Room temperature aqueous synthesis of bipyramidal silver nanostructures

The proposed strategy demonstrates a simple method to synthesize the pentagonal right bipyramidal silver nanostructures in aqueous phase at room temperature. Aqueous synthesis enables the materials for direct use in biological systems. The sharp edges of silver nanostructures multiply SERS (surface enhanced Raman spectroscopy) signals by many folds. We have explored a combination of a cationic surfactant, namely, cetyl tri-methyl ammonium bromide (CTAB) and a well-known polymer, polyvinyl pyrrolidone (PVP) for capping preferential crystallographic facets of silver nanosurface. The structural transformation of these anisotropic nanostructures was studied by following various factors, such as, effect of Ag seed concentration, the ratio of concentration of CTAB to the concentration of silver nitrate, the effect of PVP, the ascorbic acid concentration dependence and the effect of pH. CTAB functions as template directing agent while PVP acts as a shape directing agent. Zeta potential measurements and Fourier Transform Infra-red (FTIR) spectral analysis reveal that PVP substitutes CTAB over the facets of silver nanobypiramids.