Salmonella-Derived Fluorescent Carbon Dots for Reprogramming Tumor-Associated Macrophages and Enhancing Tumor Photodynamic Therapy

Carbon dots (CDs) are used as photosensitizers for the photodynamic therapy of tumors while retaining the specific functional groups and biochemical properties of carbon precursors. However, the short-wavelength excitation of photosensitizers limits their application in the photodynamic therapy of tumors. Upconversion nanoparticles (UCNPs) effectively solve the problem of low penetration of photosensitizers due to short-wavelength excitation by converting low-energy near-infrared light into high-energy ultraviolet light or visible light. In this paper, carbon dots were prepared by a hydrothermal method using Salmonella and alendronic acid as raw materials, while the phosphate groups on the surface of carbon dots were coordinated with upconversion nanoparticles (UCNPs) to form UCNP@CD nanoprobes. Under the irradiation of an 808 nm laser, the emitted light from upconversion nanoparticles (UCNPs) can further catalyze carbon dots (CDs) to enhance the generation of reactive oxygen species for killing tumor cells. Meanwhile, carbon dots reprogrammed M2 macrophages into M1 macrophages to improve the tumor immunosuppressive microenvironment. The UCNP@CD nanoprobes were used for tumor-associated macrophage reprogramming and photodynamic therapy of tumors, which provides an effective strategy for multimodal synergistic tumor treatment.