Shape controlled synthesis of multi-branched gold nanocrystals through a facile one-pot bifunctional biomolecular approach

Abstract

Anisotropic nanocrystals of gold and silver are promising candidates for sensing and therapeutic applications because of their high extinction coefficient, increased NIR response and localization of hot spots at their tips. Herein, we report a viable room temperature synthetic strategy to prepare multi-branched gold nanocrystals of varying morphologies without the aid of additional nanoseeds or shape directing agents. By systematically modulating the bifunctional ligand to the Au³⁺ ion molar ratio ([L-DOPA]/[HAuCl₄] = 0.15–1), the plasmon absorption was tuned from visible (530 nm) to NIR (930 nm). The corresponding microscopic studies showed a gradual transformation of the nanomaterial's morphology from multiply twinned spheres to branched stars and flowers. The detailed spectroscopic and microscopic studies have revealed that evolution of these branched nanocrystals proceeds through aggregation and subsequent overgrowth of initially produced spherical particles.