Human tear protein analysis enabled by an alkaline microfluidic homogeneous immunoassay

GNN-Based Concentration Prediction With Variable Input Flow Rates for Microfluidic Mixers

Recent years have witnessed significant advances brought by microfluidic biochips in automating biochemical protocols. Accurate preparation of fluid samples is an essential component of these protocols, where concentration prediction and generation are critical. Equipped with the advantages of convenient fabrication and control, microfluidic mixers demonstrate huge potential in sample preparation. Although finite element analysis (FEA) is the most commonly used simulation method for accurate concentration prediction of a given microfluidic mixer, it is time-consuming with poor scalability for large biochip sizes. Recently, machine learning models have been adopted in concentration prediction, with great potential in enhancing the efficiency over traditional FEA methods. However, the state-of-the-art machine learning-based method can only predict the concentration of mixers with fixed input flow rates and fixed sizes. In this paper, we propose a new concentration prediction method based on graph neural networks (GNNs), which can predict output concentrations for microfluidic mixters with variable input flow rates. Moreover, a transfer learning method is proposed to transfer the trained model to mixers of different sizes with reduced training data. Experimental results show that, for microfluidic mixers with fixed input flow rates, the proposed method obtains an average reduction of 88% in terms of prediction errors compared with the state-of-the-art method. For microfluidic mixers with variable input flow rates, the proposed method reduces the prediction error by 85% on average. Besides, the proposed transfer learning method reduces the training data by 84% for extending the pre-trained model for microfluidic mixers of different sizes with acceptable prediction error.

Amplified fluorogenic immunoassay for early diagnosis and monitoring of Alzheimer's disease from tear fluid

Accurate diagnosis of Alzheimer's disease (AD) in its earliest stage can prevent the disease and delay the symptoms. Therefore, more sensitive, non-invasive, and simple screening tools are required for the early diagnosis and monitoring of AD. Here, we design a self-assembled nanoparticle-mediated amplified fluorogenic immunoassay (SNAFIA) consisting of magnetic and fluorophore-loaded polymeric nanoparticles. Using a discovery cohort of 21 subjects, proteomic analysis identifies adenylyl cyclase-associated protein 1 (CAP1) as a potential tear biomarker. The SNAFIA demonstrates a low detection limit (236 aM), good reliability (R2 = 0.991), and a wide analytical range (0.320-1000 fM) for CAP1 in tear fluid. Crucially, in the verification phase with 39 subjects, SNAFIA discriminates AD patients from healthy controls with 90% sensitivity and 100% specificity in under an hour. Utilizing tear fluid as a liquid biopsy, SNAFIA could potentially aid in long-term care planning, improve clinical trial efficiency, and accelerate therapeutic development for AD.

Biomedical Applications of Lactoferrin on the Ocular Surface

Lactoferrin (LF) is a first-line defense protein with a pleiotropic functional pattern that includes anti-inflammatory, immunomodulatory, antiviral, antibacterial, and antitumoral properties. Remarkably, this iron-binding glycoprotein promotes iron retention, restricting free radical production and avoiding oxidative damage and inflammation. On the ocular surface, LF is released from corneal epithelial cells and lacrimal glands, representing a significant percentage of the total tear fluid proteins. Due to its multifunctionality, the availability of LF may be limited in several ocular disorders. Consequently, to reinforce the action of this highly beneficial glycoprotein on the ocular surface, LF has been proposed for the treatment of different conditions such as dry eye, keratoconus, conjunctivitis, and viral or bacterial ocular infections, among others. In this review, we outline the structure and the biological functions of LF, its relevant role at the ocular surface, its implication in LF-related ocular surface disorders, and its potential for biomedical applications.

Biomechanical analysis of ocular diseases and its in vitro study methods

Ocular diseases are closely related to the physiological changes in the eye sphere and its contents. Using biomechanical methods to explore the relationship between the structure and function of ocular tissue is beneficial to reveal the pathological processes. Studying the pathogenesis of various ocular diseases will be helpful for the diagnosis and treatment of ocular diseases. We provide a critical review of recent biomechanical analysis of ocular diseases including glaucoma, high myopia, and diabetes. And try to summarize the research about the biomechanical changes in ocular tissues (e.g., optic nerve head, sclera, cornea, etc.) associated with those diseases. The methods of ocular biomechanics research in vitro in recent years are also reviewed, including the measurement of biomechanics by ophthalmic equipment, finite element modeling, and biomechanical analysis methods. And the preparation and application of microfluidic eye chips that emerged in recent years were summarized. It provides new inspiration and opportunity for the pathogenesis of eye diseases and personalized and precise treatment.

