Design and testing of a disposable microfluidic chemiluminescent immunoassay for disease biomarkers in human serum samples

Progress in Procalcitonin Detection Based on Immunoassay

Procalcitonin (PCT) serves as a crucial biomarker utilized in diverse clinical contexts, including sepsis diagnosis and emergency departments. Its applications extend to identifying pathogens, assessing infection severity, guiding drug administration, and implementing theranostic strategies. However, current clinical deployed methods cannot meet the needs for accurate or real-time quantitative monitoring of PCT. This review aims to introduce these emerging PCT immunoassay technologies, focusing on analyzing their advantages in improving detection performances, such as easy operation and high precision. The fundamental principles and characteristics of state-of-the-art methods are first introduced, including chemiluminescence, immunofluorescence, latex-enhanced turbidity, enzyme-linked immunosorbent, colloidal gold immunochromatography, and radioimmunoassay. Then, improved methods using new materials and new technologies are briefly described, for instance, the combination with responsive nanomaterials, Raman spectroscopy, and digital microfluidics. Finally, the detection performance parameters of these methods and the clinical importance of PCT detection are also discussed.

Microfluidics-Based Nanobiosensors for Healthcare Monitoring

Efficient healthcare management demands prompt decision-making based on fast diagnostics tools, astute data analysis, and informatics analysis. The rapid detection of analytes at the point of care is ensured using microfluidics in synergy with nanotechnology and biotechnology. The nanobiosensors use nanotechnology for testing, rapid disease diagnosis, monitoring, and management. In essence, nanobiosensors detect biomolecules through bioreceptors by modulating the physicochemical signals generating an optical and electrical signal as an outcome of the binding of a biomolecule with the help of a transducer. The nanobiosensors are sensitive and selective and play a significant role in the early identification of diseases. This article reviews the detection method used with the microfluidics platform for nanobiosensors and illustrates the benefits of combining microfluidics and nanobiosensing techniques by various examples. The fundamental aspects, and their application are discussed to illustrate the advancement in the development of microfluidics-based nanobiosensors and the current trends of these nano-sized sensors for point-of-care diagnosis of various diseases and their function in healthcare monitoring.

A capillary-based microfluidic chip with the merits of low cost and easy fabrication for the rapid detection of acute myocardial infarction

Point-of-care testing methods currently utilize rapid, portable, inexpensive, and multiplexed on-site detection. Microfluidic chips have become a very promising platform with broad development prospects due to their breakthrough improvement in miniaturization and integration. However, the conventional microfluidic chips still have disadvantages, such as difficulty in fabrication processing, long production time and high cost, which hinder its applications in the fields of POCT and in vitro diagnostics. In this study, a capillary-based microfluidic chip with the characteristics of low cost and easy fabrication was developed for the rapid detection of acute myocardial infarction (AMI). Several short capillaries, which were already conjugated with the capture antibodies respectively, were connected by peristaltic pump tubes and then formed the working capillary. Two working capillaries were encapsulated in the plastic shell and ready for the immunoassay. Multiplex detection of Myoglobin (Myo), cardiac troponin I (cTnI) and creatine kinase-MB (CK-MB) were chosen to demonstrate the feasibility and analytical performance of the microfluidic chip, which requires rapid and accurate detection during diagnosis and therapy for AMI. The capillary-based microfluidic chip required tens of minutes to prepared, and its cost was less than $1. The limit of detection (LOD) was 0.5 ng/mL for Myo, 0.1 ng/mL for cTnI and 0.5 ng/mL for CK-MB respectively. The capillary-based microfluidic chips with easy fabrication and low cost hold promise for the portable and low-cost detection of target biomarkers.

Smartphone-Based Platforms for Clinical Detections in Lung-Cancer-Related Exhaled Breath Biomarkers: A Review

Lung cancer has been studied for decades because of its high morbidity and high mortality. Traditional methods involving bronchoscopy and needle biopsy are invasive and expensive, which makes patients suffer more risks and costs. Various noninvasive lung cancer markers, such as medical imaging indices, volatile organic compounds (VOCs), and exhaled breath condensates (EBCs), have been discovered for application in screening, diagnosis, and prognosis. However, the detection of markers still relies on bulky and professional instruments, which are limited to training personnel or laboratories. This seriously hinders population screening for early diagnosis of lung cancer. Advanced smartphones integrated with powerful applications can provide easy operation and real-time monitoring for healthcare, which demonstrates tremendous application scenarios in the biomedical analysis region from medical institutions or laboratories to personalized medicine. In this review, we propose an overview of lung-cancer-related noninvasive markers from exhaled breath, focusing on the novel development of smartphone-based platforms for the detection of these biomarkers. Lastly, we discuss the current limitations and potential solutions.

