Integrated microfluidic immunoassay for the rapid determination of clenbuterol

A compact microfluidic laser-induced fluorescence immunoassay system using avalanche photodiode for rapid detection of alpha-fetoprotein

Alpha-fetoprotein (AFP), commonly employed for early diagnosis of liver cancer, serves as a biomarker for cancer screening and diagnosis. Combining the high sensitivity and specificity of fluorescence immunoassay (FIA), developing a low-cost and efficient immunoassay system for AFP detection holds significant importance in disease diagnosis. In this work, we developed a miniaturized oblique laser-induced fluorescence (LIF) immunoassay system, coupled with a microfluidic PMMA/paper hybrid chip, for rapid detection of AFP. The system employed an avalanche photodiode (APD) as the detector, and implemented multi-level filtering in the excitation light channel using the dichroic mirror and optical trap. At first, we employed the Savitzky-Golay filter and baseline off-set elimination methods to denoise and normalize the original data. Then the cutoff frequency of the low-pass filter and the reverse voltage of the APD were optimized to enhance the detection sensitivity of the system. Furthermore, the effect of laser power on the fluorescence excitation efficiency was investigated, and the sampling time during the scanning process was optimized. Finally, a four-parameter logistic (4PL) model was utilized to establish the concentration-response equation for AFP. The system was capable of detecting concentrations of AFP standard solution within the range of 1-500 ng/mL, with a detection limit of 0.8 ng/mL. The entire immunoassay process could be completed within 15 min. It has an excellent potential for applications in low-cost portable diagnostic instruments for the rapid detection of biomarkers.

Single-Atomic Site Catalyst Enhanced Lateral Flow Immunoassay for Point-of-Care Detection of Herbicide

Point-of-care (POC) detection of herbicides is of great importance due to their impact on the environment and potential risks to human health. Here, we design a single-atomic site catalyst (SASC) with excellent peroxidase-like (POD-like) catalytic activity, which enhances the detection performance of corresponding lateral flow immunoassay (LFIA). The iron single-atomic site catalyst (Fe-SASC) is synthesized from hemin-doped ZIF-8, creating active sites that mimic the Fe active center coordination environment of natural enzyme and their functions. Due to its atomically dispersed iron active sites that result in maximum utilization of active metal atoms, the Fe-SASC exhibits superior POD-like activity, which has great potential to replace its natural counterparts. Also, the catalytic mechanism of Fe-SASC is systematically investigated. Utilizing its outstanding catalytic activity, the Fe-SASC is used as label to construct LFIA (Fe-SASC-LFIA) for herbicide detection. The 2,4-dichlorophenoxyacetic acid (2,4-D) is selected as a target here, since it is a commonly used herbicide as well as a biomarker for herbicide exposure evaluation. A linear detection range of 1-250 ng/mL with a low limit of detection (LOD) of 0.82 ng/mL has been achieved. Meanwhile, excellent specificity and selectivity towards 2,4-D have been obtained. The outstanding detection performance of the Fe-SASC-LFIA has also been demonstrated in the detection of human urine samples, indicating the practicability of this POC detection platform for analyzing the 2,4-D exposure level of a person. We believe this proposed Fe-SASC-LFIA has potential as a portable, rapid, and high-sensitive POC detection strategy for pesticide exposure evaluation.

Current Advances in Immunoassays for the Detection of β2-Agonists

β2-agonists are a group of synthetic phenylethanolamine compounds which are traditionally used for treating bronchospasm. These compounds can also increase skeletal muscle mass and decrease body fat. The illegal use of β2-agonists in food-producing animals results in residue of β2-agonists in edible tissues and causes adverse health effects in humans. Thus, the detection of β2-agonists at trace level in complex sample matrices is of great importance for monitoring the abuse of β2-agonists. Many methods have been developed to detect β2-agonists. Among them, a variety of antigen–antibody interaction-based techniques have been established to detect β2-agonists in various samples, including animal feed, urine, serum, milk, tissues and hair. In this review, we summarized current achievement in the extraction of β2-agonists from testing samples and detection of β2-agonists using immunological techniques. Future perspectives were briefly discussed.

