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

On-line microdevice for stress proteomics

The handling of the cells or tissues is essential for proteomics research or drug screening, where labor is not avoidable. The steps of cell wash, protein extraction, protein denaturing are complicated procedures in conventional method using centrifugation and pipetting in the laboratory. This is the bottle-neck for proteome research. To solve these problems, we propose to utilize the nanotechnology, which will improve the proteomics methodology. Utilizing the nanotechnology, we developed a novel microseparation system, where centrifugation and pipetting are needless. This system has a nanostructured microdevice, by which the cell handling, protein extraction, and antibody assay can be performed. Since cell transfer is needless, all cells are corrected without any loss during the cell-pretreatment procedures, which allowed high reproducibility and enabled the detection of low amount of protein expression. Utilizing the microdevice, we analyzed the stress induced proteins. We further succeeded the screening of food that was useful for immunity and found that an extraction from seaweed promoted the apoptosis of T-lymphoblastic cells. Here, we present an on-line microdevice for stress proteomics.

An Electrokinetically-Controlled Immunoassay for Simultaneous Detection of Multiple Microbial Antigens

An electrokinetically-controlled heterogeneous immunoassay microchip for multiple analyte detection was developed in this study. Numerical simulation was employed to study the transport process in a microfluidic network (microFN). The operation parameters obtained from numerical simulation was then applied to immunoassay experiment. The effectiveness of the automatic electrokinetic control was demonstrated in a separate experiment using fluorescein dye. The immunoassay microchip was made of poly(dimethylsiloxane)(PDMS)/PDMS-coated glass using soft lithography and replica molding. Multi-antigen immobilization was accomplished by adsorbing the antigen molecules onto a PDMS-coated glass slide and by using a microFN. Immobilized lysate antigen of Escherichia coli O157: H7 at different concentrations was assayed and the lower detect limit was 3 microg/mL. The assay also displayed very good specificity, when different microbial lysate antigens were immobilized, including Escherichia coli and Helicobacter pylori, and the primary and secondary antibodies were mixtures of different species. The time required for the immunoassay, from antigen coating to signal detection, was only one hour. While still an un-optimized prototype, this automatic-operating, high-throughput immunoassay microchip shows a great potential in detecting multiple pathogenic infections efficiently for clinical applications.

A microfluidic SELEX prototype

Aptamers are nucleic acid binding species capable of recognizing a wide variety of targets ranging from small organic molecules to supramolecular structures, including organisms. They are isolated from combinatorial libraries of synthetic nucleic acid by an iterative process referred to as SELEX (Systematic Evolution of Ligands by Exponential Enrichment). Here we describe an automated microfluidic, microline-based assembly that uses LabView-controlled actuatable valves and a PCR machine, and which is capable of the selection and synthesis of an anti-lysozyme aptamer as verified by sequence analysis. The microfluidic prototype described is 1) a simple apparatus that is relatively inexpensive to assemble, making automated aptamer selection accessible to many investigators, and 2) useful for the continued "morphing" of macro-->meso-->microfabricated structures until a convergence to a few functional systems evolves and emerges, partly or completely achieving simpler, smaller and more rapid SELEX applications.

Disposable polydimethylsiloxane/silicon hybrid chips for protein detection

This paper presents disposable protein analysis chips with single- or four-chamber-constructed from poly(dimethylsiloxane) (PDMS) and silicon. The chips are composed of a multilayer stack of PDMS layers that sandwich a silicon microchip. This inner silicon chip features an etched array of micro-cavities hosting polymeric beads. The sample is introduced into the fluid network through the top PDMS layer, where it is directed to the bead chamber. After reaction of the analyte with the probe beads, the signal generated on the beads is captured with a CCD camera, digitally processed, and analyzed. An established bead-based fluorescent assay for C-reactive protein (CRP) was used here to characterize these hybrid chips. The detection limit of the single-chamber protein chip was found to be 1 ng/ml. Additionally, using a back pressure compensation method, the signals from each chamber of the four-chamber chip were found to fall within 10% of each other.

