Determination of carcinoembryonic antigen in human sera by integrated bead-bed immunoassay in a microchip for cancer diagnosis

Three-Dimensional Microfluidic Capillary Device for Rapid and Multiplexed Immunoassays in Whole Blood

In this study, we demonstrate whole blood immunoassays using a microfluidic device optimized for conducting rapid and multiplexed fluorescence-linked immunoassays. The device is capable of handling whole blood samples without any preparatory treatment. The three-dimensional channels in poly(methyl methacrylate) are designed to passively load bodily fluids and, due to their linearly tapered profile, facilitate size-dependent immobilization of biofunctionalized particles. The channel geometry is optimized to allow for the unimpeded flow of cellular constituents such as red blood cells (RBCs). Additionally, to make the device easier to operate, the biofunctionalized particles are pretrapped in a first step, and the channel is dried under vacuum, after which it can be loaded with the biological sample. This novel approach and design eliminated the need for traditionally laborious steps such as filtering, incubation, and washing steps, thereby substantially simplifying the immunoassay procedures. Moreover, by leveraging the shallow device dimensions, we show that sample loading to read-out is possible within 5 min. Our results also show that the presence of RBCs does not compromise the sensitivity of the assays when compared to those performed in a pure buffer solution. This highlights the practical adaptability of the device for simple and rapid whole-blood assays. Lastly, we demonstrate the device's multiplexing capability by pretrapping particles of different sizes, each functionalized with a different antigen, thus enabling the performance of multiplexed on-chip whole-blood immunoassays, showcasing the device's versatility and effectiveness toward low-cost, simple, and multiplexed sensing of biomarkers and pathogens directly in whole blood.

Inkjet Printing-Based Immobilization Method for a Single-Step and Homogeneous Competitive Immunoassay in Microchannel Arrays

In this study, we report an inkjet printing-based method for the immobilization of different reactive analytical reagents on a single microchannel for a single-step and homogeneous solution-based competitive immunoassay. The immunoassay microdevice is composed of a poly(dimethylsiloxane) microchannel that is patterned using inkjet printing by two types of reactive reagents as dissolvable spots, namely, antibody-immobilized graphene oxide and a fluorescently labeled antigen. Since nanoliter-sized droplets of the reagents could be accurately and position-selectively spotted on the microchannel, different reactive reagents were simultaneously immobilized onto the same microchannel, which was difficult to achieve in previously reported capillary-based single-step bioassay devices. In the present study, the positions of the reagent spots and amount of reagent matrix were investigated to demonstrate the stable and reproducible immobilization and a uniform dissolution. Finally, a preliminary application to a single-step immunoassay of C-reactive protein was demonstrated as a proof of concept.

DNA Microsystems for Biodiagnosis

Researchers are continuously making progress towards diagnosis and treatment of numerous diseases. However, there are still major issues that are presenting many challenges for current medical diagnosis. On the other hand, DNA nanotechnology has evolved significantly over the last three decades and is highly interdisciplinary. With many potential technologies derived from the field, it is natural to begin exploring and incorporating its knowledge to develop DNA microsystems for biodiagnosis in order to help address current obstacles, such as disease detection and drug resistance. Here, current challenges in disease detection are presented along with standard methods for diagnosis. Then, a brief overview of DNA nanotechnology is introduced along with its main attractive features for constructing biodiagnostic microsystems. Lastly, suggested DNA-based microsystems are discussed through proof-of-concept demonstrations with improvement strategies for standard diagnostic approaches.

Rapid multiplex microfiber-based immunoassay for anti-MERS-CoV antibody detection

On-site multiplex biosensors for innate immunity antibodies are ideal tools for monitoring health status of individuals against various diseases. This study introduces a novel antibody immunoassay testing platform incorporating microfiber-based arrays of antigens to capture specific antibodies. The fabrication and setup of the device revolved around electrospun polystyrene (ESPS) microfibers that act as three-dimensional membrane filters, capable of rapid and multifold analyte capture. In particular, the ESPS microfibers were patterned through localized oxygen plasma to create hydrophilic zones that facilitate fluid flows and immobilizations of antigens. The bulk of this robust antibody immunoassay platform could be installed into a compact syringe-driven cassette device, which could perform multiplex antibody immunoassay for antibodies specifically against Middle East respiratory syndrome coronavirus (MERS-CoV) with rapid preparation amounting to a total of 5 min, as well as high sensitivity and specificity for the MERS-CoV down to 200 μg/mL.

