Triangular silver nanoparticles: their preparation, functionalisation and properties

Abstract

This paper reports our progress towards developing a reproducible and rapid method to prepare triangular silver nanoplates. The methods are all based on a seed-mediated procedure involving the reduction of silver ions with ascorbic acid in aqueous solution and have variously involved polyvinylalcohol, citrate, and polystyrene-sulphonate as modifiers. The triangular silver nanoplate sols have well defined local surface plasmon resonances, which can be tuned throughout the visible and near IR. Aspect ratio (the ratio of edge length to thickness)is shown to be a fundamental parameter determining the triangular silver nanoplate sol properties including, the position of their local surface plasmon resonances maxima and suppression of local surface plasmon resonance retardation effects. The high ensemble sensitivities of the triangular silver nanoplate sol local surface plasmon resonance to changes in the surrounding refractive index within the spectral range appropriate for biosensing is attributed to their high aspect ratio. Silver nanoparticles are more challenging to functionalise than the analogous gold systems, as they are prone to oxidation and are susceptible to degradation by chloride ions. Two methods to stabilise triangular silver nanoplates (treating with thiols and coating with gold) and the formation of gold nanoboxes from the triangular silver nanoplates are also described.