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At least 649 records · Page 36Linked to original sources
PubMed2000

Capillary electrophoresis separations on a planar chip with the column-coupling configuration of the separation channels

Some basic aspects of capillary electrophoresis (CE) separations on a poly(methyl methacrylate) chip provided with two separation channels in the column-coupling (CC) configuration and on-column conductivity detectors were studied. The CE methods employed in this study included isotachophoresis (ITP), capillary zone electrophoresis (CZE), and CZE with on-line ITP sample pretreatment (ITP-CZE). Hydrodynamic and electroosmotic flows of the solution in the separation compartment of the chip were suppressed, and electrophoresis was a dominant transport process in the separations performed by these methods. Very reproducible migration velocities of the separated constituents were typical under such transport conditions, and consequently, test analytes could be quantified by various ITP techniques with 1-2% RSD. The CC configuration of the separation channels provides means for an effective combination of an enhanced load capacity of the separation system with high detection sensitivities for the analytes in concentration-cascade ITP separations. In this way, for example, succinate, acetate, and benzoate could be separated also in instances when they were present in the loaded sample (1.2 microL) at 1 mmol/L concentrations while their limits of detection ranged from 8 to 12 micromol/L concentrations. A well-defined ITP concentration of the analyte(s) combined with an in-column sample cleanup (via an electrophoretically driven removal of the matrix constituents from the separation compartment) can be integrated into the separations performed on the CC chip. These sample pretreatment capabilities were investigated in ITP-CZE separations of model samples in which nitrite, phosphate, and fluoride (each at a 10 micromol/L concentration) accompanied matrix constituents (sulfate and chloride) at considerably higher concentrations. Here, both the concentration of the analytes and cleanup of the sample were included in the ITP separation in the first separation channel while the second separation channel served for the CZE separation of the ITP pretreated sample and the detection of the analytes.

Journal Article↗
PubMed2000

Microfabricated electrophoresis chips for simultaneous bioassays of glucose, uric acid, ascorbic acid, and acetaminophen.

A micromachined capillary electrophoresis chip is described for simultaneous measurements of glucose, ascorbic acid, acetaminophen, and uric acid. Fluid control is used to mix the sample and enzyme glucose oxidase (GOx). The enzymatic reaction, a catalyzed aerobic oxidation of glucose to gluconic acid and hydrogen peroxide, occurs along the separation channel. The enzymatically liberated neutral peroxide species is separated electrophoretically from the anionic uric and ascorbic acids in the separation/reaction channel. The three oxidizable species are detected at the downstream gold-coated thick-film amperometric detector at different migration times. Glucose can be detected within less than 100 s, and detection of all electroactive constituents is carried out within 4 min. Measurements of glucose in the presence of acetaminophen, a neutral compound, are accomplished by comparing the responses in the presence and absence of GOx in the running buffer. The reproducibility of the on-chip glucose measurements is improved greatly by using uric acid as an internal standard. Factors influencing the performance, including the GOx concentration, field strength, and detection potential, are optimized. Such coupling of enzymatic assays with electrophoretic separations on a microchip platform holds great promise for rapid testing of metabolites (such as glucose or lactate), as well as for the introduction of high-speed clinical microanalyzers based on multichannel chips.

Acetaminophen↗
PubMed2004

Development of a DNA microarray chip for the identification of sludge bacteria using an unsequenced random genomic DNA hybridization method.

A tool, based upon the DNA microarray chip, for the identification of specific bacteria from activated sludge, using the hybridization of genomic DNA with random probes, is described. This chip was developed using the genomic DNAs from Gordonia amarae, the natural filamentous actinomycete that causes sludge foaming and bulking, as well as a nonfilamentous floc forming bacterium (Zoogloea ramigera) and the skin pathogen Mycobacterium peregrinum without any sequence information. The sets of target probes on amine-coated glass were made from a genomic library, constructed with PCR products derived from randomly fragmented genomic DNAs extracted from pure cultures of the three strains. Initial hybridization results, when pure cultures were employed, showed the specificity of the probes as well as the resolution of the system, demonstrating the capabilities of this system to identify specific bacterial strains. The microarray was also tested for its ability to distinguish specific bacteria from among mixed bacterial communities, such as in sludge, soil, or spiked genomic DNA samples. The results showed that the probes are specific, with only mild cross-hybridization occurring in a small number of cases. Furthermore, the chip clearly discriminated the presence of all three strains when they were present alone or together within mixed samples. Moreover, using the spot intensity and DNA hybridization kinetics, the starting genomic DNA concentrations could be estimated relatively well, which would make it possible to predict the number of specific bacteria present within the test samples. Therefore, the random genomic hybridization approach, i.e., without any sequence information available for the probes, is a practical protocol for the identification of and screening for specific bacteria within any complex bacterial community from the environmental samples, such as in activated sludge, although the possibility of cross-hybridization may still exist.

