Novel Zwitterionic Copolymers with Dihydrolipoic Acid: Synthesis and Preparation of Nonfouling Nanorods

We report the synthesis of hydrophilic, zwitterionic copolymers containing pendent disulfide and dithiol groups along a phosphorylcholine methacrylate backbone. These novel copolymers were prepared by controlled free radical copolymerization of methacryloyloxyethyl phosphorylcholine (MPC) and the methacrylate of lipoic acid (LA), using reversible addition-fragmentation chain transfer (RAFT) polymerization, followed by reduction of the disulfides to give dihydrolipoic acid (DHLA) pendent groups. Poly(MPC-co-DHLA) proved useful for surface functionalization of gold nanorods (Au NRs), resulting in removal of the cationic surfactant stabilizing layer present initially on the Au NRs. Au NRs coated with poly(MPC-co-DHLA) proved stable against challenging conditions, and resisted cyanide ion digestion. Au NRs coated with poly(MPC-co-DHLA) also showed nonfouling properties resulting from their surface coating, and the noncytotoxicity of these structures was confirmed in the presence of live cells. The novel polymer materials and the methodology we describe hold promise for enabling new opportunities that utilize surface-coated metallic and semiconductor nanostructures in both materials and biological applications.