Fabrication of PEGylated graphitic carbon nitride quantum dots as traceable, pH-sensitive drug delivery systems

A simple approach is developed to produce fluorescent PEGylated graphitic carbon nitride quantum dots (g-CNQDs-PEG) by refluxing bulk graphitic carbon nitride (g-C3N4) in HNO3 followed by a hydrothermal treatment using diamine-terminated oligomeric poly(ethylene glycol) (PEG) as a surface passivation agent. During the hydrothermal process, g-C3N4 quantum dots (g-CNQDs) are formed in situ and become embedded in the PEG matrix, while the presence of PEG enhances their luminescence, stability in the physiological environment, and biocompatibility. The as-prepared g-CNQDs-PEG are then loaded with the anti-cancer drug doxorubicin (DOX), and the drug system exhibits a pH-sensitive release profile. Based on the inherent fluorescence of g-CNQDs-PEG and DOX, the controlled drug release behavior is successfully monitored and confirmed without employing external dyes. The results suggest that g-CNQDs-PEG are suitable as a drug carrier and for cell imaging.