Bacteria↗
PubMed2003

Millisecond kinetics on a microfluidic chip using nanoliters of reagents.

This paper describes a microfluidic chip for performing kinetic measurements with better than millisecond resolution. Rapid kinetic measurements in microfluidic systems are complicated by two problems: mixing is slow and dispersion is large. These problems also complicate biochemical assays performed in microfluidic chips. We have recently shown (Song, H.; Tice, J. D.; Ismagilov, R. F. Angew. Chem., Int. Ed. 2003, 42, 768-772) how multiphase fluid flow in microchannels can be used to address both problems by transporting the reagents inside aqueous droplets (plugs) surrounded by an immiscible fluid. Here, this droplet-based microfluidic system was used to extract kinetic parameters of an enzymatic reaction. Rapid single-turnover kinetics of ribonuclease A (RNase A) was measured with better than millisecond resolution using sub-microliter volumes of solutions. To obtain the single-turnover rate constant (k = 1100 +/- 250 s(-1)), four new features for this microfluidics platform were demonstrated: (i) rapid on-chip dilution, (ii) multiple time range access, (iii) biocompatibility with RNase A, and (iv) explicit treatment of mixing for improving time resolution of the system. These features are discussed using kinetics of RNase A. From fluorescent images integrated for 2-4 s, each kinetic profile can be obtained using less than 150 nL of solutions of reagents because this system relies on chaotic advection inside moving droplets rather than on turbulence to achieve rapid mixing. Fabrication of these devices in PDMS is straightforward and no specialized equipment, except for a standard microscope with a CCD camera, is needed to run the experiments. This microfluidic platform could serve as an inexpensive and economical complement to stopped-flow methods for a broad range of time-resolved experiments and assays in chemistry and biochemistry.

Biocompatible Materials↗
PubMed2004

Carbohydrate chips for studying high-throughput carbohydrate-protein interactions.

Carbohydrate-protein interactions play important biological roles in living organisms. For the most part, biophysical and biochemical methods have been used for studying these biomolecular interactions. Less attention has been given to the development of high-throughput methods to elucidate recognition events between carbohydrates and proteins. In the current effort to develop a novel high-throughput tool for monitoring carbohydrate-protein interactions, we prepared carbohydrate microarrays by immobilizing maleimide-linked carbohydrates on thiol-derivatized glass slides and carried out lectin binding experiments by using these microarrays. The results showed that carbohydrates with different structural features selectively bound to the corresponding lectins with relative binding affinities that correlated with those obtained from solution-based assays. In addition, binding affinities of lectins to carbohydrates were also quantitatively analyzed by determining IC(50) values of soluble carbohydrates with the carbohydrate microarrays. To fabricate carbohydrate chips that contained more diverse carbohydrate probes, solution-phase parallel and enzymatic glycosylations were performed. Three model disaccharides were in parallel synthesized in solution-phase and used as carbohydrate probes for the fabrication of carbohydrate chips. Three enzymatic glycosylations on glass slides were consecutively performed to generate carbohydrate microarrays that contained the complex oligosaccharide, sialyl Le(x). Overall, these works demonstrated that carbohydrate chips could be efficiently prepared by covalent immobilization of maleimide-linked carbohydrates on the thiol-coated glass slides and applied for the high-throughput analyses of carbohydrate-protein interactions.

Carbohydrate Metabolism↗
PubMed2004

Molecular recognition in a supramolecular hydrogel to afford a semi-wet sensor chip.

This communication describes a new molecular recognition chip using a semi-wet microenvironment provided by a self-assembled hydrogel. On the basis of the evidence that the molecular recognition capability of artificial chemosensors are practically retained even in the hydrogel compared to those in aqueous solution, we miniaturized the functionalized hydrogel to produce an unprecedented molecular recognition chip. We believe that the present noncovalent immobilization method is generally applicable to many chemosensors, which leads to a unique semi-wet sensor chip suitable to convenient and high-throughput assay to plural analytes.

Amino Acids↗
PubMed2006

Characterization of volatiles in extracts from oak chips obtained by accelerated solvent extraction (ASE).