Discovering the Secret of Diseases by Incorporated Tear Exosomes Analysis via Rapid-Isolation System: iTEARS

Nanoscale small extracellular vesicles (sEVs, exosomes) in tears allow us to investigate the multisignatures of diseases. However, the translations of tear sEVs for biomarker discovery and clinical diagnostics are practically limited by low recovery, long processing time, and small sample volume. Here, we report an incorporated tear-exosomes analysis via rapid-isolation system (iTEARS) via nanotechnology to discover the secrets of ocular disorders and systemic diseases. We isolate exosomes rapidly with high yield and purity from a few teardrops (∼10 μL) within 5 min via nanoporous membrane-based resonators for the quantitative detection and biomarker discovery through proteomic and transcriptomic analysis. We have identified 904 proteins, among which 228 proteins are discovered, 426 proteins are detected from exosomes of dry eye disease, and demonstrate CALML5, KRT6A, and S100P for the classification of dry eye disease. We have also investigated 484 miRNAs in tear exosomes and show miR-145-5p, miR-214-3p, miR-218-5p, and miR-9-5p are dysregulated during diabetic retinopathy development. We believe iTEARS can be used for improving molecular diagnostics via tears to identify ocular disorders, systemic diseases, and numerous other neurodegenerative diseases and cancer.

Tear fluid collection methods: Review of current techniques

Tear fluid, composed of lipid, aqueous, and mucin layers, contains electrolytes, water, proteins, peptides, and glycoproteins. Its components may serve as diagnostic indicators of local and systemic diseases. The aim of the study was to conduct literature review in order to identify the current methods of tear collection. The most commonly used method which was relatively easy to perform and allowed to obtain sufficient tear volume for further chemical and physical analysis was selected through PubMed database search for the following keywords: tear sampling, human tears, chemical analysis of tears, physical tear analysis, animal tear sampling. Final criteria of articles selection were: human tears, tear sample collection, chemical and physical analysis of tears. Time of publication of the articles not older than 1995. The analysis of 70 articles revealed that the most common tear fluid collection methods are Schirmer tear strips and capillary tubes. Thus, we recommend the use of Schirmer strips and microcapillary tubes as the cheapest and easiest methods for sampling of tear fluid for further chemical analysis.

Recent Advances in Smart Biomaterials for the Detection and Treatment of Autoimmune Diseases

Autoimmune diseases are a group of debilitating illnesses that are often idiopathic in nature. The steady rise in the prevalence of these conditions warrants new approaches for diagnosis and treatment. Stimuli-responsive biomaterials also known as "smart", "intelligent" or "recognitive" biomaterials are widely studied for their applications in drug delivery, biosensing and tissue engineering due to their ability to produce thermal, optical, chemical, or structural changes upon interacting with the biological environment. This critical analysis highlights studies within the last decade that harness the recognitive capabilities of these biomaterials towards the development of novel detection and treatment options for autoimmune diseases.

Development of a Quantitative Immunoassay for Tear Lacritin Proteoforms

Purpose

Lacritin is a tear glycoprotein with pro-tearing and pro-ocular surface homeostasis activities that is selectively deficient in most dry eye tears. Proteoforms include an active monomer, inactive polymers, and a splice variant termed lacritin-c. Quantitation of the different proteoforms of tear lacritin may provide a diagnostic tool for ocular diseases. Here, we report the development of an immunoassay for the quantification of multiple lacritin proteoforms in human tear samples.

Methods

Basal tears collected on Schirmer test strips with anesthesia were eluted by diffusion and centrifugation under optimized conditions. Tear protein concentrations were determined, and 2.56 µg of each sample was separated by SDS-PAGE followed by western blot analysis. Blots were challenged with anti-Pep Lac N-term antibodies. Detection was with fluorescent secondary antibodies visualized by the LI-COR Odyssey CLx imaging system and quantified with standard curves of recombinant lacritin.

Results

The percent total lacritin (ng lacritin/100 ng total protein) ranged from 1.8% to 14.8%. Monomer, lacritin-c, and polymer proteoform percent total protein ranged from 1.1% to 6.3%, 0.3% to 5.4%, and 0.7% to 5.7%, respectively. Monomer lacritin was detected at concentrations of 6 to 176 µM, with lacritin-c and polymer proteoforms at 2 to 46 µM and 1 to 23 µM, respectively.

Conclusions

This assay greatly exceeds the power and sensitivity of our prior lacritin enzyme-linked immunosorbent assay that was not capable of distinguishing monomer from polymers and lacritin-c proteoforms.

Translational Relevance

A new method has been developed to quantitate multiple proteoforms of tear lacritin in preparation for analyses of samples from clinical trials.

