Self-driven charge transfer mechanism of Bi NPs/PCN-224 for enhanced photodynamic antimicrobial chemotherapy effect

Semiconductor nanomaterials with photocatalytic activity have been identified as a promising class of antimicrobial agents to combat bacterial infections. In this study, a photocatalytic antibacterial and anticancer agent, Bi NPs/PCN-224, was synthesized by doping Bi NPs in PCN-224, obtained through hydrothermal process of porphyrin, using benzoic acid as a morphology modifier. The resulting Bi NPs/PCN-224 exhibited impressive photocatalytic activity with a great potential for therapeutic treatment of bacterial infections. An in-situ reductive growth method was adopted to form interfaces between the Bi NPs and the Schottky groups of PCN-224, which was believed to play key role to sustain the photo-induced electron-hole separation. The underlying mechanism is then revealed, where Bi NPs initiate a self-driven charge transfer to PCN-224 MOF through the Schottky interface, exerting large quantities of free electrons to surrounding oxygen species, thereby generating radical oxygen species (ROS). Furthermore, when exposed to the physiological environment of bacteria, the redox potential of Bi NPs/PCN-224 enable the electron to transfer to the interior of bacterial cells through electron pathways located on cell membrane, which interferes with the respiratory process and subsequent metabolism of the bacteria. In a similar mechanism, Bi NPs/PCN-224 demonstrated inhibition of the growth of HepG2 cells. The combination of Density Functional Theory (DFT) calculations and experimental characterization indicated that Bi clusters are bound to the MOFs via the N site on the TCPP ligand.