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At least 865 records · Page 48Linked to original sources

PubMed2001

Porous polymer monoliths: simple and efficient mixers prepared by direct polymerization in the channels of microfluidic chips.

Porous monolithic polymers have been prepared by photoinitiated polymerization of mixtures consisting of 2-hydroxyethyl methacrylate, ethylene dimethacrylate, UV-sensitive free radical initiator and porogenic solvent within channels of specifically designed microfluidic chips and used as micromixers. Substituting azobisisobutyronitrile with 2,2-dimethoxy-2-phenylacetophenone considerably accelerated the kinetics of the polymerization. Mixtures of cyclohexanol and 1 -dodecanol and of hexane and methanol were used, respectively, to control the porous properties and therefore the mixing efficiency of the device. The performance of the monolithic mixers has been tested by pumping aqueous solutions of two fluorescent dyes at various flow rates and monitoring the point at which the boundary of both streams completely disappears. Best results were achieved with a monolithic mixer containing very large irregular pores.

Acetophenones↗

PubMed2001

Miniaturized multichannel electrospray ionization emitters on poly(dimethylsiloxane) microfluidic devices.

A multichannel electrospray ionization (ESI) emitter was fabricated as part of a poly(dimethylsiloxane) (PDMS) microfluidic device using a three-layer photoresist process which also produces a self-alignment system to make a bonding between the top and bottom PDMS parts. The prototype device (2 cm high x 5 cm wide x 5 cm long) had 16-channels (30 microm wide x 50 microm deep) with emitters of 1 mm length and 60 degrees point angle. The PDMS emitter tips enabled interfacing the device to ESI-mass spectrometry; a stable electrospray from the tips was performed with limits of detection under 1 microM for reference peptides (adrenocorticotropic hormone fragment 1-17, angiotensin I and III).

Adrenocorticotropic Hormone↗

PubMed2002

Liposomes as signal amplification reagents for bioassays in microfluidic channels.

Liposomes with encapsulated carboxyfluorescein were used in an affinity-based assay to provide signal amplification for small-volume fluorescence measurements. Microfluidic channels were fabricated by imprinting in a plastic substrate material, poly(ethylene terephthalate glycol) (PETG), using a silicon template imprinting tool. Streptavidin was linked to the surface through biotinylated-protein for effective immobilization with minimal nonspecific adsorption of the liposome reagent. Lipids derivatized with biotin were incorporated into the liposome membrane to make the liposomes reactive for affinity assays. Specific binding of the liposomes to microchannel walls, dependence of binding on incubation time, and nonspecific adsorption of the liposome reagent were evaluated. The results of a competitive assay employing liposomes in the microchannels are presented.

Electrophoresis, Capillary↗

PubMed2002

Polymer microfluidic chips for electrochemical and biochemical analyses.

Our recent developments concerning the fabrication of polymer microchips and their applications for biochemical analyses are reviewed. We first describe two methods of fabrication of polymer microfluidic chips, namely UV-laser photoablation and plasma etching that are well suited for the prototyping and mass fabrication of microchannel networks with integrated microelectrodes. These microanalytical systems can be coupled with various detection means including mass spectrometry, and their applications in capillary electrophoresis are presented here. We also present how UV laser photoablation can be used for the patterning of biomolecules on polymer surfaces for generating two-dimensional arrays of microspots to carry out affinity assays. Finally, the use of the microchips for the development of fast affinity and immunological assays with electrochemical detection is presented, demonstrating the potential of these polymer microchips for medical diagnostics and drug discovery.

Biochemical Phenomena↗

PubMed2002

Indirect fluorescence detection of simple sugars via high-pH electrophoresis in poly(dimethylsiloxane) microfluidic chips.

This article describes the successful electrophoretic separation of simple carbohydrates in a polymeric microfluidic chip. The device fabricated in poly(dimethylsiloxane) (PDMS) is found to be stable in high-pH solutions. This allows sugars to be separated electrophoretically at pH values at or above their pK(a) using indirect fluorescence detection. Signal-to-noise values greater than 10:1 were obtained using a mercury arc lamp excitation source and a fluorescein-containing mobile phase for the detection of sugars at concentrations as low as 5 mM. The results obtained compare favorably with published results for the same system using a traditional fused-silica capillary. Analysis of the data revealed a significant experimental sensitivity of the migration times measured in these PDMS devices, an aging effect that leads to considerable systematic drift over the course of a series of replicate measurements. These experiments highlighted the importance of the surface chemistry of PDMS, especially as it pertains to its ability to support stable electroosmotic flow within the separation device. Channel priming at high pH provides a necessary, but by itself insufficient, means by which this instability can be minimized.

Carbohydrates↗

PubMed2002

Performance of an in-plane detection cell with integrated waveguides for UV/Vis absorbance measurements on microfluidic separation devices.

