Red fluorescent carbon dots for tumor imaging and photodynamic-enzyme catalyzed combined therapy

Photodynamic therapy (PDT) has been attracted much attention due to noninvasive and low toxicity characteristics, but the most photosensitizers possess some disadvantages such as hydrophobicity, which seriously affects their application. Carbon dots (CDs) had been widely used in the biomedical field due to its good water-dispersion and biosecurity. However, the development of red fluorescence carbon dots (R-CDs) with high water dispersibility and photosensitivity for integrated tumor imaging and treatment remains a challenge. Herein, CDs with red fluorescence (BCC-CDs) were prepared by solvothermal method using Chlorin e6 (Ce6) and natural biomass Bupleurum chinense (BC) as precursors. The abundant molecular structure of BC, it not only enabled the functionalization of the retained porphyrin structure of Ce6, but also caused electron transfer under illumination conditions. Therefore, BCC-CDs not only exhibited well dispersibility and steady red fluorescence emission in water, successfully achieved red fluorescence imaging in vivo/vitro, but also achieved the dual-mode PDT of type I/type II under illumination conditions. This function can synergistic anti-tumor with enzyme-like property. For enzyme-catalyzed treatment, the BCC-CDs mainly increased the levels of reactive oxygen species (ROS) in cancer cells through peroxidase (POD) and GSH oxidase-like activities, thus caused cell death. This enzyme-like property of BCC-CDs played a synergistic anti-tumor role with the PDT effect, and provided a new idea for the application of CDs in image-guided tumor precision therapy.