Biogenic Syntheses of Gold Nanoparticles Using Plant Extracts

Abstract

A biogenic approach for the synthesis of gold nanoparticles (GNPs) by reducing chloroauric acid (HAuCl4) with three different plant extracts (from Angelica, Hypericum, and Hamamelis) is described. The content of reducing compounds (polyphenols) in each plant extract was determined by photometric dosing. The formation of GNPs was tracked by ultraviolet-visible spectroscopy and their characterization was performed using transmission electron microscopy (TEM) and atomic force microscopy (AFM) imaging and FTIR spectra. GNPs, with diameters ranging from about 4 nm to 8 nm, were obtained at room temperature and pH value about 8. They present various shapes from spherical, to ovals, heart or polyhedral forms. Generally, the GNPs colloidal dispersions are rather stable in time, and the self assembly of GNPs is sparsely observed. However, at lower concentration of the plant extract the tendency to self aggregation of the GNPs increased. The plant extracts contain reducing agents, compounds with stabilizing effect on the GNPs, but also components which mediate their self assembly. The GNPs obtained by these biogenic syntheses have potential biological and medical applications, taking into account at least two characteristics, their size and aqueous stability.