Genotoxic, cytotoxic, antimicrobial and antioxidant properties of gold nanoparticles synthesized by Nocardia sp. GTS18 using response surface methodology

This work focused on production of the gold nanoparticles (AuNPs) by easily available, safe to handle, eco-friendly, and cost effective method based on utilization of Nocardia sp. GTS18 supernatant. The different process variables affecting AuNPs synthesis were evaluated using both 'one factor at time' and 'response surface' methodologies. The optimum levels, detected through central composite design, were HAuCl₄ concentration of 1.1 mM, pH 4.68, and 17.01 h incubation time. The AuNPs (40–45 nm) synthesized under optimum condition exhibited surface plasmon resonance band centered at 540–545 nm, characteristically. The x-ray diffraction analysis revealed that the crystallite size of synthesized nanoparticle was about 11.4 nm. Fourier transform infrared spectroscopy confirms that the significance of proteins and carbohydrates present in supernatant for reduction of HAuCl₄ ions and stabilization of synthesized AuNPs. The synthesized AuNPs showed excellent antibacterial and moderate antioxidant properties. Furthermore, the AuNPs showed no particular signs of genotoxicity and cytotoxicity on lymphocytes at 12.5–100 μg ml⁻¹ concentrations. This study is, as far as we know, the first report on microbial AuNPs synthesized through this statistical approach and their biological properties. (paper)