Tweaking anisotropic gold nanostars: covariant control of a polymer–solvent mixture complex

A binary solvent mixture (N, N-dimethylformamide (DMF)-propanol in the present case) has been employed for the first time in a simple yet versatile approach for the in situ intuitive and highly tweaked formation of complex anisotropic gold nanostructures. In this novel approach, the uncommon usage of a polar/nonpolar binary solvent mixture provides extra degrees of freedom in tailoring the intrinsic solution properties via simultaneously modifying dipole-dipole and H-bonding interactions with the universally soluble amphiphilic polymer PVP. Interactions are carefully monitored through NMR, which further establishes a rational paradigm in better understanding the kinetic control over both nucleation and size/shape transition/evolution of reproducible anisotropic Au nanostructures, as revealed/correlated through optical absorption and TEM measurements respectively. This unusual size/shape transformation strategy for gold nanostructures allows precise tuning of their respective plasmonic characteristics over the entire visible/NIR spectral range, significantly enabling them to serve as excellent candidates/substrates for tunable surface enhanced Raman spectroscopy (SERS), the preliminary measurements of which are systematically illustrated.