Immobilized microfluidic enzymatic reactors

The use of enzymes for cleavage, synthesis or chemical modification represents one of the most common processes used in biochemical and molecular biology laboratories. The continuing progress in medical research, genomics, proteomics, and related emerging biotechnology fields leads to exponential growth of the applications of enzymes and the development of modified or new enzymes with specific activities. Concurrently, new technologies are being developed to improve reaction rates and specificity or perform the reaction in a specific environment. Besides large-scale industrial applications, where typically a large processing capacity is required, there are other, much lower-scale applications, benefiting form the new developments in enzymology. One such technology is microfluidics with the potential to revolutionize analytical instrumentation for the analyses of very small sample amounts, single cells or even subcellular assemblies. This article aims at reviewing the current status of the development of the immobilized microfluidic enzymatic reactors (IMERs) technology.

Development of a Microchip-Based Bioassay System Using Cultured Cells

We developed a novel bioassay system using a glass microchip and cultured cells. A microchamber for cell culture and microchannels for reactions and detection were fabricated on a Pyrex glass substrate by photolithography and wet etching techniques. Cell culture, chemical and enzymatic reactions, and detection were integrated into the microchip. To keep different temperatures locally in three areas of the microchip, we designed and fabricated a temperature control device. Nitric oxide released from macrophage-like cells stimulated by lipopolysaccharide was successfully monitored with the microchip, the temperature control device, and a thermal lens microscope. The total assay time was reduced from 24 to 4 h, and detection limit of NO was improved from 1 x 10(-6) to 7 x 10(-8) M compared with conventional methods. Moreover, the system could monitor a time course of the release, which is difficult to measure by conventional batch methods. We conclude that this system is promising for a rapid bioassay system with very small consumption of cells.

Development of a Micro Total Analysis System Incorporating Chemiluminescence Detection and Application to Detection of Cancer Markers

We developed a micro total analysis system (mu-TAS) incorporating chemiluminescence detection, in which the chemiluminescence reaction of isoluminol isothiocyanato (ILITC) (as a chemiluminescence reagent for labeling)-microperoxidase (as a catalyst)-hydrogen peroxide (as an oxidant) was adopted. The analysis system performed the following three processes on a microchip: immune reaction for high selectivity, electrophoresis for formation and transportation of the sample plug, and chemiluminescence detection for high sensitivity. The three processes were compactly integrated onto the microchip to give the mu-TAS. The microchip contained two microchannels that crossed at an intersection, while the ends of the microchannels accessed four reservoirs. As the first process, the immune reaction was performed using an antibody-immobilized glass bead. The glass bead was placed in one of the reservoirs along with antigen (analyte) and a known amount of ILITC-labeled antigen to set up a competitive immune reaction. For electrophoresis, as the second process, the reactant after the immune reaction was fed electrophoretically into the intersection resulting in a sample plug. The sample plug was then moved into another reservoir containing hydrogen peroxide solution. At this point, chemiluminescence detection was performed as the third process: the labeled antigen mixed with the hydrogen peroxide and the catalyst included in the migration buffer to produce chemiluminescence. Chemiluminescence was detected by a photomultiplier tube located under the reservoir. The mu-TAS described here was capable of determining, with high selectivity and sensitivity, human serum albumin or immunosuppressive acidic protein as a cancer marker in human serum.

Prototype of immunochromatographic assay strips using colloidal CdTe nanocrystals as biological luminescent label

Colloidal semiconductor nanocrystals have attracted considerable attention as a novel biological luminescent label. The bioinorganic conjugates of luminescent CdTe nanocrystals and protein, including CdTe/BSA (bovine serum albumin) and CdTe/MAB (mouse monoclonal antibody against hepatitis B surface antigen), were formed via electrostatic/coordination self-assembly. Pure CdTe nanocrystals, CdTe/BSA and CdTe/MAB were used in the immunochromatographic assay experiments, respectively. And the results indicated that CdTe nanocrystals could be used and developed as a novel label with good stability, high sensitivity and facile determination of several analytes in immunochromatographic assay strips.

