Contributions of Surface Oxidizing Species and Cu⁺ to the Antibacterial Activities of Cu₂O with Different Crystalline Structures

Although precise regulation of the crystalline structures of metal oxides is an effective method to improve their antibacterial activities, the corresponding mechanisms involved in this process are still unclear. In this study, three kinds of cuprous oxide (Cu₂O) samples with different structures of cubes, octahedra, and rhombic dodecahedra (c-Cu₂O, o-Cu₂O, and r-Cu₂O) have been successfully synthesized and their antibacterial activities are compared. The antibacterial activities follow the order of r-Cu₂O > o-Cu₂O > c-Cu₂O, revealing the significant dependence of the antibacterial activities on the crystalline structures of Cu₂O. Quenching experiments, as well as the NBT and DPD experiments indicate that ≡Cu^II─OO^• superoxo and ≡Cu^II─OOH peroxo, instead of •OH, O₂^•-, and H₂O₂, are the primary oxidizing species in the oxidative damage to <i>E. coli</i>. Raman analysis further confirms the presence of both ≡Cu^II─OO^• superoxo and ≡Cu^II─OOH peroxo on the surface of r-Cu₂O. On the other hand, the NCP experiment reveals that Cu⁺, instead of Cu²⁺, also contributes to the antibacterial process. This study provides new insight into the antibacterial mechanisms of Cu₂O.