Hyperbranched Polymer-old Nanoparticle Assemblies: Role of Polymer Architecture in Hybrid Assembly Formation and SERS Activity

Plasmonic gold nanoassemblies that self-assemble with the aid of linking molecules or polymers have the potential to yield controlled hierarchies of morphologies and consequently result in materials with tailored optical (e.g., localized surface plasmon resonances (LSPR)) and spectroscopic properties (e.g., surface-enhanced Raman scattering (SERS)). Molecular linkers that are structurally well-defined are promising for forming hybrid nanoassemblies which are stable in aqueous solution and are increasingly finding application in nanomedicine. Despite much ongoing research in this field, the precise role of molecular linkers in governing the morphology and properties of the hybrid nanoassemblies remains unclear. Previously we have demonstrated that branched linkers, such as hyperbranched polymers, with specific anchoring end groups can be successfully employed to form assemblies of gold NPs demonstrating near-infrared SPRs and intense SERS scattering. We herein introduce a tailored polymer as a versatile molecular linker, capable of manipulating nanoassembly morphologies and hot-spot density. In addition, this report explores the role of the polymeric linker architecture, specifically the degree of branching of the tailored polymer in determining the formation, morphology, and properties of the hybrid nanoassemblies. The degree of branching of the linker polymer, in addition to the concentration and number of anchoring groups, is observed to strongly influence the self-assembly process. The assembly morphology shifts primarily from 1D-like chains to 2D plates and finally to 3D-like globular structures, with increase in degree of branching of the macromolecular linker. Insights have been gained into how the morphology influences the SERS performance of these nanoassemblies with respect to hot-spot density. These findings supplement the understanding of the morphology determining nanoassembly formation and pave the way for the possible application of these nanoassemblies as SERS biosensors for medical diagnostics.