Carbon-Bridged-Mediated Electron Transfer in Cu₂O-ZnO Nanocomposites Enabling ROS-Driven Antimicrobial Activity

Engineering interfacial electronic interactions between physically distinct metal oxides without phase transformation, doping, or lattice fusion remains a central challenge of interface science. Conventional Cu₂O-ZnO systems rely on heterojunction formation or compositional mixing, whereas carbon-mediated electronic coupling between discrete phases remains largely unexplored. Here, we report strongly electronically coupled carbon-bridged Cu₂O/ZnO nanocomposites (Cu₂O-C-ZnO NCs) synthesized by incorporating spherical Cu₂O and diamond-shaped ZnO nanoparticles into a gallic-acid-derived carbon framework. Structural and compositional analyses confirm the coexistence of crystalline Cu₂O and ZnO interlocked in a homogeneous carbon matrix, with oxygenated carbon functionalities verified spectroscopically. X-ray photoelectron spectroscopy reveals binding energy shifts in Cu and Zn core levels, providing direct evidence of interfacial electronic coupling and charge redistribution without lattice fusion or heterojunction formation. This electronic interface coupling helps regulate charge transfer between the oxide materials, allowing the controlled release of metal ions and enhancing the generation of reactive oxygen species. As a functional consequence, the NCs exhibit significant antibacterial activity against Gram-negative and Gram-positive bacteria, as well as substantial antialgal activity against freshwater species. Mechanistic evidence validates that the activity stems from a synergy of phenomena, including controlled ion release, ROS, and membrane damage due to oxidative stress, supported by findings from enzymatic and cellular assays. These results demonstrate that carbon-mediated interfacial electronic coupling is a viable method for controlling the surface reactivity of multicomponent oxide systems with the intact structural integrity of individual components.