Large-Scale Synthesis of Gold Nanorods through Continuous\nSecondary Growth

Abstract

Gold\nnanorods (GNRs) exhibit a tunable longitudinal surface plasmon\nresonance (LSPR) that depends on the GNR aspect ratio (AR). Independently\ncontrolling the AR and size of GNRs remains challenging but is important\nbecause the scattering intensity strongly depends on the GNR size.\nHere, we report a secondary (seeded) growth procedure, wherein continuous\naddition of ascorbic acid (AA) to a stirring solution of GNRs, stabilized\nby cetyltrimethylammonium bromide (CTAB) and synthesized by a common\nGNR growth procedure, deposits the remaining (∼70%) of the\nAu precursor onto the GNRs. The growth phase of GNR synthesis is often\nperformed without stirring, since stirring has been believed to reduce\nthe yield of rod-shaped nanoparticles, but we report that stirring\ncoupled with continuous addition of AA during secondary growth allows\nimproved control over the AR and size of GNRs. After a common primary\nGNR growth procedure, the LSPR is ∼820 nm, which can be tuned\nbetween ∼700 and 880 nm during secondary growth by adjusting\nthe rate of AA addition or adding benzyldimethylhexadecylammonium\nchloride hydrate (BDAC). This approach for secondary growth can also\nbe used with primary GNRs of different ARs to achieve different LSPRs\nand can likely be extended to nanoparticles of different shapes and\nother metals.