Biocampatible Modification Of CdTe Quantum Dots And Its Interactions With Proteins

Currently, quantum dots (QDs) received tremendous applications in fields of biology and medicine. However, relatively little is known about the interactions of QDs with bio-macromolecules. A deep understanding of their biological and potential toxic effects requires a detailed description of the binding of bio-macromolecules to QDs in terms of stoichiometry, affinity, enthalpy, entropy, and the underlying driving forces. Each of these parameters is likely to be strongly dependent on both the properties of QDs and bio-macromolecules, as well as the solution conditions. It is of theoretical and practical significance to develop an accurate and credible method which can be applied to investigate QDs-bio-macromolecules interactions qualitatively and quantitatively, and to characterize the QDs- bio-macromolecules complex in aqueous solution or physiological fluid.The work can be separated into three parts choosing protein as research object in this thesis based on the issues mentioned above:1. Narrow and symmetrical CdTe semiconductor QDs were synthesized in aqueous solution using N-acetyl-L-cysteine and L-cysteine as modifier and stabilizer. The quenching effects of N-acetyl-L-cysteine modified and stabilized CdTe QDs(NAC-CdTe QDs) on bovine serum albumin and human serum albumin were investigated respectively by fluorescence spectroscopy. Affinity constant (K), reaction enthalpy and entropy changes (ΔH,ΔS), and the binding sites (n) of NAC-CdTe QDs with the two serum albumins were obtained by isothermal titration calorimeter(ITC). The results showed that the fluorescence of serum albumins can be quenched by NAC-CdTe QDs, and when the concentration of NAC-CdTe QDs is lower, the quenching is dynamic, and when the concentration of NAC-CdTe QDs is higher,the quenching is static. It was concluded that the interactions of NAC-CdTe QDs with serum albumins are mainly of diffusion-controlled collision due to hydrophobic bonding forces, and that serum albumins may participate in the action stabilizing CdTe QDs associated with N-acetyl-L- cysteine.2. Variation of the fluorescence intensity with time (t) on mixing NAC-CdTe QDs and lysozyme solutions was investigated by fluorescence spectroscopy. Affinity constant (K), reaction enthalpy and entropy changes (ΔH,ΔS), and the binding sites (n) of the QDs with lysozyme were determined by ITC. The results showed that NAC-CdTe QDs can enhance the fluorescence intensity of lysozyme at low concentration, Weaken it at high concentration. and meanwhile the fluorescence intensity of NAC-CdTe QDs can be quenched by lysozyme. The interactions of NAC-CdTe QDs with lysozyme are mainly controlled by electrostatic interaction and hydrogen bonding.3. Affinity constants (K), reaction enthalpy and entropy changes (ΔH,ΔS), and the binding sites (n) of NAC-CdTe QDs with three heme-proteins (myoglobin, hemoglobin, cytochrome c) were determined by ITC. The results showed that electrostatic attraction is the driving force in the bindings of NAC-CdTe QDs with myoglobin and hemoglobin, while the binding of NAC-CdTe QDs with cytochrome c is mainly controlled by hydrophobic force.