Laser modification of preformed polymer microchannels: Application to reduce band broadening around turns subject to electrokinetic flow

A pulsed UV excimer laser (KrF, 248 nm) was used to modify the surface char ge on the side wall of hot-embossed microchannels fabricated in a poly(meth yl methacrylate) substrate. Subablation level fluences, less than 2385 mJ/c m(2), were used to prevent any changes in the physical morphology of the su rface. It is shown that the electroosmotic mobility, induced by an electric field applied along the length of the channel, increases by an average of 4% in the regions that have been exposed to UV laser pulses compared to non exposed regions. Furthermore, application of UV modification to electroosmo tic flow around a 90 degrees turn results in a decrease in band broadening, as measured by the average decrease in the plate height of 40% compared to flow around a nonmodified tam. The ability to modify the surface charge on specific surfaces within a preformed plastic microchannel allows for fine control, adjustment, and modulation of the electroosmotic flow without usin g wall coatings or changing the geometry of the channel to achieve the desi red flow profile.