human diseases grows, so does our need to understand functions and pathways on a proteomic level. Protein arrays are a way of analyzing proteins and pathways within single molecule detection. A new concept of fabricating protein arrays based on self assembly of protein/gold nanoparticle conjugates onto nanometer patterns formed by e-beam lithography. Hydrophilic gold nanoparticles (AuNPs) are formed using the Brust-Schiffrin method without stabilizer, and are exposed to a model hydrophobic surface with hydrophilic patterns etched within. The AuNPs bind to the exposed hydrophilic surfaces, while the hydrophobic surfaces repel the gold. This method can be used to bind different proteins to specific size AuNPs, which in turn, when serially added to nanometer patterns, will self assemble onto their respective sized patterns.
• Yoon, J., Garrell, R. L., Choi, S., Kim, J., & Kim, W. (2005). Using a stirred cell to evaluate structural changes in proteins adsorbed on particles. AIChE Journal, 51(3), 1048-1052.
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  Abstract: A stirred cell technique was used to evaluate structural changes in proteins adsorbed on particles. Stirred cell geometry was used to obtain a series of breakthrough curves, which is the change in the concentration of the adsorbate in the effluent as a function of effluent volume. The breakthrough curves can be asymmetric, which arises from the combination of factors related to the efficiency of the sorption process. The substrate consisted of a 1.5 volume percent suspension of nonporous latex particles mixed at high rotation speed. The adsorption of proteins on to hydrophobic surfaces, such as polystyrenes (PS) was modeled as a two-step process, reversible adsorption until the surface was fully covered with protein molecules, followed by irreversible structural changes in the adlayer. The pH values were chosen to match the isoelectric point of each protein, to minimize electrostatic interactions between the proteins and the PS latex, and to simultaneously maximize the amount of protein adsorbing through hydrophobic interactions. The results show that structural changes can be assessed as a function of protein concentration, and may include orientational and/or conformational changes, association and dissociation.
• Choi, S., Park, J., Chang, Y., Yoon, J., Haam, S., Kim, J., & Kim, W. (2003). Effect of electrostatic repulsive force on the permeate flux and flux modeling in the microfiltration of negatively charged microspheres. Separation and Purification Technology, 30(1), 69-77.
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  Abstract: A study on the permeate flux was performed in a stirred cell filled with monodispersed carboxylated microspheres (polystyrene/polymethacrylic acid, PS/PMAA), to investigate the effects of surface charge (the number density of surface carboxyl group, Nc; 0.45, 5.94, 9.14, and 10.25 nm-2) and the stirrer speed (300, 400, and 600 rpm) under constant transmembrane pressure. The permeate flux was found to be dependent on the surface charge, the ionic strength, and the stirrer speed. The permeate flux was proportional to the surface charge of microspheres and inversely proportional to the ionic strength because of electrostatic repulsive interaction and steric hindrance. The cake porosity was estimated by Kozeny-Carman equation from the steady-state permeate flux data. Experimental data elucidated that the cake porosity was extended from 0.211 to 3.04 upon the introduction of carboxyl group on the microsphere surface, leading to the high permeate flux. Consequently, resistance-in-series model was employed for the modeling of the permeate flux and showed a good agreement with the experimental results. © 2002 Elsevier Science B.V. All rights reserved.
• Huang, J., Egan, V. M., Guo, H., Yoon, J., Briseno, A. L., Rauda, I. E., Garrell, R. L., Knobler, C. M., Zhou, F., & Kaner, R. B. (2003). Enantioselective discrimination of D-and L-phenylalanine by chiral polyaniline thin films. Advanced Materials, 15(14), 1158-1161.
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  Abstract: An overview is given of the visual, circular dichroism (CD), and UV-vis evidence for chiral discrimination between D- and L-phenylalanine by (R)-camphorsulfonic acid ((R)-CSA) developed polyaniline. Kinetic studies using a flow-injection quartz crystal microbalance demonstrate quantitatively the enantioselective incorporation of L-phenylalanine over D-phenylalanine. These results support a re-doping type interaction between the de-doped polymer and L-phenylalanine.
• Yoon, J. Y., Kim, K. H., Choi, S. W., Kim, J. H., & Kim, W. S. (2003). Effects of surface characteristics on non-specific agglutination in latex immunoagglutination antibody assay. Colloids and Surfaces B: Biointerfaces, 27(1), 3-9.
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  Abstract: To monitor the non-specific agglutination (NSA) in latex immunoagglutination assay, antigen-coated structured latex particles, which have carboxyl and sulphonate groups as hydrophilic domains, were tested for an antibody assay. Sulphonated particles showed NSA in high antibody concentrations, where no surface antigen left to match with. This was further justified with the more stable highly sulphonated particles, which showed higher degree of NSA. It can therefore be confirmed that sulphonate groups cause (or at least promote) NSA, while carboxyl groups do not. Surface coverage over 17% was not fully utilized for antigen-antibody reaction, due to the prozone effect. The difference in sensitivity of particles was explained in terms of our new explanations on the governing interactions of protein adsorption. © 2002 Elsevier Science B.V. All rights reserved.
• Yoon, J., & Garrell, R. L. (2003). Preventing biomolecular adsorption in electrowetting-based biofluidic chips. Analytical Chemistry, 75(19), 5097-5102.
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  Abstract: Electrowetting-on-dielectric (EWOD) is a new method for moving liquids in biofluidic chips through electrical modification of the surface hydrophobicity. EWOD-based devices are reconfigurable, have low power requirements, and can handle neutral and charged analytes, as well as particulates. We show that biomolecular adsorption in EWOD is minimized by limiting the time during which no potential is applied and through choice of solution pH and electrode polarity. The same approach may be useful for controlling biomolecular adsorption in other applications of hydrophobic dielectric materials. These results demonstrate the feasibility of implementing EWOD for fluid actuation in biofluidic chips.
• Choi, S., Yoon, J., Haam, S., Jung, J., Kim, J., & Kim, W. (2000). Modeling of the permeate flux during microfiltration of BSA-adsorbed microspheres in a stirred cell. Journal of Colloid and Interface Science, 228(2), 270-278.
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  Abstract: A study on the variation of the permeate flux was performed in a stirred cell charged with microspheres, to investigate the effects of the stirrer speeds (300, 400, and 600 rpm) and the BSA concentration (0.1, 0.2, 0.4, and 0.8 g/L) under constant pressure. The permeate flux increased over time before the saturation point, but it began to decrease after that point. An increase of the BSA concentration and the stirrer speed resulted in the rapid increase of the permeate flux. This is contrary to the observation of the conventional filtration experiments using a stirred cell. A resistance-in-series model was employed for the modeling of the permeate flux. The cake resistance (R(c), induced by the concentration polarization of microspheres) and the fouling resistance (R(f), induced by the adsorption of BSA inside the membrane pore) must be considered simultaneously for the modeling. These modeling results were in good agreement with the experimental data. These can be applied to the special system considering both R(c) and R(f) as well as the general filtration systems using a stirred cell. (C) 2000 Academic Press.
