Silicon microtechnology and microstructures in separation science

The development of miniaturized total analysis systems, is driven by the desire to automate sample handling, separation or sensing, and detection of analytical instrumentation. Interest in planar structures for separation techniques, especially capillary zone electrophoresis (CZE), has grown rapidly. Initially most of those structures were realized in quartz, but recently polymers have been used to make planar microchannels. In spite of its attractiveness with respect to the potential integration of electronics and electrochemical and optical detectors, silicon has not been used very often, mainly because of its incompatibility with the high voltages used in CZE. In this contribution, an overview of the advantages and disadvantages of silicon for electroosmotically driven separation techniques is presented. Some silicon-derived insulating microstructures and their potential application in chemical analysis are also shown. The microtechnologies used comprise (deep) dry etching, thin-layer growth and anodic bonding. With this combination it is possible to create high resolution electrically isolating silicon dioxide structures with aspect ratios similar to those possible in silicon. Besides these channel structures, a capillar; connector is presented with a very low dead and mixing volume for use in (correlation) electrophoresis, and tested by means of precision of consecutive single injections. Finally, the potential of integrated optical detectors in combination with micro-separation structures is presented. (C) 1998 Elsevier Science B.V. All rights reserved.