Hyaluronan-assisted photoreduction synthesis of silver nanostructures: From nanoparticle to nanoplate

In this work, a new photoreduction method is developed to fabricate different Ag nanostructures by using biopolymer hyaluronan (HA) as a reductant and stabilizing agent. In the experiment, a very interesting phenomenon is discovered that the shape of nanostructrues is highly dependent on the storage time of HA and AgNO3 solution before their mixing for the photoreduction. With fresh and aged solution, spherical nanoparticle and triangular nanoplate can be simply synthesized in only 15 min, respectively. The nanostructures were characterized by UV-vis, SEM, HR-TEM, and XRD. The formation mechanism of the silver nanoplates from an aged solution is discussed and ascribed to the radicals generated from aged HA and small silver clusters generated from the aged AgNO3 solution. This work maybe gives a new clue for fast photoreduction synthesis of silver nanoplates. The application of the nanostructures in surface enhanced Raman scattering (SERS) of HA was investigated, showing that the enhancement effect of the Ag nanoplate is much stronger than that of the Ag spherical nanoparticle. The enhancement efficiency is greatly dependent on the shape and the irradiation time. This work renders not only a fast photoreduction simple route for shape-controlling synthesis of Ag nanostructures, but also a facile approach to investigate the Raman spectra of HA by in situ generated Ag nanostructures.