Biogenic Synthesis of Gold Nanoparticles

The cells-free supernatant of S. albogriseolus was used to synthesize GNPs. A stock solution of 1000 μg/mL gold (III) was prepared by dissolving precise amount of Gold (III) chloride trihydrate (HAuCl₄.3H₂O) in distilled water. The cells-free supernatant of S. albogriseolus was mixed with varying concentrations of HAuCl₄ solution at a 1:2 volume-to-volume ratio, and the mixture was then incubated at 37 °C in the dark for 24–96 h. After the incubation period, the mixture's color changed to red or dark purple as a result of the reduction of gold chloride and GNPs formation. As a control, the cells-free supernatant was used without the addition of HAuCl₄ solution.