Dual Functional, Polymeric Self-Assembled Monolayers as a Facile Platform for Construction of Patterns of Biomolecules

We report a facile approach to the construction of patterns of biomolecules based on polymeric self-assembled monolayers (pSAMs) that possess dual functions:  “bio-reactive (post-functionalizable)” and “bio-inert (anti-biofouling)” properties. To prepare pSAMs on Si/SiO₂ wafers were synthesized new random copolymers by radical polymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMA), 3-(trimethoxysilyl)propyl methacrylate (TMSMA), and N-acryloxysuccinimide (NAS), and referred to as poly(TMSMA-r-PEGMA-r-NAS). Poly(TMSMA-r-PEGMA-r-NAS) was designed to play triple roles:  “surface-reactive”, “bio-reactive”, and “bio-inert” ones. The pSAMs of poly(TMSMA-r-PEGMA-r-NAS) were formed on Si/SiO₂ wafers with 1 h incubation of the substrates in the polymer solution, which showed approximately a 1 nm-thick film as measured by ellipsometry. After the formation of the pSAMs, the feasibility of the pSAMs as a dual functional surface (bio-inert and bio-reactive properties) was examined. The ability of the pSAMs to block nonspecific adsorption of proteins was evaluated against bovine serum albumin as a model protein. High-resolution N(1s) X-ray photoelectron spectroscopy (XPS) analysis on the protein adsorption revealed that significant reduction up to ∼97% was observed compared to the unmodified Si/SiO₂ wafer. In addition, micropatterns of streptavidin with high signal-to-noise ratios were achieved using microcontact printing (μCP) of NH₂-bearing biotin onto the pSAMs of poly(TMSMA-r-PEGMA-r-NAS) on glass slides, which suggests that other biomolecules could also be efficiently immobilized onto the pSAMs with high specificity while minimizing nonspecific adsorption. On the other hand, the surface density of both bio-reactive and anti-biofouling functionality could be tailored by simply changing initial feed ratios of each monomer in the polymer synthesis:  different molar ratios of the bio-reactive group (NAS:  33%, 20%, and 10%, respectively) were employed. When micropatterns of streptavidin were constructed, the pSAMs with 33% NAS moiety showed the highest immobilization of the protein. Taken together, the present dual functional, random copolymers may have warrant applications in the field of biosensors and biochips.