DNA-accelerated atom transfer radical polymerization on a gold surface.

A significantly increased polymer growth rate was observed during a surface-initiated ATRP reaction in the presence of DNA molecules. To investigate this phenomenon, thiolated single-stranded DNA molecules (ssDNAs) with ATRP initiators coupled at the distal point were used as the model molecule in the study. In comparison, a small molecule, HS-(CH(2))(11)NHCOC(CH(3))(2)Br, was used to provide a less-polar surface coating for polymer grafting. 2-Hydroxyethyl methacrylate (HEMA) and monomethoxy-capped oligo(ethylene glycol) methacrylate (OEGMA) were used as the ATRP monomers. The polymer growth rates were monitored by measuring the thickness of the polymer films formed at different times. Our results show that the presence of DNA molecules, although at a less-than-1% surface coverage, significantly accelerated the growth rates of both poly(2-hydroxyethyl methacrylate) (PHEMA) and poly(oligoethylene glycol methacrylate) (POEGMA) at the beginning of the ATRP reactions. This accelerating effect was suspected to be a combined result of the highly charged sugar-phosphate backbones of DNA molecules and the formation of Cu complexes with DNA bases. After the initial polymer growth, a smaller yet constant polymer growth rate was observed, suggesting the reduced influence of DNA molecules as the ATRP reaction centers moved farther away from the surface. Similar to conventional ATRP reactions, the polymer growth from surface-anchored DNA molecules was found to be strongly dependent on the composition and the concentration of the catalysts used. Specifically, a catalyst mixture of CuCl/30% CuBr(2)/bpy with 23 mM CuCl was found to provide the optimal reaction condition to yield the fastest polymer film growth among the conditions tested.