• Yoon, J., Kim, J., & Kim, W. (1999). The relationship of interaction forces in the protein adsorption onto polymeric microspheres. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 153(1-3), 413-419.
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  Abstract: The relationship between hydrophobic and electrostatic interactions in protein adsorption was studied with various sulfonated microspheres, and it was compared with carboxylated microspheres. Hydrophobic interaction governed the adsorption in the low sulfonated microspheres and electrostatic interaction did in the high sulfonated ones. The transition point was observed when the two forces were exactly balanced, but it was shifted to the left compared to the case of the carboxylated microspheres. The above adsorption experiments with different kinds of surface functionality revealed the following general mechanism of protein adsorption. The protein adsorption mainly occurs by hydrophobic interaction when the hydrophobic surface is slightly modified with weak or strong acid, while it primarily occurs by hydrogen bonding (or electrostatic) interaction when the surface is mostly modified with weak (or strong) acid. The adsorption by electrostatic interaction is higher than that by any other interactions, but the rate of adsorption is slowest. Copyright (C) 1999 Elsevier Science B.V. All rights reserved.
• Lee, J. H., Yoon, J., & Kim, W. (1998). Continuous separation of serum proteins using a stirred cell charged with carboxylated and sulfonated microspheres. Biomedical Chromatography, 12(6), 330-334.
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  PMID: 9861492;Abstract: We contrived a new separation system using a stirred cell charged with uncoupled microsphere similar to the chromatographic separation. Microspheres, carboxylated PS/PMAA and sulfonated PS/PNaSS, were prepared by emulsifier-free emulsion polymerization. To complement the submicron size weakness and the absence of ligands, we employed the latex form, the dispersion of microsphere, and took advantage of interaction relationships between proteins and microspheres. Adsorption isotherm is contemplated to investigate continuous separation behaviours of serum proteins. Selectivity of separation is in the following order: PS/PNaSS-2.0 (high sulfonated) < PS/PNaSS-0.3 (low sulfonated) < PS/PMAA-0.5 (low carboxylated). Unlike previous works on batch separation, not only the adsorbed amount in equilibrium (C(m)), but also adsorption coefficient (K), played an important role in continuous separation. Functional groups (carboxyl and sulfonate), induced from the co-monomer, also affected the adsorption behaviours.
• Seo, J., Yoon, J., Oh, J., & Kim, W. (1998). Optimum growth conditions and pH control solution for PHB biosynthesis in A. eutrophus. Journal of Industrial and Engineering Chemistry, 4(3), 215-220.
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  Abstract: Optimum growth conditions and pH control solution were obtained in the biosynthesis of PHB(poly-β-hydroxybutyrate) with Alcaligenes eutrophus. Optimum carbon and nitrogen sources were fructose and (NH4) 2SO4, respectively, and optimum additive was 1:1 mixture of yeast extract and polypeptone. To select the optimum pH control solution, various pH control solutions (NaOH, KOH, Na2CO3, and NaOH+KOH) were tested. Na2CO3 solution was found to be the best out of the four solutions tested, because CO2 generated from Na2CO3 could be used as a carbon source. Mixture of NaOH and KOH showed better results than the solution of NaOH or KOH alone. This could be due to the balanced amount of cations (Na+ and K+), which might promote not only the permeation of substrates, but also pumping out Na+ ions.
• Yoon, J., Kim, J., & Kim, W. (1998). Interpretation of protein adsorption phenomena onto functional microspheres. Colloids and Surfaces B: Biointerfaces, 12(1), 15-22.
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  Abstract: The relationship between hydrophobic and electrostatic interactions in protein adsorption was studied for the various sulfonated microspheres, and it was compared with that for carboxylated microspheres. Hydrophobic interaction governed the adsorption in the low sulfonated microspheres whereas electrostatic interaction governed it in the high sulfonated microspheres. The transition point was observed when the two forces were exactly balanced, but it was shifted to the left compared with the case of the carboxylated microspheres. The above adsorption experiments with different kinds of surface functionality revealed the following general mechanism of protein adsorption. The protein adsorption occurs mainly by hydrophobic interaction when the hydrophobic surface is slightly modified with weak or strong acid, while it occurs primarily by hydrogen bonding (or electrostatic) interaction when the surface is mostly modified with weak (or strong) acid. Adsorption by electrostatic interaction is higher than that by any other interactions, but the rate of adsorption is slowest. Bovine serum albumin adsorbed onto carboxylated microspheres always undergoes an irreversible conformational change to the end-on mode, while this would not occur around the transition point in the case of the sulfonated microspheres. Copyright (C) 1998 Elsevier Science B.V.
• Yoon, J., Lee, J. H., Kim, J., & Kim, W. (1998). Separation of serum proteins with uncoupled microsphere particles in a stirred cell. Colloids and Surfaces B: Biointerfaces, 10(6), 365-377.
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  Abstract: Submicron microspheres were used directly without ligand coupling for the batch and continuous separations of proteins. In the batch experiments for separating BSA (bovine serum albumin) from BHb (bovine hemoglobin), introducing both hydrophobic effects for BSA and electrostatic repulsion for BHb (and vice versa) was required for high selectivity, and microspheres with low number density of surface groups were advantageous. For the continuous experiments, the utilization of a stirred cell was successful, where the microspheres were in the form of latex with good dispersion of particles. The flow rate without a pump was 0.5-1.3 ml min-1, and the ratio of BSA and BHb was varied. In the experiments for eliminating BHb from BSA, elution curves of BHb corresponded to the single component breakthrough curves, while those for BSA did not. The latter is believed to be due to the interference by BHb in the adsorption of BSA.
• Yoon, J., Park, H., Kim, J., & Kim, W. (1996). Adsorption of BSA on highly carboxylated microspheres - Quantitative effects of surface functional groups and interaction forces. Journal of Colloid and Interface Science, 177(2), 613-620.
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  Abstract: In order to elucidate the relations between the amount of surface functional groups and interaction forces, BSA adsorption experiments were performed, using highly carboxylated PS/PMAA microspheres as well as conventional ones. Two kinds of interaction forces were considered in this study, hydrogen bonding and hydrophobic interactions, while ionic interactions were assumed to be small or constant. Hydrophobic interactions were dominant in the low Nc (number density of surface carboxyl groups) region, below 1 carboxyl group nm-2, and were relatively sensitive to pH, while hydrogen bonding was dominant in the high Nc region, above 2 carboxyl groups nm-2, irrespective of pH. The transition region between these two interaction forces was 1 ∼ 2 carboxyl groups nm-2 on the surface of a microsphere. When comparing the two extremes of hydrophobic interaction and hydrogen bonding, the latter was stronger, which was different from earlier studies. It can be explained that the conventional carboxylated microspheres do not have enough carboxyl groups on their surfaces. Adsorption constant K diminished as Nc increased, which means that the affinity itself is reduced by hydrogen bonding. Adsorbed layer thicknesses calculated from the Cm (adsorbed amount in equilibrium) were 4.66 ∼ 7.08 nm; this means that the BSA molecules exist between the side-on and end-on mode. © 1996 Academic Press, Inc.

