Poly(2-hydroxyethyl methacrylate) Hydrogels Doped with Gold Nanoparticles for Surface-Enhanced Raman Spectroscopy

Poly(2-hydroxyethyl methacrylate) hydrogels doped with gold nanoparticles (Au-PHEMA) were prepared via photochemically and thermally induced phase separation polymerization of aqueous formulations containing 2-hydroxyethyl methacrylate (HEMA), a cross-linker, an initiator, and either KAuCl4 or (CH3)(2)SAuCl. In photopolymerizations, 2,2-dimethoxy-2-phenylacetophenone (DPAP) served as the photoinitiator of polymerization of HEMA but also appeared to play a role in the reduction of Au(III) to Au(0). For thermal polymerizations, potassium persulfate (K2S2O8) was used to initiate polymerization of HEMA, and it appeared that the resulting PHEMA was responsible for the reduction of Au(III) to Au(0). The Au-PHEMA hydrogels exhibited the morphology based on a network of polymer droplets and interconnected pores characteristic of PHEMA formed via polymerization-induced phase separation, with only minor differences in the sizes of the polymer droplets and mechanical properties. The application of Au-PHEMA as a platform for surface-enhanced Raman scattering was demonstrated using an 80 ppb solution of 4-ethynylbenzaldehyde as an analyte.