A microfluidic device with integrated waveguides and a long path length detection cell for UV/Vis absorbance detection is presented. The 750 microm U-cell detection geometry was evaluated in terms of its optical performance as well as its influence on efficiency for electrophoretic separations in the microdevice. Stray light was found to have a strong effect on both, the sensitivity of the detection and the available linear range. The long path length U-cell showed a 9 times higher sensitivity when compared to a conventional capillary electrophoresis (CE) system with a 75 microm inner diameter (ID) capillary, and a 22 times higher sensitivity than with a 50 microm ID capillary. The linear range was comparable to that achieved in a 75 microm ID capillary and more than twice as large as in a 50 microm ID capillary. The use of the 750 microm U-cell did not contribute significantly to band broadening; however, a clear quantification was made difficult by the convolution of several other band broadening sources.

Absorption↗

PubMed2002

Poly(vinyl alcohol)-coated microfluidic devices for high-performance microchip electrophoresis.

The channels of microfluidic glass chips have been coated with poly(vinyl alcohol) (PVA). Applied for microchip electrophoresis, the coated devices exhibited a suppressed electroosmotic flow and improved separation performance. The superior performance of PVA-coated channels could be demonstrated by electrophoretic separations of labeled amines and by video microscopy. While a distorted sample zone is injected using uncoated channels the application of PVA-coated channels results in an improved shape of the sample zone with less band broadening. Applying PVA-coated microchips for the separation of amines labeled with Alexa Fluor 350 even sub-second separations, utilizing a separation length of only 650 microm, could be obtained, while this was not possible using uncoated devices. By using PVA-coated devices rather than an uncoated chip a threefold increase in separation efficiencies could be observed. As the electroosmotic flow (EOF) was suppressed, the anionic compounds were detected at the anode whereas the dominant EOF in uncoated devices resulted in an effective mobility to the cathode. Besides improved separation performance another important feature of the PVA-coated channels was the suppressed adsorption of fluorescent compounds in repetitive runs which results in an improved robustness and detection sensitivity. Applying PVA-coated channels, rinsing or etching steps could be omitted while this was necessary for a reliable operation of uncoated devices.

Amines↗

PubMed2002

Determination of monoclonal antibody production in cell culture using novel microfluidic and traditional assays.

This study compares microfluidic technology (Protein 200 LabChip Assay kit, Agilent 2100 Bioanalyzer, referred to here as Protein 200) to the traditional approach for protein analysis, one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), for the sizing and quantification of immunoglobulin G (IgG) in hybridoma cell cultures. Internal references differ between each method: purified IgG was used alone in SDS-PAGE while myosin (the upper marker) was added to each sample in Protein 200. The IgG used here were produced in cultures propagated in either a serum-free or a serum-containing medium. With serum-containing samples, there was a significant difference in the IgG concentrations (p < 0.05) between SDS-PAGE and Protein 200. The concentration determined by SDS-PAGE was significantly higher (> 30%) than by Protein 200 or by high-pressure liquid chromatography (HPLC) because the large amounts of serum albumin in the samples affect the accuracy of SDS-PAGE. Protein 200 can determine size similarly to SDS-PAGE in serum-free samples (standard error of the mean, SEM, < 1%, 95% confidence < +/-1%), unlike in serum-containing samples. The Protein 200 assay was more effective than the traditional one-dimensional SDS-PAGE in determining concentration and size of IgG in cell culture samples and it provided a miniaturized and convenient platform for rapid analysis.

Animals↗

PubMed2001

Stable sol-gel microstructured and microfluidic networks for protein patterning.

We demonstrate the formation of micropatterned sol-gel structures containing active proteins by patterning with polydimethylsiloxane (PDMS) microchannels. To transport sol solution efficiently into the hydrophobic PDMS microchannels, a hydrophilic-hydrophobic block copolymer was used to impart hydrophilicity to the PDMS microchannels. Poor adhesion of the micropatterned gel structure onto glass slides was improved by treating the glass surface with a polymeric substrate. To minimize cracks in the gel microstructure, hybrid matrices of interpenetrating organic and inorganic networks were prepared containing the reactive organic moieties polyvinylalcohol or polyvinylpyrrolidone. Retention of biochemical activity within the micropatterned gel was demonstrated by performing immunobinding assays with immobilized immunoglobulin G (IgG) antibody. The potential application of microfluidics technology to immobilized-enzyme biocatalysis was demonstrated using PDMS-patterned microchannels filled with trypsin-containing sol-gels. This work provides a foundation for the microfabrication of functional protein chips using sol-gel processes.

Catalysis↗

PubMed2005

In situ and online monitoring of hydrodynamic flow profiles in microfluidic channels based upon microelectrochemistry: concept, theory, and validation.

