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At least 235 records · Page 13Linked to original sources
PubMed2005

A capillary electrophoresis chip with hydrodynamic sample injection for measurements from a continuous sample flow.

A microchip-based capillary electrophoresis device supported by a microfluidic network made of poly(dimethylsiloxane), used for measuring target analytes from a continuous sample flow, is presented. The microsystem was fabricated by means of replica molding in combination with standard microfabrication technologies, resulting in microfluidic components and an electrochemical detector. A new hydrodynamic sample injection procedure is introduced, and the maximum number of consecutive measurements that can be made with a poly(dimethylsiloxane) capillary electrophoresis chip with amperometric detection is investigated with respect to reproducibility. The device features a high degree of functional integration, so the benefits associated with miniaturized analysis systems apply to it.

Biosensing Techniques↗
PubMed2004

Direct electrochemical detection of glucose in human plasma on capillary electrophoresis microchips.

We developed an electrochemical detector on a hybrid chip for the determination of glucose in human plasma. The microchip system described in this paper consists of a poly(dimethylsiloxane) (PDMS) layer containing separation and injection channels and an electrode plate. The copper microelectrode is fabricated by selective electroless deposition. The fabrication of the decoupler is performed by platinum electrochemical deposition on the metal film formed by electroless deposition. Factors influencing the performance, including detection potential, separation field strength, and buffer concentration, were studied. The electrodes exhibited good stability and durability in the analytical procedures. Under optimized detection conditions, glucose responded linearly from 10 microM to 1 mM. Finally, glucose in human plasma from three healthy individuals and two diabetics was successfully determined, giving a good prospect for a new clinical diagnostic instrument.

Blood Glucose↗
PubMed2002

Sampling BIAS at channel junctions in gated flow injection on chips.

The commonly used gated injection scheme was examined and found to suffer from multiple levels of electrokinetic sampling bias, including a new type based on transradial electrokinetic selection (TREKS). TREKS occurs as analytes of differing electrophoretic mobilities migrate around the corner at a channel junction in a microchip. The overall sample bias in gated injection was shown to be time-dependent and resulted in a larger sample bias against components of negative electrophoretic mobility. A new injection procedure for microchip devices based on interstream diffusion at zero potential is proposed. Diffusion of molecules into the separation channel is the main driving force for this type of injection. The new scheme is shown to be useful for injection of complex samples with multiply charged components, such as peptide mixtures. This procedure allows sampling of volumes from 12 to 45 pL, reproducible retention times (RSD < 1.5%), and reproducible peak areas (RSD < 2.3%).

Electrophoresis↗
PubMed2005

Development of a microfabricated disposable microchip with a capillary electrophoresis and integrated three-electrode electrochemical detection.

We have developed microsystems with a capillary electrophoresis and an electrochemical detector. The microfabricated CE-ECD systems are adequate for a disposable type and the characteristics are optimized for application in electrochemical detection. The system was realized by means of a polydimethylsiloxane (PDMS)-glass chip and an indium tin oxide electrode. The injection and separation channels were produced by relatively simple and inexpensive methods. A capillary electrophoresis and a three-electrode electrochemical detector were fabricated on the same substrate with the same fabrication procedure. We measured electropherograms for the testing analytes consisting of catechol and dopamine with different concentrations of 1mM and 0.1mM, respectively. The results showed an efficient and rapid separation and detection of all compounds within a very short time of around 80s using a separate electric field 60 V/cm. We could also successfully achieve an electropherogram of the separation of the 1 kb DNA ladder (8.4 ng/mul) from the 500 bp to 10 kb DNA fragments within just 150 s.

Catechols↗
PubMed2004

Microchip capillary electrophoresis with amperometric detection for rapid separation and detection of phenolic acids.

A microchip capillary-electrophoresis protocol for rapid and effective measurements of food-related phenolic acids (including chlorogenic, gentisic, ferulic, and vanillic acids) is described. Relevant parameters of the chip separation and amperometric detection are examined and optimized. Under optimum conditions, the analytes could be separated and detected in a 15 mM borate buffer (pH 9.5, with 10% of methanol) within 300 s using a separation voltage of 2000 V and a detection voltage of +1.0 V. Linear calibration plots are observed for micromolar concentrations of the phenolic acid compounds. The negligible sample volumes used in the microchip procedure obviates surface fouling common to amperometric measurements of phenolic compounds. The new microchip protocol offers great promise for a wide range of food applications requiring fast measurements and negligible sample consumption. An application on a commercial red wine was performed with minimal sample preparation and promising results.

Buffers↗
PubMed2005

Microchip capillary electrophoresis with amperometric detection for rapid separation and detection of seleno amino acids.

