Surface confined living radical polymerization and its application in coating microfluidics for use in protein electrophoretic separation

Electrophoretic separations of proteins on microfluidic chips made of glass, silica or polymer materials are limited by their electrostatic or hydrophobic interactions with microchannel surfaces. Hydrophilic polymer coating on the surface by surface confined living radical polymerization is investigated to solve these problems.; Surface initiated atom transfer radical polymerization (ATRP) of acrylamide is achieved on silica at room temperature by using a catalytic system of CuCl/CbCl ₂/tris(2-dimethylaminoethyl)amine. The thickness of the polyacrylamide film is controllable either by monomer concentration or by reaction time. Kinetics of the reaction is studied and compared with the same reaction using a CuCl/bipyridine catalytic system. It is concluded that at room temperature, both the rate for chain propagation and termination are higher, despite a much higher concentration of Cu(II) to reduce the radical population at room temperature. Termination is caused by radical combination and most of the chlorine loss is due to the combination of initiator radicals.; The surface of polydimethysiloxane (PDMS) is modified by surface oxidation, forming of a monolayer and coating of polyacrylamide by ATRP. ATR-FTIR is used to characterize the functional groups on the surface. Optimum oxidation time and reaction conditions are probed. The modified surface exhibits a 20-fold improvement in resisting irreversible adsorption of lysozyme, compared to bare PDMS, and a 10-fold improvement compared to bare glass. The hydrophobic recovery of oxidized PDMS, is prevented. The surface remains hydrophilic for at least one month.; The modification of PDMS microchips with polyacrylamide by ATRP is investigated. The resistance to protein adsorption in open-channel electrophoresis is studied by analyzing the voltage-dependence of the electropherogram of bovine serum albumin. Plate heights of 35 μm were obtained at all voltages, and this was shown to be due to a distribution of species. There is no detectable contribution to broadening from adsorption. No evidence of irreversible adsorption of the protein was observed. The separation of lysozyme and cytochrome C was achieved in a separation length of 3.5 cm. It is concluded that the growth of polyacrylamide chains on PDMS reduced hydrophobic and electrostatic interactions to avoid protein adsorption to the inner wall of the PDMS microchannels.