Contact Lens Technology: From Fundamentals to Applications

Contact lenses are ocular prosthetic devices used by over 150 million people worldwide. Primary applications of contact lenses include vision correction, therapeutics, and cosmetics. Contact lens materials have significantly evolved over time to minimize adverse effects associated with contact lens wearing, to maintain a regular corneal metabolism, and to preserve tear film stability. This article encompasses contact lens technology, including materials, chemical and physical properties, manufacturing processes, microbial contamination, and ocular complications. The function and the composition of the tear fluid are discussed to assess its potential as a diagnostic media. The regulatory standards of contact lens devices with regard to biocompatibility and contact lens market are presented. Future prospects in contact lens technology are evaluated, with particular interest given to theranostic applications for in situ continuous monitoring the ocular physiology.

Differential proteomics analysis of bile between gangrenous cholecystitis and chronic cholecystitis

To establish human biliary protein expression profiles of gangrenous cholecystitis, chronic cholecystitis, and to discover differently expressed proteins for gangrenous cholecystitis by comparative proteomics, we gathered human gallbladder bile samples from gangrenous cholecystitis and chronic cholecystitis patients, respectively After removing the bile salts and lipid peptide fragments were identified by the iTRAQ-coupled LC-MS/MS technology,then identified in SwissProt with Mascot software. A total of 2251 proteins from chronic cholecystitis patients and 2180 proteins from gangrenous cholecystitis patients were identified. A total of 575 differential proteins were found between gangrenous cholecystitis and chronic cholecystitis, 159 proteins were over-expressed and 416 proteins were under-expressed in gangrenous cholecystitis. By bio-informatics analysis, in gangrenous cholecystitis, cell death, necrosis,immune response of neutrophils, apoptosis and degranulation of cells were activated; while cell survival, fatty acid metabolism, transport of molecular and proliferation of cells were inhibited, which might reflect the de-compensatory phase. Pathway analysis showed acute phase proteins were changed, indicating the role of the inflammatory response in the pathogenesis of gangrenous cholecystitis. Six acute phase proteins were found up-regulated,implying a close linkage to gangrenous gallbladder. Our study could be applicable in the biomarker discovery of gangrenous cholecystitis.

3D Microfabricated Scaffolds and Microfluidic Devices for Ocular Surface Replacement: a Review

In recent years, there has been increased research interest in generating corneal substitutes, either for use in the clinic or as in vitro corneal models. The advancement of 3D microfabrication technologies has allowed the reconstruction of the native microarchitecture that controls epithelial cell adhesion, migration and differentiation. In addition, such technology has allowed the inclusion of a dynamic fluid flow that better mimics the physiology of the native cornea. We review the latest innovative products in development in this field, from 3D microfabricated hydrogels to microfluidic devices.

Asynchrony of spectral blue-shifts of quantum dot based digital homogeneous immunoassay

We present a femtomolar digital homogeneous immunoassay for the detection of cancer biomarkers.

Paper-based microfluidic system for tear electrolyte analysis

The analysis of tear constituents at point-of-care settings has a potential for early diagnosis of ocular disorders such as dry eye disease, low-cost screening, and surveillance of at-risk subjects. However, current minimally-invasive rapid tear analysis systems for point-of-care settings have been limited to assessment of osmolarity or inflammatory markers and cannot differentiate between dry eye subclassifications. Here, we demonstrate a portable microfluidic system that allows quantitative analysis of electrolytes in the tear fluid that is suited for point-of-care settings. The microfluidic system consists of a capillary tube for sample collection, a reservoir for sample dilution, and a paper-based microfluidic device for electrolyte analysis. The sensing regions are functionalized with fluorescent crown ethers, o-acetanisidide, and seminaphtorhodafluor that are sensitive to mono- and divalent electrolytes, and their fluorescence outputs are measured with a smartphone readout device. The measured sensitivity values of Na⁺, K⁺, Ca²⁺ ions and pH in artificial tear fluid were matched with the known ion concentrations within the physiological range. The microfluidic system was tested with samples having different ionic concentrations, demonstrating the feasibility for the detection of early-stage dry eye, differential diagnosis of dry eye sub-types, and their severity staging.

