Synthesis of silver and silver/gold anisotropic nanostructures for surface enhanced Raman spectroscopy applications.

We are reporting the one pot chemical reduction synthesis of isotropic spherical silver nanoparticles of size around 4-8 nm and some anisotropic nanostructures of silver and silver-gold systems such as silver nanoprisms of size around 60-80 nm, silver/gold prismatic core/shell nanostructures of size around 30-50 nm and alloy like silver-gold prismatic nanoframes of size around 40-60 nm and investigated their plasmonic properties for the surface enhanced Raman spectroscopy (SERS) applications. Morphology and shape dependent plasmonic properties of these nanostructures were characterized by using high resolution transmission electron microscopy (HRTEM) and UV-Visible spectroscopy techniques respectively. The surface enhanced Raman spectroscopy (SERS) properties of all the fabricated nanostructures were investigated on Methylene Blue (MB) molecule. A gradual improvement in the SERS effect was observed with respect to the change of morphology from spherical to nanoframes and the order of SERS effect was found to be nanoframes > core/shell prismatic nanostructures > nanoprisms > spherical nanoparticles. Our investigation revealed that the phenomenon of the improved SERS effect of anisotropic silver and silver-gold nanostructures is primarily attributed to their prismatic geometrical configurations.