Cellular-level insight into biointerface: From surface charge modulation to boosted photocatalytic oxidative disinfection

Photocatalytic oxidative disinfection (POD) towards pathogenic bacteria has become a popular approach in public health due to its environmentally friendly antimicrobial capabilities. However, this approach is still limited by inherent fast electron-hole recombination within photocatalysts and poor interactions between bacterial cells and photogenerated reactive oxygen species (ROS) at the biointerface. Particularly, those ROS with extremely short migration distances cannot reach the bacterial cells before they deteriorate into less potent or neutral species, resulting in reduced antibacterial activities. By far, these phenomena are still poorly understood. Inspired by the fact that bacterial cells are negatively charged, we rationally designed a photocatalyst (i.e., g-C3N4/MIL-125-NH2) by coating a layer of positively charged quaternary ammonium compound (QAC) polymer onto the surface to enhance its affinity towards bacterial cells via electrostatic attractions. This surface-modulated photocatalyst is denoted as [email protected]g-C3N4/MIL-125-NH2. The visualization and quantification of the electrostatic interactions between the bacterial cells and the [email protected]g-C3N4/MIL-125-NH2 photocatalyst were conducted using a confocal laser scanning microscope and atomic force microscope, respectively. The results showed that the positively charged QAC layer did promote the bacteria-photocatalyst contact via electrostatic attractions. Due to the cooperative effects of bacterial cell adhesion and ROS generation, the POD performance of the photocatalyst is significantly enhanced. Notably, the photocatalyst achieves 3.20 logs of inactivation efficiency for Staphylococcus epidermidis within 60 min under visible light irradiation. This work provides insights into a mechanistic understanding of bacterial adhesion and disinfection at the biointerface and sheds light on rational photocatalyst design with surface charge modulation for antibacterial applications.