Proceedings Publications

• Yoon, J., Breshears, L. E., Mata-Robles, S., & Reynolds, K. A. (2022). Flow rate profile based PFAS detection on smartphone- and paper-based microfluidics. In 2022 IEEE Research and Applications of Photonics in Defense Conference (RAPID), Miramar Beach, FL, USA, doi:10.1109/RAPID54472.2022.9911269.
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  Sensitive detection of PFOA, type of PFAS (perfluorinated-alkyl substances), was demonstrated on paper-based microfluidic chip utilizing competitive binding with albumin or casein and cellulose fibers. It altered the capillary flow rate profile and monitored by a smartphone camera. Detection limit was 1-10 fg/µL (1-10 ppt).
• Chung, S., Breshears, L. E., Cho, S., Reynolds, K. A., & Yoon, J. (2017, Jul.). Rapid and Reliable Norovirus Assay at pg/mL Level Using Smartphone-Based Fluorescence Microscope and a Microfluidic Paper Analytic Device. In ASABE Annual International Meeting, 2017, 1701234.
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  Detection of norovirus from water samples typically requires extremely low limit of detection (LOD), preferably at single virus particle level, since they can be pathogenic at extremely low concentrations. Complicated equipment and/or lengthy procedures are necessary to concentrate large volume of water sample. In addition, this low LOD requirement have traditionally been associated non-reproducible and less convincing assay results. In this work, rapid and reliable detection of norovirus contamination in water samples was demonstrated using an in-house developed smartphone-based fluorescence microscope and a paper microfluidic analytic device (μPAD). Norovirus was concentrated directly on the μPAD, which was fabricated with polarity filter, to further decrease the LOD. Antibody-conjugated submicron (0.5 μm diameter) fluorescent particles were added to this μPAD, and a smartphone based fluorescence microscope imaged these beads directly from the μPAD. Since the spatial resolution of our smartphone-based fluorescence microscope is > 1 μm, only the beads immunoaggltuinated by norovirus can be identified, providing reliable, reproducible, and visually convincing assay results. Using this novel this method, extremely low LOD was demonstrated, 0.01 pg/mL with a benchtop fluorescence microscope and 10 pg/mL to 100 pg/mL with a smartphone based fluorescence microscope. This novel assay can provide a fully unmanned platform for assaying various waterborne pathogens that require extremely low LOD as well as high reliability, while providing low-cost, ease-of-use, and user friendliness appropriate for field applications.
• McCracken, K. E., Tat, T., Paz, V., Reynolds, K. A., & Yoon, J. (2017, Jul.). Immunoagglutinated Particle Rheology Sensing on a Microfluidic Paper-Based Analytical Device for Pathogen Detection. In ASABE Annual International Meeting, 2017, 1701190.
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  Particle immunoagglutination assays have been successfully used in biological sensing for food, water, and environmental applications and medical diagnostics. In this method, interactions between antibody-conjugated particles and biological targets are typically quantified by optical-based sensing, including Mie scattering detection. While these optical methods demonstrate favorable sensitivity and specificity, those that measure light intensity changes are vulnerable to environmental perturbations, such as variations in ambient lighting or humidity. In this work, we investigated a new sensing method based on the particle rheology of immunoagglutinated samples, as seen in droplet spreading on a microfluidic paper-based analytical device (µPAD). By monitoring the overall bulk movement of a particle suspension on paper, these assays are not as critically affected by the sensing environment. Capillary flow of the particle suspension on µPAD channels was tuned by adjusting various parameters, including paper thickness, channel width, channel morphology, particle concentration, and particle size. We then tested the most favorable lateral flow channel design for E. coli K12 sensing in water samples, and applied this overall technique to Zika virus (ZIKV) sensing in biological matrices. From these assays, we achieved similar limits of detection as compared with other demonstrated methods (2 log CFU/mL E. coli; 0.53x10^4 transcription copies/mL). Based on this work, direct detection of immunoagglutinated particle rheology through droplet spreading shows promise as a unique and simple method with applications in automated biosensors for environmental and health samples.
• Yoon, J. (2015, May-June). [Invited talk] Smartphone biosensors and organ-on-a-chip. In In Vitro Cellular & Developmental Biology, 51, S6-S7.
• Angus, S. V., Cho, S., Harshman, D. K., & Yoon, J. (2014, Oct). Quantitative, surface heated, droplet polymerase chain reaction for detecting pathogens. In The 18th International Conference on Miniaturized Systems for Chemistry and Life Sciences (MicroTAS 2014), 1452-1454.
• Baynes, C., Park, T. S., & Yoon, J. (2014, May). Enhanced fluorescent light scatter detection of cancer biomarkers using paper microfluidics. In Biosensors 2014: World Congress on Biosensors.
• Harshman, D. K., Reyes, R., & Yoon, J. (2014, Oct). Rapid molecular diagnosis of infective endocarditis: developing uREx Dx. In The 18th International Conference on Miniaturized Systems for Chemistry and Life Sciences (MicroTAS 2014), 1051-1053.
• Nicolini, A. M., & Yoon, J. (2014, Oct). Pro-adhesive extracellular matrix mimic for use in organ-on-a-chip. In The 18th International Conference on Miniaturized Systems for Chemistry and Life Sciences (MicroTAS 2014), 760-762.
• Nicolini, A. M., Cohn, C. M., Gamboa, J. R., Slepian, M. J., Wu, X., & Yoon, J. (2014, Apr). Fabrication of a pro-adhesive surface using electrospun PCL nanofibers interspersed with peptide conjugated polystyrene particles. In IEEE-NEMS 2014.
• Nicolini, A. M., Fronczek, C. F., & Yoon, J. (2014, May). Rapid, single-step, droplet-based bacterial assay platform on a nanofibrous substrate. In Biosensors 2014: World Congress on Biosensors.
• Park, T. S., Baynes, C., & Yoon, J. (2014, May). Paper microfluidics for red wine tasting. In Biosensors 2014: World Congress on Biosensors.
• Park, T. S., Baynes, C., Cho, S., & Yoon, J. (2014, Apr). Paper Microfluidics for Red Wine Tasting. In IEEE-NEMS 2014.