An introduction to microfluidics and their applications

In the past decade, microfluidics and lab-on-chip are rapidly growing area. It has been used for number of biology to biotechnology and medicine applications. It has the potential to reduce cost of reagent and time of experiment. It has been used integrated with automation for extraction and detection of protein, nucleic acids, enzymes, metabolites and delivery of drug to target location. It has been used for drug discovery, high throughput screening of potent drug and used for delivery. Paper based microfluidics was used for point-of-care diagnosis for accurate treatment of diseases. In this chapter, we highlight advances of microfluidics devices for number of biological and translational science applications.

Active droplet-array microfluidics-based chemiluminescence immunoassay for point-of-care detection of procalcitonin

The application of conventional chemiluminescence immunoassay (CLIA) in resource-limited settings is limited due to the large apparatus footprint, cumbersome operation and maintenance process, and high consumption of reagents. To address this issue, we developed an active droplet-array (ADA) microfluidics-based CLIA system, which consists of a compact microchip analyzer and microfluidic chips with preloaded reagents. The microfluidic chip contains microslit-connected microchambers, in which all the required reagents were preloaded in water-in-oil droplets. The microfluidic chip analyzer can manipulate five microfluidic chips in parallel in a single run. By interacting the microchip with magnetic, thermal, optical mechanisms programmatically, the entire workflow of CLIA can be accomplished in an automated manner. With the proposed CLIA, the detection of procalcitonin (PCT) can be completed in 12 min, with a limit of detection (LOD) of 0.044 ng mL^-1 and a detection range from 0.044 to 100 ng mL^-1. We found a good linear correlation between the microfluidic CLIA and the conventional electrochemiluminescence immunoassay (R²=0.98).The microfluidic CLIA has significant advantages over the conventional ELISA in detection sensitivity, dynamic range, instrument size and turnaround time, and can provide more consistent and reliable results than the lateral flow immunoassays. The compact microfluidic system can perform automated and parallelized CLIA in a short turnaround time, and thus well suited to Point-of-Care detection of disease biomarkers.

Handheld Microfluidic Filtration Platform Enables Rapid, Low-Cost, and Robust Self-Testing of SARS-CoV-2 Virus

Here, a novel microfluidic test kit combining ultrahigh throughput hydrodynamic filtration and sandwich immunoassay is reported. Specifically, nano and microbeads coated with two different, noncompetitive antibodies, are used to capture the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleocapsid (N) proteins simultaneously, forming larger complexes. Microfluidic filtration discards free nanobeads but retains antigen-bridged complexes in the observation zone, where a display of red color indicates the presence of antigen in the sample. This testing platform exhibits high throughput separation (<30 s) and enrichment of antigen that exceeds the traditional lateral flow assays or microfluidic assays, with a low limit of detection (LoD) < 100 copies mL-1 . In two rounds of clinical trials conducted in December 2020 and August 2021, the assays demonstrate high sensitivities of 95.4% and 100%, respectively, which proves this microfluidic test kit is capable of detecting SARS-CoV-2 virus variants evolved over significant periods of time. Furthermore, the mass-produced chip can be fabricated at a cost of $0.98/test and the robust design allows the chip to be reused for over 50 times. All of these features make the microfluidic test kit particularly suitable for areas with inadequate medical infrastructure and a shortage of laboratory resources.

Digital Microfluidic Thermal Control Chip-Based Multichannel Immunosensor for Noninvasively Detecting Acute Myocardial Infarction

Rapid and automated detection of acute myocardial infarction (AMI) at its developing stage is very important due to its high mortality rate. To quantitatively diagnose AMI, Myo, CK-MB, and cTnI are chosen as three biomarkers, which are usually detected through an immunosorbent assay, such as the enzyme-linked immunosorbent assay. However, the approach poses many drawbacks, such as long detection time, the cumbersome process, the need for professionals, and the difficulty of realizing automatic operation. Here, a multichannel digital microfluidic (DMF) thermal control chip integrated with a sandwich-based immunoassay strategy is proposed for the automated, rapid, and sensitive detection of AMI biomarkers. A miniaturized temperature control module is integrated on the back of the DMF chip, meeting the temperature requirement for the immunoassay. With this DMF thermal control chip, sample and reagent consumption are reduced to several microliters, significantly alleviating reagent consumption and sample dependence, and the automated and multichannel detection of biomarkers can be achieved. In this work, the simultaneously noninvasive detection of the human serum sample containing the three biomarkers of AMI is also achieved within 30 min, which improves the diagnostic accuracy of AMI. Due to the features of automation and miniaturization, the multichannel immunosensor can be used in community hospitals to increase the speed of diagnosis of patients with various acute diseases.