Solid supports for micro analytical systems

The development of micro analytical systems requires that fluids are able to interact with the surface of the microfluidic chip in order to perform analysis such as chromatography, solid phase extraction, and enzymatic digestion. These types of analyses are more efficient if there are solid supports within the microfluidic channels. In addition, solid supports within microfluidic chips are useful in producing devices with multiple functionalities. In recent years there have been many approaches introduced for incorporating solid supports within chips. This review will explore several state of the art methods and applications of introducing solid supports into chips. These include packing chips with beads, incorporating membranes into chips, creating supports using microfabrication, and fabricating gels and polymer monoliths within microfluidic channels.

Reagent-Loaded Cartridges for Valveless and Automated Fluid Delivery in Microfluidic Devices

An important problem in the life sciences and in health care is simple and rapid detection of biomarkers. Although microfluidic devices are potentially useful in addressing this problem, current techniques for automating fluid delivery--which include valves and electroosmosis--require sophisticated microfabrication of the chip, bulky instrumentation, or both. In this paper, we describe a simple and reliable technique for storing and delivering a sequence of reagents to a microfluidic device. The technique is low-cost, requires minimal user intervention, and can be performed in resource-poor settings (e.g., outside of a laboratory) in the absence of electricity and computer-controlled equipment. In this method, cartridges made of commercially available tubing are filled by sequentially injecting plugs of reagents separated by air spacers. The air spacers prevent the reagents from mixing with each other during cartridge preparation, storage, and usage. As an example, we used this "plug-in cartridge" technology to complete a solid-phase immunoassay in a microchannel in 2 min with low-nanomolar sensitivity and demonstrate the diagnosis of HIV in 13 min.

Immunosorbent assay microchip system for analysis of human immunoglobulin G on MagnaBind™ carboxyl derivatized beads

An immunosorbent assay system was integrated into a PMVS microchip. MagnaBind carboxyl derivatized beads were introduced into a microchannel, and then human immunoglobulin G (IgG) was bound to the bead surface in the microchannel of the chip. Immunoreaction was conducted in the microchannel for the bead-bounded antigen IgG with the antibody FITC-labelled IgG. On-chip detection was performed using a laser-induced fluorescence (LIF) system. The integration shortened the overall analysis time from 7 h to less than 40 min.

Electrochemical sensor for immunoassay of carcinoembryonic antigen based on thionine monolayer modified gold electrode

A sensor based on thionine monolayer modified gold electrode for determination of carcinoembryonic antigen (CEA) in human serum is proposed. The sensor is prepared by covalently binding thionine to a cysteamine self-assembled monolayer with p-phthaloyl chloride as a linkage, which gives a surface coverage of 8.97+/-3.28 x 10(-12)mol/cm(2) for thionine. The electrochemistry of the immobilized thionine displays a surface-controlled electrode process with an average electron transfer rate constant of 1.47+/-0.84 s(-1). Based on an electrochemical enzyme-linked immunoassay by using the immobilized thionine as an electron transfer mediator between the electrode and the horseradish peroxidase (HRP) labeled anti-CEA antibody, a calibration curve with two linear ranges from 0.6 to 17 and 17 to 200 ng/mL and a detection limit of 0.2 ng/mL for CEA determination is obtained in pH 4.2 PBS containing 2.0 mmol/L H(2)O(2) and 0.5 mol/L NaCl. The sensor shows a good accuracy. The precision and reproducibility are acceptable with the intra-assay CV of 4.9% and 5.9% at 10 and 100 ng/mL CEA concentrations, respectively, and the inter-assays CV of 7.8% at 100 ng/mL CEA. The response of thionine modified electrode shows only 1.6% decrease after 100 replicate measurements and the storage stability is acceptable in a pH 7.0 PBS at 4 degrees C for 1 week. The method avoids the addition of electron transfer mediator to the solution, thus is much simpler. The proposed method would be valuable for the diagnosis and monitoring of carcinoma and its metastasis.

