Self-assembled hyperbranched polymer-gold nanoparticle hybrids: understanding the effect of polymer coverage on assembly size and SERS performance.

In the past few years, remarkable progress has been made in unveiling novel and unique optical properties of strongly coupled plasmonic nanostructures. However, the application of such plasmonic nanostructures in biomedicine remains challenging because of the lack of facile and robust assembly methods for producing stable nanostructures. Previous attempts to achieve plasmonic nanoassemblies using molecular ligands were limited by the lack of flexibility that could be exercised in forming them. Here, we report the utilization of tailor-made hyperbranched polymers (HBP) as linkers to assemble gold nanoparticles (NPs) into nanoassemblies. The ease and flexibility in tuning the particle size and number of branch ends of an HBP make it an ideal candidate as a linker, as opposed to DNA, small organic molecules, and linear or dendrimeric polymers. We report a strong correlation of polymer (HBP) concentration with the size of the hybrid nanoassemblies and "hot-spot" density. We have shown that such solutions of stable HBP-gold nanoassemblies can be barcoded with various Raman tags to provide improved surface-enhanced Raman scattering (SERS) compared to that of nonaggregated NP systems. These Raman-barcoded hybrid nanoassemblies, with further optimization of the NP shape, size, and hot-spot density, may find application as diagnostic tools in nanomedicine.