Bladder cancer hunting: A microfluidic paper-based analytical device

Bladder cancer is the fourth most common cancer in men, and it is becoming a prevalent malignancy. Most of the regular clinical examinations are prompt evaluations with cystoscopy, renal function testing, which require high-precision instrument, well-trained operators, and high cost. In this study, a microfluidic paper-based analytical device (μPAD) was fabricated to detect nuclear matrix protein 22 (NMP22) and bladder cancer antigen (BTA) from the urine samples. Urine samples were collected from 11 bladder cancer patients and 10 well-beings as experiment and control groups, respectively, to verify the working efficiency of μPAD. A remarkable checkout efficiency of up to 90.91% was found from the results. Meanwhile, this method is feasible for home-based self-detection from urine samples within 10 min for the total process, which provides a new way for quick, economical, and convenient tumor diagnosis, prognosis evaluation, and drug response.

VT, Nguyen T, Han J, Ahn CH. A new microchannel capillary flow assay (MCFA) platform with lyophilized chemiluminescence reagents for a smartphone-based POCT detecting malaria

There has been a considerable development in microfluidic based immunodiagnostics over the past few years which has greatly favored the growth of novel point-of-care-testing (POCT). However, the realization of an inexpensive, low-power POCT needs cheap and disposable microfluidic devices that can perform autonomously with minimum user intervention. This work, for the first time, reports the development of a new microchannel capillary flow assay (MCFA) platform that can perform chemiluminescence based ELISA with lyophilized chemiluminescent reagents. This new MCFA platform exploits the ultra-high sensitivity of chemiluminescent detection while eliminating the shortcomings associated with liquid reagent handling, control of assay sequence and user intervention. The functionally designed microchannels along with adequate hydrophilicity produce a sequential flow of assay reagents and autonomously performs the ultra-high sensitive chemiluminescence based ELISA for the detection of malaria biomarker such as PfHRP2. The MCFA platform with no external flow control and simple chemiluminescence detection can easily communicate with smartphone via USB-OTG port using a custom-designed optical detector. The use of the smartphone for display, data transfer, storage and analysis, as well as the source of power allows the development of a smartphone based POCT analyzer for disease diagnostics. This paper reports a limit of detection (LOD) of 8 ng/mL by the smartphone analyzer which is sensitive enough to detect active malarial infection. The MCFA platform developed with the smartphone analyzer can be easily customized for different biomarkers, so a hand-held POCT for various infectious diseases can be envisaged with full networking capability at low cost.

Serological and molecular rapid diagnostic tests for Toxoplasma infection in humans and animals

Infection by Toxoplasma gondii is prevalent worldwide. The parasite can infect a broad spectrum of vertebrate hosts, but infection of fetuses and immunocompromised patients is of particular concern. Easy-to-perform, robust, and highly sensitive and specific methods to detect Toxoplasma infection are important for the treatment and management of patients. Rapid diagnostic methods that do not sacrifice the accuracy of the assay and give reproducible results in a short time are highly desirable. In this context, rapid diagnostic tests (RDTs), especially with point-of-care (POC) features, are promising diagnostic methods in clinical microbiology laboratories, especially in areas with minimal laboratory facilities. More advanced methods using microfluidics and sensor technology will be the future trend. In this review, we discuss serological and molecular-based rapid diagnostic tests for detecting Toxoplasma infection in humans as well as animals.

A multichannel microchip containing 16 chambers packed with antibody-functionalized beads for immunofluorescence assay

A multichannel chip containing 16 microchambers was developed for fast and sensitive immunoassays. In each chamber, antibody-functionalized nonmagnetic beads were applied as the solid phase to capture target antigens. Four types of IgGs (human, rabbit, chicken, and mouse) could be detected simultaneously by our combining this microchip with a sandwich immunoassay technique. A three-layer chip structure was investigated for integration of multiple processes, including washing, immune reaction, and detection, in one microchip. Moreover, the proposed chip design could improve batch-to-batch repeatability and avoid interferences between different channels without the preparation of complex microvalves. The total operation time of this system was less than 30 min, with a desirable detection limit of 0.2 pg/mL. The results indicate that the microfluidic platform is promising for the immunoassay of multiple clinical biomarkers. Graphical abstract.

