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.
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