Defining the Role of Iodide in the Synthesis of Gold Nanotriangles

Plate-like Au nanotriangles have unique LSPR properties and high anisotropic properties which can produce significant hot spot enhancement effect and signal amplification originating from their sharp vertices. Although the iodide in the reaction has been assigned a role (as I^-) of inhibiting Au(111) facet growth and a digestion agent (as I₃^-) of non-nanotriangle impurities neither iodide ions nor triiodide ions are detected in the growth solution. In this study, a complex, [AuI_yCl_2-y], has been identified as the precursor to the Au(0) seeds in the synthesis of Au nanotriangles (AuNT). Preferential adsorption of I^- on the Au (111) facets relative to the Au (100) facets of the Au(0)NP seeds, results in selective growth along the Au(100) facets. The role of iodide therefore has been re-defined two functions in the formation of the AuNT, first as a constituent in this complex and second as a surface adsorbate that preferentially binds to the Au (111) facets cf the Au(100) edges of a developing plate. Control of the formation and reaction conditions of the seed precursor complex provides an entry point to the sought after reproducible, one-pot synthesis of AuNT.