Direct high-yield synthesis of high aspect ratio gold nanorods

We report a new development for the direct high-yield synthesis of high aspect ratio gold nanorods. By using a modified seed-mediated synthesis approach for the preparation of high aspect ratio gold nanorods with the addition of an appropriate amount of nitric acid during nanorod growth, uniform and monodispersed gold nanorods were synthesized in large quantity. The formation of triangular nanoplate byproducts was substantially reduced by replacing trisodium citrate with cetyltrimethylammonium bromide (CTAB) surfactant as the capping agent in the preparation of gold seeds. The percent yield of nanorods produced can be as high as over 90% after a simple purification step. The nanorods have an average length of 355.3 +/- 31.3 nm and an average diameter of 18.7 nm, giving them an average aspect ratio of 19. These nanorods can spontaneously self-assemble into highly ordered side-by-side packing structures over a large area. The X-ray diffraction pattern revealed a very strong (111) diffraction peak. The ultra-small gold seeds used for nanorod growth were similar to 1-2 nm in diameter and showed a weak surface plasmon resonance (SPR) absorption band centered at similar to 480 nm. The nanorods showed a transverse SPR absorption band at 497 nm and a longitudinal SPR band at similar to 2135 nm. Because of the large reduction in the amount of triangular and truncated triangular nanoplates formed, the absorbance of the nanoplates at 830 nm has been lowered substantially.