Oxidative stress-mediated selective antimicrobial ability of nano-VO₂ against Gram-positive bacteria for environmental and biomedical applications

Vanadium dioxide (VO₂) is a unique thermochromic material as a result of its semiconductor-metal transition, holding great promise for energy-saving intelligent windows. Herein, pure nano-VO₂ from discrete nanoparticles to continuous films were successfully deposited on quartz glass by controlling the sputtering parameters. It was demonstrated that, for Gram-positive S. aureus and S. epidermidis, the nano-VO₂ could effectively disrupt bacteria morphology and membrane integrity, and eventually cause death. By contrast, the nano-VO₂ did not exhibit significant toxicity towards Gram-negative E. coli and P. aeruginosa. To our knowledge, this is the first report on a selective antimicrobial effect of nano-VO₂ materials on Gram-positive bacteria. Based on the experimental results, a plausible mechanism was proposed for the antimicrobial selectivity, which might originate from the different sensitivity of Gram-positive and Gram-negative bacteria to intracellular reactive oxygen species (ROS) level. Elevated intracellular ROS levels exceed the threshold that bacteria can self-regulate to maintain cellular redox homeostasis and thus cause oxidative stress, which can be alleviated by the intervention of glutathione (GSH) antioxidant. In addition, nano-VO₂ did not produce significant cytotoxicity (hemolysis) against human erythrocytes within 12 h. Meanwhile, potential cytotoxicity against HIBEpiC revealed a time- and dose-dependent behavior that might be controlled and balanced by careful design. The findings in the present work may contribute to understanding the antimicrobial behavior of nano-VO₂, and to expanding the new applications of VO₂-based nanomaterials in environmental and biomedical fields.