Recent progress of microfluidic technology for pharmaceutical analysis

In recent years, the progress of microfluidic technology has provided new tools for pharmaceutical analysis and the proposal of pharm-lab-on-a-chip is appealing for its great potential to integrate pharmaceutical test and pharmacological test in a single chip system. Here, we summarize and highlight recent advances of chip-based principles, techniques and devices for pharmaceutical test and pharmacological/toxicological test focusing on the separation and analysis of drug molecules on a chip and the construction of pharmacological models on a chip as well as their demonstrative applications in quality control, drug screening and precision medicine. The trend and challenge of microfluidic technology for pharmaceutical analysis are also discussed and prospected. We hope this review would update the insight and development of pharm-lab-on-a-chip.

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.

Fluorescence enhanced lab-on-a-chip patterned using a hybrid technique of femtosecond laser direct writing and anodized aluminum oxide porous nanostructuring

A nanoporous array structure detection chip with strong spectral resolution, fabricated by femtosecond laser direct writing and anodized aluminum oxide.

Development of a single-step immunoassay microdevice based on a graphene oxide-containing hydrogel possessing fluorescence quenching and size separation functions

An immunoassay, which is an indispensable analytical method both in biological research and in medical fields was successfully integrated into a "single-step" by developing a microdevice composed of a graphene oxide (GO)-containing hydrogel and a poly (dimethylsiloxane) (PDMS) microchannel array with a polyethylene glycol (PEG) coating containing a fluorescently-labelled antibody. Here we used 2-hydroxyethylmethacrylate (HEMA) as a monomer that is easily, and homogeneously, mixed with GO to synthesize the hydrogel. The fluorescence quenching and size separation functions were then optimized by controlling the ratios of HEMA and GO. Free fluorescently-labelled antibody was successfully separated from the immunoreaction mixture by the hydrogel network structure, and the fluorescence was subsequently quenched by GO. In comparison to the previously reported immunoassay system using GO, the present system achieved a very high fluorescence resonance energy transfer (FRET) efficiency (∼90%), due to the use of direct adsorption of the fluorescently-labelled antibody to the GO surface; in contrast, the former reported method relied on indirect adsorption of the fluorescently-labelled antibody via immunocomplex formation at the GO surface. Finally, the single-step immunoassay microdevice was made by combining the developed hydrogel and the PDMS microchannel with a coating containing the fluorescently-labelled antibody, and successfully applied for the single-step analysis of IgM levels in diluted human serum by simple introduction of the sample via capillary action.

Fast and single-step immunoassay based on fluorescence quenching within a square glass capillary immobilizing graphene oxide-antibody conjugate and fluorescently labelled antibody

A single-step, easy-to-use, and fast capillary-type immunoassay device composed of a polyethylene glycol (PEG) coating containing two kinds of antibody-reagents, including an antibody-graphene oxide conjugate and fluorescently labelled antibody, was developed in this study. The working principle involved the spontaneous dissolution of the PEG coating, diffusion of reagents, and subsequent immunoreaction, triggered by the capillary action-mediated introduction of a sample solution. In a sample solution containing the target antigen, two types of antibody reagents form a sandwich-type antigen-antibody complex and fluorescence quenching takes place via fluorescence resonance energy transfer between the labelled fluorescent molecules and graphene oxide. Antigen concentration can be measured based on the decrease in fluorescence intensity. An antigen concentration-dependent response was obtained for the model target protein sample (human IgG, 0.2-10 μg mL(-1)). The present method can shorten the reaction time to within 1 min (approximately 40 s), while conventional methods using the same reagents require reaction times of approximately 20 min because of the large reaction scale. The proposed method is one of the fastest immunoassays ever reported. Finally, the present device was used to measure human IgG in diluted serum samples to demonstrate that this method can be used for fast medical diagnosis.

Microfluidic flow cytometry: The role of microfabrication methodologies, performance and functional specification

Flow cytometry is an invaluable tool utilized in modern biomedical research and clinical applications requiring high throughput, high resolution particle analysis for cytometric characterization and/or sorting of cells and particles as well as for analyzing results from immunocytometric assays. In recent years, research has focused on developing microfluidic flow cytometers with the motivation of creating smaller, less expensive, simpler, and more autonomous alternatives to conventional flow cytometers. These devices could ideally be highly portable, easy to operate without extensive user training, and utilized for research purposes and/or point-of-care diagnostics especially in limited resource facilities or locations requiring on-site analyses. However, designing a device that fulfills the criteria of high throughput analysis, automation and portability, while not sacrificing performance is not a trivial matter. This review intends to present the current state of the field and provide considerations for further improvement by focusing on the key design components of microfluidic flow cytometers. The recent innovations in particle focusing and detection strategies are detailed and compared. This review outlines performance matrix parameters of flow cytometers that are interdependent with each other, suggesting trade offs in selection based on the requirements of the applications. The ongoing contribution of microfluidics demonstrates that it is a viable technology to advance the current state of flow cytometry and develop automated, easy to operate and cost-effective flow cytometers.

