Reactive oxygen species production by photoexcited (CuInS₂)_x(ZnS)_1-x quantum dots and their phototoxicity towards Staphylococcus aureus bacteria

The photoproduction of reactive oxygen species (ROS) by semiconductor nanocrystals is of high interest for biological and environmental applications. Herein, water-dispersible 3-mercaptopropionic (MPA)-capped (CuInS2)(x)(ZnS)(1-x) quantum dots (ZCIS@MPA QDs) were prepared from dodecanethiol-capped ZCIS QDs by a ligand exchange and their photoreactivity was evaluated. By combining colorimetric and fluorescent probes with electron spin resonance (ESR) measurements, we showed that ZCIS@MPA QDs can photogenerate ROS like hydroxyl (OH)-O-center dot and superoxide O-2(center dot-) radicals and singlet oxygen O-1(2) that alter the MPA ligand and participate in photoluminescence quenching. The phototoxicity of ZCIS@MPA QDs against S. aureus bacteria and the inhibition of the cell growth on a surface were further investigated. These deleterious effects of ROS photoproduced by ZCIS@MPA QDs could significantly be reduced by coupling the antioxidant glutathione peptide with the QDs. Our findings enrich the understanding of photochemical reactions mediated by ZCIS@MPA QDs but also provide new pathways for ROS production, even under ambient light, that may be valuable for antibacterial applications like surface disinfection.