• Fronczek, C. F., Park, T. S., & Yoon, J. (2013, Oct). Paper Microfluidic Extraction of Bacterial and Viral Nucleic Acid from Field and Clinical Samples towards a Direct MicroTAS Apparatus. In The 17th International Conference on Miniaturized Systems for Chemistry and Life Sciences (MicroTAS 2013), 1114-1116.
• Harshman, D. K., Reyes, R., & Yoon, J. (2013, Oct). Direct Detection of Plasmid-Mediated Antibiotic Resistance in Bloodstream Infection by PCR Using Wire-Guided Droplet Manipulation (WDM). In The 17th International Conference on Miniaturized Systems for Chemistry and Life Sciences (MicroTAS 2013), 470-472.
• Park, T. S., Harshman, D. K., Fronczek, C. F., & Yoon, J. (2013, Oct). Smartphone Detection of Escherichia coli from Wastewater Utilizing Paper Microfluidics. In The 17th International Conference on Miniaturized Systems for Chemistry and Life Sciences (MicroTAS 2013), 1347-1349.
• Angus, S. V., Kwon, H., & Yoon, J. (2012, Jan). Low-level detection of Cryptosporidium parvum in field water using optical microfluidic biosensors. In SPIE Photonics West, 8229.
• Fronczek, C. F., Kwon, H., & Yoon, J. (2012, May). Single-pipetting microfluidic assay device for Salmonella in poultry package water. In Biosensors 2012: World Congress on Biosensors.
• Stemple, C. C., Kwon, H., & Yoon, J. (2012, May). Rapid and sensitive detection of malaria antigen in whole blood using a handheld LOC device. In Biosensors 2012: World Congress on Biosensors.
• You, D. J., & Yoon, J. (2012, May). Cell-phone-based measurement of TSH using Mie scatter optimized lateral flow assays. In Biosensors 2012: World Congress on Biosensors.
• You, D. J., Tran, P. L., Kwon, H., & Yoon, J. (2012, May). Extremely rapid and fully reprogrammable total PCR assays using wire-guided droplet microfluidics. In Biosensors 2012: World Congress on Biosensors.
• Kwon, H., Angus, S. V., You, D. J., Stemple, C. C., & Yoon, J. (2011, Oct). Development of a Handheld Optofluidic Immunosensor to Track the Transport and Distribution of H1N1/2009 Virus in a Mock Classroom. In The 15th International Conference on Miniaturized Systems for Chemistry and Life Sciences (MicroTAS 2011), 1421-1423.

Presentations

• Breshears, L. E., Mata Robles, S., Reynolds, K. A., & Yoon, J. (2021, Aug.). Flow rate profile based PFOA detection on paper-based microfluidics using competitive interactions with albumin and nitrocellulose. ACS Fall 2021 National Meeting & Exposition. Atlanta, GA: American Chemical Society (ACS).
• Day, A. S., Ulep, T., Budiman, E., Safavinia, B., & Yoon, J. (2021, July). Emulsion nucleic acid amplification for bacterial identification via angle-dependent light scatter analysis. 31st Anniversary World Congress on Biosensors. Online: Elsevier.
• Day, A. S., Ulep, T., Safavinia, B., Hertenstein, T., Budiman, E., Dieckhaus, L., & Yoon, J. (2021, Apr.). Emulsion-based Isothermal Nucleic Acid Amplification for Rapid SARS-CoV-2 Detection via Angle-dependent Light Scatter Analysis. 2021 Annual Conference of the Institute of Biological Engineering. Online: Institute of Biological Engineering (IBE).
• Kaarj, K., Akarapipad, P., Breshears, L. E., Sosnowski, K., Nguyen, B. T., Baker, J., Worobey, M., & Yoon, J. (2021, July). Rapid and sensitive detection of SARS-CoV-2 from human clinical samples using flow-based smartphone analysis on paper microfluidic chip. 31st Anniversary World Congress on Biosensors. Online: Elsevier.
• Kim, S., Lee, M., Wiwasuku, T., Day, A. S., Youngme, S., Hwang, D. S., & Yoon, J. (2021, Apr.). Taste sensor inspired peptide-based bacterial identification on smartphone-based paper microfluidic device. 2021 Annual Conference of the Institute of Biological Engineering. Online: Institute of Biological Engineering (IBE).
• Sosnowski, K., Bills, M. V., Loh, A., Nguyen, B. T., Yim, U. H., & Yoon, J. (2021, July). Raspberry Pi based, UV-fluorescent spectrophotometer device for the analysis of oil types obtained from oil spills. 31st Anniversary World Congress on Biosensors. Online: Elsevier.
• Sosnowski, K., Loh, A., Kim, T. J., Shir, H., Zubler, A. V., Ha, S. Y., Kim, U. H., & Yoon, J. (2021, Apr.). Raspberry Pi based, UV-fluorescent spectrophotometer device for the analysis of oil types obtained from oil spills. 2021 Annual Conference of the Institute of Biological Engineering. Online: Institute of Biological Engineering (IBE).
• Yoon, J. (2021, Feb.). IoT Biosensors for Agricultural, Food, Environmental & Public Health Applications. Graduate Seminar, Department of Biosystems Engineering, The University of Arizona. Online: University of Arizona.
• Yoon, J. (2021, June). Direct Detection of COVID-19 and Other Respiratory Viruses from Air and Wastewater. Department of Mechanical Engineering, Sogang University. Seoul, South Korea: Sogang University.
• Yoon, J. (2021, June). Direct Detection of COVID-19 and Other Respiratory Viruses from Air and Wastewater. Division of Integrative Biosciences & Biotechnology, Pohang University of Science and Technology (POSTECH). Pohang, South Korea: Pohang University of Science and Technology (POSTECH).
• Yoon, J. (2021, June). Direct Detection of COVID-19 and Other Respiratory Viruses from Air and Wastewater. Korea Institute of Ocean Science and Technology (KIOST). Geoje, South Korea: Korea Institute of Ocean Science and Technology (KIOST).
• Yoon, J. (2021, Mar.). Smartphone-based biosensors for medical diagnostics and public health applications. Planetary Protection Center of Excellence, Jet Propulsion Laboratory (JPL). Online: Jet Propulsion Laboratory (JPL).
• Yoon, J. (2021, Nov.). Smartphone Based Biosensors. COE Faculty Lecture Series. Online: University of Arizona.
• Yoon, J. (2020, Apr.). IoT Biosensors for Agricultural, Food, Environmental & Public Health Applications. USDA-ARS Western Regional Research Center. Albany, CA: USDA-ARS.
• Bills, M. V., & Yoon, J. (2019, Oct.). Label-Free, Light Scatter Detection of Colorectal Carcinoma Using an Angular Photodiode Array. BMES Annual Meeting. Philadelphia, PA: BMES.