Determination of equilibrium dissociation constants for recombinant antibodies by high-throughput affinity electrophoresis

High-quality immunoreagents enhance the performance and reproducibility of immunoassays and, in turn, the quality of both biological and clinical measurements. High quality recombinant immunoreagents are generated using antibody-phage display. One metric of antibody quality – the binding affinity – is quantified through the dissociation constant (K_D) of each recombinant antibody and the target antigen. To characterize the K_D of recombinant antibodies and target antigen, we introduce affinity electrophoretic mobility shift assays (EMSAs) in a high-throughput format suitable for small volume samples. A microfluidic card comprised of free-standing polyacrylamide gel (fsPAG) separation lanes supports 384 concurrent EMSAs in 30 s using a single power source. Sample is dispensed onto the microfluidic EMSA card by acoustic droplet ejection (ADE), which reduces EMSA variability compared to sample dispensing using manual or pin tools. The K_D for each of a six-member fragment antigen-binding fragment library is reported using ~25-fold less sample mass and ~5-fold less time than conventional heterogeneous assays. Given the form factor and performance of this micro- and mesofluidic workflow, we have developed a sample-sparing, high-throughput, solution-phase alternative for biomolecular affinity characterization.

Instrument-Free Synthesizable Fabrication of Label-Free Optical Biosensing Paper Strips for the Early Detection of Infectious Keratoconjunctivitides

We introduce a surface-enhanced Raman scattering (SERS)-functionalized, gold nanoparticle (GNP)-deposited paper strip capable of label-free biofluid sensing for the early detection of infectious eye diseases. The GNP biosensing paper strip was fabricated by the direct synthesis and deposition of GNPs on wax-divided hydrophilic areas of a permeable porous substrate through a facile, power-free synthesizable, and highly reproducible successive ionic layer absorption and reaction (SILAR) technique. To maximize localized surface plasmon resonance-generated SERS activity, the concentration of the reactive solution and number of SILAR cycles were optimized by controlling the size and gap distance of GNPs and verified by computational modeling with geometrical hypotheses of Gaussian-estimated metallic nanoparticles. The responses of our SERS-functionalized GNP paper strip to Raman intensities exhibited an enhancement factor of 7.8 × 10(8), high reproducibility (relative standard deviation of 7.5%), and 1 pM 2-naphthalenethiol highly sensitive detection limit with a correlation coefficient of 0.99, achieved by optimized SILAR conditions including a 10/10 mM/mM HAuCl4/NaBH4 concentration and six SILAR cycles. The SERS-functionalized GNP paper is supported by a multivariate statistics-preprocessed machine learning-judged bioclassification system to provide excellent label-free chemical structure sensitivity for identifying infectious keratoconjunctivitis. The power-free synthesizable fabrication, label-free, rapid analysis, and high sensitivity feature of the SILAR-fabricated SERS-functionalized GNP biosensing paper strip makes it an excellent alternative in point-of-care applications for the early detection of various infectious diseases.

Distance-based microfluidic quantitative detection methods for point-of-care testing

Equipment-free devices with quantitative readout are of great significance to point-of-care testing (POCT), which provides real-time readout to users and is especially important in low-resource settings. Among various equipment-free approaches, distance-based visual quantitative detection methods rely on reading the visual signal length for corresponding target concentrations, thus eliminating the need for sophisticated instruments. The distance-based methods are low-cost, user-friendly and can be integrated into portable analytical devices. Moreover, such methods enable quantitative detection of various targets by the naked eye. In this review, we first introduce the concept and history of distance-based visual quantitative detection methods. Then, we summarize the main methods for translation of molecular signals to distance-based readout and discuss different microfluidic platforms (glass, PDMS, paper and thread) in terms of applications in biomedical diagnostics, food safety monitoring, and environmental analysis. Finally, the potential and future perspectives are discussed.

Making the diagnosis of Sjögren's syndrome in patients with dry eye

Sjögren’s syndrome (SS) is a chronic and progressive systemic autoimmune disease that often presents initially with symptoms of dry eye and dry mouth. Symptoms are often nonspecific and develop gradually, making diagnosis difficult. Patients with dry eye complaints warrant a step-wise evaluation for possible SS. Initial evaluation requires establishment of a dry eye diagnosis using a combination of patient questionnaires and objective ocular tests, including inflammatory biomarker testing. Additional work-up using the Schirmer test and tear film break-up time can differentiate between aqueous-deficient dry eye (ADDE) and evaporative dry eye. The presence of ADDE should trigger further work-up to differentiate between SS-ADDE and non-SS-ADDE. There are numerous non-ocular manifestations of SS, and monitoring for SS-related comorbid findings can aid in diagnosis, ideally in collaboration with a rheumatologist. The clinical work-up of SS can involve a variety of tests, including tear function tests, serological tests for autoantibody biomarkers, minor salivary gland and lacrimal gland biopsies. Examination of classic SS biomarkers (SS-A/Ro, SS-B/La, antinuclear antibody, and rheumatoid factor) is a convenient and non-invasive way of evaluating patients for the presence of SS, even years prior to confirmed diagnosis, although not all SS patients will test positive, particularly those with early disease. Recently, newer biomarkers have been identified, including autoantibodies to salivary gland protein-1, parotid secretory protein, and carbonic anhydrase VI, and may allow for earlier diagnosis of SS. A diagnostic test kit is commercially available (Sjö^®), incorporating these new biomarkers along with the classic autoantibodies. This advanced test has been shown to identify SS patients who previously tested negative against traditional biomarkers only. All patients with clinically significant ADDE should be considered for serological assessment for SS, given the availability of new serological diagnostic tests and the potentially serious consequences of missing the diagnosis.

