Abstract

We describe a novel method to control the shape and size of Au nanoparticles using a protection–reduction technique. The remarkable feature of this method is that the reducing and protecting agents were mixed first prior to addition to the solution of KAu(CN)₂.The reactivity and concentration of reducing agent, the molar ratio of ascorbic acid (AA)/poly(vinylpyrrolidone) (PVP) and the redox potential of the Au complex anion have significant effects on the formation and growth of these novel nanostructures. The Au nanoparticles self-assembly into dendritic structures at molar ratios of AA/PVP > 7 while spherical and cubic nanoparticles form at ratios of AA/PVP ≤ 3 and 4–6, respectively. This simple and effective method can be used for other noble metals.