Herein, we propose a method for reconstructing any plausible macroscopic hydrodynamic flow profile occurring locally within a rectangular microfluidic channel. The method is based on experimental currents measured at single or double microband electrodes embedded in one channel wall. A perfectly adequate quasiconformal mapping of spatial coordinates introduced in our previous work [Electrochem. Commun. 2004, 6, 1123] and an exponentially expanding time grid, initially proposed [J. Electroanal. Chem. 2003, 557, 75] in conjunction with the solution of the corresponding variational problem approached by the Ritz method are used for the numerical reconstruction of flow profiles. Herein, the concept of the method is presented and developed theoretically and its validity is tested on the basis of the use of pseudoexperimental currents emulated by simulation of the diffusion-convection problem in a channel flow cell, to which a random Gaussian current noise is added. The flow profiles reconstructed by our method compare successfully with those introduced a priori into the simulations, even when these include significant distortions compared with either classical Poiseuille or electro-osmotic flows.

Journal Article↗

PubMed2006

In situ and online monitoring of hydrodynamic flow profiles in microfluidic channels based upon microelectrochemistry: optimization of electrode locations.

Herein, we extend our previous approach concerning the reconstruction of profiles of pressure-driven hydrodynamic flow in microfluidic channels based on current measurements at band electrode(s) [see the preceding paper ChemPhysChem 2005, 6, 1581]. We address the central issue of optimization of geometrical parameters describing the electrode(s) assembly (a single band and two bands working in generator-collector mode) within the channel flow cell to enhance the speed and precision of the flow profile reconstruction method.

Journal Article↗

PubMed2005

Multilayer poly(vinyl alcohol)-adsorbed coating on poly(dimethylsiloxane) microfluidic chips for biopolymer separation.

A poly(dimethylsiloxane) (PDMS) microfluidic chip surface was modified by multilayer-adsorbed and heat-immobilized poly(vinyl alcohol) (PVA) after oxygen plasma treatment. The reflection absorption infrared spectrum (RAIRS) showed that 88% hydrolyzed PVA adsorbed more strongly than 100% hydrolyzed one on the oxygen plasma-pretreated PDMS surface, and they all had little adsorption on original PDMS surface. Repeating the coating procedure three times was found to produce the most robust and effective coating. PVA coating converted the original PDMS surface from a hydrophobic one into a hydrophilic surface, and suppressed electroosmotic flow (EOF) in the range of pH 3-11. More than 1,000,000 plates/m and baseline resolution were obtained for separation of fluorescently labeled basic proteins (lysozyme, ribonuclease B). Fluorescently labeled acidic proteins (bovine serum albumin, beta-lactoglobulin) and fragments of dsDNA phiX174 RF/HaeIII were also separated satisfactorily in the three-layer 88% PVA-coated PDMS microchip. Good separation of basic proteins was obtained for about 70 consecutive runs.

DNA↗

PubMed2005

An integrated microfluidic device in polyester for electrophoretic analysis of amino acids.

A precolumn reaction chamber was integrated into a polyester microfluidic device with a miniaturized detection system. The reaction chamber was designed to be a zigzag channel, 70 microm in width, 8 mm in length, followed by a wider straight channel, 150 microm in width, 2 mm in length. The detection system is composed of an embedded light-emitting diode (LED), an integrated optical fiber, and a photomultiplier tube (PMT). A success in amino acid analysis using the integrated microchemical analysis device proved that the precolumn reaction chamber was compatible with the integrated detection system. Three kinds of amino acids, arginine, glycine, and phenylalanine, mixed and reacted with 7-fluoro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-F) in the precolumn reaction chamber to produce fluorescent products, were separated by micellar eletrokinetic chromatography (MEKC) and detected by LED-excited fluorescence. The detection limits for arginine, glycine, and phenylalanine were 1, 1, and 0.5 mM, respectively, which can be improved by further optimizations of the reaction system and detection system.

4-Chloro-7-nitrobenzofurazan↗

PubMed2005

Chip-based microfluidic devices coupled with electrospray ionization-mass spectrometry.

We present the current status of the development of microfluidic devices fabricated on different substrates for coupling with electrospray ionization-mass spectrometry (ESI-MS). Until now, much success has been gained in fabricating the ESI chips, which show better performances due to miniaturization when compared with traditional methods. Integration of multiple steps for sample preparation and ESI sample introduction, however, remains a great challenge. This review covers the main technical development of electrospray device that were published from 1997 to 2004. This article does not attempt to be exclusive. Instead, it focuses on the publications that illustrated the breath of the development and applications of microchip devices for MS-based analysis.

Electrophoresis, Microchip↗

PubMed2005

Development of a new hybrid technique for rapid speciation analysis by directly interfacing a microfluidic chip-based capillary electrophoresis system to atomic fluorescence spectrometry.