A paper-based competitive lateral flow immunoassay for multi β-agonist residues by using a single monoclonal antibody labelled with red fluorescent nanoparticles

An ultrasensitive paper based lateral flow assay is described for rapid and simultaneous fluorometric detection of several β-agonists including clenbuterol and its chemical analogues (mabuterol, brombuterol, cimaterol, cimbuterol, bromchlorbuterol and banbuterol). A nonspecific monoclonal antibody (mAb) against clenbuterol and its analogues was prepared and employed in a competitive immunoassay where mAb conjugated to fluorescent nanoparticles and free β-agonists compete for the binding sites. This enables rapid screening for the 7 β-agonists in a single run that takes about 8 min. Detection limits for the seven β-agonists are <50 pg g⁻¹ of pork. Recoveries ranged from 69.5% to 102.4%, and relative standard deviations were ±15%. The assay was applied to the analysis of both using spiked and unspiked pork for β-agonists, and the results compare well to those obtained by HPLC-MS.

Graphical abstract

Enhancing a clenbuterol immunosensor based on poly(3,4-ethylenedioxythiophene)/multi-walled carbon nanotube performance using response surface methodology

A clenbuterol immunosensor was developed with a poly(3,4-ethylenedioxythiophene)/multi-walled carbon nanotube-modified screen-printed carbon electrode and optimized using response surface methodology.

Investigation of osteogenic activity of primary rabbit periosteal cells stimulated by multi-axial tensile strain

Periosteum-derived cells was indicated to respond to mechanical force and have stem cell potential capable of differentiating into multiple tissue. Investigation of osteogenic activity under mechanical stimulation is important to understand the therapeutic conditions of fracture healing. In this work, a cell culture platform was developed for respectively providing isotropic and anisotropic axial strain. Primary rabbit periosteal cells were isolated and cultured in the chamber. Multi-axial tensile strain was received and osteogenic activity was investigated by mRNA expressions of CBFA1 and OPN. The highest mRNA expression was found in moderate strain (5-8%) under anisotropic axial strain. These results provided important foundation for further in vivo studies and development of tailor-made stretching rehabilitation equipment.

Paper-based assays for urine analysis

A transformation of the healthcare industry is necessary and imminent: hospital-centered, reactive care will soon give way to proactive, person-centered care which focuses on individuals' well-being. However, this transition will only be made possible through scientific innovation. Next-generation technologies will be the key to developing affordable and accessible care, while also lowering the costs of healthcare. A promising solution to this challenge is low-cost continuous health monitoring; this approach allows for effective screening, analysis, and diagnosis and facilitates proactive medical intervention. Urine has great promise for being a key resource for health monitoring; unlike blood, it can be collected effortlessly on a daily basis without pain or the need for special equipment. Unfortunately, the commercial rapid urine analysis tests that exist today can only go so far-this is where the promise of microfluidic devices lies. Microfluidic devices have a proven record of being effective analytical devices, capable of controlling the flow of fluid samples, containing reaction and detection zones, and displaying results, all within a compact footprint. Moving past traditional glass- and polymer-based microfluidics, paper-based microfluidic devices possess the same diagnostic ability, with the added benefits of facile manufacturing, low-cost implementation, and disposability. Hence, we review the recent progress in the application of paper-based microfluidics to urine analysis as a solution to providing continuous health monitoring for proactive care. First, we present important considerations for point-of-care diagnostic devices. We then discuss what urine is and how paper functions as the substrate for urine analysis. Next, we cover the current commercial rapid tests that exist and thereby demonstrate where paper-based microfluidic urine analysis devices may fit into the commercial market in the future. Afterward, we discuss various fabrication techniques that have been recently developed for paper-based microfluidic devices. Transitioning from fabrication to implementation, we present some of the clinically implemented urine assays and their importance in healthcare and clinical diagnosis, with a focus on paper-based microfluidic assays. We then conclude by providing an overview of select biomarker research tailored towards urine diagnostics. This review will demonstrate the applicability of paper-based assays for urine analysis and where they may fit into the commercial healthcare market.

