Formation of naturally-occurring gold nanoparticles by photosensitive surfactant Tween 80/85 under light irradiation: A new origin in aquatic environment

The induced-formation of natural nanoparticles by photosensitive chemicals in aquatic environment may be a ubiquitous process, however, we still know very little on this issue. Here, we reported a potential original pathway for naturally-occurring gold nanoparticles (N-AuNPs) via the reduction of Au ions by photosensitive surfactant Tween 80/85 under light irradiation in the aquatic environment. The heterolytic reaction of hydroxyl groups in Tween 80/85 with the aid of UV light yielded radical anions (Tween 80/85-O •− ) and subsequently transferred electrons to oxygen to generate superoxide radicals (O 2 •− ), which reduced Au(III) to Au(0). The negatively charged Tween 80/85-O •− could bind to the surface of Au with coordinate bonds to form the surface coating of N-AuNPs. Due to the enhanced negative charge density, the Tween 80/85-induced N-AuNPs showed a higher colloidal stability than other N-AuNPs (induced by humic acid) or engineered AuNPs (E-AuNPs). The surface coating of Tween 80/85 might hinder the attachment and internalization of N-AuNPs into bacterial cells, and bacteria could also extend the utilization range of carbon sources substrates to mitigate the adverse effects of N-AuNPs. Therefore, Tween 80/85-induced N-AuNPs exhibited relative lower ecotoxicity but could stay in water for long periods of time. This study makes us more aware of the role of anthropogenic organic pollutants in the geochemical process of metal elements.