Advances in isolation and detection of circulating tumor cells based on microfluidics

Circulating tumor cells (CTCs) are the cancer cells that circulate in the peripheral blood after escaping from the original or metastatic tumors. CTCs could be used as non-invasive source of clinical information in early diagnosis of cancer and evaluation of cancer development. In recent years, CTC research has become a hotspot field wherein many novel CTC detection technologies based on microfluidics have been developed. Great advances have been made that exhibit obvious technical advantages, but cannot yet satisfy the current clinical requirements. In this study, we review the main advances in isolation and detection methods of CTC based on microfluidics research over several years, propose five technical indicators for evaluating these methods, and explore the application prospects. We also discuss the concepts, issues, approaches, advantages, limitations, and challenges with an aim of stimulating a broader interest in developing microfluidics-based CTC detection technology.

Combining Porous Magnetic Ni@C Nanospheres and CaCO3 Microcapsule as Surface-Enhanced Raman Spectroscopy Sensing Platform for Hypersensitive C-Reactive Protein Detection

In this work, we have designed an efficient and rapid surface-enhanced Raman spectroscopy (SERS) immunosensor for a supersensitive analysis of hypersensitive C-reactive protein (hs-CRP) with a label-free method by combining porous magnetic Ni@C nanospheres to aggregate together for simplifying the experiment operation and CaCO₃ microcapsule to encapsulate rhodamine B as the Raman signal. The final solution containing the signal molecule was dropped on the Ag nanoparticle substrate, and the signal could be enhanced by Ag particles. First, rhodamine B was encapsulated in the CaCO₃ microcapsule when it precipitated to form microcubes. Subsequently, the porous CaCO₃ microcapsule was assembled layer by layer with poly(ether imide) (PEI) and a second antibody to obtain rhodamine B@CaCO₃@PEI@Ab₂. Then, the functionalized magnetic Ni@C nanospheres were prepared to immobilize the primary antibody (Ab₁). Finally, the immunosensor was fabricated by the sandwiched antibody-antigen interactions. Compared to the DNA hydrogel, the low-cost CaCO₃ microcapsule would be rapidly dissolved by ethylene diamine tetraacetic acid, releasing rhodamine B to produce a strong Raman signal for a rapid and efficient detection of hs-CRP. With the hs-CRP concentration ranging from 0.1 pg mL^-1 to 1 μg mL^-1, the SERS intensity of the platform has a linear relationship with the logarithm of hs-CRP concentration, and the detection limit was 0.01 pg mL^-1. By this smart design, this work can give a direction for a rapid label-free SERS analysis.

Bench-Top Fabrication of an All-PDMS Microfluidic Electrochemical Cell Sensor Integrating Micro/Nanostructured Electrodes

In recent years, efforts in the development of lab-on-a-chip (LoC) devices for point-of-care (PoC) applications have increased to bring affordable, portable, and sensitive diagnostics to the patients' bedside. To reach this goal, research has shifted from using traditional microfabrication methods to more versatile, rapid, and low-cost options. This work focuses on the benchtop fabrication of a highly sensitive, fully transparent, and flexible poly (dimethylsiloxane) (PDMS) microfluidic (μF) electrochemical cell sensor. The μF device encapsulates 3D structured gold and platinum electrodes, fabricated using a shape-memory polymer shrinking method, which are used to set up an on-chip electrochemical cell. The PDMS to PDMS-structured electrode bonding protocol to fabricate the μF chip was optimized and found to have sufficient bond strength to withstand up to 100 mL/min flow rates. The sensing capabilities of the on-chip electrochemical cell were demonstrated by using cyclic voltammetry to monitor the adhesion of murine 3T3 fibroblasts in the presence of a redox reporter. The charge transfer across the working electrode was reduced upon cell adhesion, which was used as the detection mechanism, and allowed the detection of as few as 24 cells. The effective utilization of simple and low cost bench-top fabrication methods could accelerate the prototyping and development of LoC technologies and bring PoC diagnostics and personalized medicine to the patients' bedside.

Tuning the chemiluminescence of a luminol flow using plasmonic nanoparticles

We have discovered a strong increase in the intensity of the chemiluminescence of a luminol flow and a dramatic modification of its spectral shape in the presence of metallic nanoparticles. We observed that pumping gold and silver nanoparticles into a microfluidic device fabricated in polydimethylsiloxane prolongs the glow time of luminol. We have demonstrated that the intensity of chemiluminescence in the presence of nanospheres depends on the position along the microfluidic serpentine channel. We show that the enhancement factors can be controlled by the nanoparticle size and material. Spectrally, the emission peak of luminol overlaps with the absorption band of the nanospheres, which maximizes the effect of confined plasmons on the optical density of states in the vicinity of the luminol emission peak. These observations, interpreted in terms of the Purcell effect mediated by nano-plasmons, form an essential step toward the development of microfluidic chips with gain media. Practical implementation of the discovered effect will include improving the detection limits of chemiluminescence for forensic science, research in biology and chemistry, and a number of commercial applications.

