Carbon Dots with Absorption Red-Shifting for Two-Photon Fluorescence Imaging of Tumor Tissue pH and Synergistic Phototherapy.Phototherapy exhibits significant potential as a novel tumor treatment method, and the development of highly active photosensitizers and photothermal agents has drawn considerable attention.  In this work, S and N atom co-doped carbon dots (S,N-CDs) with an absorption redshift effect were prepared by hydrothermal synthesis with lysine, o-phenylenediamine, and sulfuric acid as raw materials.  The obtained heteroatom co-doped CDs can be used not only as an NIR imaging probe but also as an effective photodynamic therapy/photothermal therapy (PDT/PTT) therapeutic agent.  It was found that the S,N-CDs showed higher therapeutic efficiency than N-doped CDs, the efficiency of producing 1O2 was 27%, and the photothermal conversion efficiency reached 34.4%. 
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