Tuning of Morphology and Stability of Gold Nanostars Through pH Adjustment

In this study, the morphology and stability of gold nanostars (AuNSs) were investigated under different pH environments. The surface morphologies and plasmonic properties were observed for nanostars (NSs) deposited on glass substrates, using SEM and ultraviolet and visible (UV-Vis) spectroscopy. It is found that gold nanostars can be readily stabilized just by adjusting the initial pH condition of the growth solution. The particle size distribution of gold nanostars under different pH environments has been investigated using UV-Vis spectroscopy and found to be highly dependent on pH. At the optimal pH of 11, the gold nanostars are highly monodisperse, they have longer branches and the Au Localized Surface Plasmon Resonance band (LSPR) at 720 nm. For other pH conditions, particles are non-uniform and polydisperse, showing a red-shift of the plasmon peak due to aggregation and a large particle size distribution. Time-dependent UV-Vis spectra studies hypothesize the pH dependent stabilization mechanism, where the formation and stabilization of AuNS were affected greatly by the aggregation induced by pH of the growth solution. The information obtained in this study can be used to design stable gold nanostars with longer shelf life for biosensing applications.