Unexpected Enhancement of the Antibacterial Activity of Copper Ions in the Presence of Nanobubbles

Copper ions (Cu 2+ ) exhibit broad-spectrum antibacterial properties, but their efficacy is often constrained by bacterial homeostasis and concentration limitations. Herein, we report a remarkable enhancement of the antibacterial activity of Cu 2+ ions in the presence of nanobubbles (NBs). While NBs alone had no bactericidal effect, their combination with Cu 2+ significantly reduced the survival of Escherichia coli . Synchrotron radiation Fourier-transform infrared (SR-FTIR) spectroscopy revealed that the Cu 2+ –NBs mixture induced substantial changes in protein and lipid components, while nucleic acids and polysaccharides remained largely unaffected. Furthermore, NBs accelerated the decomposition of hydrogen peroxide catalyzed by Cu 2+, generating hydroxyl radicals as confirmed by electron spin resonance (ESR) spectroscopy. These results indicate that NBs enhance the catalytic activity of Cu 2+ toward the formation of reactive oxygen species, leading to increased oxidative damage to bacterial membranes. This work provides new insights into the synergistic antibacterial mechanism of Cu 2+ and NBs and proposes a potential strategy for improving copper-based antibacterial materials.