Engineered g-C₃N₄ Quantum Dots for Tunable Two-Photon Imaging and Photodynamic Therapy

Near-infrared (NIR)-light-triggered diagnostic and therapeutic systems normally are the integration of several components, whose complex structures and low reproducibility restrict their further applications. Herein, we proposed a single component of defect graphitic phase carbon nitride quantum dots (g-C₃N₄ QDs) as a dual-functional nanoplatform, which could synchronously achieve two-photon imaging (TPI) and two-photon excited photodynamic therapy (TPE-PDT) under an 800 nm NIR laser. In order to regulate the competitive capability between TPI and PDT, three kinds of engineered g-C₃N₄ QDs (CN, CN-DPT, and CN-THDT QDs) with different two-photon catalytic capabilities to generate reactive oxygen species (ROS) were prepared through copolymerization melamine with selected monomers. In the evaluation of in vitro cytotoxicity, three g-C₃N₄ QDs possessed very good biocompatibilities, which could be delivered to tumor cells for imaging and therapy. Under an 800 nm NIR light, CN-DPT QDs exhibited a bright TPI effect and produced an efficient ROS to achieve TPE-PDT, thus suggesting that the single component of CN-DPT QDs could perform as an appropriate dual-functional TPI and TPE-PDT probe triggered by an 800 nm NIR light. The engineered g-C₃N₄ QDs with a high stability and excellent biocompatibility have contributed to the method of TPI and TPE-PDT, which may lead to g-C₃N₄-based nanomaterials as novel imaging and therapeutic agents in cancer treatment.