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At least 1,657 records · Page 92Linked to original sources
PubMed2000

The "chip" as a specific genetic tool.

DNA microarrays are powerful tools for the analysis of the organization and regulation of the brain, in both illness and health. Such messenger RNA expression methods are outgrowths of a marriage between the several genome sequencing projects and a wide variety of physical, chemical, optical, and electronic systems. The advantages of microarray analyses include the ability to study the regulation of several genes or even the entire genome in a single experiment. However, there are substantive issues associated with the use of these tools that need to be considered before drawing conclusions about the genomic regulation of the brain. These issues include the loss of most anatomic (i.e., cellular and circuit) specificity, only fair sensitivity, lack of absolute quantitative data, poor comparability between studies, and high variability in sample values, to mention the most obvious. In this review we point to some of the solutions proposed for these problems and novel techniques and approaches for newer methods. Among these are methods for making arrays more sensitive, including nonarray messenger RNA expression systems. The future of this field and its links to deeper protein and cell biology are both emphasized.

Clinical Laboratory Techniques↗
PubMed2001

Bilayer reconstitution of voltage-dependent ion channels using a microfabricated silicon chip.

Painted bilayers containing reconstituted ion channels serve as a well defined model system for electrophysiological investigations of channel structure and function. Horizontally oriented bilayers with easy solution access to both sides were obtained by painting a phospholipid:decane mixture across a cylindrical pore etched into a 200-microm thick silicon wafer. Silanization of the SiO(2) layer produced a hydrophobic surface that promoted the adhesion of the lipid mixture. Standard lithographic techniques and anisotropic deep-reactive ion etching were used to create pores with diameters from 50 to 200 microm. The cylindrical structure of the pore in the partition and the surface treatment resulted in stable bilayers. These were used to reconstitute Maxi K channels in the 100- and 200-microm diameter pores. The electrophysiological characteristics of bilayers suspended in microchips were comparable with that of other bilayer preparations. The horizontal orientation and good voltage clamping properties make the microchip bilayer method an excellent system to study the electrical properties of reconstituted membrane proteins simultaneously with optical probes.

Alkanes↗
PubMed2003

Detection of achondroplasia G380R mutation from PCR amplicons by using inosine modified carbon electrodes based on electrochemical DNA chip technology.

The detection of Achondroplasia G380R mutation from real samples was performed by monitoring the oxidation signal of guanine. Inosine-substituted 12-mer capture probes related to the homozygous or heterozygous alleles of Achondroplasia G380R mutation were adsorbed onto carbon paste electrode (CPE) surface. No guanine signal was obtained from the capture probes, since the inosine bases were electroinactive. Then, these probes were hybridized with the denatured PCR samples on the CPE surface. The hybridization between the probe and target sequences was determined by using the oxidation signal of guanine in connection with differential pulse voltammetry (DPV). The oxidation signal of guanine was observed as a result of the specific hybridization between the probe and PCR sample. The changes in the peak height of the guanine signal provided the information whether the PCR sample contained heterozygous allele or homozygous allele. Numerous factors affecting the hybridization and nonspecific binding events were optimized to detect down to 41.24 fmol/ml target DNA. The electrochemical detection of Achondroplasia G380R mutation from PCR samples greatly shortened and simplified the diagnosis for the homozygous mutant type, which is lethal for the newborn.

Achondroplasia↗
PubMed2000

Chips ahoy!

Explore the source record for details and available documents.

Human Genome Project↗
PubMed2001

Rapid chiral on-chip separation with simplified amperometric detection.

The enantiomers of adrenaline, noradrenaline, ephedrine and pseudoephedrine were separated by capillary electrophoresis on a micromachined device. Detection was carried out with a new two-electrode amperometric detector, eliminating the need for individual counter and reference electrodes. Separation of the isomers was achieved by employing carboxymethyl-beta-cyclodextrin as chiral selector in the buffer, partly with the additional inclusion of the crown ether 18-crown-6. Plate numbers of up to 20,000, chiral resolutions of 2.5 and detection limits of the order of 10(-7) M were achieved. All separations were completed in less then 3 min.

Electrochemistry↗
PubMed2002

Capillary electrochromatography of peptides on microfabricated poly(dimethylsiloxane) chips modified by cerium(IV)-catalyzed polymerization.

Vinylsulfonic acid, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid (AMPS), 4-styrenesulfonic acid, and stearyl methacrylate were used for successful modification of the surface of poly(dimethylsiloxane) (PDMS) by cerium(IV) catalyzed polymerization on microfabricated collocated monolith support structures microchips. Reproducible and stable coatings were obtained allowing highly efficient separations of a peptide mixture with RSD for retention times below 2.6%. AMPS-coated PDMS channels were shown to give a reproducible separation of a synthetic peptide mixture for over a month. Subsequent modification of microchip channels by AMPS and methoxydimethyloctadecylsilane allowed selective separation of complex bovine serum albumin digest with high reproducibility, and efficiency of about 620,000 plates/m.

Catalysis↗
PubMed2001

Flow-through sampling for electrophoresis-based microfluidic chips using hydrodynamic pumping.

