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

Copper ions (Cu²⁺) 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 Cu²⁺ ions in the presence of nanobubbles (NBs). While NBs alone had no bactericidal effect, their combination with Cu²⁺ significantly reduced the survival of <i>Escherichia coli</i>. Synchrotron radiation Fourier-transform infrared (SR-FTIR) spectroscopy revealed that the Cu²⁺-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 Cu²⁺, generating hydroxyl radicals as confirmed by electron spin resonance (ESR) spectroscopy. These results indicate that NBs enhance the catalytic activity of Cu²⁺ 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 Cu²⁺ and NBs and proposes a potential strategy for improving copper-based antibacterial materials.