Seeded Growth of Large Gold Nanorods Modulated by Halide-Mediated Kinetics

We report a robust and versatile method to overgrow pentatwinned gold nanorods using a combination of cetyltrimehylammonium chloride (CTAC) and bromide (CTAB), thereby expanding current protocols to the production of larger nanorod dimensions. When increasing CTAB content in the reaction medium, the aspect ratio of the resulting nanorods was found to decrease, due to the higher binding energy of bromide on gold surfaces, compared to chloride. A further handle to tailor the dimensions of larger nanorods can be achieved by tuning the Au3+/Au0 ratio. At a fixed CTAB concentration, increasing Au3+/Au0 ratio resulted in larger nanorods with minor variation of the aspect ratio, which again highlights the central role of CTAB in the overgrowth process. Our findings highlight the effect of CTAB on both growth kinetics and facet stabilization, offering a simple approach to finely tune the dimensions of pentatwinned gold nanorods. We also demonstrate the versatile use of CTAB/CTAC ratio in a more standard synthesis method, again leading to fine tuning of nanorod dimensions.