• Chung, S., Breshears, L. E., Perea, S., Morrison, C. M., Betancourt, W. Q., Reynolds, K. A., & Yoon, J. (2019, Aug.). Smartphone-Based Paper Microfluidic Particulometry of Norovirus from Environmental Water Samples at Single Copy Level. ACS National Meeting & Expo. San Diego, CA: ACS.
• Chung, S., Jennings, C., Perea, S., Yim, U. H., & Yoon, J. (2019, Jul.). Classifying Origin of Crude Oil Using Raspberry Pi and Paper Microfluidic Chip. ASABE Annual International Meeting. Boston, MA: ASABE.
• Day, A. S., Ulep, T., Dieckhaus, L., Budiman, E., Safavinia, B., & Yoon, J. (2019, Oct.). Emulsion Nucleic Acid Amplification Device for Septic Bacterium Identification via Mie Light Scatter. BMES Annual Meeting. Philadelphia, PA: BMES.
• Klug, K. E., Reynolds, K. A., & Yoon, J. (2019, Aug.). Capillary Flow Dynamics-Based Sensing Modality for Direct Environmental Pathogen Monitoring. ACS National Meeting & Expo. San Diego, CA: ACS.
• Yoon, J. (2019, Aug.). Smartphone Detection of Plant Health and Diseases. Controlled Environment Agriculture Center (CEAC), The University of Arizona. Tucson, AZ: The University of Arizona.
• Yoon, J. (2019, Aug.). Smartphone-Based Device for Detecting Norovirus, the 'Cruise Ship' Microbe. ACS Press Conference. San Diego, CA: ACS.
• Yoon, J. (2019, Jun.). IoT Biosensors for Environmental, Public Health & Healthcare Applications. Department of Rural & Biosystems Engineering, Chonnam National University. Gwangju, South Korea: Chonnam National University.
• Yoon, J. (2019, Jun.). Mimicking Human Senses from Machine Learning. BK21 Plus Program for Biotechnology, Korea University. Seoul, South Korea: Korea University.
• Yoon, J. (2019, Jun.). Mimicking Human Senses through Machine Learning. Sogang-Harvard University Disease Biophysics Research Center. Seoul, South Korea: Sogang University - Harvard University.
• Yoon, J. (2019, May). IoT Biosensors for Environmental, Public Health, and Healthcare Applications. Division of Integrative Biosciences & Biotechnology, Pohang University of Science & Technology (POSTECH). Pohang, South Korea: Pohang University of Science & Technology (POSTECH).
• Zenhausern, R., Ulep, T., Gonzales, A., & Yoon, J. (2019, Oct.). Dual Quantification of Chronic Lymphocytic Leukemia Using On-Chip Fluorescence Imaging-Based and Capillary Flow Dynamics-Based Paper Microfluidic Assays. BMES Annual Meeting. Philadelphia, PA: BMES.
• Bills, M. V., & Yoon, J. (2018, Apr.). Cell Chromatography: Two-Layer, Paper-Based Microfluidic Purification and Quantification of Red Blood Cells, Granular, and Agranular White Blood Cells. Annual Meeting of IBE. Norfolk, VA: IBE.
• Chung, S., Breshears, L. E., Morrison, C. M., Betancourt, W. Q., Reynolds, K. A., & Yoon, J. (2018, May). Single Particle Level Norovirus Detection Assay Using Smartphone-Based Fluorescence Microscope and a Microfluidic Paper Analytic Device. 2nd KU-UA Joint International Symposium. Seoul, South Korea: Korea University.
• Chung, S., Breshears, L. E., Reynolds, K. A., & Yoon, J. (2018, Jan.). Rapid and Reliable Norovirus Assay Using Smartphone-Based Fluorescence Microscope and a Microfluidic Paper Analytic Device. 1st KU-UA Joint International Symposium. Tucson, AZ: University of Arizona.
• Chung, S., Breshears, L., Vedder, A., & Yoon, J. (2018, Jul.). Smartphone Monitoring of Plant Water Stress. ASABE Annual International Meeting. Detriot, MI: ASABE.
• Kaarj, K., Madias, M., Cho, S., & Yoon, J. (2018, Oct.). Flexible, Foldable and Reconfigurable Paper-based Angiogenesis Chip towards Developing Personalized Cancer Therapeutic Strategies. BMES Annual Meeting. Atlanta, GA: BMES.
• Ngo, J., Kaarj, K., & Yoon, J. (2018, Oct.). Paper-based Liver Organ-on-a-chip for Herbal Drug Toxicity Screening. BMES Annual Meeting. Atlanta, GA: BMES.
• Ulep, T., Day, A., & Yoon, J. (2018, Jan.). Real-time Quantification of Droplet Isothermal Nucleic Acid Amplification through Measurements of Interfacial Effects. 1st KU-UA Joint International Symposium. Tucson, AZ: University of Arizona.
• Ulep, T., Day, A., & Yoon, J. (2018, Mar.). Real-Time Quantification of Droplet Isothermal Nucleic Acid Amplification through Measurements of Interfacial Effect. ACS National Meting. New Orleans, LA: ACS.
• Ulep, T., Day, A., Sosnowski, K., Shumaker, A., & Yoon, J. (2018, Oct.). Interfacial Effect-Based Real-Time Quantification of Droplet Isothermal Nucleic Acid Amplification. BMES Annual Meeting. Atlanta, GA: BMES.
• Yoon, J. (2018, Jan.). New Trends in Biosensor Research towards Healthcare-at-Home. 1st KU-UA Joint International Symposium. Tucson, AZ: University of Arizona.
• Yoon, J. (2018, Mar.). New Trends in Biosensor Research towards Healthcare-at-Home. Seminar, Department of Chemical Engineering, University of Arizona. Tucson, AZ: Department of Chemical Engineering, Unversity of Arizona.
• Yoon, J. (2018, May). Biosensors for Healthcare-at-home and Personalized Medicine. 2nd KU-UA Joint International Symposium. Seoul, South Korea: Korea University.
• Yoon, J. (2018, Sep.). Biosensors for Healthcare-at-Home and Personalized Medicine. Seminar, Digital Health Interest Group (dHIG), University of Arizona. Tucson, AZ: College of Nursing, University of Arizona.
• Zenhausern, R., Ulep, T., Gonzales, A., & Yoon, J. (2018, Oct.). Smartphone Based Vertical Flow Immunoassay of Circulating Tumor Cells. BMES Annual Meeting. Atlanta, GA: BMES.
• Cho, S., Kaarj, K., & Yoon, J. (2017, Feb.). Paper angiogenesis-on-a-chip. SLAS 2017 International Conference & Exhibition. Washington, DC: SLAS.
• Kaarj, K., Cho, S., & Yoon, J. (2017, Oct.). Liver-on-a-paper model for drug screening. BMES 2017 Annual Meeting. Phoenix, AZ: BMES.
