Near-Infrared Light-Mediated Photodynamic Therapy Nanoplatform by the Electrostatic Assembly of Upconversion Nanoparticles with Graphitic Carbon Nitride Quantum Dots

Photodynamic therapy (PDT) is a promising antitumor treatment that is based on photosensitizers. This therapy kills cancer cells by generating reactive oxygen species (ROS) after irradiation with specific laser wavelengths. Being a potential photosensitizer, graphitic carbon nitride (g-C₃N₄) quantum dots (QDs) are noncytotoxic. Although the use of g-C₃N₄ QDs is challenged by the limited tissue penetration of UV light, g-C₃N₄ QDs display excellent ultraviolet (UV) light-triggered cytotoxicity. The g-C₃N₄ QDs were synthesized using a solid-phase hydrothermal method. The well-distributed hydrophilic g-C₃N₄ can be combined with NaYF₄:Yb³⁺/Tm³⁺ upconversion nanoparticles via the positive ligand poly(l-lysine) to produce the final nanocomposite, NaYF₄:Yb/Tm-PLL@g-C₃N₄. Upconversion nanoparticles can transfer IR light into UV light and promote g-C₃N₄ to release blue-to-green visible light to generate different images. Moreover, g-C₃N₄ is a promising photosensitizer in PDT because g-C₃N₄ can transfer oxygen into toxic ROS. The singlet oxygen formed by g-C₃N₄ displays great potential for use in the treatment of cancer.