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At least 1,063 records · Page 59Linked to original sources
PubMed2005

Integrated microfluidic device for solid-phase extraction coupled to micellar electrokinetic chromatography separation.

An integrated microdevice was utilized for the autonomous coupling of solid-phase extraction (SPE) to micellar electrokinetic chromatography (MEKC). Porous plugs of polymethacrylate polymer approximately 200 microm in length) were fabricated by ultraviolet irradiation in microchannels. Microcolumns of hydrophobic beads packed against the polymethacrylate plugs were utilized for the quantitative extraction of rhodamine B, yielding preconcentration factors over 200 for a 90-s extraction. The calculated detection limit for this dye was 60 fM. A sample of coumarin dyes were concentrated by SPE, eluted in a nonaqueous solvent from a separate on-chip reservoir, and injected by a gated valve onto a separate column for MEKC analysis. Using the integrated device, a completely automated sequence of extraction, elution, injection, separation, and detection were performed in less than 5 min. Observed separation efficiencies were high, with plate heights below 2 microm. The analysis was at least 3 times faster than semiautomated, conventional, solid-phase extraction, while requiring no user intervention. The design, fabrication, and autonomous operation of the device is discussed.

Chromatography, Micellar Electrokinetic Capillary↗
PubMed2006

Analytical performance of polymer-based microfluidic devices fabricated by computer numerical controlled machining.

A study comparing the electrophoretic separation performance attainable from microchips molded by masters fabricated using conventional CNC machining techniques with commercial microchips, wire imprinted microchips, and microchips from LIGA molding devices is presented. An electrophoresis-based detection system using fluorescence microscopy was used to determine the analytical utility of these microchips. The separation performance of CNC microchips was comparable to commercially available microchips as well as those fabricated from LIGA masters. The important feature of the CNC machined masters is that they have rapid design-to-device times using routinely available machining tools. This low-cost prototyping approach provides a new entry point for researchers interested in thermoplastic microchips and can accelerate the development of polymer-based lab-on-a-chip devices.

Computer-Aided Design↗
PubMed2006

Monitoring and kinetics study of a single particle on a simple microfluidic chip.

A single-channel poly(dimethylsiloxane) microchip was developed for the desorption process monitoring and kinetics studies of a single particle. The microchannel consisting of a narrow section following a relatively wide part enabled particle introduction, transfer, and location. A microinfusion pump was employed to delivery eluting solution at a precise rate. Once the particle contacted with the eluting solution, the solute transferred from particle into eluting solution and would be detected by laser-induced fluorescence or a chemiluminescence detector. Desorption process of a single particle was sensitively monitored. Depending on the desorption curves obtained, kinetics studies were carried out. The sediment desorption process analyses of single resin particles and single active carbon particles were performed.

Carbon↗
PubMed2005

A low-threshold, high-efficiency microfluidic waveguide laser.

This communication describes a long (1 cm), laser-pumped, liquid core-liquid cladding (L2) waveguide laser. This device provides a simple, high intensity, tunable light source for microfludic applications. Using a core solution of 2 mM rhodamine 640 perchlorate, optically pumped by a frequency-doubled Nd:YAG laser, we found that the threshold for lasing was as low as 22 muJ (16-ns pulse length) and had a slope efficiency up to 20%. The output wavelength was tunable over a 20-nm range by changing the ratio of solvent components (dimethyl sulfoxide and methanol) in the liquid core.

Equipment Design↗
PubMed2006

Cellular immobilization within microfluidic microenvironments: dielectrophoresis with polyelectrolyte multilayers.

The development of biomimetic microenvironments will improve cell culture techniques by enabling in vitro cell cultures that mimic in vivo behavior; however, experimental control over attachment, cellular position, or intercellular distances within such microenvironments remains challenging. We report here the rapid and controllable immobilization of suspended mammalian cells within microfabricated environments using a combination of electronic (dielectrophoresis, DEP) and chemical (polyelectrolyte multilayers, PEMS) forces. While cellular position within the microsystem is rapidly patterned via intermittent DEP trapping, persistent adhesion after removal of electronic forces is enabled by surface treatment with PEMS that are amenable to cellular attachment. In contrast to DEP trapping alone, persistent adhesion enables the soluble microenvironment to be systematically varied, facilitating the use of soluble probes of cell state and enabling cellular characterization in response to various soluble stimuli.

Animals↗
PubMed2005

Analysis of the microfluid flow in an evaporating sessile droplet.

The axisymmetric time-dependent flow field in an evaporating sessile droplet whose contact line is pinned is studied numerically and using an analytical lubrication theory with a zero-shear-stress boundary condition on the free surface of the droplet at low capillary and Reynolds numbers. A finite element algorithm is developed to solve simultaneously the vapor concentration and flow field in the droplet under conditions of slow evaporation. The finite element solution confirms the accuracy of the lubrication solution, especially when terms of higher order in the droplet flatness ratio (the ratio of droplet height to radius, h/R) are included in the lubrication theory to account more accurately for the singular flow near the contact line.

Biopolymers↗
PubMed2004

A microfluidic device for electrofusion of biological vesicles.

This paper reports a microfabricated device with high aspect-ratio electrodes and low power consumption for the electrofusion of liposomes and cells. The applications may range from gene transfection or cell tracking to biophysical studies of membrane proteins. The device consists of 250 microm thick silicon electrodes bonded to a glass substrate and covered by a PDMS-coated glass slide. Liposomes were first aligned by AC voltage at 300 kHz and then fused with short DC pulses. The fusion yield can reach 75% and is globally better for liposome diameters larger than 10 microm. The encapsulation of microbeads inside liposomes has also been demonstrated and opens up the route towards fusion-based delivery of artificial microstructures into cells.

Cell Membrane↗
PubMed2004

Identification of endothelial proteins by MALDI-MS using a compact disc microfluidic system.

Vascular endothelial proteins have been analyzed using two-dimensional (2D) gel electrophoresis and subsequent mass spectrometry, with separate methods for the intervening sample preparations. Compact disc (CD) technology was found to be rapid, giving high overall yield both with ordinary Coomassie staining and with Sypro Ruby staining. Combined with automatic in-gel digestion, the CD technology has great capacity for large numbers of protein analysis, although for limited sample numbers, manual methods can give similar sequence coverage. In a test set of 48 samples, 45 proteins were identified using the CD preparation technique, 32 identified with higher sequence coverage using the CD technique, 7 with higher using ZipTips in a robotic workstation, and 5 with higher coverage using dried droplets of unpurified samples. In the process of these methodological comparisons, basic patterns for 116 endothelial proteins were defined, representing 297 separate protein spots on the 2D gels.

Compact Disks↗
PubMed2006

Control and detection of chemical reactions in microfluidic systems.

Recent years have seen considerable progress in the development of microfabricated systems for use in the chemical and biological sciences. Much development has been driven by a need to perform rapid measurements on small sample volumes. However, at a more primary level, interest in miniaturized analytical systems has been stimulated by the fact that physical processes can be more easily controlled and harnessed when instrumental dimensions are reduced to the micrometre scale. Such systems define new operational paradigms and provide predictions about how molecular synthesis might be revolutionized in the fields of high-throughput synthesis and chemical production.

Combinatorial Chemistry Techniques↗