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Upconversion Nanoparticles-Induced Multi-Mode Photodynamic Therapy Based on Metal-Organic Framework/Titanium Dioxide Nanocomposite.

Photodynamic therapy (PDT) possesses two pathways depending on the type of high toxicity reactive oxygen species (ROS), superoxide anion radical (O2•-) and hydroxyl radical (•OH) generated through Type I and singlet oxygen (1O2) generated through Type II, inducing cancer cell apoptosis. However, the low efficiency of ROS generation and poor biocompatibility are the limitations of the traditional photosensitizers for PDT. Herein, inspired by photochemical reactions of titanium dioxide and porphyrin-based metal-organic frameworks (MOFs), we developed a nanoplatform by covering ultra-small titanium dioxide nanoparticles on a heterodimer made up of upconversion nanoparticle and metal-organic frameworks, realizing multi-mode PDT through Type I and Type II mechanisms. Once irradiated by near-infrared light, upconversion nanoparticles could generate ultraviolet and visible light, which was not only able to stimulate different photochemical reactions of titanium dioxide and porphyrin, but also accomplishing deep penetration photodynamic therapy. Our photosensitive agent exhibited good biocompatibility and effective multi-mode PDT performance, which could meet the needs of different situations of photodynamic therapy in the future.