One-step purification and concentration of DNA in porous membranes for point-of-care applications

The emergence of rapid, user-friendly, point-of-care (POC) diagnostic systems is paving the way for better disease diagnosis and control. Lately, there has been a strong emphasis on developing molecular-based diagnostics due to their potential for greatly increased sensitivity and specificity. One of the most critical steps in developing practical diagnostic systems is the ability to perform sample preparation, especially the purification of nucleic acids (NA), at the POC. As such, we have developed a simple-to-use, inexpensive, and disposable sample preparation system for in-membrane purification and concentration of NAs. This system couples lateral flow in a porous membrane with chitosan, a linear polysaccharide that captures NAs via anion exchange chromatography. The system can also substantially concentrate the NAs. The combination of these capabilities can be used on a wide range of sample types, which are prepared for use in downstream processes, such as qPCR, without further purification.

Advances in miniaturized instruments for genomics

In recent years, a lot of demonstrations of the miniaturized instruments were reported for genomic applications. They provided the advantages of miniaturization, automation, sensitivity, and specificity for the development of point-of-care diagnostics. The aim of this paper is to report on recent developments on miniaturized instruments for genomic applications. Based on the mature development of microfabrication, microfluidic systems have been demonstrated for various genomic detections. Since one of the objectives of miniaturized instruments is for the development of point-of-care device, impedimetric detection is found to be a promising technique for this purpose. An in-depth discussion of the impedimetric circuits and systems will be included to provide total consideration of the miniaturized instruments and their potential application towards real-time portable imaging in the “-omics” era. The current excellent demonstrations suggest a solid foundation for the development of practical and widespread point-of-care genomic diagnostic devices.

High-density immobilization of antibodies onto nanobead-coated cyclic olefin copolymer plastic surfaces for application as a sensitive immunoassay chip

Our research efforts have been devoted to development of nanobead multilayer-based sensitive immunoassays on cyclic olefin copolymer (COC) plastic surfaces. To facilitate nanobead attachment and impart antibiofouling properties to a COC substrate, we used an amphiphilic copolymer comprising benzyl, polyethylene glycol, and reactive ester moieties to coat the hydrophobic COC surface in an aqueous environment. Subsequently, NH2-modified polystyrene nanobeads were reacted with the polymer-coated COC surface and further assembled into multilayers that increased the overall surface area available for attaching capture antibodies. After treatment of the nanobead multilayers with an amine-reactive homobifunctional crosslinker, a model capture antibody (anti-rabbit IgG) was covalently immobilized onto the activated surface of nanobeads. Finally, a sandwich immunoassay was carried out using rabbit IgG as a target analyte and rhodamine-labeled anti-rabbit IgG as a probe. Compared with a nanobead-free, polymer-coated COC surface, the nanobead multilayer-based immunoassay exhibited ~4-fold higher fluorescence intensity. In addition, our nanobead-based assay system exhibited a wide dynamic range of detection (0.1 to 1,000 ng/mL) and high specificity for rabbit IgG. Furthermore, much better detection sensitivity for rabbit IgG was attained in the nanobead multilayer-based immunoassay than with a conventional ELISA system (0.1 ng/mL versus 10 ng/mL), indicating the potential value of the proposed immunoassay system in plastic-based portable biochip applications.

Real-time electrical impedimetric monitoring of blood coagulation process under temperature and hematocrit variations conducted in a microfluidic chip

Blood coagulation is an extremely complicated and dynamic physiological process. Monitoring of blood coagulation is essential to predict the risk of hemorrhage and thrombosis during cardiac surgical procedures. In this study, a high throughput microfluidic chip has been developed for the investigation of the blood coagulation process under temperature and hematocrit variations. Electrical impedance of the whole blood was continuously recorded by on-chip electrodes in contact with the blood sample during coagulation. Analysis of the impedance change of the blood was conducted to investigate the characteristics of blood coagulation process and the starting time of blood coagulation was defined. The study of blood coagulation time under temperature and hematocrit variations was shown a good agreement with results in the previous clinical reports. The electrical impedance measurement for the definition of blood coagulation process provides a fast and easy measurement technique. The microfluidic chip was shown to be a sensitive and promising device for monitoring blood coagulation process even in a variety of conditions. It is found valuable for the development of point-of-care coagulation testing devices that utilizes whole blood sample in microliter quantity.

