Self-Illuminating Photodynamic Therapy with Enhanced Therapeutic Effect by Optimization of the Chemiluminescence Resonance Energy Transfer Step to the Photosensitizer

The major obstacles to the wider application of photodynamic therapy (PDT) are drawbacks of the current photo-sensitizers and the tissue penetration limit of the common outer light source. In the present study, the chemiluminescence (CL) from the luminol-H2O2-horseradish peroxidase reaction was explored as a potential inner light source for the intracellular activation of carbon dots (CDs)-based PDT system. To fully use the light and enhance the overall PDT yield, the nanocarrier of CDs, the light of CL, and the PDT agent chlorin e6 (Ce6) were carefully selected and designed to form an efficient and united system. Bright-yellow-emissive CDs (y- CDs) were synthesized through purposeful regulation of the ) absorption and emission spectra to enhance the overlapping areas in the chemiluminescence resonance energy transfer (CRET) and fluorescence resonance energy transfer (FRET) processes. Our results reflected CL-induced y-CDs-Ce6 system (10 mu M) successfully generated reactive oxygen species (ROS, 35.93%), killed similar to 90% SMMC-7721 cells in vitro, and significantly delayed tumor growth in vivo. On the basis of immunohistochemical observations of proliferating cell nuclear antigen (PCNA) and platelet/endothelial cell adhesion molecule-1 (PECAM-1 or CD31) results, we concluded that the CL-induced y-CDs-Ce6 system had excellent performance in cancer therapy. The enhanced therapeutic effect was ascribed to two pathways: a direct CRET process and another process of CRET with subsequent y-CD-mediated FRET (CRET-to-FRET).