• Sweeney, R. E., Nguyen, V., Budiman, E., Wong, R. K., & Yoon, J. (2017, Feb.). Stand-alone, multichannel, paper microfluidic-based device that allows for automated quantification of blood coagulation in human whole blood and patient-specific dosing of heparin/protamine during and after surgery. SLAS 2017 International Conference & Exhibition. Washington, DC: SLAS.
• Toth, T. D., M, N. A., Mandel, M. A., Yoon, J., & Galbraith, D. W. (2017, Summer). In situ optical detection of pathogens using emulsion loop-mediated isothermal amplification. CYTO2017, Congress of the International Society for Advancement of Cytometry. Boston MA: International Society for Advancement of Cytometry.
• Yoon, J. (2017, Jan.). Biosensors for Monitoring Airborne Pathogens. Department of Homeland Security. Washington, DC: Department of Homeland Security.
• Yoon, J. (2017, Jun.). Smartphone-Based Health Monitoring Tools. Sogang University. Seoul, South Korea: Sogang University.
• Yoon, J. (2017, Mar.-Apr.). Immunoagglutinated Particle Rheology Detection from Paper Microfluidic Analytic Device for E. coli and Zika Virus Assays. Annual Meeting of IBE. Salt Lake City, UT: IBE.
• Yoon, J. (2017, Mar.-Apr.). Organ-on-a-Chip for Assessing Environmental Toxicants. Annual Meeting of IBE. Salt Lake City, UT: IBE.
• Yoon, J. (2017, May). Future Developments in Lab-on-a-Chip: Field-Ready Nucleic Acid Amplifications and Organ-on-a-Chip. Korea University. Seoul, South Korea: Korea University.
• Yoon, J. (2017, May). Smartphone-Based Health Monitoring Tools. Chemistry & Biochemistry Departmental Seminar. Tucson, AZ: University of Arizona.
• Yoon, J. (2017, May). Smartphone-Based Health Monitoring Tools. Korea Research Institute of Bioscience and Biotechnology. Daejeon, South Korea: Korea Research Institute of Bioscience and Biotechnology.
• Yoon, J. (2017, Oct.). New Trends in Biosensor Research towards Healthcare-at-Home. Korea Institute of Ocean Science & Technology. Busan, South Korea: Korea Institute of Ocean Science & Technology.
• Yoon, J. (2017, Oct.). [Keynote Speech] New Trends in Biosensor Research towards Healthcare-at-Home. KSBB Fall Meeting and International Symposium. Busan, South Korea: KSBB (Korean Society for Biotechnology and Bioengineering).
• Cho, S., Islas-Robles, A., Nicolini, A. M., Monks, T. J., & Yoon, J. (2016, Apr.). In Situ Monitoring of Induced Nephrotoxicity in Organ-on-a-Chip with Smartphone-Based Fluorescence Microscope. Annual Meeting of IBE. Greenville, SC: IBE.
• Cho, S., Park, T. S., Nahapetian, T. G., & Yoon, J. (2016, Apr.). Smartphone-Based, Sensitive uPAD Detection of Urinary Tract Infection and Gonorrhea. Annual Meeting of IBE. Greenville, SC: IBE.
• Nicolini, A. M., Harshman, D. K., Toth, T. D., Mandel, M. A., Galbraith, D. W., & Yoon, J. (2016, Apr.). DOTS qPCR: A Handheld, Rapid Molecular Diagnostic Tool for Ebola. Annual Meeting of IBE. Greenville, SC: IBE.
• Sweeney, R. E., & Yoon, J. (2016, Apr.). Rapid and Non-Destructive Detection of Tissue Bacterial Infection. Annual Meeting of IBE. Greenville, SC: IBE.
• Yoon, J. (2016, Aug.). Biomedical Wearables Pannel Discussion. UA/BIO5 Workshop on Biomedical Wearables. Tucson, AZ: BIO5 Institute.
• Yoon, J. (2016, May). Smartphone-Based Biosensors. Kyungpook National University, Bio-Industrial Machinery Engineering Department Seminar. Daejeon, South Korea.
• Yoon, J. (2016, May). Smartphone-Based Health Monitoring Tools. Kyungpook National University, Applied Chemistry Department Seminar. Daejeon, South Korea.
• Yoon, J. (2016, Oct.). Smartphone-Based Health Monitoring Tools. UA/BIO5 Interdisciplinary Series on Biomedical Sensors and Diagnostics. Tucson, AZ: BIO5 Institute.
• Harshman, D. K., Rao, B. M., McLain, J. E., Watts, G. S., & Yoon, J. (2015, Mar). Interfacial effects revolutionize qPCR by low threshold cycle detection and inhibition relief. Annual Meeting of IBE. St. Louis, MO: IBE.
• McCracken, K. E., Angus, S. V., Park, T. S., Reynolds, K. A., & Yoon, J. (2015, Mar). Smartphone for water quality. Annual Meeting of IBE. St. Louis, MO: IBE.
• Nicolini, A. M., Cho, S., & Yoon, J. (2015, Mar). Pro-adhesive extracellular matrix mimic for use on organ-on-a-chip. Annual Meeting of IBE. St. Louis, MO: IBE.
• Yoon, J. (2015, Feb). Smartphone biosensors and organ-on-a-chip. BME Data Blitz, University of Arizona. Tucson, AZ.
• Yoon, J. (2015, Jan). Smartphone biosensors and organ-on-a-chip. Departmental Seminar, Ajou University. Suwon, South Korea.
• Yoon, J. (2015, Jan). Smartphone biosensors and organ-on-a-chip. Special Seminar, ETRI. Daejeon, South Korea.
• Yoon, J. (2015, Jul). Innovative qPCR using interfacial effects to enable low threshold cycle detection and inhibition relief. ASABE Annual International Meeting. New Orleans, LA: ASABE.
• Yoon, J. (2015, Jul). Smartphone biosensors and organ-on-a-chip. Departmental Seminar, Yonsei University. Wonju, South Korea.
• Yoon, J. (2015, Jul). Smartphone-based health monitoring tools. Departmental Seminar, Korea University. Seoul, South Korea.
• Yoon, J. (2015, Jul). Smartphone-based health monitoring tools. Special Seminar, ETRI. Daejeon, South Korea.
• Yoon, J. (2015, Mar). Biosensors for monitoring airborne pathogens. Annual Meeting of IBE. St. Louis, MO: IBE.
• Yoon, J. (2015, Mar). Smartphone biosensors for food and water safety. FPAA (Fresh Produce Association of the Americas) Meeting. Nogales, AZ.
• Yoon, J. (2015, Mar). [Keynote address] IBE today: a platform for the future - niche areas for IBE. Annual Meeting of IBE. St. Louis, MO: IBE.
• Yoon, J. (2015, Sep). Smartphone biosensors and organ-on-a-chip. CHEE Departmental Seminar, University of Arizona. Tucson, AZ.