Thermal Lens Micro Optical Systems

This paper describes two types of miniaturized thermal lens optical systems that use optical fibers, SELFOC microlenses and light sources. The first system consists of a compact diode pumped solid-state laser (532 nm) as an excitation light source, a laser diode (635 nm) as a probe light source, an acoustoptic modulator as an excitation light modulator, fiber-based and conventional optics, and a detection system that combines a pinhole, an interference filter, and a photodiode. The second system consists of two laser diodes as the excitation (658 nm) and probe (780 nm) light sources, fiber-based optics, and the same detection system as the first one. The performance of the two systems was evaluated by the limit of detection (LOD) using standard solutions of sunset yellow (SY) and nickel(II) phthalocyaninetetrasulfonic acid tetrasodium salt (NiP). The LODs of the first system for SY and second system for NiP were calculated to be 3.7 x 10(-8) (1.7 x 10(-6) AU) and 7.7 x 10(-9) M (3.4 x10(-6) AU), respectively. These results were consistent with the expected values obtained from photothermal parameters.

High-power blue/UV light-emitting diodes as excitation sources for sensitive detection

With advances in III-V nitride manufacturing processes, high-power light-emitting diode (LED) chips in the blue and UV wavelengths are now commercially available at reasonable cost and can be used as excitation sources in optical sensing. We describe the use of these high-power blue and UV LEDs for sensitive fluorescence detection, including chip-based flow cytometry, capillary electrophoresis (CE), and single-molecule imaging. By using a blue LED with a focusable power of approximately 40 mW as the excitation source for fluorescent beads, we demonstrate a simple chip-based bead sorter capable of enriching the concentration of green fluorescent beads from 63% to 95%. In CE experiments, we show that a mixture of analyte solution containing 30 nM 6-carboxyrhodamine 6G and 10 nM fluorescein can be separated and detected with excellent signal-to-noise ratio (approximately 17 for 10 nM fluorescein) using the collimated emission from a blue LED; the estimated mass detection limit was approximately 200 zmol for fluorescein. We also demonstrated ultrasensitive fluorescence imaging of single rhodamine 123 molecules and individual lambda-DNA molecules. At a small fraction of the cost of an Ar+ laser, high-power blue and UV LEDs are effective alternatives for lasers and arc lamps in fluorescence applications that demand portability, low cost, and convenience.

Photothermal spectrometry for detection in miniaturized systems: relevant features, strategies and recent applications

There is a growing interest in using miniaturized analytical devices because they allow to execute the different steps of an analytical process within very short times and with drastic reduction in the amounts of solvents, reagents and samples. As for capillary electrophoresis, these systems require detectors which are sensitive, versatile and adaptable to very small detection volumes. In this respect, photothermal spectrometry which is complementary to fluorescence seems to be a promising detection method. This review describes the basic principle of photothermal spectrometry along with the related methods based on colinear-beam or crossed-beam configuration of the pump and probe lasers. Two experimental set ups especially designed for microfluidic systems as well as for capillary electrophoresis are described. Their characteristics and key features are discussed and the main applications are outlined.

Pulsed-laser crossed-beam thermal lens spectrometry for detection in a microchannel: influence of the size of the excitation beam waist

Crossed-beam thermal lens spectrometry is especially designed for the detection of very small samples in capillary tubes and more generally in microfluidic devices. In this work, the effect of the size of the excitation beam with respect to the size of the sample microchannel has been investigated. Although the signal is inversely proportional to the size of the excitation waist into the sample, the use of large waists may provide greater sensitivities when short-pulse excitation lasers are used and allows easier optimization of the optical design. On the contrary, the use of small beam waists reduces the edge effects that can arise depending on the nature and thickness of the walls of the sample holder. Moreover, small beams provide better spatial resolution and have allowed the measurement of flow velocities as low as 1 mm s(-1).

Capillary electrophoresis-based immunoassay

Capillary electrophoresis-based immunoassay (CEIA) is a developing analytical technique with a number of advantages over conventional immunoassay, such as reduced sample consumption, simpler procedure, easy simultaneous determination of multiple analytes, and short analysis time. However, there are still a number of technical issues that researchers on CEIA have to solve before the assay can be more widely used. These issues include method to improve the concentration sensitivity of the assay, requirement for robust separation strategy for different analytes, and method to increase the throughput of the assay. The approaches to solve these issues are reviewed. Several studies have been devoted to develop general separation strategies for CEIA, and to enhance the sensitivity of detection. The recent development of microchip-based CEIA is encouraging and is likely to address more drawbacks of CEIA, particularly on the throughput issue.

