Shape-controlled synthesis of nanostructured gold by a protection-reduction technique

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 less than or equal to 3 and 4-6, respectively. This simple and effective method can be used for other noble metals.