Sunlight-Mediated Antibacterial Activity Enhancement of Gold Nanoclusters and Graphene Co-decorated Titanium Dioxide Nanocomposites

Titanium dioxide (TiO2) as one of the most important biocompatible semiconductor nanomaterials, has been widely used as antibacterial agents. However, since it is only active under ultraviolet radiation, its application has been dramatically limited. Here, TiO2 nanoparticle (NP)-Au nanocluster (NC)-graphene (TAG) nanocomposites were designed to improve the antibacterial activity of TiO2 NPs under sunlight condition. Incorporation of Au NCs and graphene into TiO2 NPs can significantly enhance the solar energy utilization efficiency and promote the electron–hole separation, leading to enhanced reactive oxygen species (ROS) production in TAG, as evidenced by dihydrorhodamine 123 and DCF assays. Bacterial growth inhibition assessments revealed that TAG nanocomposites possessed more potent antibacterial activity against both gram-negative Escherichia coli (E. coli) and gram-positive Staphylococcus aureus (S. aureus) bacteria than TiO2 NPs alone. Scanning electron microscope images of bacteria further displayed that TAG could cause severe damage on the surface membrane structure of both E. coli and S. aureus bacteria. Intracellular ROS production, glutathione depletion, and lipid peroxidation of bacteria were found to be elicited by TAG, suggesting the molecular mechanism underlying their antibacterial activity is possibly based on oxidative stress.