Upconversion Nanoparticle-Induced Multimode Photodynamic Therapy Based on a 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, we developed a nanoplatform by covering ultrasmall titanium dioxide nanoparticles on a heterodimer made up of upconversion nanoparticles and metal–organic frameworks, realizing a multimode PDT through Type I and Type II mechanisms. Once irradiated by a near-infrared light, upconversion nanoparticles could generate ultraviolet and visible lights, which were not only able to stimulate different photochemical reactions of titanium dioxide and porphyrin but also accomplish deep penetration photodynamic therapy. Our photosensitive agent exhibited good biocompatibility and an effective multimode PDT performance, which could meet the needs of different situations of photodynamic therapy in the future.