Controlling the Optical Properties of Gold Nanorods in One-Pot Syntheses

We present the characterization of the CTAB-oleate controlled synthesis of gold nanorods (AuNRs). Concentrations of key compounds in the synthetic system were varied in the presence of oleate, including HCl, borohydride, silver nitrate, and ascorbic acid. The longitudinal surface plasmon resonance peak was sensitive to changes in all concentrations. Reducing the concentration of Ag ions below 66 μM led to slower reaction kinetics and incomplete Au reduction. Variation of the ascorbic acid concentration revealed that oleate is responsible for around 44% of reduction of Au³⁺ to Au⁺ before nucleation in these experiments. Increasing the oleate concentration significantly slows the growth kinetics and leads to much longer synthesis times of above 12 h for reaction completion. These observations will enable the design of better methods of synthesizing of AuNRs using binary surfactants.