Effects of Growth Solutions Ageing Time to the Formation of Gold Nanorods via Two-Step Approach for Plasmonic Applications

We demonstrate the structural reorganization of gold nanorods (GNRs) that could fine-tune localized surface plasmon resonance (LSPR) by using modified wet chemical synthesis on the solid substrate. Controlling the growth solution ageing time using the modifiable GNRs is an approach to overcome the limitations of rods formation due to inhomogeneous and uncontrollable size and aspect ratio. In this study, the suitable ageing time of GNRs was determined to produce optimum GNRs in terms of surface density and aspect ratio. As the ageing time was increased from 30 min to 24 h, the colour of the growth solution was changed from light to dark purple. The change is associated with the density of the nanorods formation. The optical spectral peaks of GNRs occur in a range between 500 nm and 800 nm in the visible and near-infrared region spectrum for transverse surface resonance (t-SPR) and longitudinal surface resonance (l-SPR), respectively. From the morphological analysis, it was found that 20 h ageing time resulting in high density and homogeneous GNRs with 74.81% surface density with 4.23 ± 0.04 aspect ratio. Hence, the growth ageing time of GNRs can be manipulated to control their shape evolution and dimension in terms of size and aspect ratio. The controllable aspect ratio and size GNRs can be potentially used as sensing material in plasmonic applications.