Functionalization of Poly(oligo(ethylene glycol) methacrylate) Films on Gold and Si/SiO2 for Immobilization of Proteins and Cells: SPR and QCM Studies

Abstract

Thin films of a biocompatible and nonbiofouling poly(oligo(ethylene glycol) methacrylate) (pOEGMA) with various thicknesses were formed on gold and Si/SiO₂ substrates by a combination of the formation of self-assembled monolayers (SAMs) terminating in bromoester—an initiator of atom transfer radical polymerization (ATRP)—and surface-initiated ATRP. After the formation of the pOEGMA films, terminal hydroxyl groups of side chains divergent from the methacrylate backbones were activated with N,N′-disuccinimidyl carbonate (DSC), and the DSC-activated pOEGMA films were reacted with (+)-biotinyl-3,6,9-trioxaundecanediamine (Biotin-NH₂) to form biotinylated pOEGMA films. By surface plasmon resonance experiments with the target protein (streptavidin) and model proteins (fibrinogen and lysozyme), we verified that the resulting films showed the enhanced signal-to-noise ratio (∼10-fold enhancement) for the biospecific binding of streptavidin compared with the biotinylated substrate prepared from carboxylic acid-terminated SAMs. Quartz crystal microbalance measurements were also carried out to obtain the surface coverage of streptavidin and fibrinogen adsorbed onto the biotinylated pOEGMA films with various thicknesses and to investigate the effect of film thicknesses on the biospecific binding of streptavidin. Both the binding capacity of streptavidin and the signal-to-noise ratio of streptavidin/fibrinogen were found to be saturated at the 20 nm thick pOEGMA film. In addition, to demonstrate a wide applicability of the pOEGMA films, we constructed micropatterns of streptavidin and cells by microcontact-printing biotin-NH₂ and poly-l-lysine onto the DSC-activated pOEGMA films, respectively.