Surface Modification of Siliceous Materials Using Maleimidation and Various Functional Polymers Synthesized by Reversible Addition-Fragmentation Chain Transfer Polymerization

A novel surface modification method was investigated. The surface of siliceous materials was modified using polystyrene, poly(acrylic acid), poly(N-isopropylacrylamide), and poly(p-acrylamidophenyl-alpha-mannoside) synthesized by reversible addition-fragmentation chain transfer polymerization. Thiol-terminated polymers were obtained by reduction of the thiocarbonate group using sodium borohydride. The polymers were immobilized on the surface via the thiol-ene click reaction, known as the Michael addition reaction. Immobilization of the polymers on the maleimidated surface was confirmed by X-ray photoelectron spectroscopy, infrared spectroscopy, and contact angle measurements. The polymer-immobilized surfaces were observed by atomic force microscopy, and the thickness of the polymer layers was determined by ellipsometry. The thickness of the polymer immobilized by the maleimide-thiol reaction was less than that formed by spin coating, except for polystyrene. Moreover, the polymer-immobilized surfaces were relatively smooth with a roughness of less than 1 nm. The amounts of amine, maleimide, and polymer immobilized on the surface were determined by quartz crystal microbalance measurements. The area occupied by the amine-containing silane coupling reagent was significantly less than the theoretical value, suggesting that a multilayer of the silane coupling reagent was formed on the surface. The polymer with low molecular weight had the tendency to efficiently immobilize on the maleimidated surface. When poly(p-acrylamidophenyl-alpha-mannoside)-immobilized surfaces were used as a platform for protein microarrays, strong interactions were detected with the mannose-binding lectin concanavalin A. The specificity of poly(p-acrylamidophenyl-alpha-mannoside)-immobilized surfaces for concanavalin A was compared with poly-L-lysine-coated surfaces. The poly-L-lysine-coated surfaces nonspecifically adsorbed both concanavalin A and bovine serum albumin, while the poly(p-acrylamidophenyl-alpha-mannoside)-immobilized surface preferentially adsorbed concanavalin A. Moreover, the poly(p-acrylamidophenyl-alpha-mannoside)-immobilized surface was applied to micropatterning with photolithography. When the micropattern was formed on the poly(p-acrylamidophenyl-alpha-mannoside)-spin-coated surface by irradiation with ultraviolet light, the pattern of the masking design was not observed on the surface adsorbed with fluorophore-labeled concanavalin A using a fluorescent microscope because of elution of poly(p-acrylamidophenyl-alpha-mannoside) from the surface. In contrast, fluorophore-labeled concanavalin A was only adsorbed on the shaded region of the poly(p-acrylamidophenyl-alpha-mannoside)-immobilized surface, resulting in a distinctive fluorescent pattern. The surface modification method using maleimidation and reversible addition-fragmentation chain transfer polymerization can be used for preparing platforms for microarrays and micropatterning of proteins.