This paper represents the first study on direct interfacing of microfluidic chip-based capillary electrophoresis (chip-CE) to a sensitive and selective detector, atomic fluorescence spectrometry (AFS) for rapid speciation analysis. A volatile species generation technique was employed to convert the analytes from the chip-CE effluent into their respective volatile species. To facilitate the chip-CE effluent delivery and to provide the necessary medium for subsequent volatile species generation, diluted HCl solution was introduced on the chip as the makeup solution. The chip-CE-AFS interface was constructed on the basis of a concentric "tube-in-tube" design for introducing a KBH4 solution around the chip effluent as sheath flow and reductant for volatile species generation as well. The generated volatile species resulting from the reaction of the chip-CE effluent and the sheath flow were separated from the reaction mixture in a gas-liquid separator and swept into the AFS atomizer by an argon flow for AFS determination. Inorganic mercury (Hg(II)) and methylmercury (MeHg(I)) were chosen as the targets to demonstrate the performance of the present technique. Both mercury species were separated as their cysteine complexes within 64 s. The precision (relative standard deviation, RSD, n = 5) of migration time, peak area, and peak height for 2 mg.L(-1) Hg(II) and 4 mg.L(-1) MeHg(I) (as Hg) ranged from 0.7 to 0.9%, 2.1 to 2.9%, and 1.5 to 1.8%, respectively. The detection limit was 53 and 161 microg.L(-1) (as Hg) for Hg(II) and MeHg(I), respectively. The recoveries of the spikes of mercury species in four locally collected water samples ranged from 92 to 108%.

Electrophoresis, Microchip↗

PubMed2005

Static adsorptive coating of poly(methyl methacrylate) microfluidic chips for extended usage in DNA separations.

A simple and robust static adsorptive (dynamic) coating process using 2% hydroxyethylcellulose was developed for surface modification of poly(methyl methacrylate) (PMMA) microfluidic chips for DNA separations, suitable for usage over extended periods, involving hundreds of runs. The coating medium was also used as a sieving matrix for the DNA separations following the coating process. Four consecutive static treatments, by simply filling the PMMA chip channels with sieving matrix once every day, were required for obtaining a stable coating and optimum performance. The performance of the coated chips at different phases of the coating process was studied by consecutive gel electrophoretic separations with LIF detection using a PhiX-174/HaeIII DNA digest sample. The coated chip, with daily renewal of the sieving matrix, showed high stability in performance during a 25-day period of systematic study, involving more than 100 individual runs. The performance of the coated chip also remained almost the same after 3 months of continuous usage, during which over 200 separations were performed. The average precision of migration time for the 603-bp fragment was 1.31% RSD (n = 6) during the 25-day study, with a separation efficiency of 6.5 x 10(4) plates (effective separation length 5.4 cm).

Adsorption↗

PubMed2005

Detection of polymerase chain reaction fragments using a conducting polymer-modified screen-printed electrode in a microfluidic device.

A simple and fast method for electrochemical detection of amplified fragments by PCR was successfully developed using CE in a microfluidic device with a modified screen-printed carbon electrode (SPCE). The surfaces of the SPCE were modified with poly-5,2'-5',2''-terthiophene-3'-carboxylic acid, which improves the analysis performance by lowering the detection potential, enhancing the S/N characteristics, and avoiding electrode poisoning. DNA fragments amplified by PCR were separated within 210 s in a 75.5 mm-long coated-separation channel at a separation field strength of -200 V/cm. To minimize the sample adsorption into the inner surface of the capillary wall, which disturbs the separation, a dynamically coated capillary with an acrylamide solution was used. Furthermore, the analysis procedure was simplified and rendered reproducible by using 0.50% w/v hydroxyethylcellulose as a separation matrix in a coated channel. The reproducibility of the analysis employing the coated channel yielded RSD of 4.3% for the peak areas and 1.4% for the migration times in eight repetitive measurements at a modified electrode, compared with 21.3 and 9.4% for a bare electrode. The sensitivity of the assay was 18.74 pAs/(pg/microL) with a detection limit of 584.31 +/- 1.3 fg/microL.

Drug Stability↗

PubMed2006

Studying protein-drug interaction by microfluidic chip affinity capillary electrophoresis with indirect laser-induced fluorescence detection.

We developed a microfluidic chip-affinity CE method based on indirect LIF detection to study protein-drug interactions. The interaction between heparin and BSA was quantitatively studied, as a model system. In our method, sodium fluorescein was chosen as background, and redistilled water as marker to monitor EOF. The electrophoretic mobility changes of BSA were measured, with various concentrations of heparin added to the running buffer. Each run was completed within 80 s. The binding constant was determined to be (1.24 +/- 0.05) x 10(3) M(-1), which was in good agreement with that reported in the literature.

Electrophoresis, Microchip↗