Homogeneous agglutination assay based on micro-chip sheathless flow cytometry

Homogeneous assays possess important advantages that no washing or physical separation is required, contributing to robust protocols and easy implementation which ensures potential point-of-care applications. Optimizing the detection strategy to reduce the number of reagents used and simplify the detection device is desirable. A method of homogeneous bead-agglutination assay based on micro-chip sheathless flow cytometry has been developed. The detection processes include mixing the capture-probe conjugated beads with an analyte containing sample, followed by flowing the reaction mixtures through the micro-chip sheathless flow cytometric device. The analyte concentrations were detected by counting the proportion of monomers in the reaction mixtures. Streptavidin-coated magnetic beads and biotinylated bovine serum albumin (bBSA) were used as a model system to verify the method, and detection limits of 0.15 pM and 1.5 pM for bBSA were achieved, using commercial Calibur and the developed micro-chip sheathless flow cytometric device, respectively. The setup of the micro-chip sheathless flow cytometric device is significantly simple; meanwhile, the system maintains relatively high sensitivity, which mainly benefits from the application of forward scattering to distinguish aggregates from monomers. The micro-chip sheathless flow cytometric device for bead agglutination detection provides us with a promising method for versatile immunoassays on microfluidic platforms.

Steric-dependent label-free and washing-free enzyme amplified protein detection with dual-functional synthetic probes

Enzyme-catalyzed signal amplification with an antibody-enzyme conjugate is commonly employed in many bioanalytical methods to increase assay sensitivity. However, covalent labeling of the enzyme to the antibody, laborious operating procedures, and extensive washing steps are necessary for protein recognition and signal amplification. Herein, we describe a novel label-free and washing-free enzyme-amplified protein detection method by using dual-functional synthetic molecules to impose steric effects upon protein binding. In our approach, protein recognition and signal amplification are modulated by a simple dual-functional synthetic probe which consists of a protein ligand and an inhibitor. In the absence of the target protein, the inhibitor from the dual-functional probe would inhibit the enzyme activity. In contrast, binding of the target protein to the ligand perturbs this enzyme-inhibitor affinity due to the generation of steric effects caused by the close proximity between the target protein and the enzyme, thereby activating the enzyme to initiate signal amplification. With this strategy, the fluorescence signal can be amplified to as high as 70-fold. The generality and versatility of this strategy are demonstrated by the rapid, selective, and sensitive detection of four different proteins, avidin, O6-methylguanine DNA methyltransferase (MGMT), SNAP-tag, and lactoferrin, with four different probes.

An antibody-free microfluidic paper-based analytical device for the determination of tear fluid lactoferrin by fluorescence sensitization of Tb3+

An inkjet-printed microfluidic paper-based analytical device (μPAD) for the detection of lactoferrin has been developed. The analyte concentration dependent fluorescence emission, caused by the sensitization of pre-deposited terbium (Tb(3+)) upon complexation with lactoferrin on the paper device, is captured using a digital camera. The dynamic response range (0.5-3 mg mL(-1)) and the limit of detection (0.30 mg mL(-1)) of the μPAD are suitable for the analysis of normal human tears and the detection of eye disorders. Finally, lactoferrin concentrations in human tear samples were analyzed by the μPADs and the assay results corresponded within 6% error to those obtained by an immunoassay (ELISA). The μPADs provide a simple, rapid and accurate method for lactoferrin detection in tear fluid. Results are obtained within 15 min of a single application of 2.5 μL of sample. To the best of our knowledge, this is the first report of a device for lactoferrin quantification relying neither on an immunoassay nor on high cost analytical instrumentation.

