Microbial Synthesis of Multishaped Gold Nanostructures

The development of methodologies for the synthesis of nanoparticles of well‐defined size and shape is a challenging one and constitutes an important area of research in nanotechnology. This Full Paper describes the controlled synthesis of multishaped gold nanoparticles at room temperature utilizing a simple, green chemical method by the interaction of chloroauric acid (HAuCl4 · 3H20) and cell‐free extract of the fungal strain Rhizopus oryzae. The cell‐free extract functions as a reducing, shape‐directing, as well as stabilizing, agent. Different shapes of gold nanocrystals, for example, triangular, hexagonal, pentagonal, spherical, spheroidal, urchinlike, two‐dimensional nanowires, and nanorods, are generated by manipulating key growth parameters, such as gold ion concentration, solution pH, and reaction time. The synthesized nanostructures are characterized by UV/Vis and Fourier‐transform infrared spectroscopy, transmission electron microscopy, and energy dispersive X‐ray analysis studies. Electron diffraction patterns reveal the crystalline nature of the nanoparticles and a probable mechanism is proposed for the formation of the different structural entities. A simple, protein‐mediated, green chemical methodology is proposed for the synthesis of multishaped (triangular, hexagonal, pentagonal, spherical, spheroidal, urchinlike, two‐dimensional nanowires, and nanorods) gold nanostructures. The proteins function as a reducing, shape directing, and stabilizing agent.