Ultrasensitive detection of disease biomarkers using an immuno-wall device with enzymatic amplification

We present an ultrasensitive immunoassay system for disease biomarkers utilizing the immuno-wall device and an enzymatic amplification reaction. The immuno-wall device consisted of 40 microchannels, each of which contained an antibody-modified wall-like structure along the longitudinal axis of the microchannel. The wall was fabricated with a water-soluble photopolymer containing streptavidin by photolithography, and biotinylated capture antibodies were immobilized on the sides through streptavidin-biotin interaction. For an assay, introducing the target biomarker and secondary and labeled antibodies produced a sandwich complex anchored on the sides of the wall. A conventional immuno-wall device uses a fluorescence-labeled antibody as a labeling antibody. To achieve an ultrasensitive detection of a trace biomarker, we used an enzyme label and amplified the signal with the enzymatic reaction with a fluorogenic substrate in the microchannel. The highest signal/background ratio was obtained by using alkaline phosphatase-labeled antibody and 9H-(1,3-dichloro-9,9-dimethylacridin-2-one-7-yl) phosphate. To evaluate the device performance, we detected human C-reactive protein (CRP) as a model biomarker. The detection limit (LOD) of CRP in phosphate-buffered saline was 2.5 pg mL^-1 with a sample volume of 0.25 μL. This LOD was approximately 3 orders of magnitude lower than that obtained with fluorescent-dye (DyLight 650)-labeled antibody. In addition, the present device provided a wide detection range of 0.0025-10 ng mL^-1 for CRP. We successfully developed an ultrasensitive immunoassay system with simple operation and only a small sample volume.

Enzyme-linked immunosorbent assay utilizing thin-layered microfluidics

An antibody-immobilized thin-layered glass microfluidic channel with a high surface-to-volume ratio was developed for rapid and sensitive enzyme-linked immunosorbent assay.

Bioorthogonal Reaction-Mediated ELISA Using Peroxide Test Strip as Signal Readout for Point-of-Care Testing

This work demonstrates a highly sensitive peroxide test strip (PTS)-based enzyme-linked immunosorbent assay (ELISA) for both qualitative and quantitative detection of drugs of abuse (morphine) and disease biomarkers (interleukin-6 and HIV-1 capsid antigen p24). This color-based PTS is a commercially available product with advantages of low cost, easy operation, and portability, and it is an ideal signal readout strategy in ELISA to simplify the immunoassay procedures and enable point-of-care testing (POCT). In addition, we introduce the bioorthogonal reaction that can effectively amplify the signal by controlling the cycles of bioorthogonal reaction to achieve the desirable sensitivity depending on different analytes. The limit of detection is 0.2 ng/mL for morphine, 3.98 pg/mL for interleukin-6, and 11.6 pg/mL for detection of HIV-capsid antigen (p24). This PTS-ELISA applies to both the qualitative and quantitative detection of IL-6 and p24 in clinical serum samples with good accuracy, which provides a promising tool for the POCT in clinical diagnosis.

Fabrication and Evaluation of Microfluidic Immunoassay Devices with Antibody-Immobilized Microbeads Retained in Porous Hydrogel Micropillars

Due to the inherent characteristics including confinement of molecular diffusion and high surface-to-volume ratio, microfluidic device-based immunoassay has great advantages in cost, speed, sensitivity, and so on, compared with conventional techniques such as microtiter plate-based ELISA, latex agglutination method, and lateral flow immunochromatography. In this paper, we explain the detection of C-reactive protein as a model antigen by using our microfluidic immunoassay device, so-called immuno-pillar device. We describe in detail how we fabricated and used the immuno-pillar devices.

Nanoslit-concentration-chip integrated microbead-based protein assay system for sensitive and quantitative detection

A nanoslit-integrated microfluidic chip is developed as a microbead-based assay platform for the sensitive and quantitative detection of protein.

Design, fabrication and test of a pneumatically controlled, renewable, microfluidic bead trapping device for sequential injection analysis applications

This paper describes the design, fabrication, and testing of a pneumatically controlled, renewable, microfluidic device for conducting bead-based assays in an automated sequential injection analysis system.