A simple and highly sensitive spectroscopic fluorescence-detection system for multi-channel plastic-microchip electrophoresis based on side-entry laser-beam zigzag irradiation

A five-color fluorescence-detection system for eight-channel plastic-microchip electrophoresis was developed. In the eight channels (with effective electrophoretic lengths of 10 cm), single-stranded DNA fragments were separated (with single-base resolution up to 300 bases within 10 min), and seventeen-loci STR genotyping for forensic human identification was successfully demonstrated. In the system, a side-entry laser beam is passed through the eight channels (eight A channels), with alternately arrayed seven sacrificial channels (seven B channels), by a technique called "side-entry laser-beam zigzag irradiation." Laser-induced fluorescence from the eight A channels and Raman-scattered light from the seven B channels are then simultaneously, uniformly, and spectroscopically detected, in the direction perpendicular to the channel array plane, through a transmission grating and a CCD camera. The system is therefore simple and highly sensitive. Because the microchip is fabricated by plastic-injection molding, it is inexpensive and disposable and thus suitable for actual use in various fields.

An automated and portable microfluidic chemiluminescence immunoassay for quantitative detection of biomarkers

Microfluidic platforms capable of automated, rapid, sensitive, and quantitative detection of biomarkers from patient samples could make a major impact on clinical or point-of-care (POC) diagnosis. In this work, we realize an automated diagnostic platform composed of two main components: (1) a disposable, self-contained, and integrated microfluidic chip and (2) a portable instrument that carries out completely automated operations. To demonstrate its potential for real-world application, we use injection molding for mass fabrication of the main components of disposable microfluidic chips. The assembled three-layered chip with on-chip mechanical valves for fluid control consists of (1) a top silicone fluidic layer with embedded zigzag microchannels, reagent reservoirs and a negative pressure port, (2) a middle tinfoil layer with patterned antibody/antigen stripes, and (3) a bottom silicone substrate layer with waste reservoirs. The versatility of the microfluidics-based system is demonstrated by implementation of a chemiluminescence immunoassay for quantitative detection of C-reactive protein (CRP) and testosterone in real clinical samples. This lab-on-a-chip platform with features of quantitation, portability and automation provides a promising strategy for POC diagnosis.

Magnetic separation of clenbuterol based on competitive immunoassay and evaluation by surface-enhanced Raman spectroscopy

The elimination of β-agonist has attracted considerable interest due to its harmfulness to human health when it existed in pork.

Rapid, automated, parallel quantitative immunoassays using highly integrated microfluidics and AlphaLISA

Immunoassays represent one of the most popular analytical methods for detection and quantification of biomolecules. However, conventional immunoassays such as ELISA and flow cytometry, even though providing high sensitivity and specificity and multiplexing capability, can be labor-intensive and prone to human error, making them unsuitable for standardized clinical diagnoses. Using a commercialized no-wash, homogeneous immunoassay technology ('AlphaLISA') in conjunction with integrated microfluidics, herein we developed a microfluidic immunoassay chip capable of rapid, automated, parallel immunoassays of microliter quantities of samples. Operation of the microfluidic immunoassay chip entailed rapid mixing and conjugation of AlphaLISA components with target analytes before quantitative imaging for analyte detections in up to eight samples simultaneously. Aspects such as fluid handling and operation, surface passivation, imaging uniformity, and detection sensitivity of the microfluidic immunoassay chip using AlphaLISA were investigated. The microfluidic immunoassay chip could detect one target analyte simultaneously for up to eight samples in 45 min with a limit of detection down to 10 pg mL(-1). The microfluidic immunoassay chip was further utilized for functional immunophenotyping to examine cytokine secretion from human immune cells stimulated ex vivo. Together, the microfluidic immunoassay chip provides a promising high-throughput, high-content platform for rapid, automated, parallel quantitative immunosensing applications.

