Synthesis of gold nanostructures using glycine as the reducing agent

Abstract

Biological synthesis of gold nanostructures could potentially offer an environmentally friendly alternative to traditional chemical synthetic methods. During the last decades, amino acids have been successfully used as reducing and capping agent to synthesize multi-shaped gold nanostructures. A grand challenge in this field is to increase our ability to control size, shape and morphology of gold nanostructures formed precisely. In this study, using glycine as the model amino acid and chloroaurate (AuCl4-) ions as the precursor solution, we report the finding that the shape and amount of the gold nanostructures synthesized can be tuned by controlling the gold speciation and ionic state of the amino acid. The gold chloro-hydroxy speciation [AuClx(OH)4-x]- (with x = 0-4) influenced the shape of the gold nanostructure formed, with gold nanoplatelets, nanotriangles, nanokites and nanoribbons observed at x=4, 3, 2 and 1 respectively. Gold nanoparticles were observed for x =0. The ionic state of the glycine played an important role in regulating the concentration of synthesized gold nanostructures with the concentration increasing with decreasing [AuClx(OH)4-x]-/glycine ratio. These results collectively provide a rationale to controllably synthesize non-spherical to spherical gold nanostructures using amino acids as the reducing agent.