Near-Infrared Light Mediated Photodynamic Therapy Based on Nanocomposite of Upconversion Nanoparticles and Graphitic Carbon Nitride Quantum Dots

Based on the latest statistics from the Ministry of Health and Welfare, malignant tumor continues to be on top of disease, and then followed by the heart disease and cerebrovascular disease, so the diagnosis and medical treatment has become one of the major issues. Nowadays, cancer treatments still focus on surgical resection, chemotherapy and radiation therapy, but it still can be improved for the more effective treatment. As a result, human beings have continued to investigate novel adjuvant cancer therapy in recent years, photodynamic therapy (PDT) is now becoming a widely used medical tool. Compared with the traditional therapy, photodynamic therapy is recognized as a minimally invasive procedure, also has little side effect and can selectively lead to tumor necrosis. The purposes of this research is to fabricate a lanthanide-doped upconversion nanoparticles (UCNPs) nanocomposite by combining with graphitic carbon nitride (g-C 3 N 4 ) photosensitizer for near-infrared (NIR) light mediated PDT application. First, we synthesized upconversion nanoparticles by high temperature co-precipitation method, and then the ligand on the surface were removed via the treatment with hydrochloric acid to obtain water-dispersible nanoparticles. Furthermore, ligand-free upconversion nanoparticles modified with poly-L-lysine (PLL) in order to render the positive-charged group which can allow the attachment of the g-C 3N4 by electrostatic assembling. Through the excitation of continuous wave NIR laser, upconversion nanoparticles can convert the low-energy NIR light to high energy ultraviolet (UV) or visible light. Owing to this unique optical property of upconversion nanoparticles, the UV light will further photoexcites g-C3N4 at 365 nm, emit the green light and release reaction oxygen species (ROS). Meanwhile, we also modified different concentration of PLL to achieve a moderate condition for high g-C3N4 loading and ensuring maximum energy transfer from UCNPs to g-C3N4 photosensitizer, so as to generate a significant amount of ROS, which can result in tumor cell necrosis and apoptosis for efficient PDT effect.