Development of a low-volume, highly sensitive microimmunoassay using computational fluid dynamics-driven multiobjective optimization

Immunoassays are one of the most versatile and widely performed biochemical assays and, given their selectivity and specificity, are used in both clinical and research settings. However, the high cost of reagents and relatively large sample volumes constrain the integration of immunoassays into many applications. Scaling the assay down within microfluidic devices can alleviate issues associated with reagent and sample consumption. However, in many cases a new device is designed and empirically optimized for each specific analyte, a costly and time consuming approach. In this paper, we report the development of a microfluidic bead-based immunoassay which, using antibody coated microbeads, can potentially detect any analyte or combination of analytes for which antibody coated microbeads can be generated. We also developed a computational reaction model and optimization algorithm that can be used to optimize the device for any analyte. We applied this technique to develop a low volume IL-6 immunoassay with high sensitivity (358 fM, 10 pg/mL) and a large dynamic range (4 orders of magnitude). This device design and optimization technique can be used to design assays for any protein with an available antibody and can be used with a large number of applications including biomarker discovery, temporal in vitro studies using a reduced number of cells and reagents, and analysis of scarce biological samples in animal studies and clinical research settings.

High-efficiency immunoassay platforms with controllable surface roughness and oriented antibody immobilization

High-efficiency immunoassay platforms were facilely prepared by combining a layer-by-layer particle deposition with site-specific antibody immobilization through boronic acid moieties.

A single-step enzyme immunoassay capillary sensor composed of functional multilayer coatings for the diagnosis of marker proteins

A single-step, easy-to-use enzyme immunoassay capillary sensor, composed of substrate-immobilized hydrophobic coating, hydrogel coating, and soluble coating containing an enzyme-labeled antibody, was developed.

Various on-chip sensors with microfluidics for biological applications

In this paper, we review recent advances in on-chip sensors integrated with microfluidics for biological applications. Since the 1990s, much research has concentrated on developing a sensing system using optical phenomena such as surface plasmon resonance (SPR) and surface-enhanced Raman scattering (SERS) to improve the sensitivity of the device. The sensing performance can be significantly enhanced with the use of microfluidic chips to provide effective liquid manipulation and greater flexibility. We describe an optical image sensor with a simpler platform for better performance over a larger field of view (FOV) and greater depth of field (DOF). As a new trend, we review consumer electronics such as smart phones, tablets, Google glasses, etc. which are being incorporated in point-of-care (POC) testing systems. In addition, we discuss in detail the current optical sensing system integrated with a microfluidic chip.

Fabrication and multifunction integration of microfluidic chips by femtosecond laser direct writing

In the pursuit of modern microfluidic chips with multifunction integration, micronanofabrication techniques play an increasingly important role. Despite the fact that conventional fabrication approaches such as lithography, imprinting and soft lithography have been widely used for the preparation of microfluidic chips, it is still challenging to achieve complex microfluidic chips with multifunction integration. Therefore, novel micronanofabrication approaches that could be used to achieve this end are highly desired. As a powerful 3D processing tool, femtosecond laser fabrication shows great potential to endow general microfluidic chips with multifunctional units. In this review, we briefly introduce the fundamental principles of femtosecond laser micronanofabrication. With the help of laser techniques, both the preparation and functionalization of advanced microfluidic chips are summarized. Finally, the current challenges and future perspective of this dynamic field are discussed based on our own opinion.

An ELISA Lab-on-a-Chip (ELISA-LOC)

Laminated object manufacturing (LOM) technology using polymer sheets is an easy and affordable method for rapid prototyping of Lab-on-a-Chip (LOC) systems. It has recently been used to fabricate a miniature 96 sample ELISA lab-on-a-chip (ELISA-LOC) by integrating the washing step directly into an ELISA plate. LOM has been shown to be capable of creating complex 3D microfluidics through the assembly of a stack of polymer sheets with features generated by laser micromachining and by bonding the sheets together with adhesive. A six layer ELISA-LOC was fabricated with an acrylic (poly(methyl methacrylate) (PMMA)) core and five polycarbonate layers micromachined by a CO(2) laser with simple microfluidic features including a miniature 96-well sample plate. Immunological assays can be carried out in several configurations (1 × 96 wells, 2 × 48 wells, or 4 × 24 wells). The system includes three main functional elements: (1) a reagent loading fluidics module, (2) an assay and detection wells plate, and (3) a reagent removal fluidics module. The ELISA-LOC system combines several biosensing elements: (1) carbon nanotube (CNT) technology to enhance primary antibody immobilization, (2) sensitive ECL (electrochemiluminescence) detection, and (3) a charge-coupled device (CCD) detector for measuring the light signal generated by ECL. Using a sandwich ELISA assay, the system detected Staphylococcal enterotoxin B (SEB) at concentrations as low as 0.1 ng/ml, a detection level similar to that reported for conventional ELISA. ELISA-LOC can be operated by a syringe and does not require power for operation. This simple point-of-care (POC) system is useful for carrying out various immunological assays and other complex medical assays without the laboratory required for conventional ELISA, and therefore may be more useful for global healthcare delivery.

