Characterization of polyelectrolyte multilayers coated on capillary electrophoresis microchips

The characterization of polyelectrolyte layers adsorbed on the surface of poly(dimethyl siloxane)/glass microchannels is presented. The effect of polyelectrolyte structure, pH, and NaCl on electroosmotic flow (EOF) and film stability was determined in an attempt to develop coatings to control EOF in microchip devices. Polymer rigidity and cross-sectional area influenced the stability of cationic coatings with poly (diallyl dimethyl ammonium chloride) being the least stable while hexadimethrine and poly (allyl amine) (PAA) were more stable. The addition of NaCl to the deposition solution improved the stability while slightly reducing the total EOF for PAA films. PAA coated microchannels showed pH dependent reversible electroosmotic flow. At acidic pH, the flow direction proceeded from cathode to anode while at basic pH the flow direction proceeded from anode to cathode. Single layer PAA films were stable for more than 6 hours. The formation of double layer systems showed consistent EOF as a function of pH from 4--10 for 6 different double layer coatings. EOF on ceramic chips was tested. Channels of the 15 mum, the 30 mum and the 60 mum exhibited stable EOF. This material has the potential for generating desirable EOF especially when high potential is applied.