Tear proteomic analysis of Sjögren syndrome patients with dry eye syndrome by two-dimensional-nano-liquid chromatography coupled with tandem mass spectrometry

We examined the tear film proteome of patients with Sjögren's syndrome (SS) and dry eye syndrome (group A), patients with dry eye symptoms (group B) and normal volunteers (group C). Tear samples were pooled from 8 subjects from each group and were subjected to two-dimensional-nano-liquid chromatography coupled with tandem mass spectrometry (2D-nano-LC-MS/MS). The tear breakup time for group A was significantly reduced compared with group B and C (P < 0.001). Group A (Schirmer I test, 2.13 ± 2.38 mm/5 min) had markedly lower tear volume than group B (5.94 ± 4.75 mm/5 min) and C (14.44 ± 6.57 mm/5 min) (P < 0.001). Group A had significantly higher normalized tear protein content (1.8291 ± 0.2241 μg/mm) than group B (1.0839 ± 0.1120 μg/mm) (P = 0.001) and C (0.2028 ± 0.0177 μg/mm) (P = 0.001). The 2D-nano-LC-MS/MS analysis identified a total of 435 proteins, including 182 (54.8%), 247 (74.4%) and 278 (83.7%) in group A, B, and C, respectively, with 56 (16.7%) proteins including defensin α1, clusterin and lactotransferrin unique to group A. In conclusion, dry eye syndrome in SS patients is associated with an altered proteomic profile with dysregulated expression of proteins involved in a variety of important cellular process including inflammation, immunity, and oxidative stress.

New testing options for diagnosing and grading dry eye disease

PURPOSE

To describe new options for diagnosis and severity grading of dry eye disease.

DESIGN

Perspective on technological advancements to identify tear dysfunction and their value in diagnosing and grading dry eye disease.

METHODS

Evidence is presented on new and evolving technologies to measure tear stability, composition, and meniscus height and their role in dry eye diagnosis and therapeutic efficacy grading is assessed.

RESULTS

Evolving concepts regarding pathogenesis and new technologies to evaluate the tears and ocular surface have improved the ability to diagnose, classify, and grade the severity of dry eye disease. New technologies include noninvasive imaging of tear stability and tear meniscus height as a measure of tear volume and tear composition (osmolarity, lacrimal factors, inflammatory mediators, growth and differentiation factors). Approved tests, such as tear osmolarity and tear imaging, are being integrated into clinical practice and may eventually supplant certain traditional tests that have greater variability and less sensitivity. Other tests, such as molecular assays of tears and conjunctival cells, are currently being used in studies investigating pathogenesis and therapeutic mechanism of action. They may eventually translate to routine clinical practice.

CONCLUSIONS

New technologies have emerged that can noninvasively evaluate the tears and measure disease-associated compositional changes. These tests are being integrated into clinical practice and therapeutic trials for diagnosis, classification, and severity grading of dry eye disease.

Microfluidic electrophoretic mobility shift assays for quantitative biochemical analysis

Electrophoretic mobility shift assays (EMSAs) play an important role in analytical chemistry, quantitative bioscience, and point-of-care diagnostics. Emerging microfluidic lab-on-a-chip technologies bring high throughput and multiplexed analysis to affinity-based electrophoretic separations, greatly advancing the performance of traditional EMSAs. This review elaborates on the relevant theoretical basis for EMSAs, surveys microfluidic-based EMSA applications in molecular conformation analyses, immunoassays, affinity assays and genomics, and outlines challenges and potential future improvements needed from this powerful assay.

Protein immobilization techniques for microfluidic assays

Microfluidic systems have shown unequivocal performance improvements over conventional bench-top assays across a range of performance metrics. For example, specific advances have been made in reagent consumption, throughput, integration of multiple assay steps, assay automation, and multiplexing capability. For heterogeneous systems, controlled immobilization of reactants is essential for reliable, sensitive detection of analytes. In most cases, protein immobilization densities are maximized, while native activity and conformation are maintained. Immobilization methods and chemistries vary significantly depending on immobilization surface, protein properties, and specific assay goals. In this review, we present trade-offs considerations for common immobilization surface materials. We overview immobilization methods and chemistries, and discuss studies exemplar of key approaches-here with a specific emphasis on immunoassays and enzymatic reactors. Recent "smart immobilization" methods including the use of light, electrochemical, thermal, and chemical stimuli to attach and detach proteins on demand with precise spatial control are highlighted. Spatially encoded protein immobilization using DNA hybridization for multiplexed assays and reversible protein immobilization surfaces for repeatable assay are introduced as immobilization methods. We also describe multifunctional surface coatings that can perform tasks that were, until recently, relegated to multiple functional coatings. We consider the microfluidics literature from 1997 to present and close with a perspective on future approaches to protein immobilization.

An on-chip, multichannel droplet sorter using standing surface acoustic waves

The emerging field of droplet microfluidics requires effective on-chip handling and sorting of droplets. In this work, we demonstrate a microfluidic device that is capable of sorting picoliter water-in-oil droplets into multiple outputs using standing surface acoustic waves (SSAW). This device integrates a single-layer microfluidic channel with interdigital transducers (IDTs) to achieve on-chip droplet generation and sorting. Within the SSAW field, water-in-oil droplets experience an acoustic radiation force and are pushed toward the acoustic pressure node. As a result, by tuning the frequency of the SSAW excitation, the position of the pressure nodes can be changed and droplets can be sorted to different outlets at rates up to 222 droplets s(-1). With its advantages in simplicity, controllability, versatility, noninvasiveness, and capability to be integrated with other on-chip components such as droplet manipulation and optical detection units, the technique presented here could be valuable for the development of droplet-based micro total analysis systems (μTAS).

