Revisiting the Role of Seed Size for the Synthesis of Highly Uniform Sub-10 nm Length Gold Nanorods

Despite the advances achieved in the past decade in the seed-mediated synthesis of colloidal single-crystal gold nanorods (Au NRs), the seed size role in the Au NR formation is not fully understood. Moreover, although the anisotropic growth of single-crystal seeds typically occurs at sizes between 4 and 6 nm, synthesizing high-quality Au NRs with sub-10 nm lengths remains challenging. We investigated herein the effect of seed dimensions on the silver-assisted seed-mediated growth of single-crystal Au NRs with lengths below 10 nm in the presence of hexadecyltrimethylammonium bromide (CTAB). A strong relationship was found between the seed dimensions and the yield of Au NR formation, where 3.1 nm seeds displayed an optimal anisotropic grow behavior. This effect could be related to the different abilities of CTAB micelles to passivate gold seeds with distinct dimensions, as suggested by molecular dynamic experiments. Compared with the 1-2 nm seeds traditionally used in the Au NR synthesis, the enhanced ability of 3.1 nm seeds to evolve anisotropically facilitates the growth of high-quality Au NRs with sub-10 nm lengths in an unprecedented manner. An optimal concentration of silver was also critical for the efficient evolution of 3.1 nm seeds into sub-10 nm Au NRs. Moreover, the synthesized small Au NRs were used as anisotropic seeds to fabricate sub-10 nm diameter Au NRs with tunable aspect ratios and core-shell electrocatalysts. The insight gained on the role of seed size enabled us to develop an advanced reproducible and scalable route for the synthesis of Au NRs with sub-10 nm lengths.