This article describes an effective microchip capillary-electrophoresis protocol for rapid and effective measurements of food-related seleno amino acids, including Se-methionine (Se-Met), Se-ethionine (Se-Eth), Se-methyl cysteine (Se-Cys), utilizing o-phtaldialdeyde/2-mercaptoethanol (OPA/2-ME) derivatization. Relevant parameters of the chip separation and amperometric detection are examined and optimized using a response surface methodology (RSM). Under optimum conditions, the analytes could be separated and detected in a 30 mM borate buffer (pH 9.3, with 28 mM sodium dodecul sulfate) within 300 s using a separation voltage of 2000V and a detection voltage of +0.9 V. Linear calibration plots are observed for micromolar concentrations of the Se-amino acid compounds. The negligible sample volumes used in the microchip procedure obviates surface fouling common to amperometric measurements of selenoamino-acid compounds. The new microchip protocol offers great promise for a wide range of food applications requiring fast measurements and negligible sample consumption.

Amino Acids↗
PubMed2006

Experimental and numerical investigation into leakage effect in injectors of microfluidic devices.

This paper performs an experimental and numerical investigation into low-leakage injectors designed for electrophoresis microchips. The principal material transport mechanisms of electrokinetic migration, fluid flow, and diffusion are considered in developing a mathematical model of the electrophoresis process. Low-leakage injectors designed with injection channels orientated at various included angles are designed and tested. The numerical and experimental results indicate that the injector with a 30 degrees included angle successfully minimizes sample leakage and has an exciting potential for use in high-quality, high-throughput chemical analysis procedures and in many other applications in the field of micro-total analysis systems.

Computer Simulation↗
PubMed2005

Capillary electrochromatography using polyelectrolyte multilayer coatings.

This review covers recent progress in polyelectrolyte multilayer (PEM) coatings applied to analytical separations using open-tubular capillary electrochromatography (OT-CEC). The simple preparation procedure involved in the PEM approach has provided some attractive features over other modes of capillary electrophoresis-based separations including packed column capillary electrochromatography (PC-CEC) and micellar electrokinetic chromatography (MEKC). PEM coatings have been used to alleviate the adsorption of basic analytes, to improve separations, and to improve the stability of the electroosmotic flow. Fundamental aspects of PEM coatings on surfaces and analytical separation platforms are briefly outlined in this review. In addition, applications of PEM coatings to fused-silica capillaries or microchip separation devices for the separation of small achiral or chiral analytes, as well as large biomolecules, are discussed.

Journal Article↗
PubMed2003

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.

Antigen-Antibody Reactions↗
PubMed1998

Use of capillary electrophoresis methods to characterize the pharmacokinetics of antisense drugs.

As antisense drugs become mature for clinical trials, analytical techniques to analyze antisense DNA in biological media for characterization of their pharmacokinetics will be in demand. Due to the superior resolving power of capillary gel electrophoresis (CGE), CGE will likely be a preferred method in quantifying intact oligonucleotides as well as the putative metabolic products. Nonetheless, biological mediums can influence the stability of the gel column, making a CGE assay time-consuming. In one approach, high-performance liquid chromatography (HPLC) was used to quantify the total amount of antisense compounds to increase the sample throughput and CGE was used to determine the relative percentage of the intact and metabolic species on specific samples. Alternatively, extensive sample pretreatment procedures were performed and the samples were quantified and characterized directly by CGE alone with the use of an internal standard. Both methods have been used to characterize the pharmacokinetics of antisense compounds. This review focuses on the instrumental and technical aspects of analyzing antisense DNA in biological mediums using CGE either as a single or a combined method towards better understanding of the pharmacokinetics of antisense DNA. Moreover, the newer analytical technologies of capillary electrophoresis (CE), which hold great potential to be used for pharmacokinetic applications, such as the replenishable sieving matrix combined with an innovative coupling approach and microchip CE, will also be explored.

Animals↗
PubMed2003

Fabrication of integrated microelectrodes for electrochemical detection on electrophoresis microchip by electroless deposition and micromolding in capillary technique.

A new method for the fabrication of an integrated microelectrode for electrochemical detection (ECD) on an electrophoresis microchip is described. The pattern of the microelectrode was directly made on the surface of a microscope slide through an electroless deposition procedure. The surface of the slide was first selectively coated with a thin layer of sodium silicate through a micromolding in capillary technique provided by a poly(dimethylsiloxane) (PDMS) microchannel; this left a rough patterned area for the anchoring of catalytic particles. A metal layer was deposited on the pattern guided by these catalytic particles and was used as the working electrode. Factors influencing the fabrication procedure were discussed. The whole chip was built by reversibly sealing the slide to another PDMS layer with electrophoresis microchannels at room temperature. This approach eliminates the need of clean room facilities and expensive apparatus such as for vacuum deposition or sputtering and makes it possible to produce patterned electrodes suitable for ECD on microchip under ordinary chemistry laboratory conditions. Also once the micropattern is ready, it allows the researchers to rebuild the electrode in a short period of time when an electrode failure occurs. Copper and gold microelectrodes were fabricated by this technique. Glucose, dopamine, and catechol as model analytes were tested.

