Microcapillary electrophoresis devices fabricated using polymeric substrates and X-ray lithography

Abstract

An integrated microdevice for the analysis of DNA restriction fragments or sequencing fragments is currently being constructed in our laboratory and consists of two principal components: a piezo-driven micropump and a microelectrophoresis device with integrated fluorescence detector. The syringe pump consisted of a piezoelectric actuator and a pivoted lever for amplification to deliver solvents free from pump pulsations at volumetric flow rates approaching 1 nL/min, even at high loading levels (high output pressures). The flow was programmed by controlling the voltage waveform to the piezo-actuator to produce a linear displacement of 80 μm and, by using the pivoted lever, a total linear displacement of 650 μm was achieved. The total volume delivered in a single pump stroke was 565 nL. The piezo-pump was found to adequately deliver stable flow of solutions with loading pressures as high as 3.79×105 Pa (actual loading pressure at the piezo is 3.41×106 Pa). The second component consisted of an electrophoresis device micromachined in polymethylmethacrylate (PMMA) using X-ray lithography (LIGA). The device was fabricated using a transfer mask technique, in which the channel topography was transferred to a PMMA substrate coated with a positive photoresist and a thin Au/Cr plating base using an optical mask with subsequent X-ray exposure to produce the desired channel topography. The channels were found to be 20 μm in width (determined by optical mask) with channel depths of 50 μm (determined by X-ray exposure time) and aspect ratios of approximately 1:10,000, significantly better than those obtained using wet-chemical etching in glass. The detection apparatus used a fiber optic to deliver the laser light to the electrophoresis device with the emission collected via the same fiber and the wavelength sorting accomplished with a dichroic filter. Since the electroosmotic flow in the PMMA was found to be approximately 5 times smaller compared to glass at typical separation pH for DNA (8.6), the walls of the PMMA device would not require a polymer coating to reduce this flow when performing high-resolution DNA separations. © 1998 John Wiley & Sons, Inc. J Micro Sep 10: 413–422, 1998