Fabrication of Graphitic Carbon Nitride Quantum Dots and Their Application for Simultaneous Fluorescence Imaging and pH-Responsive Drug Release

A simple approach is developed to produce fluorescent graphitic carbon nitride quantum dots (g-CNQDs) by refluxing bulk graphitic carbon nitride (g-C3N4) in HNO3 followed by a direct hydrothermal treatment. Owing to their small size, intrinsic optical properties, low toxicity, and useful non-covalent interactions with the antitumor drug doxorubicin (DOX), g-CNQDs are investigated as fluorescent nanocarriers for DOX without any pre-modification. The inherent fluorescence of g-CNQDs and DOX provides the drug delivery system (g-CNQDs-DOX) with dual-color imaging for revealing the intracellular localization of g-CNQDs and DOX release. The release profiles of DOX from g-CNQDs-DOX reveal a strong dependence on the environmental pH value, which is beneficial for mollifying side effects following chemotherapy. Cellular uptake of g-CNQDs-DOX indicates that not only DOX but also some g-CNQDs penetrate cell nuclei after 16 h of incubation, which leads g-CNQDs-DOX to be more toxic than DOX. The results demonstrate the feasibility of using g-CNQDs as a traceable and pH-responsive drug delivery system due to their unique structural properties.