Carbon quantum dots/Bi4O5Br2 photocatalyst with enhanced photodynamic therapy: killing of lung cancer (A549) cells in vitro

Inorganic photocatalysts have been regarded as a promising candidate in the domain of tumor photodynamic therapy (PDT) due to their inspirational photocatalytic activity. In this study, a Bi4O5Br2 photocatalyst was synthesized and it exhibited effective photo-killing activity of A549 cells (a human lung carcinoma epithelial cell line) in vitro. On this basis, we modified Bi4O5Br2 with carbon quantum dots (CQDs) via a hydrolysis method at room temperature, which resulted in an improved photo-killing effect of Bi4O5Br2 to A549 cells. The samples and the interaction between samples and cells were fully characterized. It has been found that the loading of CQDs on Bi4O5Br2 can reduce the hydration ratio, increase the cellular uptake and improve the photogenerated reactive oxygen species (ROS) as compared with pristine Bi4O5Br2. Electron spin resonance (ESR) analysis and radical-trapping experiments manifested that the ROS contributed to PDT may be center dot O-2(-) and center dot OH. This study may provide a useful strategy to ameliorate the penetrability, cell compatibility and PDT effect upon cancer cells of other inorganic photocatalysts. Graphic abstract