Fabrication and characterization of a fritless microfabricated electroosmotic pump with reduced pH dependence

A fritless electroosmotic pump with reduced pH dependence has been fabricated on a glass microchip and its performance characterized. The chip design consists of two 500-microm channels, one packed with anion exchange beads and the other packed with cation exchange beads, which produce convergent electroosmotic flow streams. The electroosmotically pumped solution flows away from the intersection of the two pumping channels through a field-free channel. This simple design allows for the production of a fritless electroosmotic pump and easy replacement of the ion exchange beads whose charged surfaces generate the flow. The pump was found to produce volumetric flow rates of up to 2 microL/min for an applied voltage of 3 kV at a pH of 6.8. Moreover, the electroosmotic pump can generate high flow rates over an extended pH range of at least 2-12, a significant advantage over previously fabricated electroosmotic pumps, which typically have a more limited range in which they can achieve high flow rates.

On-chip electrochromatography using sol–gel immobilized stationary phase with UV absorbance detection

A chromatography column on a chip was fabricated by immobilizing reversed-phase stationary phase particles (5 microm, C4) using sol-gel technology. Channels were fabricated in quartz using photolithography and wet etching. Localization of the stationary phase was achieved by immobilizing the stationary phase at the desired location in the separation channel prior to bonding of the cover plate. Cross channel design was employed for gated injection. An optical fiber setup was developed for carrying out on-chip UV absorbance detection. The effective optical path length was theoretically determined for the trapezoidal shaped channel and the result was shown to match closely with the experimentally determined value. The effect of applied voltage on velocity was evaluated using thiourea as an unretained marker. Separation performance of the stationary phase was demonstrated by separation of three peptides (Trp-Ala, Leu-Trp and Trp-Trp) under isocratic chromatographic conditions.

Electrophoretic Concentration of Proteins at Laser-Patterned Nanoporous Membranes in Microchips

Laser-patterning of nanoporous membranes at the junction of a cross channel in a microchip is used to integrate protein concentration with an electrokinetic injection scheme. Upon application of voltage, linear electrophoretic concentration of charged proteins is achieved at the membrane surface because buffer ions can easily pass through the membrane while proteins larger than the molecular weight cutoff of the membrane (>5700) are retained. Simple buffer systems can be used, and the concentration results constitute outward evidence that the uniformity of buffer ion concentration is maintained throughout the process. Local and spatially averaged concentration are increased by 4 and 2 orders of magnitude, respectively, upon injection with moderate voltages (70-150 V) and concentration times (100 s). The degree of concentration is limited only by the solubility limit of the proteins. The porous polymer membrane can be used repeatedly as long as care is taken to avoid protein precipitation.

Self-Contained On-Chip Cell Culture and Pretreatment System

In this study, we describe a simple on-chip cell culture and pretreatment system that requires no external machines. Conventional cell culture utilizes culture dishes or microtiter plates, where pipetting and centrifugation are indispensable for washing cells and changing media. However, our microdevice requires no external centrifugation or pump. Utilizing this microdevice, we attained dramatically shorter total analytical time with a high-throughput screening system for proteomic analysis (1 min per 12 samples; one eightieth of the conventional time). Protein expression of Jurkat cells during stress-shock induced apoptosis was readily analyzed using this system. We found that a seaweed extraction effectively induced apoptosis of Jurkat cells.

Development of an Automated Sample Preparation Module for Environmental Monitoring of Biowarfare Agents

An automated sample preparation module, based upon sequential injection analysis (SIA), has been developed for use within an autonomous pathogen detection system. The SIA system interfaced aerosol sampling with multiplexed microsphere immunoassay-flow cytometric detection. Metering and sequestering of microspheres using SIA was found to be reproducible and reliable, over 24-h periods of autonomous operation. Four inbuilt immunoassay controls showed excellent immunoassay and system stability over five days of unattended continuous operation. Titration curves for two biological warfare agents, Bacillus anthracis and Yersinia pestis, obtained using the automated SIA procedure were shown to be similar to those generated using a manual microtiter plate procedure.

