Red-emission hydrophobic porphyrin structure carbon dots linked with transferrin for cell imaging

A porphyrin structure carbon dots (CDs) with red fluorescence is prepared by the reaction of terephthalaldehyde with pyrrole under the trifluoroacetic acid catalyst. The CDs with an average particle size of 5.70 nm are red-emission with a maximum fluorescent wavelength at 650 nm due to the large conjugate structure of the porphyrin ring, giving rise to a quantum yield of 14%. The aldehyde groups in CDs make self-aggregation possible, and promote the effective coating of CDs around Transferrin (Trf) via the Schiff base reaction, forming CDs@Trf nanocomposites with a particle size of 19.7 nm. Trf can specifically target cells with Trf receptors on the surface of cell membrane. CDs@Trf exhibits stable red-emission in low polarity solvents, and are able to generate singlet oxygen (¹O₂), which facilitates cell imaging and photodynamic therapy. In vitro cell experiments demonstrate that CDs@Trf greatly inhibits the growth of tumor cells under laser irradiation at 635 nm. After incubation of 3 mg mL^-1 CDs@Trf with Bend.3 cells, the survival rate of the cells is only 26% under laser irradiation of 4.78 mW cm^-2 for 5 min.