• Angus, S. V., Cho, S., Harshman, D. K., & Yoon, J. (2014, Mar). Wire-Guided Droplet Manipulation Based Quantitative PCR Device towards Food and Veterinary Diagnostics. Annual Meeting of IBE. Lexington, KY: IBE.
• Nicolini, A. M., Cohn, C. M., Slepian, M. J., Wu, X., & Yoon, J. (2014, Mar). Fabrication of a pro-adhesive surface using electrospun PCL nanofibers interspersed with peptide conjugated polystyrene particles. Annual Meeting of IBE. Lexington, KY: IBE.
• Tran, P. L., Martin, D. A., Gamboa, J. R., Yoon, J., & Slepian, M. J. (2014, Apr). Nanopost Fence: A Novel Strategy of Preventing Smooth Muscle Cells Topographic Migration. Society for Biomaterials (SFB) 2014 Annual Meeting and Exposition. Denver, CO: Society for Biomaterials (SFB).
• Yoon, J. (2014, Jun). Smartphone biosensors and organ-on-a-chip. Yonsei University, Department of Chemical & Biomolecular Engineering, Departmental Seminar. Yonsei University, Seoul, South Korea.
• Yoon, J. (2014, Mar). Smartphone-based immunosensors. Global Health Conference. Tucson, AZ: Arizona Health Sciences Center.
• Yoon, J. (2014, Oct). Smartphone biosensors and organ-on-a-chip. 2014 KSBB Fall Meeting and International Symposium. Changwon, South Korea: Korean Society for Biotechnology and Bioengineering (KSBB).
• Yoon, J. (2014, Oct). Smartphone biosensors and organ-on-a-chip. University of Arizona, Department of Chemistry & Biochemistry, Analytical Division Seminar. University of Arizona, Tucson, AZ.
• Yoon, J., & Park, T. S. (2014, Mar). Smartphone-Based Paper Microfluidic Detection of E. coli from Field or Waste Water. Annual Meeting of IBE. Lexington, KY: IBE.
• Harshman, D. K., Reyes, R., Park, T. S., You, D. J., & Yoon, J. (2013, Mar). Extremely Fast Nucleic Acid Amplification by Droplet Manipulation for Point-of-Care Diagnosis of Blood Infection. Annual Meeting of IBE. Raleigh, NC: IBE.
• Liang, P., & Yoon, J. (2013, Jul). Rapid detection of foodborne pathogens within meat utilizing a smartphone biosensor. ASABE Annual International Meeting. Kansas City, MO: ASABE.
• Liang, P., Kleiman, M., & Yoon, J. (2013, Jul). Use of biosensor in secondary education curriculum to improve students' interest and awareness of science, engineering, and current worldwide issues. ASABE Annual International Meeting. Kansas City, MO: ASABE.
• Park, T. S., Li, W., & Yoon, J. (2013, Mar). Paper microfluidics detection of Salmonella using a smart phone. Annual Meeting of IBE. Raleigh, NC: IBE.
• Reynolds, K. A., & Yoon, J. -. (2013, December). Use of Paper Microfluidics and Smartphone Mie Scattering Sensors for Water Quality Monitoring. NSF Water and Environmental Technology Center Industrial Advisory Board Annual MeetingNational Science Foundation.
• Yoon, J. (2013, Jul). Organ-on-a-chip and biosensors. Yonsei University College of Medicine, Department of Radiology, Special Seminar. Seoul, South Korea: Department of Radiology, College of Medicine, Yonsei Univeristy.
• Yoon, J. (2013, Jul). Smartphone-based immunosensor, fast PCR diagnostics, and organ-on-a-chip. Yonsei University, Department of Chemical & Biomolecular Engineering, Special Seminar. Seoul, South Korea: Department of Chemical and Biomolecular Engineering, Yonsei University.
• Yoon, J. (2013, Jul). Smartphone-based immunosensor, fast PCR diagnostics, and organ-on-a-chip. Yonsei University, Nanosphere Process & Technology National Research Laboratory Seminar. Seoul, South Korea: Nanosphere Process & Technology National Research Laboratory, Yonsei University.
• Yoon, J. (2013, Jul). Smartphone-based immunosensors and fast PCR devices for food and water safety. Rural Development Administration Special Seminar. Suwon, South Korea: Rural Development Administration.
• Yoon, J. (2013, Mar). Smartphone-based immunosensors and fast PCR device for veterinary diagnostics. University of Arizona, School of Animal & Comparative Biomedical Sciences, Graduate Seminar. Tucson, AZ: School of Animal & Comparative Biomedical Sciences, University of Arizona.
• Yoon, J. (2013, Oct). Mie Scatter BasedPaper Microfluidic BiosensorUtilizing UV LED. Seoul VioSys Special Seminar. Ansan, South Korea: Seoul VioSys.
• Yoon, J. (2013, Oct). Smartphone-based immunosensors, fast PCR diagnostics, and organ-on-a-chip. UCLA Bioengineering Graduate Seminar. Los Angeles, CA: Department of Bioengineering, UCLA.
• Yoon, J., Park, T. S., Li, W., & Liang, P. (2013, Jul). Paper microfluidics detection of Salmonella using a smartphone. ASABE Annual International Meeting. Kansas City, MO.
• Fronczek, C. F., You, D. J., & Yoon, J. (2012, Jul/Aug). Single-pipetting microfluidic assay device for Salmonella in poultry package water. ASABE Annual International Meeting. Dallas, TX: ASABE.
• Gamboa, J. R., Tran, P. L., Slepian, M. J., & Yoon, J. (2012, Mar). Linear fibroblast alignment on sinusoidal wave micropatterns. Annual Meeting of IBE. Indianapolis, IN: IBE.
• Harshman, D. K., Reyes, R., You, D. J., & Yoon, J. (2012, Oct). Device for near-instant diagnosis of clinical infection by convective droplet thermocycling and 16s rRNA hypervariable region probes. BMES 2012 Annual Meeting. Atlanta, GA: BMES.
• Yoon, J. (2012, June). Nanoparticle-Trapped Nanowells for Flow-Resistant HUVEC Adhesion / Smartphone-Based Lab-on-a-Chip Immunosensors. Seoul National University, School of Mechanical & Aerospace Engineering, Graduate Seminar. Seoul, South Korea: School of Mechanical & Aerospace Engineering, Seoul National University.
• Yoon, J. (2012, June). Nanoparticle-Trapped Nanowells for Flow-Resistant HUVEC Adhesion / Smartphone-Based Lab-on-a-Chip Immunosensors. Yonsei University, Nanosphere Process & Technology National Research Laboratory Seminar. Seoul, South Korea: Department of Chemical and Biomolecular Engineering, Yonsei University.
