Improved biological synthesis of gold nanoparticles using methanobactin

The present study reported a novel approach for the green synthesis of gold nanoparticles (AuNPs) by using methanobactin (Mb) from the spent medium of Methylosinus trichosporium 3011. This paper explored the synthesis of AuNPs under different Mb concentrations, temperatures, and reaction times. The biosynthesized AuNPs were characterized by using UV-Visible spectroscopy, fluorescence spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). Comparing with the previous research using hydroquinone as an extra electron donor to synthesis of AuNPs, this research was the first to show that rising temperature improved the formation rate of AuNPs in a higher concentration of Mb itself. The formation of AuNPs was confirmed by surface plasmon resonance using UV-Visible spectrophotometry. Fluorescence spectroscopy experiments revealed that Mb sample showed three prominent peaks. In addition, the fluorescence exhibited by Mb was rapidly quenched upon addition of HAuCl4. According to the image analysis performed on a TEM micrograph, the obtained AuNPs were predominantly spherical with an average size of 19.3 +/- 5.5 nm. XPS analysis demonstrated that Mb molecules reduced Au(III) to Au(0). FTIR spectrum confirmed the involvement of biomass groups in capping and reduction of AuNPs, which increased the stability of the synthesized AuNPs.