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At least 1,639 records · Page 91Linked to original sources
PubMed2005

Chipping away at the embryonic stem cell network.

Critical transcription factors, notably OCT4, SOX2, and NANOG, are necessary to maintain self-renewal and pluripotency, two properties characteristic of embryonic stem (ES) cells. By analyzing the genome-wide localization of these factors at promoter regions in human ES cells, Boyer et al. (2005) demonstrate frequent promoter co-occupancy at numerous target genes. As they discuss in this issue of Cell, their findings indicate the presence of a complex network of autoregulatory and feedforward loops in human ES cells.

Cell Differentiation↗
PubMed2004

In-channel dual-electrode amperometric detection in electrophoretic chips with a palladium film decoupler.

An electrophoretic microchip integrated with a Pd-film decoupler and a series-dual electrode was proven practical (200-800 V/cm) for routine amperometric detection. In fluidic systems, amperometric enhancement of parallel-opposed dual-electrode detection is due to redox cycling of analytes between the electrodes. We, however, found that the oxidation current of catecholamines was enhanced significantly (1.9-3.8 folds) by switching from the single electrode mode to dual-series mode. This novel finding was unexpected because the unidirectional flow characteristic of the microfluidic system should eliminate the possibility for analytes physically migrating back and forth between the upstream and downstream electrodes. We attribute the enhancement to turbulence generated by impinging of the flow onto the edge of the downstream electrode. The linear range, sensitivity, limit of detection (S/N = 3) and number of theoretical plates for DA and CA are, respectively, 0.5-50 microM, 47 pA/microM, 0.25 microM, 7000 m(-1) and 1.0-100 microM, 28 pA/microM, 0.49 microM, 15,000 m(-1).

Catecholamines↗
PubMed2004

Computational study of the band broadening in two-dimensional etched packed bed columns for on-chip high-performance liquid chromatography.

The chromatographic performance of several straightforward two-dimensional etched packed bed column lay-outs (equilaterally staggered arrays of, respectively, circular, hexagonal, and diamond-like pillars) has been compared using commercial computational fluid dynamics software. In all cases, the bed porosity was kept at epsilon = 0.4 and a retained component with zone capacity ratio k" = 2 was considered. Exploring the use of six different possible characteristic dimensions to bring the Van Deemter plots of the three different considered particle shapes into agreement, none of them yielded a perfect agreement. Using the pillar volume-based equivalent cylinder diameter (deq) as the characteristic dimension, the diamond-like pillars yielded a significantly smaller h(min) value than the cylinders and the hexagons (h(min) approximately equal to 0.74 for the former versus h(min) approximately equal to 0.83 for the two latter). Including the flow resistance into the analysis, it was found that the "hydrodynamic" shape of the particles has an important influence on the separation impedance E. The more axially elongated diamond pillars yielded an Emin number as small Emin = 180 (for a retained component with k" = 2), i.e. about 40% smaller than the cylinders and the hexagons (Emin = 300-330). The obtained h(min) and Emin values are also significantly smaller than the values often cited for the best possible packed bed HPLC columns. We believe this is a consequence of the assumed perfect homogeneity of the etched structures, and hence hints at the potential benefits of perfectly ordered chromatographic columns, as was already inferred by Knox [J. Chromatogr. A 831 (1999) 3; 960 (2002) 7] and He et al. [Anal. Chem. 70 (1998) 3790].

Chromatography, High Pressure Liquid↗
PubMed2004

Monolayer-protected gold nanoparticles as an efficient stationary phase for open tubular gas chromatography using a square capillary model for chip-based gas chromatography in square cornered microfabricated channels.

The application of a dodecanethiol monolayer-protected gold nanoparticle (MPN) stationary phase within a microchannel environment was explored using a square capillary column as a model for high-speed, microfabricated gas chromatography (microGC). Successful deposition and evaluation of a dodecanethiol MPN phase within a 1.3 m long, 100 microm x 100 microm square capillary is reported. The thickness of the MPN phase was evaluated using SEM analysis. An average thickness of 15 nm along the capillary walls was determined. While the film depth along the walls was very uniform, the corner depths were greater with the largest observed depth being 430 nm. Overall, an efficient chromatographic system was obtained with a minimum reduced plate height, h(min), of 1.2 for octane (k = 0.22). Characterization of the MPN column was completed using four compound classes (alkanes, alcohols, ketones, and aromatics) that were used to form a seven-component mixture with a 2-s separation. A mixture consisting of a nerve agent simulant in a sample containing analytes that may commonly interfere with detection was also separated in only 2 s, much faster than a similar separation previously reported using a microGC system requiring 50 s. A comparison of the MPN stationary phase to phases employed in previously reported microGC systems is also made. Application of the square capillary MPN column for a high-speed separation as the second column of a comprehensive 2-D gas chromatography system (GC x GC) was also explored.