Development of an automated on-chip bead-based ELISA platform

We present a lab-on-a-chip and associated instrument for heterogeneous enzyme-linked immunosorbent assay (ELISA)-based detection of proteins from liquid samples. The system performs all necessary ELISA steps (starting from antigen incubation) in a quarter of the time required for corresponding plate-based protocols. We have previously described the instrument, which automates fluidic control via remote valve switching and detects fluorescence from reacted substrate, for use in a molecular diagnostics application. The ELISA chip reported here utilizes a high surface area bead bed to enhance capture efficiency and increase the dynamic range of the assay as compared to a standard plate-based ELISA. Its functionality is demonstrated using human IL-10 as a model antigen, but theoretically any sandwich ELISA could be ported onto this "open source platform." We show that our automated on-chip assays have greater sensitivities than the corresponding standard manual plate-based ELISAs, and that single samples can be assayed in a fraction of the time.

Simultaneous Detection of α-Fetoprotein and Carcinoembryonic Antigen Based on Si Nanowire Field-Effect Transistors

Primary hepatic carcinoma (PHC) is one of the most common malignancies worldwide, resulting in death within six to 20 months. The survival rate can be improved by effective treatments when diagnosed at an early stage. The α-fetoprotein (AFP) and carcinoembryonic antigen (CEA) have been identified as markers that are expressed at higher levels in PHC patients. In this study, we employed silicon nanowire field-effect transistors (SiNW-FETs) with polydimethylsiloxane (PDMS) microfluidic channels to simultaneously detect AFP and CEA in desalted human serum. Dual-channel PDMS was first utilized for the selective modification of AFP and CEA antibodies on SiNWs, while single-channel PDMS offers faster and more sensitive detection of AFP and CEA in serum. During the SiNW modification process, 0.1% BSA was utilized to minimize nonspecific protein binding from serum. The linear dynamic ranges for the AFP and CEA detection were measured to be 500 fg/mL to 50 ng/mL and 50 fg/mL to 10 ng/mL, respectively. Our work demonstrates the promising potential of fabricated SiNW-FETs as a direct detection kit for multiple tumor markers in serum; therefore, it provides a chance for early stage diagnose and, hence, more effective treatments for PHC patients.

An immune sandwich assay of carcinoembryonic antigen based on the joint use of upconversion phosphors and magnetic beads

A sensitive and selective new immunosensor for carcinoembryonic antigen (CEA) is constructed based on the joint use of upconversion phosphors (UCPs) and magnetic beads (MBs), which may find applications in clinical analysis.

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.

Aptamer-based microfluidic beads array sensor for simultaneous detection of multiple analytes employing multienzyme-linked nanoparticle amplification and quantum dots labels

This study reports the development of an aptamer-mediated microfluidic beads-based sensor for multiple analytes detection and quantification using multienzyme-linked nanoparticle amplification and quantum dots labels. Adenosine and cocaine were selected as the model analytes to validate the assay design based on strand displacement induced by target-aptamer complex. Microbeads functionalized with the aptamers and modified electron rich proteins were arrayed within a microfluidic channel and were connected with the horseradish peroxidases (HRP) and capture DNA probe derivative gold nanoparticles (AuNPs) via hybridization. The conformational transition of aptamer induced by target-aptamer complex contributes to the displacement of functionalized AuNPs and decreases the fluorescence signal of microbeads. In this approach, increased binding events of HRP on each nanosphere and enhanced mass transport capability inherent from microfluidics are integrated for enhancing the detection sensitivity of analytes. Based on the dual signal amplification strategy, the developed aptamer-based microfluidic bead array sensor could discriminate as low as 0.1 pM of adenosine and 0.5 pM cocaine, and showed a 500-fold increase in detection limit of adenosine compared to the off-chip test. The results proved the microfluidic-based method was a rapid and efficient system for aptamer-based targets assays (adenosine (0.1 pM) and cocaine (0.5 pM)), requiring only minimal (microliter) reagent use. This work demonstrated the successful application of aptamer-based microfluidic beads array sensor for detection of important molecules in biomedical fields.

A lipobead microarray assembled by particle entrapment in a microfluidic obstacle course and used for the display of cell membrane receptors