High-throughput immunoassay through in-channel microfluidic patterning

We have developed an integrated microfluidic immunoassay chip for high-throughput sandwich immunoassay tests. The chip creates an array of reactive patterns through mechanical protection by actuating monolithically embedded button valves. We have demonstrated that this chip can achieve highly sensitive immunoassay tests within an hour, and requires only microliter samples.

Microfluidic chemical analysis systems

The field of microfluidics has exploded in the past decade, particularly in the area of chemical and biochemical analysis systems. Borrowing technology from the solid-state electronics industry and the production of microprocessor chips, researchers working with glass, silicon, and polymer substrates have fabricated macroscale laboratory components in miniaturized formats. These devices pump nanoliter volumes of liquid through micrometer-scale channels and perform complex chemical reactions and separations. The detection of reaction products is typically done fluorescently with off-chip optical components, and the analysis time from start to finish can be significantly shorter than that of conventional techniques. In this review we describe these microfluidic analysis systems, from the original continuous flow systems relying on electroosmotic pumping for liquid motion to the large diversity of microarray chips currently in use to the newer droplet-based devices and segmented flow systems. Although not currently widespread, microfluidic systems have the potential to become ubiquitous.

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.

Integrated microfluidic bioprocessor for solid phase capture immunoassays

A microfluidic device for solid-phase immunoassays based on microparticle labeling is developed using microvalve-control structures for automated sample processing. Programmable microvalve control in a multilayer structure provides automated sample delivery, adjustable hydrodynamic washing and compatibility with a wide range of substrates. Capture antibodies are derivatized on glass surfaces within the processor using an APTES patterning method, and magnetic microspheres conjugated with a secondary detection antibody are used as labels in a capture-sandwich format. In this microfluidic processor, washing force can be precisely controlled to remove the nonspecifically bound microparticles. Automated microfluidic immunoassays are demonstrated for mouse immunoglobulin (IgG) and human prostate specific antigen (PSA) with limits of detection of 1.8 and 3 pM, respectively. The sample processor architecture is easily parallelized for high-throughput analysis and easily interfaced with various assay substrates.

An automated point-of-care system for immunodetection of staphylococcal enterotoxin B

An automated point-of-care (POC) immunodetection system for immunological detection of staphylococcal enterotoxin B (SEB) was designed, fabricated, and tested. The system combines several elements: (i) enzyme-linked immunosorbent assay-lab-on-a-chip (ELISA-LOC) with fluidics, (ii) a charge-coupled device (CCD) camera detector, (iii) pumps and valves for fluid delivery to the ELISA-LOC, (iv) a computer interface board, and (v) a computer for controlling the fluidics, logging, and data analysis of the CCD data. The ELISA-LOC integrates a simple microfluidic system into a miniature 96-well sample plate, allowing the user to carry out immunological assays without a laboratory. The analyte is measured in a sandwich ELISA assay format combined with a sensitive electrochemiluminescence (ECL) detection method. Using the POC system, SEB, a major foodborne toxin, was detected at concentrations as low as 0.1 ng/ml. This is similar to the reported sensitivity of conventional ELISA. The open platform with simple modular fluid delivery automation design described here is interchangeable between detection systems, and because of its versatility it can also be used to automate many other LOC systems, simplifying LOC development. This new POC system is useful for carrying out various immunological and other complex medical assays without a laboratory and can easily be adapted for high-throughput biological screening in remote and resource-poor areas.

Urine analysis in microfluidic devices

Microfluidics has attracted considerable attention since its early development in the 1980s and has experienced rapid growth in the past three decades due to advantages associated with miniaturization, integration and automation. Urine analysis is a common, fast and inexpensive clinical diagnostic tool in health care. In this article, we will be reviewing recent works starting from 2005 to the present for urine analysis using microfluidic devices or systems and to provide in-depth commentary about these techniques. Moreover, commercial strips that are often treated as chips and their readers for urine analysis will also be briefly discussed. We start with an introduction to the physiological significance of various components or measurement standards in urine analysis, followed by a brief introduction to enabling microfluidic technologies. Then, microfluidic devices or systems for sample pretreatments and for sensing urinary macromolecules, micromolecules, as well as multiplexed analysis are reviewed, in this sequence. Moreover, a microfluidic chip for urinary proteome profiling is also discussed, followed by a section discussing commercial products. Finally, the authors' perspectives on microfluidic-based urine analysis are provided. These advancements in microfluidic techniques for urine analysis may improve current routine clinical practices, particularly for point-of-care (POC) applications.