Continuous monitoring of inflammation biomarkers during simulated cardiopulmonary bypass using a microfluidic immunoassay device - a pilot study

This work demonstrates the use of a continuous online monitoring system for tracking systemic inflammation biomarkers during cardiopulmonary bypass (CPB) procedures. The ability to monitor inflammation biomarkers during CPB will allow surgical teams to actively treat inflammation and reduce harmful effects on postoperative morbidity and mortality, enabling improved patient outcomes. A microfluidic device has been designed which allows automation of the individual processing steps of a microbead immunoassay to allow continuous tracking of antigen concentrations. Preliminary experiments have demonstrated that the results produced by the microimmunoassay are comparable to results produced from a standard enzyme-linked immunosorbent assay (r = 0.98). Additionally, integration of the assay with a simulated CPB circuit has been demonstrated with temporal tracking of C3a concentrations within blood continuously sampled from the circuit. The presented work describes the motivation, design challenges, and preliminary experimental results of this project.

Lab on a chip for in situ diagnosis: From blood to point of care

As the point of care diagnosis devices are becoming ever more popular, this paper suggest a miniaturized testing device from a drop of blood to diagnosis of disease for the global healthcare. The minimal requirements for the POC blood-testing device are blood microsampling, blood separation, immunoassay, and detection and communication of the signals. The microsampling of the blood can be achieved by specialized needle, which can be connected to the microchip or analytical devices. The sampled blood is then separated using either a filter (weir or pillar type), or by the phenomena unique to microfluidic system. The separated blood should then go through sandwich, homogeneous non-competitive, or competitive immunoassay, which can effectively diagnose diverse diseases. Lastly, the device should detect and translate the immune-signals to readable, and clinically significant signals. The development of such device will play a great role for improving healthcare technology.

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.

Integration of biosensors and drug delivery technologies for early detection and chronic management of illness

Recent advances in biosensor design and sensing efficacy need to be amalgamated with research in responsive drug delivery systems for building superior health or illness regimes and ensuring good patient compliance. A variety of illnesses require continuous monitoring in order to have efficient illness intervention. Physicochemical changes in the body can signify the occurrence of an illness before it manifests. Even with the usage of sensors that allow diagnosis and prognosis of the illness, medical intervention still has its downfalls. Late detection of illness can reduce the efficacy of therapeutics. Furthermore, the conventional modes of treatment can cause side-effects such as tissue damage (chemotherapy and rhabdomyolysis) and induce other forms of illness (hepatotoxicity). The use of drug delivery systems enables the lowering of side-effects with subsequent improvement in patient compliance. Chronic illnesses require continuous monitoring and medical intervention for efficient treatment to be achieved. Therefore, designing a responsive system that will reciprocate to the physicochemical changes may offer superior therapeutic activity. In this respect, integration of biosensors and drug delivery is a proficient approach and requires designing an implantable system that has a closed loop system. This offers regulation of the changes by means of releasing a therapeutic agent whenever illness biomarkers prevail. Proper selection of biomarkers is vital as this is key for diagnosis and a stimulation factor for responsive drug delivery. By detecting an illness before it manifests by means of biomarkers levels, therapeutic dosing would relate to the severity of such changes. In this review various biosensors and drug delivery systems are discussed in order to assess the challenges and future perspectives of integrating biosensors and drug delivery systems for detection and management of chronic illness.

Applications of microfluidics for molecular diagnostics

Diagnostic assays implemented in microfluidic devices have developed rapidly over the past decade and are expected to become commonplace in the next few years. Hundreds of microfluidics-based approaches towards clinical diagnostics and pathogen detection have been reported with a general theme of rapid and customizable assays that are potentially cost-effective. This chapter reviews microfluidics in molecular diagnostics based on application areas with a concise review of microfluidics in general. Basic principles of microfabrication are briefly reviewed and the transition to polymer fabricated devices is discussed. Most current microfluidic diagnostic devices are designed to target a single disease, such as a given cancer or a variety of pathogens, and there will likely be a large market for these focused devices; however, the future of molecular diagnostics lies in highly multiplexed microfluidic devices that can screen for potentially hundreds of diseases simultaneously.

Miniaturized technology for protein and nucleic acid point-of-care testing

The field of point-of-care (POC) testing technology is developing quickly and producing instruments that are increasingly reliable, while their size is being gradually reduced. Proteins are a common target for POC analyses and the detection of protein markers typically involves immunoassays aimed at detecting different groups of proteins such as tumor markers, inflammation proteins, and cardiac markers; but other techniques can also be used to analyze plasma proteins. In the case of nucleic acids, hybridization and amplification strategies can be used to record electromagnetic or electric signals. These techniques allow for the identification of specific viral or bacterial infections as well as specific cancers. In this review, we consider some of the latest advances in the analysis of specific nucleic acid and protein biomarkers, taking into account their trend toward miniaturization and paying special attention to the technology that can be implemented in future applications, such as lab-on-a-chip instruments.