Journal Article↗
PubMed2003

Gel and polymer-solution mediated separation of biopolymers by capillary electrophoresis.

In the age of genomics and proteomics, high-resolution separation techniques are routinely utilized in an integrated and automated fashion to solve formidable separation problems and provide the means for large-scale analysis of biological samples with excellent resolution. By automating the current manual procedures, capillary gel (CGE) and polymer-solution mediated electrophoresis greatly enhance the productivity of biopolymer analysis while also reducing both analysis time and the human intervention necessary from sample loading to data processing. The advent of this novel and high-performance bioseparation technique has made it possible to sequence the human genome and revealed global changes in the genome and proteome level, bringing about a revolutionary transition in our views of living systems on the molecular basis. CGE and polymer-solution mediated electrophoresis and related microseparation methods (e.g., electrophoresis microchips) are quickly becoming important separation and characterization tools in analytical biochemistry and molecular biology. This review gives an overview of the key application areas of DNA, protein, and complex carbohydrate analysis, and summarizes the latest developments on CGE column technology, including capillary coatings and sieving polymer matrices. Micropreparative aspects and related microseparation techniques are also discussed.

Biopolymers↗
PubMed2000

Voltammetry on microfluidic chip platforms

Microfluidic chip devices are shown to be attractive platforms for performing microscale voltammetric analysis and for integrating voltammetric procedures with on-chip chemical reactions and fluid manipulations. Linear-sweep, square-wave, and adsorptive-stripping voltammograms are recorded while electrokinetically "pumping" the sample through the microchannels. The adaptation of voltammetric techniques to microfluidic chip operation requires an assessment of the effect of relevant experimental variables, particularly the high voltage used for driving the electroosmotic flow, upon the background current, potential window, and size or potential of the voltammetric signal. The exact potential window of the chip detector is dependent upon the driving voltage. Manipulation of the electroosmotic flow opens the door to hydrodynamic modulation (stopped-flow) and reversed-flow operations. The modulated analyte velocity permits compensation of the microchip voltammetric background. Reversal of the driving voltage polarity offers extended residence times in the detector compartment. Rapid square-wave voltammetry/flow injection operation allows a detection limit of 2 x 10(-12) mol (i.e., 2 pmol) of 2,4,6-trinitrotoluene (TNT) in connection with 47 nL of injected sample. The ability of integrating chemical reactions with voltammetric detection is demonstrated for adsorptive stripping measurements of trace nickel using the nickel-dimethylglyoxime model system. The voltammetric response is characterized using catechol, hydrazine, TNT, and nickel as test species. The ability to perform on-chip voltammertic protocols in advantageous over nanovial voltammetric operations that lack a liquid-handling capability. Coupling the versatility of microfluidic chips with the rich information content of voltammetry thus opens an array of future opportunities.

Journal Article↗
PubMed2004

A simple mechanism for reliable particle sorting in a microdevice with combined electroosmotic and pressure-driven flow.

Selective transport and sorting of particles in microfluidic devices by electroosmosis is complicated due to superposition of uncontrolled hydrodynamic pressure contributions on the electroosmotic force. In this paper, we present a microfluidic concept for the reliable and simple separation and sorting of particles in a microchip by electroosmosis combined with pressure-driven flow. The presented device allows fluid quantities to be switched and particles to be sorted within a channel manifold using only a single power supply with fixed voltage and an electric switch. Consequently, chip operation and fluid switching procedure are greatly simplified compared to a situation, in which several independent power sources are used for flow balancing, as is the common procedure. With the triple-T channel design presented, backpressure flow disturbing the electrokinetic fluid and particle separation process is eliminated by introducing controlled opposed hydrodynamic flow of buffer from side channels. This pressure-driven flow is generated on-chip by setting up differences in the reservoir pressures in a defined manner. A detailed flow analysis based on the equivalence of fluid flow and electric current is performed and the conditions for reliable chip function are worked out.

Cell Separation↗
PubMed2006

Capillary electrophoresis using copolymers of different composition as physical coatings: a comparative study.

