Enhanced catalytic and SERS performance of shape/size controlled anisotropic gold nanostructures

In the present work, we have effectively utilised the reducing/capping ability of polyvinylpyrrolidone (PVP, 40 000 molecular weight) for the versatile synthesis of various anisotropically shaped (hexagonal, triangle, decahedral and star) gold nanostructures. Controllable size, shape and stability of the nanoparticles (NPs) were achieved by merely changing the surrounding reaction media (such as water, alcohol, DMF etc.). It has been well-established that variations in the inherent chemical structure of the polymer, PVP, in different solvents essentially play a crucial role in the stabilisation of these as-synthesized Au NPs. In particular, for the star-shaped Au NPs, the core size, tip length and the number of tips were effortlessly controlled using different molar ratios of PVP to Au metal ions under varying pH of the reaction medium. The corresponding localised surface plasmon resonance (LSPR) peaks of these different Au NPs were broadly tunable right from the visible to the near-infrared (NIR) region. Also, all our as-prepared Au NPs are shown to be enhanced refractive index sensors by way of their linearly increased LSPR stability with the dielectric constant of the surrounding media. Further, the higher number of sharp tips and the highest tip-to-core ratio of star-shaped Au NPs demonstrate excellent performance both in catalysis and surface-enhanced Raman scattering (SERS) activities. An excellent catalytic rate constant and a SERS enhancement factor as high as B109 are evaluated from detailed, careful studies and established from the comparative performance analysis of our present Au NPs.