• Yoon, J. (2012, June). Smartphone-Based Lab-on-a-Chip Immunosensors / Nanoparticle-Trapped Nanowells for Flow-Resistant HUVEC Adhesion. Catholic University of Korea, Department of Biomedical Engineering, Special Seminar. Bucheon, South Korea: Department of Biomedical Engineering, Catholic University of Korea.
• Yoon, J. (2012, May). Cell-Phone-Based Measurement of TSH using Mie Scatter Optimized Lateral Flow Assays. UA mHealth Data Blitz. Tucson, AZ.
• Yoon, J. (2012, May). Smartphone-Based Lab-on-a-Chip Immunosensors. Applied Energetics Special Seminar. Tucson, AZ: Applied Energetics.
• Yoon, J. (2012, September). Nanoparticle-Trapped Nanowells for Flow-Resistant HUVEC Adhesion / Smartphone-Based Lab-on-a-Chip Immunosensors. University of Arizona, Department Aerospace & Mechanical Engineering, Graduate Seminar. Tucson, AZ: Department of Aerospace and Mechanical Engineering, University of Arizona.
• You, D. J., Tran, P. L., Kwon, H., & Yoon, J. (2012, Jul/Aug). Extremely rapid and fully reprogrammable total PCR assays using wire-guided droplet microfluidics. ASABE Annual International Meeting. Dallas, TX: ASABE.
• Kwon, H., You, D. J., Angus, S. V., & Yoon, J. (2011, Mar). Development of a handheld lab-on-a-chip immunosensor to track the transport and distribution of H1N1/09 virus in a mock classroom. Annual Meeting of IBE. Atlanta, GA: IBE.
• Liang, P., & Yoon, J. (2011, Aug). Macroscopic and microscopic subsurface bacterial transport model for soil bioremediation and aquifer contamination with on-site, real-time, handheld lab-on-a-chip device. ASABE Annual International Meeting. Louisville, KY: ASABE.
• Tran, P. L., Gamboa, J. R., McCracken, K. E., Riley, M. R., Slepian, M. J., & Yoon, J. (2011, Apr). Confluent and aligned growth of endothelial cells on nanoparticle arrays through focal adhesion and endocytitic mechanisms. Society for Biomaterials (SFB) 2011 Annual Meeting and Exposition. Orlando, FL: Society for Biomaterials (SFB).
• Tran, P. L., Gamboa, J. R., McCracken, K. E., Riley, M. R., Slepian, M. J., & Yoon, J. (2011, Mar). Confluent and aligned growth of endothelial cells on nanoparticle arrays through focal adhesion and endocytitic mechanisms. Annual Meeting of IBE. Atlanta, GA: IBE.
• Tran, P. L., Gamboa, J. R., McCracken, K. E., Riley, M. R., Slepian, M. J., & Yoon, J. (2011, Oct). Nanowell-trapped charged ligand-bearing nanoparticle surfaces - a novel method of enhancing flow resistant cell adhesion. BioInterface 2011 Workshop and Symposium. Minneapolis, MN: Surfaces in Biomaterials Foundation.
• Yoon, J. (2011, November). Field-deployable Handheld Biosensors for Food Safety. Food Safety Retreat. Tucson, AZ: University of Arizona Food Safety Consortium.
• Yoon, J., You, D. J., & Geshell, K. J. (2011, Aug). Single cell level Escherichia coli detection from iceberg lettuce using a handheld microfluidic immunosensor with Mie scattering measurement. ASABE Annual International Meeting. Louisville, KY: ASABE.

Poster Presentations

• Yoon, J. (2015, Jul). Mobile paper-based water quality monitoring via smartphones. ASABE Annual International Meeting. New Orleans, LA: ASABE.
• Park, T. S., Baynes, C., & Yoon, J. (2014, Mar). Paper Microfluidics for Red Wine Tasting. Annual Meeting of IBE. Lexington, KY: IBE.
• Angus, S. V., & Yoon, J. (2012, Oct). Field-Deployable and Near-Real-Time Microfluidic Biosensor with Mie Scatter Detection for Single-Oocyst-Level Detection of Cryptosporidium parvum from Field Water Samples. Food Safety Conference. Tucson, AZ: University of Arizona Food Safety Consortium.
• Fronczek, C. F., & Yoon, J. (2012, Oct). Single-Pipetting Microfluidic Assay Device for Rapid Detection of Salmonella from Poultry Package. Food Safety Conference. Tucson, AZ: University of Arizona Food Safety Consortium.
• Gamboa, J. R., Yoon, J., Smith, R. G., & Slepian, M. J. (2012, Mar). Evaluation of the performance of a left ventricular assist device in a novel in vitro heart failure model. Annual Meeting of IBE. Indianapolis, IN.
• Harshman, D. K., & Yoon, J. (2012, Oct). Device for Near-Instant Diagnosis of Bacterial Infection by Convective Droplet Thermocycling and 16s rRNA Hypervariable Region Probes. Food Safety Conference. Tucson, AZ: University of Arizona Food Safety Consortium.
• McCracken, K. E., Tran, P. L., Slepian, M. J., & Yoon, J. (2012, Mar). Nanoscale patterning under shear stress for guided endothelial cell growth. Annual Meeting of IBE. Indianapolis, IN.
• Park, T. S., & Yoon, J. (2012, Oct). Paper Microfluidic Detection of Salmonella Using a Smart Phone. Food Safety Conference. Tucson, AZ: University of Arizona Food Safety Consortium.
• Fronczek, C. F., & Yoon, J. (2011, Nov). Lab-on-a-chip Optical Immunoassay for Rapid Detection of Salmonella in Poultry. Food Safety Retreat. Tucson, AZ: University of Arizona Food Safety Consortium.
• Kwon, H., & Yoon, J. (2011, Nov). Development of a Handheld Optofluidic Immunosensor to Track the Transportation and Distribution of Respiratory Viruses in Animal and Human Environment. Food Safety Retreat. Tucson, AZ: University of Arizona Food Safety Consortium.
• Liang, P., & Yoon, J. (2011, Nov). Subsurface Bacterial Transport for Crop and Aquifer Contamination with Handheld Lab-on-a-chip Device. Food Safety Retreat. Tucson, AZ: University of Arizona Food Safety Consortium.
• Tran, P. L., & Yoon, J. (2011, Nov). Nanowell-trapped Charged Ligand-bearing Nanoparticles Surfaces - a Novel Method of Enhancing Flow Resistant Cell Adhesion. UA College of Medicine Frontiers in Biomedical Research Poster Forum. Tucson, AZ.
• You, D. J., & Yoon, J. (2011, Nov). Wire-guided Droplet Manipulations for PCR Detection of Food-borne Pathogens. Food Safety Retreat. Tucson, AZ: University of Arizona Food Safety Consortium.

Reviews

• Yoon, J. (2012. Who we are & what we can do(pp 19-21). Resource Magazine, Vol. 19, No. 3.