Cysteine-induced growth of jagged gold bipyramids from penta-twinned nanorod seeds

The understanding on the growth mechanism of complex gold nanostructures both experimentally and theoretically can guide their design and fabrication toward various applications. In this work, we report a cysteine-directed overgrowth of penta-twinned nanorod seeds into jagged gold bipyramids with discontinuous stepped {hhk} facets. By monitoring the growth process, we find that {hhk} facets with large k/h values (∼7) are formed first at two ends of the nanorods, followed by the protrusion of the middle section exposing {hhk} facets with smaller indices (k/h ∼ 2-3). Molecular dynamics simulations indicate that the strong adsorption of cysteine molecules on {110} facets is likely responsible for the formation of stepped {hhk} facets, and the stronger adsorption of cysteine molecules on {hhk} facets with smaller k/h compared to that on {hhk} facets with larger k/h is a possible cause of the discontinuity of {hhk} facets at the middle of gold bipyramids. The obtained jagged gold bipyramids display large field enhancement under illumination due to their sharp nanostructures, demonstrating their application potentials in surface-enhanced spectroscopy and catalysis.