Mitochondria-targeting supra-carbon dots: Enhanced photothermal therapy selective to cancer cells and their hyperthermia molecular actions

Carbon dots (CDs) have been widely used in biological research including bioimaging, biosensing, and biomedicine because of their excellent biocompatibility. However, inefficient absorption of these CDs in the visible-to-near-infrared window limits their applications for photo-sensitive cancer therapeutic strategies and in vivo imaging. Herein, novel supra-carbon dots (SCDs, approximately 20 nm) with high visible-NIR absorption, large photothermal efficiency, and specific cancer cell and mitochondria-targeting feature were prepared by the self-assembly of small-sized CDs (approximately 5 nm) under an acidic environment, followed by modification of cancer cell- and mitochondria-targeting peptides. These targeting SCDs were applied for precisely damaging cancer cells by an NIR photothermal therapy (PTT), and the viability rate difference between the cancer and normal cells is as large as 70%, indicating high specificity and high selectivity. In addition, the destruction of mitochondria was observed by confocal fluorescence microscopy, and the real-time dynamics of the cellular molecules during this process were further evaluated by surface-enhanced Raman spectroscopy. The results reveal that the produced hyperthermia may first incite structural changes in lipid, protein, and deoxyribonucleic acid and then induce cell death. Our results are helpful for the preparation of new CDs-based photothermal materials and the development of more efficient photothermal therapeutic platforms.