Sixteen commercially available oak chips, differing in origin (French or American) and toasting level, were extracted by an accelerated solvent extraction method and characterized by their volatile composition. About 80 compounds were identified and quantified, a great part of them from the thermodegradation of lignin and cellulose. One furanone (solerone) and two C-13 norisoprenoids (3-oxo-alpha-ionol and a 3-oxoretro-alpha-ionol isomer) were also tentatively identified and reported for the first time in toasted wood. Quantitative data demonstrated the oak chips to be not so different from the composition of light- or medium-toasted wood barrels, which was reported by other authors. The same data suggest that toasting level had the strongest influence on the volatile composition of chip samples. Phenyl ketones, volatile phenols, and some furanic compounds were the most influenced. On the other hand, the influence of wood origin was found to be weaker.

Cellulose↗
PubMedDate not supplied

Direct identification of ubiquitination sites on ubiquitin-conjugated CHIP using MALDI mass spectrometry.

The study of protein ubiquitination, a post-translational modification by ubiquitin, has emerged as one of the most active areas in biology because of the important role of this type of modification on the regulation of various cellular proteins. Advances in techniques for the determination and site mapping of protein ubiquitination can facilitate the elucidation of molecular mechanisms of this modification. We have recently described a novel method for identifying peptides containing ubiquitinated amino acid residues, based on the MALDI-MS/MS analysis of tryptic peptide derivatives. In particular, we have utilized N-terminal sulfonation of these peptides to provide a unique fragmentation pattern that leads to the direct identification and sequencing of ubiquitin modified peptides. Here we present an application of this new method on the characterization of ubiquitin conjugated C-terminal Hsc70-interacting protein (CHIP), a recently identified U-box containing E3 enzyme. Three peptides bearing ubiquitination sites have been identified from the digest of ubiquitinated CHIP; one of these was a site on CHIP, while the other two were found on the ubiquitin molecules, demonstrating that sulfonation of tryptic peptides is a general and efficient method for characterizing protein ubiquitination.

Amino Acid Sequence↗
PubMed2002

Effect of a controlled-release chlorhexidine chip on clinical and microbiological parameters of periodontal syndrome.

AIM: The aim of this study was to evaluate the effectiveness of a controlled-released chlorhexidine chip (CHX) as adjunctive therapy to scaling and root planing (SRP) in the treatment of chronic periodontitis. MATERIAL AND METHODS: Twenty patients with at least four sites with probing depth >or= 5 mm and bleeding on probing were selected. This randomized single-blind study was carried out in parallel design. The control group received SRP alone, while the test group received SRP plus CHX chip. The clinical parameters, Plaque Index (PlI), Papillary Bleeding Score (PBS), Bleeding on Probing (BOP), Gingival Recession (GR), Probing Depth (PD) and Relative Attachment Level (RAL), and the microbiological parameter BANA test were recorded at baseline and after 3, 6 and 9 months. RESULTS: Both groups presented significant improvements in all parameters analyzed over the study period. There were no statistically significant differences between the two groups for any parameter analyzed after 9 months, except for BOP, which was significantly reduced in the control group. The mean reductions on PD and RAL were 2.4 mm and 1.0 mm for the control group and 2.2 mm and 0.6 mm for the test group, respectively. CONCLUSION: The CHX chip did not provide any clinical or microbiological benefit beyond that achieved with conventional scaling and root planning, after a 9-month period.

Adult↗
PubMed1997

Mr. Chips: an ideal-observer model of reading.

The integration of visual, lexical, and oculomotor information is a critical part of reading. Mr. Chips is an ideal-observer model that combines these sources of information optimally to read simple texts in the minimum number of saccades. In the model, the concept of the visual span (the number of letters that can be identified in a single fixation) plays a key, unifying role. The behavior of the model provides a computational framework for reexamining the literature on human reading saccades. Emergent properties of the model, such as regressive saccades and an optimal-viewing position, suggest new interpretations of human behavior. Because Mr. Chip's "retina" can have any (one-dimensional) arrangement of high-resolution regions and scotomas, the model can simulate common visual disorders. Surprising saccade strategies are linked to the pattern of scotomas. For example, Mr. Chips sometimes plans a saccade that places a decisive letter in a scotoma. This article provides the first quantitative model of the effects of scotomas on reading.

Algorithms↗
PubMed2001

Bose-Einstein condensation on a microelectronic chip.

Although Bose-Einstein condensates of ultracold atoms have been experimentally realizable for several years, their formation and manipulation still impose considerable technical challenges. An all-optical technique that enables faster production of Bose-Einstein condensates was recently reported. Here we demonstrate that the formation of a condensate can be greatly simplified using a microscopic magnetic trap on a chip. We achieve Bose-Einstein condensation inside the single vapour cell of a magneto-optical trap in as little as 700 ms-more than a factor of ten faster than typical experiments, and a factor of three faster than the all-optical technique. A coherent matter wave is emitted normal to the chip surface when the trapped atoms are released into free fall; alternatively, we couple the condensate into an 'atomic conveyor belt', which is used to transport the condensed cloud non-destructively over a macroscopic distance parallel to the chip surface. The possibility of manipulating laser-like coherent matter waves with such an integrated atom-optical system holds promise for applications in interferometry, holography, microscopy, atom lithography and quantum information processing.