Drug Response Assay System in a Microchip Using Human Hepatoma Cells

A microchip-based cell response assay system to an anticancer agent was developed. The hepatoma cell line HepG2 was used to assess the effects of an anticancer agent, doxorubicin. The required cell number was reduced by two orders, and the observation of the time course of cell response became possible. The system clearly showed that treatment with higher doses of the drug or longer exposure times gave more effects to cells. The possibilities of novel drug response studies or toxicity assay system were demonstrated.

Fluorometric Determination of Sulfite and Nitrite in Aqueous Samples Using a Novel Detection Unit of a Microfluidic Device

On-chip fluorescence determination of sulfite and nitrite with N-(9-acridinyl)maleimide (NAM) and 2,3-diaminonaphthalene (DAN) has been developed using a novel fluorescence detection unit for microchip analysis. Usually, these fluorescence reagents are derivatized and detected separately in microchip analysis because different fluorescence wavelengths are emitted. The proposed fluorescence detection unit has optical fibers with no optical filter, and plural wavelengths of fluorescence were detected sensitively, even in the microchip. In this study, the simultaneous determination of sulfite and nitrite in environmental samples was performed with a polymer microchip analysis system. The calibration curves of sulfite and nitrite showed linear relations (R2 = 0.998 (sulfite) and R2 = 0.990 (nitrite)), and the relative standard deviations (RSD) for 4 runs were 2.1% (20 microM sulfite) and 1.3% (20 microM nitrite), respectively. The proposed method was applied to the recovery test of sulfite and nitrite in environmental samples.

Microfluidic enzyme immunosensors with immobilised protein A and G using chemiluminescence detection

Affinity proteins were covalently immobilised on silicon microchips with overall dimensions of 13.1 x 3.2 mm, comprising 42 porous flow channels of 235 microm depth and 25 microm width, and used to develop microfluidic immunosensors based on horseradish peroxidase (HRP), catalysing the chemiluminescent oxidation of luminol/p-iodophenol (PIP). Different hydrophilic polymers with long flexible chains (polyethylenimine (PEI), dextran (DEX), polyvinyl alcohol, aminodextran) and 3-aminopropyltriethoxysilane (APTS) were employed for modification of the silica surfaces followed by attachment of protein A or G. The resulting immunosensors were compared in an affinity capture assay format, where the competition between the labelled antigen and the analyte for antibody-binding sites took place in the bulk of the solution. The formed immunocomplexes were then trapped by the microchip affinity capture support and the amount of bound tracer was monitored by injection of luminol, PIP and H2O2. All immunosensors were capable of detecting atrazine at the sub-microg l(-1) level. The most sensitive assays were obtained with PEI and DEX polymer modified supports and immobilised protein G, with limits of detection of 0.006 and 0.010 microg l(-1), and IC50 values of 0.096 and 0.130 microg l(-1), respectively. The protein G based immunosensors were regenerated with 0.4 M glycine-HCl buffer pH 2.2, with no loss of activity observed for a storage and operating period of over 8 months. To estimate the applicability of the immunosensors to the analysis of real samples, PEI and DEX based protein G microchips were used to detect atrazine in surface water and fruit juice, spiked with known amounts of the atrazine, giving recovery values of 87-102 and 88-124% at atrazine fortification levels of 0.5-3 and 80-240 microg l(-1), respectively.