Microfluidic systems for diagnostic applications: a review

Because of intensive developments in recent years, the microfluidic system has become a powerful tool for biological analysis. Entire analytic protocols including sample pretreatment, sample/reagent manipulation, separation, reaction, and detection can be integrated into a single chip platform. A lot of demonstrations on the diagnostic applications related to genes, proteins, and cells have been reported because of their advantages associated with miniaturization, automation, sensitivity, and specificity. The aim of this article is to review recent developments in microfluidic systems for diagnostic applications. Based on the categories of various fluid-manipulating mechanisms and biological detection approaches, in-depth discussion of the microfluidic-based diagnostic systems is provided. Moreover, a brief discussion on materials and manufacturing techniques will be included. The current excellent integration of microfluidic systems and diagnostic applications suggests a solid foundation for the development of practical point-of-care devices.

Quantification of proteins on gold nanoparticles by combining MALDI-TOF MS and proteolysis

Protein-coated nanoparticles have been used in many studies, including those related to drug delivery, disease diagnosis, therapeutics, and bioassays. The number and density of proteins on the particles' surface are important parameters that need to be calculable in most applications. While quantification methods for two-dimensional surface-bound proteins are commonly found, only a few methods for the quantification of proteins on three-dimensional surfaces such as nanoparticles have been reported. In this paper, we report on a new method of quantifying proteins on nanoparticles using matrix assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry (MS). In this method, the nanoparticle-bound proteins are digested by trypsin and the resulting peptide fragments are analyzed by MALDI-TOF MS after the addition of an isotope-labeled internal standard (IS) which has the same sequence as a reference peptide of the surface-bound protein. Comparing the mass intensities between the reference peptide and the IS allows the absolute quantification of proteins on nanoparticles, because they have the same molecular milieu. As a model system, gold nanoparticles were examined using bovine serum albumin (BSA) as a coating protein. We believe that our strategy will be a useful tool that can provide researchers with quantitative information about the proteins on surfaces of three-dimensional materials.

Microfluidic reactors for diagnostics applications

Diagnostic assays are an important part of health care, both in the clinic and in research laboratories. In addition to improving treatments and clinical outcomes, rapid and reliable diagnostics help track disease epidemiology, curb infectious outbreaks, and further the understanding of chronic illness. Disease markers such as antigens, RNA, and DNA are present at low concentrations in biological samples, such that the majority of diagnostic assays rely on an amplification reaction before detection is possible. Ideally, these amplification reactions would be sensitive, specific, inexpensive, rapid, integrated, and automated. Microfluidic technology currently in development offers many advantages over conventional benchtop reactions that help achieve these goals. The small reaction volumes and energy consumption make reactions cheaper and more efficient in a microfluidic reactor. Additionally, the channel architecture could be designed to perform multiple tests or experimental steps on one integrated, automated platform. This review explores the current research on microfluidic reactors designed to aid diagnostic applications, covering a broad spectrum of amplification techniques and designs.

Microfluidic LIPS for serum antibody detection: demonstration of a rapid test for HSV-2 infection

There is great interest in point-of-care antibody testing for the diagnosis of infectious and autoimmune diseases. As a first step in the development of self-contained and miniaturized devices for highly quantitative antibody detection, we demonstrate the application of Luciferase Immunoprecipitation Systems (LIPS) technology in a microfluidic format. Protein A/G was immobilized on the walls of PDMS-glass microchannels of 500 nL volume. The assay proceeds with the simultaneous introduction of plasma and Renilla luciferase-tagged antigens. Following washing, coelenterazine substrate was added and bound antigen-luciferase measured by chemiluminescence. Total assay time, including rinsing and detection, is under 10 min. Using these stable microfluidic devices, high diagnostic performance (100% sensitivity and 100% specificity) was achieved for the diagnosis of HSV-2 infection. Based on these findings, the LIPS microfluidic format should readily lend itself to automation and the transfer to portable instrumentation.

Microfluidic platforms for performing surface-based clinical assays

The need for fast, specific and portable diagnostic systems for clinical assays has, in recent years, led to an explosion of research into microfluidic chip-based immunoassays towards rapid point-of-care analysis. Such devices exploit small dimensions, superior fluidic control and low reagent volumes to allow a number of clinically important procedures to be achieved with improvements on conventional methods, many of which rely on the surface-based binding of antigens to antibodies. Here, we discuss recent developments and innovations in the area of on-chip surface-based immunoassays and provide an outlook on the potential of such platforms for future diagnostics.

