Manganese-doped carbon dots with catalase-like activity enable MRI-guided enhanced photodynamic therapy

The tumor microenvironment (TME) exhibits characteristics such as hypoxia, weak acidity, and enrichment of glutathione and hydrogen peroxide (H₂O₂), which greatly limits the effectiveness of tumor magnetic resonance imaging (MRI) and photodynamic therapy (PDT). Carbon dots (CDs) nanozymes are excellent candidate materials with both diagnostic and therapeutic potential. However, CDs nanozymes with both ultra-high relaxation rate and good therapeutic effect are still to be developed. Herein, novel carbon dots (MPC-CDs) were synthesized from polyethyleneimine (PEI), the photosensitizer hexahydroporphyrin (Ce6) and manganese. The Ce6 enabled the MPC-CDs to exhibit excellent PDT therapeutic ability, with a singlet oxygen yield as high as 1.52. The doping of the metal manganese gave the complexes CAT-like activity, and the singlet oxygen rate was further increased in the presence of H₂O₂, up to 1.97. In addition, manganese endowed the CDs with better MRI capabilities, and the r₁ and r₂ relaxation rates were significantly improved by 7.8-fold and 4.6-fold under acidic and H₂O₂ conditions. The in vitro and in vivo results showed that MPC-CDs could achieve TME-responsive MR imaging and synergistic anti-tumor effects, providing an effective strategy to further enhance the effectiveness of tumor diagnosis and treatment.