Chromatography, Gas↗
PubMed2005

Miniaturized thermal lens and fluorescence detection system for microchemical chips.

We have developed a miniaturized two-way detection system using thermal lens and fluorescence spectroscopies for microchip chemistry. The system was composed of laser diode (LD) modules, fiber-based optics combined with a gradient index lens, and miniaturized detection units for thermal lens and fluorescence signals. The detection limits in the thermal lens and fluorescence spectroscopies were 6.3 x 10(-9)M for Ni(II) phthalocyanine tetrasulfonic acid and 3.0 x 10(-9)M for cy5, respectively. The performance of the system with the miniaturized thermal lens was equivalent to that of a conventional thermal lens microscope. The fluorescence sensitivity was comparable to sensitivities offered by conventional miniaturized systems.

Miniaturization↗
PubMed2004

Floral development: an ABC gene chips in downstream.

In flower development, specification of stamens and carpels requires the AGAMOUS gene. A recent study has now shown that AGAMOUS also plays more specific roles in the regional activation of sporocyte formation.

Arabidopsis Proteins↗
PubMed2006

Bacterial contamination of filtered intraoral bone chips.

Intraoral bony defects can be filled with bony particles that are collected in a titanium filter. The aim of this study was to determine quantitatively and qualitatively the degree of this contamination. Over a period of 3 months, bony particles were collected from 50 patients undergoing oral surgery. The bony particles were scraped off the filter, resuspended, and incubated aerobically and anaerobically on human blood agar media. Colony forming units (CFU) were determined as well as the most common species of bacteria. All samples showed anaerobic and aerobic growth. After anaerobic incubation in 44 samples the number of bacteria was higher (38) or equal (six) to that after aerobic incubation. On average, 435,000 CFU (aerobic) and 1,013,000 CFU (anaerobic) per sample were found. The most frequently identified bacteria belonged to Veillonella spp. in the anaerobic and to Streptococcus oralis in the aerobic cultures. In 43 samples black-pigmented colonies were detected. Only bacteria common in the oral cavity were identified. Prophylactic antibiotic therapy may be indicated when using filtered bony particles for intraoral augmentation procedures.

Adolescent↗
PubMed2006

Simple approaches to close the open structure of microfluidic chips and connecting them to the macro-world.

Microchip electrophoresis has a great potential to improve the speed and throughput of chemical and biochemical analyses. Conventional electrophoresis microchip fabrication methods comprise the main steps of channel formation, cover plate binding and access hole construction. While the fabrication of appropriate cover plates and their bonding process are quite essential to the creation of closed microfluidic networks, connection means of microchips to the macro-world is one of the most important parts of microchip fabrication. In this paper the most commonly used approaches are discussed for cover plate connector fabrication in conjunction with high and low temperature glue-less binding processes. The microchannels in the glass substrate were fabricated by sawing and powder blasting under regular laboratory settings, i.e., not necessitating the use of a clean-room environment, making in this way broader availability for electrophoresis microchip technology.

Electrophoresis, Microchip↗
PubMed2006

Application of microfluidic chip with integrated optics for electrophoretic separations of proteins.

This paper describes the fabrication, the characterization and the applications of a capillary electrophoresis microchip. This hybrid device (glass/PDMS) features channels and optical waveguides integrated in one common substrate. It can be used for electrophoretic separation and fluorimetric detection of molecules. The microfluidic performance of the device is demonstrated by capillary zone and gel electrophoresis of proteins.

Carbocyanines↗
PubMed2004

Stopping for FISH and chips along the chromatin fiber superhighway.

Gilbert et al. (2004) report in a recent issue of Cell on the analysis of chromatin fiber structure across the human genome. They show that compact chromatin fibers are composed of heterochromatin but also contain some active genes, while open chromatin fibers correlate with regions of highest gene density, but not with gene expression.

