Photo-enhanced synergistic sterilization and self-regulated ion release in rGO-Ag nanocomposites under NIR irradiation.

Silver ions (Ag+) released from silver nanoparticles (Ag NPs) can help to improve the inhibition and killing ability of particles to bacteria. The leakage of Ag+ ions released from Ag NPs will lead to possible risks in cytotoxicity and environmental damage. It is still a challenge to balance particles' ions release and leakage to environment. Here, a nanocomposite of Ag NPs combined with reduced graphene oxide (rGO), labeled as rGO-Ag, was prepared by laser-induced photoreduction of Ag+ ions in solution. This composite exhibits not only a synergistic effect of Ag NPs and rGO in sterilization under normal circumstances, but also another synergistic effect from photothermal function under the 808 nm near-infrared (NIR) laser irradiation and the subsequent enhanced Ag+ ions release at high temperature. In experiments, rGO works as photothermal converter, which can directly cause the death of bacteria and force Ag+ ions to leave particle surface to assist in killing bacteria, and also as a catcher to intercepts the leakage of the released ions. After treating a 50 mg/L rGO-Ag solution with an NIR laser for 30 min, the concentration of released Ag+ ions increased, but these ions were subsequently adsorbed back onto the rGO. Compared with the no-light treatment group, the mortality rates of E. coli and S. aureus exposed to rGO-Ag under NIR irradiation increased by 39.06 % and 17.48 %, respectively. The clever combination between Ag NPs and rGO makes their composite exhibit a photo-enhanced synergistic sterilizing function, as well as a self-controlled ion release capability under NIR stimulation.