Carlo S. Effenhauser

Integrated Capillary Electrophoresis on Flexible Silicone Microdevices : Analysis of DNA Restriction Fragments and Detection of Single DNA Molecules on Microchips

Microchips for integrated capillary electrophoresis systems were produced by molding a poly(dimethylsiloxane) (PDMS) silicone elastomer against a microfabricated master. The good adhesion of the PDMS devices on clean planar surfaces allows for a simple and inexpensive generation of networks of sealed microchannels, thus removing the constraints of elaborate bonding procedures. The performance of the devices is demonstrated with both fast separations of φX-174/HaeIII DNA restriction fragments labeled with the intercalating dye YOYO-1 and fluorescently labeled peptides. Detection limits in the order of a few zeptomoles (10(-)(21) mol) have been achieved for each injected DNA fragment, corresponding to a mass detection limit of ∼2 fg for the 603 base pair fragment. Single λ-DNA molecules intercalated with YOYO-1 at a base pair-to-dye ratio of 10:1 could be detected with an uncomplicated laser-induced fluorescence detection setup. High single-molecule detection efficiency (>50%) was achieved under electrophoretically controlled mass transport conditions in PDMS microchannels.

Electroosmotic pumping and electrophoretic separations for miniaturized chemical analysis systems

Electroosmotic pumping is highly efficient in capillaries of less than 100 mu m inner diameter bearing an immobilized surface charge. Electric fields in the kV cm-1 range allow for liquid motion of several mm s-1 in the case of an aqueous electrolyte. This pumping mechanism is used for miniaturized chemical analysis systems. Flow and mixing behaviour in branched channels are characterized. A capillary electrophoresis device allows for repetitive, electroosmotic injections of 100 pL samples, for efficiencies of up to 200000 theoretical plates in less than a minute, and for external laser induced fluorescence detection at any capillary length of choice between 5 and 50 mm.

A novel approach to ion separations in solution : synchronized cyclic capillary electrophoresis (SCCE)

Abstract A novel concept for ion separation is presented. Repeated column switching in capillary electrophoresis allows for the elimination of unwanted sample components, and for the separation of species having very similar mobilities. Theoretical considerations predict good separation efficiencies, e.g., high plate numbers per volt. Using micromachining techniques, a planar glass structure has been fabricated, composed of four capillaries of 20 mm length arranged in a square. Laser fluorescence detection is used in the detection scheme. To move a component around one cycle, 1 min is needed when applying 2.5 kV. A demonstration of the peak band broadening after several cycles and a separation example are given.

µ-TAS: Miniaturized Total Chemical Analysis Systems

The miniaturized total chemical analysis system is a concept for on-line monitoring combining classical analytical techniques and photolithographically defined micro structures. Examples of silicon and glass micro structures for flow-injection analysis, capillary liquid chromatography and capillary electrophoresis are given. The results obtained indicate faster separations, dramatically reduced reagent consumption, and access to novel types of analysis techniques.

Integrated Chip-Based Microcolumn Separation Systems

The prospects of inexpensive mass production of integrated chemical separation systems with superior analytical performance through modern microfabrication technology has stimulated considerable research activity over the past five years. In addition, these devices hold the promise of being extremely rugged, capable of analysis of very small sample volumes, and suitable for high-throughput analysis through parallel sample processing. The goal of the present article is to review major recent accomplishments in this rapidly advancing field. Since most research efforts up to now have been devoted to electric field driven separation systems, in particular to chip-based capillary electrophoresis, emphasis will be laid on the discussion of the physical-chemical basis of the operation and optimization of these devices.

Planar chip technology for capillary electrophoresis

Miniaturization of separation columns implies equally reduced volumes of injectors, detectors and the connecting channels. Planar chip technology provides a powerful means for the fabrication of micron sized structures such as channels. This is demonstrated with three examples. An optical absorbance detector chip exhibits the expected behavior of a 1 mm optical pathlength cell despite its volume of 4 nL. A capillary electrophoresis device allows for integrated injections of 100 pL samples, for efficiencies of 70 000 to 160 000 theoretical plates in 10 to 20 seconds, and for external laser-induced fluorescence detection at any capillary length of choice between 5 and 50 mm. A system for synchronized cyclic capillary electrophoresis is also presented in which plate numbers per volt can be dramatically increased.