Chemiluminescence response of murine macrophages on multilayer microfluidic chips

We have demonstrated an integrated platform for microfluidics and chemiluminescence (CL) detection that is capable of parallel cell culture, convenient liquid manipulation, and sensitive chemiluminescent detection. Luminol-dependent CL responses induced by three different stimuli, phytohemagglutinin (PHA), concanavalin A (ConA), and lipopolysaccharides (LPS), which can evoke a CL response in macrophages, were evaluated on this microfluidic chip. We studied the dose-dependent effect of these three stimuli on CL response in murine macrophages. PHA produced the highest CL response compared to LPS and ConA. The CL intensity produced by PHA was 6.85 and four times higher than that by LPS and ConA, respectively, at the low concentration of 100 μg/ml. We have found microfluidic based CL to be a very useful screening tool, which is less laborious and more sensitive. This microfluidic system is disposable and capable of rapid device prototyping; it may prove to be very useful in clinical and pharmaceutical applications.

A lab-on-a-chip for rapid blood separation and quantification of hematocrit and serum analytes

In this work, a new lab-on-a-chip for rapid analysis of low volume blood samples was designed, fabricated and demonstrated for integration of serum separation, hematocrit evaluation, and protein quantitation. Blood separation was achieved using microchannel flow-based separation. A novel method for evaluating hematocrit from microfluidic flow-separated blood samples was developed using gray scale analysis of a point-and-shoot digital photograph of separated blood in a micochannel. Protein quantitation was subsequently performed in a high surface area-to-volume ratio microfluidic chemiluminescent immunoassay using cell depleted serum produced by microfluidic flow-based separation of whole blood samples. All three steps were achieved in a single microchannel with separation of blood samples and hematocrit evaluation in less than 1 min, and protein quantitation in 5 min.

Shrink-film microfluidic education modules: Complete devices within minutes

As advances in microfluidics continue to make contributions to diagnostics and life sciences, broader awareness of this expanding field becomes necessary. By leveraging low-cost microfabrication techniques that require no capital equipment or infrastructure, simple, accessible, and effective educational modules can be made available for a broad range of educational needs from middle school demonstrations to college laboratory classes. These modules demonstrate key microfluidic concepts such as diffusion and separation as well as "laboratory on-chip" applications including chemical reactions and biological assays. These modules are intended to provide an interdisciplinary hands-on experience, including chip design, fabrication of functional devices, and experiments at the microscale. Consequently, students will be able to conceptualize physics at small scales, gain experience in computer-aided design and microfabrication, and perform experiments-all in the context of addressing real-world challenges by making their own lab-on-chip devices.

Highly sensitive fluorescence detection system for microfluidic lab-on-a-chip

We demonstrate a compact, low cost and practical fluorescence detection system for lab-on-a-chip applications. The system comprises a commercially available InGaN light emitting diode (501 nm) as light source, an organic or silicon photodiode detector, absorptive dye coated colour filters and linear and reflective polarisers. An injection moulded polystyrene microfluidic chip is used as the platform for fluorescence immunoassays for cardiac markers myoglobin and CK-MB. The optical limit of detection (LOD) is measured using a TransFluoSphere® suspension at 5.6 × 10(4) beads µl(-1) which can be equated to ∼3 nM fluorescein equivalent concentration. The LOD for the human plasma immunoassays is measured as 1.5 ng ml(-1) for both myoglobin and CK-MB.

Functionalizing poly(cyclic olefins) using copper-catalyzed azide–alkyne “click” reactions

A robust method for functionalizing poly(cyclic olefin) surfaces comprised of Zeonor 1060R was developed. These surfaces were first oxidized using two separate methods, ozonolysis and oxygen plasma treatment, to increase their hydrophilic properties and produce carboxylic acids on the surface. The resulting acids enabled direct amide coupling with various amines containing azide or alkyne moieties onto the surface. These modified surfaces were further functionalized via copper-catalyzed azide–alkyne cycloadditions (CuAAC) on the surface and the method was optimized for this material. Surface modifications were characterized by water contact angle measurements, fluorescence microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. Our data demonstrates a robust method for generating “clickable” Zeonor 1060R surfaces as demonstrated through attachment and subsequent detection of a triazole-linked fluorophore. The method developed enables the systematic modification of any poly(cyclic olefin) surface for functionalization using the click reaction.