Nanobubbles as a promising bacterial deactivation tool: Deactivation mechanism and ROS detection

This study hypothesized that bacterial deactivation by NBs is primarily driven by oxidative damage. This damage results from the production of ROS and ORP of NBs, which depends on the type of gas they contain. To validate this hypothesis, a comparative antibacterial activity analysis of O₃-NBs, O₂-NBs, and Air-NBs was conducted on E. coli and S. aureus. The ROS and ORP levels were quantified for each type of gaseous NBs. Protein release from bacterial cells was measured as a biomarker of NBs-induced oxidative damage. FESEM was employed for the visual confirmation of the bacterial cell wall degradation. O₃-NBs achieved a 99.99% bacterial reduction within 15 min of treatment, outperforming O₂-NBs (83.89% for E. coli, 64.17% for S. aureus) and Air-NBs (79.38% for E. coli, 56.12% for S. aureus) over 60 min. The superior bacterial deactivation property of O₃-NBs was attributed to the elevated ORP and ROS generation. Oxidative damage was confirmed by protein release assays and FESEM data. These findings underscore that the antibacterial efficacy of NBs is primarily driven by their ORP and ROS generation properties, which depend on the type of gas in the NBs.