Heterogeneous immunoassays in microfluidic format using fluorescence detection with integrated amorphous silicon photodiodes

Miniaturization of immunoassays through microfluidic technology has the potential to decrease the time and the quantity of reactants required for analysis, together with the potential of achieving multiplexing and portability. A lab-on-chip system incorporating a thin-film amorphous silicon (a-Si:H) photodiode microfabricated on a glass substrate with a thin-film amorphous silicon-carbon alloy directly deposited above the photodiode and acting as a fluorescence filter is integrated with a polydimethylsiloxane-based microfluidic network for the direct detection of antibody-antigen molecular recognition reactions using fluorescence. The model immunoassay used consists of primary antibody adsorption to the microchannel walls followed by its recognition by a secondary antibody labeled with a fluorescent quantum-dot tag. The conditions for the flow-through analysis in the microfluidic format were defined and the total assay time was 30 min. Specific molecular recognition was quantitatively detected. The measurements made with the a-Si:H photodiode are consistent with that obtained with a fluorescence microscope and both show a linear dependence on the antibody concentration in the nanomolar-micromolar range.

Detection of immunoglobulins in a laser induced fluorescence system utilizing polydimethysiloxane microchips with advanced surface and optical properties

We developed an automated laser induced fluorescence system utilizing microfluidic chips for detection and quantification of immunoglobulins. Microchips were fabricated from polydimethysiloxane (PDMS) using the so-called "prepolymerization technique." The microchip structure helped minimize the effects of PDMS autofluorescence and light scattering. Furthermore, a thin and uniform PDMS layer forming the top of the microchip enabled proper focusing and collection of the excitation beam and the emitted fluorescence, respectively. The developed system was tested for the detection of mouse immunoglobulins. The capturing antibodies were immobilized on internal microchannel walls in the form of a polyelectrolyte. We clearly show that this immobilization technique, if correctly realized, gives results with high reproducibility. After sample incubation and washing, secondary antibodies labeled by fluorescein isothiocyanate were introduced into microchannels to build a detectable complex. We show that mouse antibodies can be quantified in a wide concentration range, 0.01-100 μg ml(-1). The lower detection limit was below 0.001 μg ml(-1) (6.7 pM). The developed laser induced fluorescence (LIF) apparatus is relatively cheap and easy to construct. The total cost of the developed LIF detector is lower than a typical price of plate readers. If compared to classical ELISA (enzyme linked immunosorbent assay) plate systems, the detection of immunoglobulins or other proteins in the developed PDMS microfluidic device brings other important benefits such as reduced time demands (10 min incubation) and low reagent consumption (less than 1 μl). The cost of the developed PDMS chips is comparable with the price of commercial ELISA plates. The main troubleshooting related to the apparatus development is also discussed in order to help potential constructors.

Thermoplastic microfluidic devices and their applications in protein and DNA analysis

Microfluidics is a platform technology that has been used for genomics, proteomics, chemical synthesis, environment monitoring, cellular studies, and other applications. The fabrication materials of microfluidic devices have traditionally included silicon and glass, but plastics have gained increasing attention in the past few years. We focus this review on thermoplastic microfluidic devices and their applications in protein and DNA analysis. We outline the device design and fabrication methods, followed by discussion on the strategies of surface treatment. We then concentrate on several significant advancements in applying thermoplastic microfluidic devices to protein separation, immunoassays, and DNA analysis. Comparison among numerous efforts, as well as the discussion on the challenges and innovation associated with detection, is presented.

