Increment of the FRET efficiency between carbon dots and photosensitizers for enhanced photodynamic therapy

Mg/N double-doped carbon dots (CDs) with a quantum yield up to 84.6% were synthesized by a one-step hydrothermal method, and the as-prepared CDs were then successfully used as carriers for an insoluble photosensitizer (chlorin e6, Ce6). Besides the high fluorescence quantum yield of the CDs, the short donor–acceptor distance and excessive acceptors per donor of the designed CDs–Ce6 system contributed to the high fluorescence resonance energy transfer (FRET) efficiency (up to 84%) and final enhanced photodynamic reaction. The CDs–Ce6 system showed excellent hydrophilicity and particularly tunable FRET efficiency. Its singlet oxygen (SO) quantum yield was double that of pure Ce6, and a significant photodynamic therapy (PDT) effect was proven on HepG2 cancer cells.