Continuous Single-Phase Synthesis Of [Au-25(Cys)(18)] Nanoclusters And Their Photobactericidal Enhancement

Thiolate-gold nanoclusters have various applications. However, most of the synthesis methods require prolonged synthesis times from several hours to days. In the present study, we report a rapid synthesis method for [Au-25(Cys)(18)] nanoclusters and their application for photobactericidal enhancement. For [Au-25(Cys)(18)] synthesis, we employed a tube-in-tube membrane reactor using CO as a reducing agent at elevated temperatures. This approach allows continuous generation of high-quality [Au-25(Cys)(18)] within 3 min. Photobactericidal tests against Staphylococcus aureus showed that crystal violet-treated polymer did not have photobactericidal activity, but addition of [Au-25(Cys)(18)] in the treated polymer demonstrated a potent photobactericidal activity at a low white light flux, resulting in >4.29 log reduction in viable bacteria numbers. Steady-state and time-resolved photoluminescence spectroscopies demonstrated that after light irradiation, photoexcited electrons in crystal violet flowed to [Au-25(Cys)(18)] in the silicone, suggesting that redox reaction from [Au-25(Cys)(18)] enhanced the photobactericidal activity. Stability tests revealed that leaching of crystal violet and [Au-25(Cys)(18)] from the treated silicone was negligible and cyclic testing showed that the silicone maintained a strong photobactericidal activity after repeated use.