Development of a microfluidic confocal fluorescence detection system for the hyphenation of nano-LC to on-line biochemical assays

One way to profile complex mixtures for receptor affinity is to couple liquid chromatography (LC) on-line to biochemical detection (BCD). A drawback of this hyphenated screening approach is the relatively high consumption of sample, receptor protein and (fluorescently labeled) tracer ligand. Here, we worked toward minimization of sample and reagent consumption, by coupling nano-LC on-line to a light-emitting diode (LED) based capillary confocal fluorescence detection system capable of on-line BCD with low-flow rates. In this fluorescence detection system, a capillary with an extended light path (bubble cell) was used as a detection cell in order to enhance sensitivity. The technology was applied to a fluorescent enhancement bioassay for the acetylcholine binding protein, a structural analog of the extracellular ligand-binding domain of neuronal nicotinic acetylcholine receptors. In the miniaturized setup, the sensitive and low void volume LED-induced confocal fluorescence detection system operated in flow injection analysis mode allowing the measurement of IC₅₀ values, which were comparable with those measured by a conventional plate reader bioassay. The current setup uses 50 nL as injection volume with a carrier flow rate of 400 nL/min. Finally, coupling of the detection system to gradient reversed-phase nano-LC allowed analysis of mixtures in order to identify the bioactive compounds present by injecting 10 nL of each mixture.

Adsorption of beta-adrenergic agonists used in sport doping on metal nanoparticles: a detection study based on surface-enhanced Raman scattering

The adsorption of beta(2)-adrenergic agonist (βAA) drugs clenbuterol, salbutamol, and terbutaline on metal surfaces has been investigated in this work by means of surface-enhanced Raman scattering (SERS). To assist in this investigation, a previous vibrational (IR and normal Raman) characterization of these drugs was performed, supported by ab initio density functional theory calculations. The application of SERS was aimed to apply this highly sensitive technique, based on localized surface plasmon resonance, in the detection of βAA at trace concentrations and as a possible alternative method which can be postulated in routine antidoping analysis. The adsorption of these drugs was studied in depth at different experimental conditions: on Au and Ag, at different pHs, and with varying adsorbate concentration. Moreover, plasmon resonance spectroscopy was employed to investigate the adsorption of these drugs on the metal nanoparticles as well as their aggregation. It was found that the adsorption of these molecules is more effective on gold nanoparticles and at acidic pH, based on the direct interaction of the aromatic or aliphatic moieties through ionic or coordination bonds with the metal. These drugs followed a Langmuir adsorption model from which the adsorption constant and the limit of detection can be determined.

ELISA-LOC: lab-on-a-chip for enzyme-linked immunodetection

A miniature 96 sample ELISA-lab-on-a-chip (ELISA-LOC) was designed, fabricated, and tested for immunological detection of Staphylococcal Enterotoxin B (SEB). The chip integrates a simple microfluidics system into a miniature ninety-six sample plate, allowing the user to carry out an immunological assay without a laboratory. Assay reagents are delivered into the assay plate without the need for separate devices commonly used in immunoassays. The ELISA-LOC was constructed using Laminated Object Manufacturing (LOM) technology to assemble six layers with an acrylic (poly(methyl methacrylate) (PMMA)) core and five polycarbonate layers micromachined by a CO(2) laser. The ELISA-LOC has three main functional elements: reagent loading fluidics, assay and detection wells, and reagent removal fluidics, a simple "surface tension" valve used to control the flow. To enhance assay sensitivity and to perform the assay without a lab, ELISA-LOC detection combines several biosensing elements: (1) carbon nanotube (CNT) technology to enhance primary antibody immobilization, (2) sensitive ECL (electrochemiluminescence) detection, and (3) a charge-coupled device (CCD) detector for measuring the light signal generated by ECL. Using a sandwich ELISA assay, the system detected SEB at concentrations as low as 0.1 ng ml(-1), which is similar to the reported sensitivity of conventional ELISA. The fluidics system can be operated by a syringe and does not require power for operation. This simple point-of-care (POC) system is useful for carrying out various immunological assays and other complex medical assays without a laboratory.

Integrated Multi-process Microfluidic Systems for Automating Analysis

Microfluidic technologies have been applied extensively in rapid sample analysis. Some current challenges for standard microfluidic systems are relatively high detection limits, and reduced resolving power and peak capacity compared to conventional approaches. The integration of multiple functions and components onto a single platform can overcome these separation and detection limitations of microfluidics. Multiplexed systems can greatly increase peak capacity in multidimensional separations and can increase sample throughput by analyzing many samples simultaneously. On-chip sample preparation, including labeling, preconcentration, cleanup and amplification, can all serve to speed up and automate processes in integrated microfluidic systems. This paper summarizes advances in integrated multi-process microfluidic systems for automated analysis, their benefits and areas for needed improvement.