Plastic microfluidic devices modified with polyelectrolyte multilayers

Control of the polymer surface chemistry is a crucial aspect of development of plastic microfluidic devices. When commercially available plastic subst rates are used to fabricate microchannels, differences in the EOF mobility from plastic to plastic can be very high. Therefore, we have used polyelect rolyte multilayers (PEMs) to alter the surface of microchannels fabricated in plastics. Optimal modification of the microchannel surfaces was obtained by coating the channels with alternating layers of poly(allylamine hydroch loride) and poly(styrene sulfonate). Polystyrene (PS) and poly(ethylene ter ephthalate) glycol (PETG) were chosen las substrate materials because of th e significant differences in the polymer chemistries and in the EOF of chan nels fabricated in these two plastic materials. The efficacy of the surface modification has been evaluated using XPS and by measuring the EOF mobilit y. When microchannels prepared in both PS and PETG are modified with PEMs, they demonstrate very similar electroosmotic mobilities. The PEMs are easil y fabricated and provide a means for controlling the now direction and the electroosmotic mobility in the channels. The PEM-coated microchannels have excellent wettability, allowing facile filling of the channels. In addition , the PEMs produce reproducible results and are robust enough to withstand long-term storage.