Seed‐Mediated Overgrowth of Gold Nanorods: Effects of Reducing Agents and Amino Acids

The seed‐mediated overgrowth reaction of anisotropic gold nanorod (GNR) has been studied with commonly used weak reducing agents such as ascorbic acid (AA), hydroquinone (HQ), and hydroxylamine (HA) in the presence or absence of amino acids as the stabilizing agents. The HQ and AA mostly show the seed‐independent reduction of Au 3+ to form aggregated spherical gold nanoparticles (NPs) irrespective of the presence or absence of neutral amino acids. However, basic amino acids can stabilize the newly formed spherical NPs without affecting the morphology of GNR, leading to seed‐independent growth. Replacing the reducing agent with HA during the overgrowth reaction yields small snowflake nanoarchitectures via an assembly and merging process. Interestingly, HA‐assisted seed‐mediated overgrowth, in the presence of basic amino acids, results in the transformation of GNR to a nanodumbbell structure via deposition of the incoming Au 0 on the curvature end of GNR. However, larger snowflake structures are formed during a similar reaction with HA in the presence of neutral amino acids due to a greater reduction of Au 3+ . Varying Au 3+ precursor concentrations indicate the formation of a smaller assembly, followed by the merging of GNRs, with both (111) and (200) crystallographic axes present, forming snowflake structures.