Carbon Quantum Dots as Drug Carriers of Methylene Blue: Preparation and Properties Study

Photodynamic therapy (PDT) has long been considered an effective way to tackle antibiotic resistance. Here, Methylene blue (MB) as photosensitizer was combined with carbon quantum dots (CQDs) as drug carriers to make a compound antibacterial agent. The fluorescent CQDs were prepared by hydrothermal method with citric acid (CA) and neutral red (NR) as raw materials. The CQDs can emit 640[Formula: see text]nm red fluorescence under 520[Formula: see text]nm laser irradiation. In the antibacterial experiment, CQDs-MB was irradiated with 660[Formula: see text]nm light. The results showed that CQDs-MB had ideal antibacterial activity against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) with 100% antibacterial concentration of 5[Formula: see text][Formula: see text]M and 10[Formula: see text][Formula: see text]M, respectively. The combination of CQDs and MB enhanced singlet oxygen ( 1 O 2 ) generation and the PDT activity of MB, which significantly increased the phototoxicity of MB to bacteria.