This work presents a novel electrophoretic microchip design which is capable of directly coupling with flow-through analyzers for uninterrupted sampling. In this device, a 3 mm wide sampling channel (SC) was etched on quartz substrate to create the sample inlet and outlet and the 75 microm wide electrophoretic channels were also fabricated on the same substrate. Pressure was used to drive the sample flow through the external tube into the SC and the flow was then split into outlet and electrophoretic channels. A gating voltage was applied to the electrophoretic channel to control the sample loading for subsequent separations and inhibit the sample leakage. The minimum gating voltage required to inhibit the sample leakage depended on the solution buffer and increased with the hydrodynamic flow-rate. A fluorescent dye mixture containing Rhodamine B and Cy3 was introduced into the sample stream at either a continuous or discrete mode via an on-line injection valve and then separated and detected on the microchip using laser-induced fluorescence. For both modes, the relative standard deviation of migration time and peak intensity for consecutive injections was determined to be below 0.6 and 8%, respectively. Because the SC was kept floating, the external sampling equipment requires no electric connection. Therefore, such an electrophoresis-based microchip can be directly coupled with any pressure-driven flow analyzers without hardware modifications. To our best knowledge, this is something currently impossible for reported electrophoretic microchip designs.

Electrophoresis↗
PubMed2003

Diffusion coefficient measurement in a microfluidic analyzer using dual-beam microscale-refractive index gradient detection. Application to on-chip molecular size determination.

We report a microchip-based detection scheme to determine the diffusion coefficient and molecular mass (to the extent correlated to molecular size) of analytes of interest. The device works by simultaneously measuring the refractive index gradient (RIG) between adjacent laminar flows at two different positions along a microchannel. The device, referred to as a microscale molecular mass sensor (micro-MMS), takes advantage of laminar flow conditions where the mixing of two streams occurs essentially by diffusion across the boundary between the two streams. Two flows merge on the microchip, one containing solvent only, referred to as the mobile phase stream and one which contains the analyte(s) of interest in the solvent, i.e. the sample stream. As these two streams merge and flow parallel to each other down the microchannel a RIG is created by the concentration gradient. The RIG is further influenced by analyte diffusion from the sample stream into the mobile phase stream. Measuring the RIG at a position close to the merging point (upstream signal) and simultaneously a selected distance further down the microchannel (downstream signal) provides real-time data related to the extent a given analyte has diffused, which can be readily correlated to analyte molecular mass by taking the ratio of the downstream-to-upstream signals. For the dual-beam RIG measurements, a diode laser output is coupled to a single mode fiber optic splitter with two output fibers. Light from each fiber passes through a graded refractive index (GRIN) lens forming a collimated beam that then passes through the microchannel and then on to a position sensitive detector (PSD). The RIG at both detection positions deflects the two collimated probe beams. The deflection angle of each beam is then measured on two separate PSDs. The micro-MMS was evaluated using polyethylene glycols (PEGs), sugars, and as a detector for size-exclusion chromatography (SEC). Peak purity can be readily identified using the micro-MMS with SEC. The limit of detection was 0.9 ppm (PEG at 11 840 g/mol) at the upstream detection position corresponding to a RI limit of detection (LOD) (3sigma) of 7-10(-8) RI. The pathlength for the RIG measurement was 200 microm and the angular LOD was 0.23 micro(rad) with a detection volume of 8 nl at both positions. The average molecular mass resolution was 9% (relative standard deviation) for a series of PEGs ranging in molecular mass from 106 to 22 800 g/mol. With this excellent mass resolution, small molecules such as monosaccharides, disaccharides, and so on, are readily distinguished. The sensor is demonstrated to readily determine unknown diffusion coefficients.

Chromatography, Gel↗
PubMed2004

Fabrication of calcium fluoride capillary electrophoresis microdevices for on-chip infrared detection.

In this paper, we demonstrate microfluidic capillary electrophoresis (CE) devices made in CaF2 , for optical detection in a broad spectral range. We have designed methods for micromachining and enclosing capillaries in CaF2. The utility of these microdevices has been shown through CE analysis of fluorescently labeled amino acids. We have also performed infrared spectroscopy for analyte identification in microfluidic CaF2 channels. These CaF2 microdevices open the door to microchip separations with optical detection in the ultraviolet, visible, and infrared spectral regions.

Calcium Fluoride↗
PubMed2003

Incorporation of DNA chip technology to the simulation and validation of flux analysis in yeast diauxic growth.

We incorporated gene expression information from cDNA microarray into flux analysis to simulate yeast diauxic growth. Expression ratios of both growth phases were applied to assign the split ratio at glyoxylate shunt during simulation, in which the equation was mathematically unsolvable due to the singularity and artificial split ratios, which were traditionally introduced without biological evidence. In addition, the directionality of microarray dataset was used as a further constraint during simulation. Metabolic fluxes obtained by this modified approach are in general consistent with microarray analysis. However, discrepancies occurred when the quantity of fluxes was compared, probably due to the substantial reduction of substrates at phase II in which the increase in the enzymatic levels was not proportional to the increase of substrate flow, as would be predicted from microarray dataset. The modified flux analysis might have brought a new approach to investigate other cellular pathways.

Algorithms↗
PubMed2001

Chipping away at complex behavior: transcriptome/phenotype correlations in the mouse brain.

Highly parallel gene expression profiling has the potential to provide new insight into the molecular mechanisms of complex brain diseases and behavioral traits. We review how gene expression profiling in various brain regions of inbred mouse strains has been used to identify genes that may contribute to strain-specific phenotypes. New data, which demonstrate the use of gene expression profiling in combination with behavioral testing to identify candidate genes involved in mediating variation in running wheel activity, are also presented. These and other studies suggest that a combination of gene expression profiling and more traditional genetic approaches, such as quantitative trait locus analysis, can be used to identify genes responsible for specific neurobehavioral phenotypes.

Animals↗