Biosynthesis of gold nanoparticles using the bacteria Rhodopseudomonas capsulata

The use of microorganisms in the synthesis of nanoparticles emerges as an eco-friendly and exciting approach. In this study, the bacteria Rhodopseudomonas capsulata was screened and found to successfully produce gold nanoparticles of different sizes and shapes. The important parameter, which controls the size and shape of gold nanoparticles, was pH value. The R. capsulata biomass and aqueous HAuCl4 solution were incubated at pH values ranging from 7 to 4. The results demonstrated that spherical gold nanoparticles in the range of 10–20 nm were observed at pH value of 7 whereas a number of nanoplates were observed at pH 4.