Functional microfabricated sample targets for matrix-assisted laser desorption/ionization mass spectrometry analysis of ribonucleic acids

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is a powerful analytical tool for the structural characterization of proteins and nucleic acids. However, many proteomics or genomics methodologies that employ MALDI-MS require external sample manipulation, which limits the overall throughput of analysis. We have focused on fabricating functional MALDI sample plates that would permit the on-probe characterization of nucleic acids. Here, we present results arising from the fabrication of functional sample plates composed of poly(methyl methacrylate) (PMMA). The PMMA sample plates were fabricated by a CNC milling technique. The key structural feature of our microfabricated samples plates is the presence of individual cylindrical posts (360 microm x 360 microm), which serve as individual sample targets within the overall PMMA-based MALDI sample plate. Functionality is added to these microposts via the covalent attachment of enzymes. As an example of the applicability of these microfabricated sample plates, enzymatic digestion of ribonucleic acids was performed on probe (i.e., on the micropost) with subsequent analysis by MALDI-MS. Advantages to such an approach include a reduction in sample handling (and concomitant sample losses) and a reduction in the amount of sample required for analysis due to the small surface area of the microposts.

Protein patterning on silicon-based surface using background hydrophobic thin film

A new and convenient protein patterning method on silicon-based surface was developed for protein array by spin coating of hydrophobic thin film (CYTOP). Photolithographic lift-off process was used to display two-dimensional patterns of spatially hydrophilic region. The background hydrophobic thin film was used to suppress nonspecific protein binding, and the hydrophilic target protein binding region was chemically modified to introduce aldehyde group after removal of the photoresist layer. The difference in surface energy between the hydrophilic pattern and background hydrophobic film would induce easier covalent binding of proteins onto defined hydrophilic areas having physical and chemical constraints. Below 1 microg/ml of total protein concentration, the CYTOP hydrophobic film effectively suppressed nonspecific binding of the protein. During the process of protein patterning, inherent property of the hydrophobic thin film was not changed judging from static and dynamic contact angle survey. Quantitative analysis of the protein binding was demonstrated by streptavidin-biotin system.

Immobilized particle arrays: coalescence of planar- and suspension-array technologies

Combining positive attributes of planar arrays and suspension arrays, immobilized particle arrays offer a new format in which immobilized submicrometer particles are arrayed on hydrogel-coated slides, providing 100+ assay replicates within each spot. This research describes how to prepare immobilized protein arrays and how to assay the binding of labeled target molecules to the arrayed capture probes. The assay system exhibits an intrinsic dynamic range of two to three decades, with coefficients of variation from 5 to 10%. For antibody-antigen binding, target capture appears to be reaction rate limited. For labeled antibody binding to antigen on the immobilized particles, the detection limit is approximately 0.5 ng/mL. When antibodies on the immobilized particles exhibit multivalent binding of target molecules, the detection limit is approximately 0.01 ng/mL. For protein arrays, potential advantages of this format are improved coating of the capture reagent, an increased number of options for protein presentation, reduced mass transport effects, and higher density multiplexing.

Microchip-based chemical and biochemical analysis systems

This review focuses on chemical and biochemical analysis systems using pressure-driven microfluidic devices or microchips. Liquid microspace in a microchip has several characteristic features, for example, short diffusion distances, high specific interfacial area and small heat capacity. These characteristics are the key to controlling micro unit operations and constructing new integrated chemical systems. By combining multiphase laminar flow and the micro unit operations, such as mixing, reaction, extraction and separation, continuous flow chemical processing systems are realized in the microchip format. By applying these concepts, several different analysis systems were successfully integrated on a microchip. In this paper, we introduce the microchip-based chemical systems for wet analysis of cobalt ion, multi-ion sensors, immunoassay, and cellular analysis.

Microchannel-assisted thermal-lens spectrometry for microchip analysis

Microchannel-assisted thermal lens spectrometry (MATLS) was developed for microchip analysis. This method utilized a photothermal effect in a very small space and rapid thermal conduction between a solid-liquid interface to produce a temperature gradient in the microchannel. In order to examine the mechanism experimentally, we constructed a detection system of laser defocus setup in which an excitation beam was not tightly focused, but it irradiated the microchannel homogeneously. The signal intensity dependence on modulation frequency of excitation and on solvent was investigated with the laser defocusing setup. The results of this investigation indicated that the mechanism of MATLS worked as expected. Since the mechanism of MATLS does not require directivity and coherence of the laser beam, other incoherent lightsources can be used as excitation light for sensitive detections. Finally, we considered some future applications utilizing the mechanism.