Low-Cytotoxic Core-Sheath ZnO NWs@TiO_2-xN_y Triggered Piezo-photocatalytic Antibacterial Activity

Sonophotodynamic antimicrobial therapy (SPDAT) is recognized as a highly efficient biomedical treatment option, known for its versatility and remarkable healing outcomes. Nevertheless, there is a scarcity of sonophotosensitizers that demonstrate both low cytotoxicity and exceptional antibacterial effectiveness in clinical applications. In this paper, a novel ZnO nanowires (NWs)@TiO_2-xN_y core-sheath composite was developed, which integrates the piezoelectric effect and heterojunction to build dual built-in electric fields. Remarkably, it showed superb antibacterial effectiveness (achieving 95% within 60 min against S. aureus and ∼100% within 40 min against E. coli, respectively) when exposed to visible light and ultrasound. Due to the continuous interference caused by light and ultrasound, the material's electrostatic equilibrium gets disrupted. The modification in electrical properties facilitates the composite's ability to attract bacterial cells through electrostatic forces. Moreover, Zn-O-Ti and Zn-N-Ti bonds formed at the interface of ZnO NWs@TiO_2-xN_y, further enhancing the dual internal electric fields to accelerate the excited carrier separation to generate more reactive oxygen species (ROS), and thereby boosting the antimicrobial performance. In addition, the TiO₂ layer limited Zn²⁺ dissolution into solution, leading to good biocompatibility and low cytotoxicity. Lastly, we suggest a mechanistic model to offer practical direction for the future development of antibacterial agents that are both low in toxicity and high in efficacy. In comparison to the traditional photodynamic therapy systems, ZnO NWs@TiO_2-xN_y composites exhibit super piezo-photocatalytic antibacterial activity with low toxicity, which shows great potential for clinical application as an antibacterial nanomaterial.