Formation of different gold nanostructures by silk nanofibrils

Metal nanostructures that have unique size- and shape-dependent electronic, optical and chemical properties gain more and more attention in modern science and technology. In this article, we show the possibility that we are able to obtain different gold nanostructures simply with the help of silk nanofibrils. We demonstrate that only by varying the pH of the reaction solution, we get gold nanoparticles, nano-icosahedrons, nanocubes, and even microplates. Particularly, we develop a practical method for the preparation of gold microplates in acid condition in the presence of silk nanofibrils, which is impossible by using other forms of silk protein. We attribute the role of silk nanofibrils in the formation of gold nanostructure to their reduction ability from several specific amino acid residues, and the suitable structural anisotropic features to sustain the crystal growth after the reduction process. Although the main purpose of this article is to demonstrate that silk nanofibrils are able to mediate the formation of different gold nanostructure, we show the potential applications of these resulting gold nanostructures, such as surface-enhanced Raman scattering (SERS) and photothermal transformation effect, as same as those produced by other methods. In conclusion, we present in this communication a facile and green synthesis route to prepare various gold nanostructures with silk nanofibrils by simply varying pH in the reaction system, which has remarkable advantages in future biomedical applications.