In this work, a comparative study on the use of different polymers as physically adsorbed coatings for CE is presented. It is demonstrated that the use of ad hoc synthesized polymers as coatings allows tailoring the EOF in CE increasing the flexibility of this analytical technique. Namely, different polymers were synthesized at our laboratory using different percentages of ethylpyrrolidine methacrylate (EpyM) and N,N-dimethylacrylamide (DMA). Thus, by modifying the percentage of EpyM and DMA monomers it is possible to manipulate the positive charge of the copolymer, varying the global electrical charge on the capillary wall and with that the EOF. These coated capillaries are obtained by simply flushing a given EpyM-DMA aqueous solution into bare silica capillaries. It is shown that by using these coated capillaries at adequate pHs, faster or more resolved CE separations can be achieved depending on the requirements of each analysis. Moreover, it is demonstrated that these coated capillaries reduce the electrostatic adsorption of basic proteins onto the capillary wall. Furthermore, EpyM-DMA coatings allow the reproducible chiral separation of enantiomers through the partial filling technique (PFT). The EpyM-DMA coated capillaries are demonstrated to provide reproducible EOF values independently of the pH and polymer composition with%RSD values lower than 2% for the same day. It is also demonstrated that the coating procedure is reproducible between capillaries. The compatibility of this coating protocol with CE in microchips is discussed.

Acrylamides↗
PubMed2005

Development of monolithic enzymatic reactors in glass microchips for the quantitative determination of enzyme substrates using the example of glucose determination via immobilized glucose oxidase.

A one-step procedure for the immobilization of glucose oxidase in fused-silica capillaries and in glass microchips was developed based on enzyme entrapment in a polyacrylamide-based monolithic column. The inner capillary surface was silanized with gamma-methacryloxypropyltrimethoxysilane (gamma-MAPS) to allow covalent binding of the gel to the surface. The composition of the polymer was optimized to prevent the formation of bubbles, allow liquid transportation by electroosmotic flow and to maintain the enzymatic activity. These requirements resulted in the addition of polyethylene glycol and poly(acrylic acid) to the acrylamide mixture. The gel containing the enzyme was formed in situ in the capillaries, respectively, in one channel of the microchip. In the microchip, it was limited to the sample injection channel by accordingly controlled silanization of the inner capillary surface. Glucose was detected via the amperometric determination of hydrogen peroxide. A linear correlation between signals and glucose concentration was observed from 0.05 to 1.1 mM glucose with a correlation coefficient of 0.999. The enzymatic monolithic microreactor showed no loss of activity during 8 h of continuous use and during storage in the running buffer at 4 degrees C for about 2 months. Interferents, such as ascorbic acid, were separated from the analyte electrophoretically, so that glucose could be quantified in diluted juices.

Acrylamides↗
PubMed2006

Deposition of PEG onto PMMA microchannel surface to minimize nonspecific adsorption.

A protein-resistant surface has been constructed on the poly(methyl methacrylate) (PMMA) microfluidic chips based on a one-step modification. The copolymer of butyl methacrylate (BMA) and poly(ethylene glycol) methyl ether methacrylate (PEGMA) is synthesized to introduce a dense PEG molecular brush-like coating on the PMMA microchannel surfaces via the anchoring effect of the hydrophobic BMA units. The PEGMA segments could produce hydrophilic domains formed on the interface so as to achieve stable electroosmotic flow, and less nonspecific adsorption toward biomolecules. The modification procedure and the properties of the poly(BMA-co-PEGMA)-coated surface have been characterized by FT-IR spectroscopy, confocal fluorescence microscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. The water contact angle and electroosmotic flow of PEG-modified PMMA microchip are measured to be 36 degrees and 5.4 x 10(-4) cm(2) V(-1) s(-1), while those of 73 degrees and 1.9 x 10(-4) cm(2) V(-1) s(-1) for native one, respectively. The PEG-modified microchip has been applied for the electrophoresis separation of proteins, corresponding to the theoretical efficiencies about 16 300 and 412 300 plates m(-1). In the interest of achieving efficient separation while minimizing biofoulings from the serum and plasma, the fabrication of PEG-coated microfluidic chips would provide a biocompatible platform for complex biological analysis.

Adsorption↗
PubMed2006

Patterning microbeads inside poly(dimethylsiloxane) microfluidic channels and its application for immobilized microfluidic enzyme reactors.

We propose a convenient and reliable approach for immobilizing microbeads on poly(dimethylsiloxane) (PDMS) microchips. It is built upon a simple fabrication procedure of PDMS chip through directly printing the master with an office laser printer which was described in our previous work (J. Chromatogr. A 2005, 1089, 270-275). On the printed toners used as the positive relief of the master, microbeads were immobilized by a thermal treatment and then transferred to the surface of the microchip by direct molding of the prepolymer on the master. With this approach, the region-selective immobilization of microbeads and the fabrication of PDMS microchips can be accomplished at the same time. Then, using these microbeads as supports, further modification with enzyme was achieved. Surface characteristics of the microbeads-modified PDMS microchannels were investigated with scanning electron microscope, atomic force microscope, and inverse fluorescence microscope. The electrokinetic properties of the native PDMS and the modified PDMS chips were also compared. Based on this approach, an immobilized glucose oxidase (GOD) reactor was constructed and the reaction using glucose as substrate was studied. All these experiments aim to show that the proposed approach may have a good potential in the study of biochemistry and other related areas.

Catalysis↗