A glass microchip column was fabricated for free-solution electrophoresis. The channels were wet chemically etched on a substrate using standard photolithographic techniques and were sealed using a direct bonding technique. Two methods * Chemical and Analytical Sciences Division.

Fast, efficient separations are sought in liquid-phase analyses which incorporate a nondiscriminatory sample injection scheme and can implement a variety of detection modes. A glass microchip device for free solution electrophoresis was fabricated using standard photolithographic procedures and chemical wet etching. Separations were performed at several separation lengths from the injector to the detector with electric field strengths from 0.06 to 1.5 kV/cm. For a separation length of 0.9 mm, electrophoretic separations with baseline resolution are achieved in less than 150 ms with an electric field strength of 1.5 kV/cm and an efficiency of 1820 plates/s. For a separation length of 11.1 mm, a minimum plate height of 0.7 jtm and a maximum number of plates per second of 18 600 were achieved.Microfabricated chemical instruments show great promise for the laboratory and as advanced chemical sensors. Microfabrications of chemical separation techniques have received noticeable attention over the past several years and have included the techniques of gas chromatography,1 liquid chromatography,1 2 3456and capillary electrophoresis.3-7 Microelectronic devices have been able to achieve even faster response times in part due to miniaturization. Similar benefits may also accrue from miniaturization of some chemical measurement techniques. The response times of chemical measurements can often be an important issue, in particular in the case of chemical sensing.With microfabrication, the performance of many liquid separation techniques improves, especially capillary electrophoresis.8-10 For capillary electrophoresis, smaller column dimensions enable the power generated to be dissipated more efficiently, and as a direct result, separation devices can be operated at higher electric field strengths. The efficiency of the separations, therefore, improves in two areas. First, Joule heating, which leads to thermal gradients within the channel and ultimately contributes to the dispersion of the analyte

A glass microchip with a postcolumn reactor was fabricated to conduct postseparation derivatization using o-phthaldialdehyde as a fluorescent "tag" for amino acids. This miniaturized separation device was constructed using standard photolithographic, wet chemical etching, and bonding techniques.Effects of the reagent stream on separation efficiency were investigated. In addition, a novel gated injector was demonstrated which maintains the integrity of the analyte, buffer, and reagent streams.For capillary separation systems, the small band volumes can limit the number of viable detection schemes. Fluorescence

An immunoassay performed using a microchip electrophoretic system is described. Separation and quantitation of free and bound labeled antigen in a competitive assay are carried out in channels micromachined into fused silica substrates. Such microchips are attractive because of their small size, ruggedness, and amenability to automated handling. The assay achieves the determination of cortisol in blood serum over the range of clinical interest (1-60 micrograms/dL) without the need for extraction or other sample preparation steps. The separation is performed in less than 30 s. Very high throughput is possible by operating the assay in multiple channels in parallel. These characteristics make microchip electrophoretic systems a promising technology for the rapid analysis of clinical samples.

We present a model that quantitatively describes the performance of microfabricated electrophoretic devices filled with linear polyacrylamide as replaceable sieving material for single-stranded DNA analyses. The dependence of resolution on various separation parameters such as selectivity, diffusion, injector size, device length, and channel folding was investigated. A previously predicted dependence of longitudinal diffusion coefficient on electric field strength has been verified. We have used this model to develop and optimize microfabricated electrophoretic devices for DNA analyses. For single-color DNA sequencing mixtures, we routinely achieve separations of 400 bases in under 14 min at 200 V/cm, and separation of 350 bases in only 7 min at 400 V/cm, with a minimum resolution of R = 0.5. Our results also indicate reduced fragment biasing and efficient sample stacking for DNA sample loading on microfabricated devices.