Plastic Advances Microfluidic Devices The devices debuted in silicon and glass, but plastic fabrication may make them hugely successful in biotechnology applica-
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he biggest changes often depend on the smallest things. This idea is nowhere more evident than in the current flurry of activity aimed at developing microfluidic systems as a key element for revolutionary miniaturized analytical instrumentation and methodologies. Using interconnected networks of microchannels and tiny reservoirs, microfluidic devices are particularly well matched to the biotech industry’s demand for technologies providing small volumes, faster responses, highly parallel analyses, and minimal cross contamination. Progress in the microfluidic arena has been spurred on by a fortunate combination of factors such as advances in microfabrication technologies; new materials; improved chip Travis D. Boone • Z. Hugh Fan • Herbert H. Hooper • Antonio J. Ricco • Hongdong Tan • Stephen J. Williams ACLARA BioSciences
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sizes are small (~1 cm2), but when making the larger fluidic devices (~100 cm2) required for DNA sequencing or parallel screening of many pharmaceutical candidates (1), costs become prohibitive. On the other hand, plastic devices can be cheap to Etched glass plate Completed manufacture in large volumes and many plastics are fluidic Electroplate compatible with biological and chemical reagents and card assays. Moreover, the injection molding, casting, or emPlastic bossing of plastics is a well-developed technology. At the cover layer moment, manufacturing an injection-molded compact Separate disc with a two-layer structure made from acrylic or Cover and polycarbonate that contains micrometer-scale features Metal electroform seal costs 801 base pairs, and differ in length by ~4% or less. The chips used in this study were from a batch of ~1000 cards produced by injection molding from a nickel electroform and were sealed with an acrylic film as previously described. Very rapid separations of dsDNA fragments are possible in microchannels because the initial width of the injection plug can be made much narrower than in conventional CE. At short separation distances and high electric field strengths, diffusional broadening of analyte zones is small and the contribution to the total peak width from injection becomes important. Thus, a reduction in injected plug size translates into improved peak resolution. In addition, short separation channels (and arrays of channels) are easily fabricated on microfluidic devices and offer detection closer to the point of injection than conventional CE systems. Figure 2b shows a rapid separation of the X174 digest performed in a plastic chip. Standard electrical injection methods were used (20), and near-baseline resolutions of all the fragments were achieved in
