Effects Of The Different Coating Interaction Modes On The Light Stability And Cellular Toxicity Of Protein-CdTe Quantum Dots

First, we briefly reviewed the physical and optical properties of quantum dots (QDs), the organic phase and aqueous phase synthesis methods, the conjugation methods of QDs with biomolecules, their toxicity effects and applications in analysis science and biomedicine fields.Secondly, different sizes cadmium telluride (CdTe) QDs with 3-mercaptopropionic acid (MPA) or N-acetyl-L-cysteine (NAC) as stabilizers were prepared by the hydrothermal synthesis method. The optical properties, structure and morphology of the as-prepared CdTe QDs were characterized detailedly by UV-visible absorption spectroscopy, fluorescence spectroscopy, Fourier transform infrared spectroscopy and transmission electron microscopy. The results show that the size distribution of QDs is almost homogeneous; the UV absorption spectra are broad and continuous and the fluorescence emission peaks are narrow and symmetric. This lay the solid material foundation for our further experiments.Thirdly, the interactions of the CdTe QDs with bovine serum albumin (BSA) and cytochrome c (cytochrome c, Cyt c) were studied by using fluorescence spectroscopy and infrared spectroscopy. It was found that the fluorescence of QDs are all enhanced no matter what interaction modes of BSA with QDs, that is, the electrostatic interaction, the coordination interaction or the covalent interaction. The fluorescence quenching effects of the UV light radiation on the QDs are significantly different due to the interaction modes of BSA with QDs:the weakest effects are on the BSA-QDs conjugating by covalent interactions, the stronger effects are on the ones by coordination interactions, and the strongest effects are on the ones by electrostatic interactions. This sequence is same as that for the light stability of these QDs. When NaN3 was added into the QDs system, the light stability of QDs under the UV light radiation was improved significantly. It may be the singlet oxygens generated by QDs under UV light that lead to the QDs fluorescence quenching. NaN3 can scavenge the singlet oxygens, and then improve the light stability of QDs. Meanwhile, we found that Cyt c has a significant fluorescence quenching effect on the QDs. These results provide a theoretical basis for further study on the interactions between the QDs with intracellular proteins.Lastly, by using laser confocal fluorescence microscopy, it was found that the QDs entered into cells mainly distribute in the cytoplasm and/or the cell organelles around the nucleus. For the effects on the cell cycle and apoptosis, the related experiments indicated that the BSA-QDs with covalent interaction mode have the weakest effects, the BSA-QDs with coordination interaction mode have the stronger effects, and the BSA-QDs with electrostatic interactions mode have the strongest effects. The cytotoxicity assay experiments agreed well to the above results:the BSA-QDs with covalent interaction mode have the weakest cytotoxicity and the CdTe QDs have the strongest cytotoxicity. The QDs distributed in the cytoplasm and/or the cell organelles around the nucleus may prevent the synthesis of RNA and other proteins and induce the arrest of cell cycle, and cause cytotoxicity and further the cell apoptosis.In a word, this study provides an experimental basis for the synthesis of protein-QDs conjugates with higher-light stability and lower-cytotoxicity to broaden their biomedical applications.