Shotgun proteomics reveals specific modulated protein patterns in tears of patients with primary open angle glaucoma naïve to therapy

Primary open angle glaucoma (POAG) is one of the main causes of irreversible blindness worldwide. The pathogenesis of POAG is still unclear. Alteration and sclerosis of trabecular meshwork with changes in aqueous humor molecular composition seem to play the key role. Increased intraocular pressure is widely known to be the main risk factor for the onset and progression of the disease. Unfortunately, the early diagnosis of POAG still remains the main challenge. In order to provide insight into the patho-physiology of glaucoma, here we report a shotgun proteomics approach to tears of patients with POAG naïve to therapy. Our proteomics results showed 27 differential tear proteins in POAG vs. CTRL comparison (25 up regulated proteins in the POAG group and two unique proteins in the CTRL group), 16 of which were associated with inflammatory response, free radical scavenging, cell-to-cell signaling and interaction. Overall the protein modulation shown in POAG tears proves the involvement of biochemical networks linked to inflammation. Among all regulated proteins, a sub-group of 12 up-regulated proteins in naïve POAG patients were found to be down-regulated in medically controlled POAG patients treated with prostanoid analogues (PGA), as reported in our previous work (i.e., lipocalin-1, lysozyme C, lactotransferrin, proline-rich-protein 4, prolactin-inducible protein, zinc-alpha-2-glycoprotein, polymeric immunoglobulin receptor, cystatin S, Ig kappa chain C region, Ig alpha-2 chain C region, immunoglobulin J chain, Ig alpha-1 chain C region). In summary, our findings indicate that the POAG tears protein expression is a mixture of increased inflammatory proteins that could be potential biomarkers of the disease, and their regulation may be involved in the mechanism by which PGA are able to decrease the intraocular pressure in glaucoma patients.

Quantitative microfluidic biomolecular analysis for systems biology and medicine

In the postgenome era, biology and medicine are rapidly evolving towards quantitative and systems studies of complex biological systems. Emerging breakthroughs in microfluidic technologies and innovative applications are transforming systems biology by offering new capabilities to address the challenges in many areas, such as single-cell genomics, gene regulation networks, and pathology. In this review, we focus on recent progress in microfluidic technology from the perspective of its applications to promoting quantitative and systems biomolecular analysis in biology and medicine.

A homogeneous chemiluminescent immunoassay method

A new homogeneous chemiluminescent immunoassay method featuring the use of specific binding members separately labeled with an acridan-based chemiluminescent compound and a peroxidase is reported. Formation of an immunocomplex brings the chemiluminescent compound and the peroxidase into close proximity. Without any separation steps, a chemiluminescent signal is generated upon addition of a trigger solution, and the intensity is directly correlated to the quantity of the analyte.

Microfluidic screening of electrophoretic mobility shifts elucidates riboswitch binding function

Riboswitches are RNA sensors that change conformation upon binding small molecule metabolites, in turn modulating gene expression. Our understanding of riboswitch regulatory function would be accelerated by a high-throughput, quantitative screening tool capable of measuring riboswitch-ligand binding. We introduce a microfluidic mobility shift assay that enables precise and rapid quantitation of ligand binding and subsequent riboswitch conformational change. In 0.3% of the time required for benchtop assays (3.2 versus 1020 min), we screen and validate five candidate SAM-I riboswitches isolated from thermophilic and cryophilic bacteria. The format offers enhanced resolution of conformational change compared to slab gel formats, quantitation, and repeatability for statistical assessment of small mobility shifts, low reagent consumption, and riboswitch characterization without modification of the aptamer structure. Appreciable analytical sensitivity coupled with high-resolution separation performance allows quantitation of equilibrium dissociation constants (K(d)) for both rapidly and slowly interconverting riboswitch-ligand pairs as validated through experiments and modeling. Conformational change, triplicate mobility shift measurements, and K(d) are reported for both a known and a candidate SAM-I riboswitch with comparison to in-line probing assay results. The microfluidic mobility shift assay establishes a scalable format for the study of riboswitch-ligand binding that will advance the discovery and selection of novel riboswitches and the development of antibiotics to target bacterial riboswitches.

