Ligand-Directed Formation of Gold Tetrapod Nanostructures

Abstract

Branched gold nanoparticles are synthesized via a soft-template-directed process using a biological buffer, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES). These branched Au nanoparticles are mainly tetrapods and show distinct absorption in the range of 700–1000 nm. A combined experimental and computational study suggests that at high concentration, the HEPES molecules self-assemble into structures with long-range order serving as soft templates to direct the formation of the anisotropic gold nanoparticles. Detailed analyses of surface chemistry and structure indicate the formation of a molecular bilayer structure for the stabilization of the branched Au nanostructures. Our density-functional theory (DFT) calculations predict that the sulfonate group of the HEPES molecules prefers to bind to the Au surfaces, while the free hydroxyl groups facilitate the self-assembly and bilayer formation through the formation of hydrogen bonds. By comparing three different buffer molecules, our study demonstr...