Chromatin↗
PubMedDate not supplied

On-chip visual perception of motion: a bio-inspired connectionist model on FPGA.

Visual motion provides useful information to understand the dynamics of a scene to allow intelligent systems interact with their environment. Motion computation is usually restricted by real time requirements that need the design and implementation of specific hardware architectures. In this paper, the design of hardware architecture for a bio-inspired neural model for motion estimation is presented. The motion estimation is based on a strongly localized bio-inspired connectionist model with a particular adaptation of spatio-temporal Gabor-like filtering. The architecture is constituted by three main modules that perform spatial, temporal, and excitatory-inhibitory connectionist processing. The biomimetic architecture is modeled, simulated and validated in VHDL. The synthesis results on a Field Programmable Gate Array (FPGA) device show the potential achievement of real-time performance at an affordable silicon area.

Models, Neurological↗
PubMed2006

An in vitro study of adherence of coagulase-negative staphylococci to bone chip columns.

Coagulase-negative staphylococci (CNS) have become a dominant cause of bone infections and their adherence to the infected bones is a prerequisite for the initiation of these infections. In the present study we investigated and compared the adherence of CNS bacteria to human, chicken and rabbit bones. The study was performed using columns made of bone powder from the three different sources, and measurement of the extent of adhesion to bones of CNS bacteria as an in vitro model which is based on particles of matrix that are closely related to the natural matrix. The adhesion to rabbit bone was relatively high, while adhesion to both human and chicken bone columns was lower and almost identical. Pretreatment of the CNS bacteria with sodium periodate, beta-galactosidase or proteinase K significantly inhibited by 50-60% the adhesion to human bones. Pretreatment of CNS bacteria with subinhibitory concentrations of vancomycin or tunicamycin increased their adherence to human bones several-fold. When the bones were pretreated with vancomycin a considerable increase in the adhesion rate of the bacteria to human and chicken bones was seen. A smaller increase in adherence was observed after pretreatment of human bones with the antibiotic tunicamycin. Salicylic acid or benzalkonium chloride (BZC) also resulted in an increase in adhesion to these pretreated bones. From the results obtained it seems that pretreatment of the CNS bacteria with certain reagents exposes adhesins on the surface of the CNS bacteria. On the other hand, pretreatment of the bones with other reagents may enable a better exposure of receptors located on the bone cells and, as a consequence, may improve the adhesion of the CNS bacteria to the treated bones.

Animals↗
PubMed2004

Rationale and design of the Rockford CHIP, a community-based coronary risk reduction program: results of a pilot phase.

PURPOSE: While residential lifestyle intervention programs have demonstrated coronary risk reduction through education, diet, and exercise, this pilot study was designed to assess the feasibility of a community-based lifestyle intervention program that is both affordable and effective in facilitating better lifestyle choices and health habits and thus effecting indicators of better clinical outcomes. MATERIALS AND METHODS: A 40-h educational curriculum, delivered over a 30-day period with clinical and nutritional assessments before and after, was offered through the SwedishAmerican Center for Complementary Medicine to the general public. The participants were instructed to exercise 30 min/day and to embrace a more optimal diet (ad libitum) of largely unrefined plant foods high in complex carbohydrates and fiber, yet quite low in fat (<15%), animal protein, sugar, and salt, and virtually free of cholesterol. RESULTS: Of the 250 enrollees, 242 "graduated" (78 men and 164 women; almost all Caucasian; mean age 54 +/- 12 years). They had coronary artery disease (CAD) (12%), diabetes (16%), hypertension (55%), most were overweight (88%), and the majority (79%) had low-density lipoprotein (LDL) levels >or=100 mg%. At 4 weeks, stratified analyses of total cholesterol (TC), LDL, triglycerides (TG), blood glucose, blood pressure, and weight showed that those at highest risk also had the greatest improvements. Depending on baseline levels, TC means dropped 10-23% in men and 6-13% in women. At the same time, LDL means declined 5-30% in men and 6-14% in women. In TG, the biggest drop (48%) was found in men who at baseline were in the highest risk category (in women, the biggest TG drop was 32%). CONCLUSION: Community-based intervention strategies can be successfully and affordably utilized to lower coronary risk factor levels in a self-selected, free-living population. The true test, however, will be to what extent social infrastructures can be modified and alumni activities sustained to facilitate long-term adherence and sustained benefits.

Adult↗