Role of hydrodynamic size in colloidal and optical stability of plasmonic Copper nanoparticles

Abstract

Metallic nanoparticles (NPs) exhibit interesting plasmonic characteristics that depend on their size, shape and dielectric medium. Any change in these parameters can lead to significant alternation in plasmonic behaviour of NPs. Plasmonic nanostructures are prepared by wet chemical approaches, which produce NPs with a moderate yield. Amongst plasmonic class of NPs, gold and silver are widely explored in sensors because of their strong plasmon excitation. Copper NPs (CNPs) are gaining increasing attention in plasmonic sensors because of its economic advantages over silver and gold. However, major limitations of these nanostructures are their low yield and poor colloidal stability. In this Letter, authors report scale up of CNPs yield by 100% and studied their colloidal stability in terms of changes in hydrodynamic size and its influence on surface plasmon resonance (SPR). It has been observed that SPR of CNPs is independent of their yield. A gradual decrease in SPR is observed with ageing. This can be attributed to the aggregation-induced microstructural changes in the dispersion. CNPs irrespective of their yield are stable up to 180 days beyond which they lose their colloidal stability and plasmonic properties. Loss of colloidal and plasmonic characteristics of CNPs can be attributed to enhanced hydrodynamic size.