Journal Article↗
PubMed2004

Application of DNA chip techniques for Yq microdeletion analysis in infertile males.

Our aim was to apply DNA chip technology as a diagnostic tool in infertility research and clinics. Six loci, including a sex-determining region on the Y chromosome and five sequence-tagged sites in azoospermia-factor regions were investigated in infertile male patients. Our method produced a sensitive signal, which showed the presence or absence of the STS regions on the Y chromosome. The results from 93 patients with non- obstructive azoospermia, oligoathenoteratozoospermia, or oligozoospermia were identical when analyzed with either the DNA chip technique or conventional PCR-gel electrophoresis. We have demonstrated its application in the molecular diagnosis of male infertility. This system provides an economic and high-throughput method for detecting the deletion of genomic DNA sequences of large groups of infertile patients, and a completely new approach to male infertility screening. The application of DNA chip technology to identify Yq deletions can also facilitate our understanding of male infertility.

Chromosome Deletion↗
PubMed2003

Ultra-high-Q toroid microcavity on a chip.

The circulation of light within dielectric volumes enables storage of optical power near specific resonant frequencies and is important in a wide range of fields including cavity quantum electrodynamics, photonics, biosensing and nonlinear optics. Optical trajectories occur near the interface of the volume with its surroundings, making their performance strongly dependent upon interface quality. With a nearly atomic-scale surface finish, surface-tension-induced microcavities such as liquid droplets or spheres are superior to all other dielectric microresonant structures when comparing photon lifetime or, equivalently, cavity Q factor. Despite these advantageous properties, the physical characteristics of such systems are not easily controlled during fabrication. It is known that wafer-based processing of resonators can achieve parallel processing and control, as well as integration with other functions. However, such resonators-on-a-chip suffer from Q factors that are many orders of magnitude lower than for surface-tension-induced microcavities, making them unsuitable for ultra-high-Q experiments. Here we demonstrate a process for producing silica toroid-shaped microresonators-on-a-chip with Q factors in excess of 100 million using a combination of lithography, dry etching and a selective reflow process. Such a high Q value was previously attainable only by droplets or microspheres and represents an improvement of nearly four orders of magnitude over previous chip-based resonators.

Journal Article↗
PubMed2005

Gene expression profiling of arthritis using a QTL chip reveals a complex gene regulation of the Cia5 region in mice.

One of the major quantitative trait loci (QTLs) associated with arthritis in crosses between B10.RIII and RIIIS/J mice is the Cia5 on chromosome 3. Early in the congenic mapping process it was clear that the locus was complex, consisting of several subloci with small effects. Therefore, we developed two novel strategies to dissect a QTL: the partial advanced inter-cross (PAI) strategy, with which we recently found the Cia5 region to consist of three loci, Cia5, Cia21 and Cia22, and now we introduce the QTL-chip strategy, where we have combined congenic mapping with a QTL-restricted expression profiling using a novel microarray design. The expression of QTL genes was compared between parental and congenic mice in lymph node, spleen and paw samples in five biological replicates and in dye-swapped experiments at three time points during the induction phase of arthritis. The QTL chip approach revealed 4 genes located in Cia21, differently expressed in lymph nodes, and 14 genes in Cia22, located within two clusters. One cluster contains six genes, differently expressed in spleen, and the second cluster contains eight genes, differently expressed in paws. We conclude the QTL-chip strategy to be valuable in the selection of candidate genes to be prioritized for further investigation.

Animals↗
PubMed2001

Miniaturized flow-through PCR with different template types in a silicon chip thermocycler.

Flow-through chip thermocyclers can be used in miniaturized rapid polymerase chain reaction (PCR) despite their high surface to volume ratio of samples. We demonstrated that a thermocycler made of silicon and glass chips and containing thin film transducers for heating and temperature control can be adapted to the amplification of various DNA templates of different sources and properties. Therefore, the concept of serial flow in a liquid/liquid two-phase system was combined with a surface management of inner side walls of the microchannel and an adaptation of PCR mixture composition. In addition, the process temperatures and the flow rates were optimized. Thus, a synthetic template originating from investigations on nucleic acid evolution with 106 base pairs [cooperative amplification of templates by cross hybridization (CATCH)], a house keeping gene with 379 base pairs [glutaraldehyde 3-phosphate dehydrogenase (GAPDH)] and a zinc finger protein relevant in human pathogenesis with 700 base pairs [Myc-interacting zinc finger protein-1, knock-out (Miz1-KO)] were amplified successfully. In all three cases the selectivity of priming and amplification could be shown by gel electrophoresis. The typical amplification time was 1 min per temperature cycle. So, the typical residence time of a sample volume inside the 25 cycle device amounts to less then half an hour. The energy consumption of the PCR chip for a 35 min PCR process amounts to less than 0.012 kW h.