Platforms which can display cell membrane ligands and receptors as a microarray library of probes for screening against a target are essential tools in drug discovery, biomarker identification, and pathogen detection. Membrane receptors and ligands require their native bilayer environment to retain their selectivity and binding affinity, and this complicates displaying them in a microarray platform. In this study, a design is developed in which the probes are first incorporated in supported lipid bilayers formed around micron-sized particles (lipobeads), and the microbeads themselves are then arrayed on a surface by hydrodynamic capture in a microfluidic obstacle course of traps. The traps are "V" shaped open enclosures, which are arranged in a wide channel of a microfluidic device, and capture the lipobeads (slightly smaller than the channel height) as they are streamed through the course. Screening assays are undertaken directly in the device after assembly, by streaming a fluorescently labeled target through the device and detecting the bead fluorescence. Conditions are first established for which the supported bilayers on the bead surface remain intact during the capture and assay steps, using fluorescent tags in the bilayer to infer bilayer integrity. Numerical calculations of the hydrodynamic drag coefficient on the entrapped beads are presented in conjunction with the stability experiments to develop criteria for the bilayer stability as a function of the screening assay perfusion rate. Simulations of the flow streamlines are also presented to quantify the trapping efficiency of the obstacle course. Screening assays are illustrated, assaying fluorescently labeled NeutrAvidin with biotin, and labeled cholera toxin with its ganglioside binding ligand, GM1. Sequential capturing of sets of lipobeads (one at a time, and with each set bearing a different probe), followed by indexing the bead positions after each set is entrapped, allows for the construction of an indexed array of multiple probes without the need for particle encoding and is illustrated using the NeutrAvidin-biotin pair. Finally, the lipobead platform is used for quantitatively measuring the kinetic rate constants for the binding of a probe (biotin) to a target (NeutrAvidin).

Simultaneous immunoassay analysis of plasma IL-6 and TNF-α on a microchip

Sandwich enzyme-linked immunosorbant assay (ELISA) using a 96-well plate is frequently employed for clinical diagnosis, but is time-and sample-consuming. To overcome these drawbacks, we performed a sandwich ELISA on a microchip. The microchip was made of cyclic olefin copolymer with 4 straight microchannels. For the construction of the sandwich ELISA for interleukin-6 (IL-6) or tumor necrosis factor-α (TNF-α), we used a piezoelectric inkjet printing system for the deposition and fixation of the 1st anti-IL-6 antibody or 1st anti-TNF-α antibody on the surface of the each microchannel. After the infusion of 2 µl of sample to the microchannel and a 20 min incubation, 2 µl of biotinylated 2nd antibody for either antigen was infused and a 10 min incubation. Then 2 µl of avidin-horseradish peroxidase was infused; and after a 5 min incubation, the substrate for peroxidase was infused, and the luminescence intensity was measured. Calibration curves were obtained between the concentration and luminescence intensity over the range of 0 to 32 pg/ml (IL-6: R² = 0.9994, TNF-α: R² = 0.9977), and the detection limit for each protein was 0.28 pg/ml and 0.46 pg/ml, respectively. Blood IL-6 and TNF-α concentrations of 5 subjects estimated from the microchip data were compared with results obtained by the conventional method, good correlations were observed between the methods according to linear regression analysis (IL-6: R² = 0.9954, TNF-α: R² = 0.9928). The reproducibility of the presented assay for the determination of the blood IL-6 and TNF-α concentration was comparable to that obtained with the 96-well plate. Simultaneous detection of blood IL-6 and TNF-α was possible by the deposition and fixation of each 1st antibody on the surface of a separate microchannel. This assay enabled us to determine simultaneously blood IL-6 and TNF-α with accuracy, satisfactory sensitivity, time saving ability, and low consumption of sample and reagents, and will be applicable to clinic diagnosis.

Development of a microplate reader compatible microfluidic chip for ELISA

We report a novel microfluidic device use for sandwich enzyme-linked immunoassay assay (ELISA). The related procedures including the introduction of reagents, dilution and distribution of samples, as well as immobilization of enzyme can be readily carried out on a poly (dimethylsiloxane) (PDMS) chip. Particularly, this microfluidic chip comprising of two distinct parallel units, and has an identical dimension as a conventional microtiter plate, which offers access to the directly quantitative detection by the microplate reader. Gradient-concentration reacting solutions at six different concentrations level generated by the microfluidic channel network are simultaneously transported to 24 reaction chambers to form enzymatic products. Alkaline phosphatase (ALP), 4-methylumbelliferyl phosphate (4-MUP) and KH(2)PO(4) are used as enzyme-substrate-inhibitor model, to demonstrate the utility of the developed microchip-based enzyme inhibitor assay. Various conditions such as the surface treatment of chip channels, fluids velocities, substrate concentration, and buffer pH are investigated. The present microfluidic device for ELISA holds several advantages, for instance frugal usage of samples and reagents, less of operating time, favorably integrated configuration, ease of manipulation, and could be explored to a variety of high throughput drug screening.