A droplet-based, optofluidic device for high-throughput, quantitative bioanalysis

Analysis of chemical or biomolecular contents in a tiny amount of specimen presents a significant challenge in many biochemical studies and diagnostic applications. In this work, we present a single-layer, optofluidic device for real-time, high-throughput, quantitative analysis of droplet contents. Our device integrates an optical fiber-based, on-chip detection unit with a droplet-based microfluidic unit. It can quantitatively analyze the contents of individual droplets in real-time. It also achieves a detection throughput of 2000 droplets per second, a detection limit of 20 nM, and an excellent reproducibility in its detection results. In a proof-of-concept study, we demonstrate that our device can be used to perform detection of DNA and its mutations by monitoring the fluorescent signal changes of the target DNA/molecular beacon complex in single droplets. Our approach can be immediately extended to a real-time, high-throughput detection of other biomolecules (such as proteins and viruses) in droplets. With its advantages in throughput, functionality, cost, size, and reliability, the droplet-based optofluidic device presented here can be a valuable tool for many medical diagnostic applications.

Continuous-flow biomolecule concentration and detection in a slanted nanofilter array

We demonstrate continuous-flow biomolecule concentration and detection in a microfabricated slanted sieving structure, which we term a herringbone nanofilter array (HNA). The HNA structure consists of periodically-patterned deep and shallow nanoslits meeting at right angles. In addition to concentration, we can discriminate different sized analytes by mixing a fluorescent probe with the sample and measuring the extent of the concentrating effect. Using this principle, we interrogate biomolecular interactions, including protein-DNA binding, protein-protein interaction and antibody-antigen binding. The final example demonstrates a novel method to perform a homogeneous immunoassay for detecting a disease marker, human C-reactive protein (CRP), using fluorescent-labeled antibodies at clinically relevant concentrations. The signal amplification potential and continuous flow operation provide a significant advantage over other microfluidic batch separation techniques for the easy integration of this device into a common point-of-care diagnostic platform.

Tear lacritin levels by age, sex, and time of day in healthy adults

PURPOSE

Several small proteomic studies suggest that the prosecretory tear protein lacritin may be selectively downregulated in dry eye syndrome and in blepharitis, yet little information is available about normal baseline levels. This study assessed lacritin levels in tears from healthy individuals and addressed whether they differ according to sex, age, or time of day.

METHODS

Rabbit antibodies against lacritin N-terminal peptide EDASSDSTGADPAQEAGTS (Pep Lac N-Term) were generated and characterized against human recombinant lacritin and N-65 truncation mutant. Basal tears were collected from 66 healthy individuals ranging in age from 18 to 52 years, and at four times during one 24-hour period from 34 other individuals. Lacritin levels were then analyzed by ELISA and Western blotting.

RESULTS

Anti-Pep Lac N-Term bound lacritin, but not truncation mutant N-65 that lacks the N-terminal antigenic site. Tear lacritin levels followed a normal distribution with a mean of 4.2 ± 1.17 ng/100 ng total tear protein. Levels differed little by age or sex, and decreased slightly between 4 and 8 hours in a 24-hour cycle. Tear-blocking effects were minimal, as suggested by spiking of tears with recombinant lacritin.

CONCLUSIONS

Anti-Pep Lac N-Term-detectable lacritin comprises ~4.2 ng/100 ng total tear protein in healthy individuals, with no significant differences between males and females or among individuals between 18 and 52 years old. Levels decrease slightly in the late afternoon. These findings provide a baseline for future immunodiagnostic studies of lacritin in dry eye and other ocular diseases.

Immunochromatographic assay on thread

Lateral-flow immunochromatographic assays are low-cost, simple-to-use, rapid tests for point-of-care screening of infectious diseases, drugs of abuse, and pregnancy. However, lateral flow assays are generally not quantitative, give a yes/no answer, and lack multiplexing. Threads have recently been proposed as a support for transporting and mixing liquids in lateral-flow immunochromatographic assays, but their use for quantitative high-sensitivity immunoassays has yet to be demonstrated. Here, we introduce the immunochromatographic assay on thread (ICAT) in a cartridge format that is suitable for multiplexing. The ICAT is a sandwich assay performed on a cotton thread knotted to a nylon fiber bundle, both of which are precoated with recognition antibodies against one target analyte. Upon sample application, the assay results become visible to the eye within a few minutes and are quantified using a flatbed scanner. Assay conditions were optimized, the binding curves for C-reactive protein (CRP) in buffer and diluted serum were established and a limit of detection of 377 pM was obtained. The possibility of multiplexing was demonstrated using three knotted threads coated with antibodies against CRP, osteopontin, and leptin proteins. The performance of the ICAT was compared with that of the paper-based and conventional assays. The results suggest that thread is a suitable support for making low-cost, sensitive, simple-to-use, and multiplexed diagnostic tests.