Base Sequence↗
PubMed2002

Field measurement of lead in workplace air and paint chip samples by ultrasonic extraction and portable anodic stripping voltammetry.

On-site measurement of lead in workplace air filter samples and paint chip samples by ultrasonic extraction and anodic stripping voltammetry (UE-ASV) was evaluated in the field during renovation and remodeling activities in residences having leaded paint. Aerosol and paint samples were collected using standard techniques, and the samples were analyzed on-site for lead content by portable UE-ASV. Lead in sample extracts was subsequently determined by atomic absorption (AA) spectrometry in a fixed-site laboratory. The remaining sample extracts plus undissolved material (air filters or paint particles) were then subjected to hot plate digestion in concentrated nitric acid-30% hydrogen peroxide prior to AA analysis for lead. Field UE-ASV lead data were thereby compared to UE-AA and hot plate digestion-AA results from fixed-site laboratory lead measurement. Determination of lead in air filter samples by UE-ASV (over the range of 5 microg to approximately 800 microg Pb per sample) was extremely well correlated with lead measurement by UE-AA and hot plate digestion-AA procedures. However, a significant negative bias associated with ASV measurement was observed, and this was attributed to a matrix effect. Lead measurement in paint chip samples by UE-ASV (over the range of approximately 10 to approximately 550 microg Pb g(-1)) was well correlated with lead measurement by UE-AA and hot plate digestion-AA procedures. However, correlation and precision were lower for lead measurement in paint samples as compared to aerosol samples, and a negative bias was also observed. Lead measurements by UE-AA were compared to lead determinations by hot plate digestion-AA; these data were highly correlated and demonstrated no significant bias. Thus it was concluded that the ultrasonic extraction procedure performed equivalently to hot plate digestion. It was reasoned that matrix effects due to the preparation and analysis of paint chip particles resulted in greater imprecision as well as negative bias by ASV measurement. Despite significant negative bias in this sample set, UE-ASV offers promise for on-site measurement of lead in samples of interest in occupational and environmental health.

Air Pollution, Indoor↗
PubMed2003

Application of plasma-polymerized films for isoelectric focusing of proteins in a capillary electrophoresis chip.

The first use of plasma polymerization technique to modify the surface of a glass chip for capillary isoelectric focusing (cIEF) of different proteins is reported. The electrophoresis separation channel was machined in Tempax glass chips with length 70 mm, 300 microm width and 100 microm depth. Acetonitrile and hexamethyldisiloxane monomers were used for plasma polymerization. In each case 100 nm plasma polymer films were coated onto the chip surface to reduce protein wall adsorption and minimize the electroosmotic flow. Applied voltages of 1000 V, 2000 V and 3000 V were used to separate mixtures of cytochrome c (pI 9.6), hemoglobin (pI 7.0) and phycocyanin (pI 4.65). Reproducible isoelectric focusing of each pI marker protein was observed in different coated capillaries at increasing concentration 2.22-5 microg microL(-1). Modification of the glass capillary with hydrophobic HMDS plasma polymerized films enabled rapid cIEF within 3 min. The separation efficiency of cytochrome c and phycocyanin in both acrylamide and HMDS coated capillaries corresponded to a plate number of 19600 which compares favourably with capillary electrophoresis of neurotransmitters with amperometric detection.

Animals↗
PubMed2003

An acoustic wave sensor incorporated with a microfluidic chip for analyzing muscle cell contraction.

We report the fabrication of a microfluidic chip or lab-on-a-chip integrated with a thickness-shear mode (TSM) acoustic wave sensor for muscle cell analysis. The sensor, essentially an AT-cut quartz crystal, serves as a detector for recording changes in acoustic wave properties occurring in an attached cardiomyocyte (single heart muscle cell) during its contraction and relaxation. Presumably, the changes resulted from alterations in viscoelastic properties (e.g. stiffness) of the cells. The effects of excitation electrode size, the presence of a microfluidic channel plate, and liquid loading on the sensor were first examined. Thereafter, muscle cell contraction analysis upon chemical stimuli were described. The potential of the chip for screening of cardiovascular drugs is discussed.

Animals↗