Biomedical subjects

H J Crabtree

Publications and source records attributed to H J Crabtree.

5 recordsLinked to original sources

PubMed2002

Frontal analysis on a microchip.

Conventional microchip applications involving capillary electrophoresis (CE) typically inject a sample along one channel and use an intersection of two channels to define the sample plug--the portion of sample to be analysed along a second channel. In contrast to this method of zone separation, frontal analysis proceeds by injecting sample continuously into a single channel or column. Frontal analysis is more common in macroscopic procedures but there are benefits in sensitivity and device density to its application to electrophoresis on microchips. This work compares conventional microchip zone analysis with frontal analysis in the separation of PCR products. Although we detect on the order of 5000 fluorophores with a compact instrument using the zone separation CE method, we found a several-fold increase in the effective signal-to-noise ratio by using a frontal analysis method. By removing the need for additional channels and reservoirs the frontal method would allow device densities to be significantly increased, potentially improving the cost-effectiveness of microchip analyses in applications such as medical diagnostics.

Animals↗

PubMed2001

Microchip injection and separation anomalies due to pressure effects.

While performing routine electroosmotically driven CE separations on microfluidic chips, we have observed peak shape, migration time, and baseline drift anomalies. Pressure-driven backflow (opposing electroosmotic flow (EOF)) has been observed and characterized, and meniscus surface tension (Laplace pressure) is cited as the likely cause. However, there are a number of interdependent factors that affect bulk flow in a microchip environment, including evaporation, buffer depletion due to hydrolysis, EOF pumping, siphoning, viscosity changes due to Joule heating, and Laplace pressure. Given the complexity of such a system, pressure effects were isolated from EOF, and to some extent, siphoning effects were isolated from suspected meniscus effects. Pressure flow observed in the absence of an applied field ranged from 0.4 to 0.8 mm/s, which was on the order of the EOF generated experimentally, 0.6 mm/s at a field of 150 V/cm, and was some 10-20 times larger than what would be predicted merely from a difference in liquid levels (siphoning). Furthermore, experiments were performed without an electric field and with the chip tilted so that meniscus flow ran "uphill" against a siphoning backflow and showed siphoning flow to have a negligible effect upon meniscus flow under the microchip conditions studied. These findings are relevant to the profusion of microfluidic and array-based technology that also use microliter liquid volumes in like-sized reservoirs with similar menisci.

Journal Article↗

PubMed2001

Sample purification on a microfluidic device.

Sample preparation has long been recognized as a significant barrier to the implementation of macroscopic protocols on microfabricated devices. Macroscopically, such tasks as removing salts, primers and other contaminants are performed by methods involving precipitation, specialized membranes and centrifuges, none of which are readily performed in microfluidic structures. Although some microfluidic systems have been developed for performing sample purification, their complexity may hinder the degree to which they can be implemented. We present a method of microchip-based sample purification that can be performed with even the simplest microfluidic designs. The technique is demonstrated by removing primers from a sample of amplified DNA, leaving only the product DNA. This provides a new sample preparation capability for microfluidic systems.

DNA↗

PubMed2000

Construction and evaluation of a capillary array DNA sequencer based on a micromachined sheath-flow cuvette.

A capillary array electrophoresis DNA sequencer is reported based on a micromachined sheath-flow cuvette as the detection chamber. This cuvette is equipped with a set of micromachined features that hold the capillaries in precise registration to ensure uniform spacing between the capillaries, in order to generate uniform hydrodynamic flow in the cuvette. A laser beam excites all of the samples simultaneously, and a microscope objective images fluorescence onto a set of avalanche photodiodes, which operate in the analog mode. A high-gain transimpedance amplifier is used for each photodiode, providing high duty-cycle detection of fluorescence.

DNA↗

PubMed1997

Developments in technology and applications of microsystems.

In the past year, microchips as applied to miniaturised total analysis systems, or microTAS, have benefited from technological improvements in their fabrication and been applied to analysis in many different biological areas. From a technological perspective, salient work includes fast, cheap and easy micromachining in polymers and integrated optical detection. From the bioapplications perspective, advances in DNA and protein separations, cell manipulations, immunoassays and polymerase chain reaction using on-chip electrophoretic separation stand out.

Chemistry Techniques, Analytical↗