Curvature-directed assembly of gold nanocubes, nanobranches, and nanospheres

Gold nanocubes, nanobranches, and nanospheres were prepared in high yields using a seeded growth method in the presence of cationic surfactants. The resultant Au nanostructures are encapsulated with a surfactant bilayer and positively charged. The nanocubes are single-crystalline and enclosed with low-index facets. The nanobranches and nanospheres are multiply twinned. Each nanobranch possesses a varying number of sharp tips, which expose high-index facets. Glutathione was used to induce the assembly of the Au nanostructures, including both monocomponent (nanocubes and nanobranches) and bicomponent (nanocube-nanosphere and nanobranch-nanosphere) systems. The assembly was observed to occur predominantly at the vertices of the nanocubes and the sharp tips of the nanobranches. This curvature-directed assembly can be attributed to the preferential bonding of glutathione to the highly curved sites of the Au nanostructures. The fact that the curvature-directed assembly occurs for both the single-crystalline nanocubes and the multiply twinned nanobranches strongly suggests that the preferential bonding of glutathione to the curved sites is due to the less ordered surfactant bilayer at the curved sites than on the flat surfaces.