Electrochemical immunoassay of carcinoembryonic antigen based on TiO2–graphene / thionine / gold nanoparticles composite

A novel multilayer film based on gold nanoparticles (AuNPs), thionine (Thi), and TiO2–graphene (TiO2–Gr) was exploited to develop a highly sensitive amperometric immunosensor for detecting carcinoembryonic antigen (CEA). Firstly, Nafion–TiO2–Gr homogeneous composite was dropped on the surface of a glassy carbon electrode (GCE). Then Thi was chemisorbed by the TiO2–Gr–Nafion composite. Furthermore, the negative ly charged AuNPs were chemisorbed onto Thi film through the electrostatic force with the amino groups of Thi. Cyclic voltammetry (CV) was employed to characterize the assembly process and the performance of the immunosensor. Because of the synergistic effect of the AuNPs, Thi, and the unique properties of TiO2–Gr, the obtained immunosensor exhibited a wide linear response to CEA in two ranges from 0.1 to 10.0 ng mL−1 and from 10.0 to 120.0 ng mL−1 with a relatively low detection limit of 0.01 ng mL−1 (S/N = 3), as well as good stability and repeatability.

Microfluidic bead-based enzymatic primer extension for single-nucleotide discrimination using quantum dots as labels

This study reports the development of an on-chip enzyme-mediated primer extension process based on a microfluidic device with microbeads array for single-nucleotide discrimination using quantum dots as labels. The functionalized microbeads were independently introduced into the arrayed chambers using the loading chip slab. A single channel was used to generate weir structures to confine the microbeads and make the beads array accessible by microfluidics. The applied allele-specific primer extension method employed a nucleotide-degrading enzyme (apyrase) to achieve specific single-nucleotide detection. Based on the apyrase-mediated allele-specific primer extension with quantum dots as labels, on-chip single-nucleotide discrimination was demonstrated with high discrimination specificity and sensitivity (0.5 pM, signal/noise > 3) using synthesized target DNA. The chip-based signal enhancement for single-nucleotide discrimination resulted in 200 times higher sensitivity than that of an off-chip test. This microfluidic device successfully achieved simultaneous detection of two disease-associated single-nucleotide polymorphism sites using polymerase chain reaction products as target. This apyrase-mediated microfluidic primer extension approach combines the rapid binding kinetics of homogeneous assays of suspended microbeads array, the liquid handling capability of microfluidics, and the fluorescence detection sensitivity of quantum dots to provide a platform for single-base analysis with small reagent consumption, short assay time, and parallel detection.

Assessment of chemokine profiles in human skin biopsies by an immunoaffinity capillary electrophoresis chip

Atopic dermatitis is a skin condition resulting in a skin rash from exposure to environmental factors. Skin biopsies taken from patients suffering from atopic dermatitis were micro-dissected and analyzed using a microchip-based immunoaffinity CE system for the presence of CXCL1, CXCL5 and CXCL8 and CCL1, CCL3 and CCL5 chemokines. Disposable immunoaffinity disks with immobilized antibodies were used to capture the CXC and CC chemokines from the homogenized skin samples. The captured analytes were then labeled with AlexaFluor 633, eluted from the disk and separated by CE. The labeled chemokines were identified and quantified by laser induced fluorescence. The total analysis time was less than 40min, including the biopsy microdissection, pre-analysis preparation of the sample and the ICE-CHIP analysis, which took less than 10min with inter- and intra-assay CV's below 6.4%. Microchip-based immunoaffinity CE could distinguish between normal skin biopsies and those with inflammation. Patients with neutrophil cellular infiltrates by histopathology showed increased concentrations of CXCL1, CXCL5 and CXCL8 while increases of CCL1, CCL3 and CCL5 corresponded to the patient group demonstrating monocytic and T-lymphocyte infiltration by histopathology. This system demonstrates the ability to identify and quantify immunochemical analytes in frozen sections taken from clinical histopathology samples.

Point-of-care oral-based diagnostics

Many of the target molecules that reside in blood are also present in oral fluids, albeit at lower concentrations. Oral fluids are, however, relatively easy and safe to collect without the need for specialized equipment and training. Thus, oral fluids provide convenient samples for medical diagnostics. Recent advances in lab-on-a-chip technologies have made minute, fully integrated diagnostic systems practical for an assortment of point-of-care tests. Such systems can perform either immunoassays or molecular diagnostics outside centralized laboratories within time periods ranging from minutes to an hour. The article briefly reviews recent advances in devices for point-of-care testing with a focus on work that has been carried out by the authors as part of a NIH program.