Application And Studies On CdTe Quantum Dots Synthesized In Aqueous Solution For Biological Produce And Medicament

In recent years, semiconductor quantum dots (QDs) have been intensively investigated due to the quantum size effect and the surface effect. QDs have a narrow, tunable, symmetric emission spectrum and a broad, continuous excitation spectrum. They are also photo-chemically stable and they have high fluorescence quantum yields and long fluorescence lifetime. The high selectivity and sensitivity should be acquired when QDs are used to detect the biomolecules. If not well passivated, the luminescence of the QDs becomes very sensitive to their local environment, and detections of some inorganic ions, DNA, proteins conformations were developed based on this property. QDs have been widely used in biology and medicine, especially in multiplexed biological detection, labelling and imaging. But there are several problems. For example, how to develop and perfect the method of synthesis, how to improve the stability and bioconjunction and how to conjunct QDs with biomolecules to make special and stable probes and so on.My dissertation is focused on some areas of QDs research. Now some new results are obtained from our experiments. The main results are outlined as followings:1. In this article, the CdTe QDs were synthesized in aqueous solution using thioglycolic acid as stabilizing agents. The quantum dots exhibit a stable, strong band luminescence. The applicability of the CdTe QDs modified by thioglycolic acid to the labeling of chymotrypsin (α-Chy) was studied in the paper. The influences of CdTe QDs were investigated by chymotrypsin, and CdTe-chymotrypsin interaction was also investigated under different experimental conditions such as reaction temperature, pH values and the concentrations of chymotrypsin, using ultraviolet-visible (UV-Vis), fluorescence, synchronous fluorescence, circular dichroism (CD) spectroscopic methods. Both the red shift of the UV-Vis spectra at 196 nm and the blue shift at 220 nm indicated that the secondary structure ofα-Chy has slight changes induced by CdTe QDs, and the intrinsic fluorescence ofα-Chy is quenched by CdTe QDs. In different pH values, the level of binding constants is determined to be 103 by Fluorescence data. The Hydrogen bonds forces or Vander waals force is involved in the binding process when pH is 9.05. The hydrophobic and Electrostatic interactions are involved in the binding process when pH is 7.20. The red-shift of synchronous fluorescence spectral ofα-Chy reveals that the microenvironments around tryptophan residues are disturbed by CdTe QDs. The secondary structure ofα-Chy has slight changes by the calculation of far-UV CD data. The study results of the activity and stability ofα-Chy induced by CdTe QDs showed thatα-Chy could maintain its high activity and stability in different pH values for 24 hours in the presence of CdTe QDs.2. In 2mM KH2PO4-Na2HPO4 buffer solution with pH=6.40, the synchronous fluorescent spectra of CdTe QDs were obtained by simultaneously scanning the excitation and emission monochrometers at a fixedΔλof 220 nm in the presence of proteins. A highly sensitive synchronous fluorescence method for the rapid determination of proteins was developed. Different influencing factors were studied, including the selection ofΔλ, the pH and concentration of buffer, quantum dots concentration, reacting time and temperature. Under optimum conditions, the calibration graph is linear over the range 0.08～2.80μg·mL-1, with a detection limit of 0.032μg·mL-1. The relative standard deviation of 10 replicate measurements for 1.80μg·mL-1 HSA is 1.05%. This method is simple, rapid and sensitive, and shows promise in the application of biologic systems.3. The fluorescence intensity of CdTe quantum dots quenched by rosmarinic acid was studied with synchronous fluorescence technology. A novel method for detecting rosmarinic acid was developed. When△λ=210 nm, synchronous fluorescence is produced at 320 nm at pH 5.70. Under optimal conditions, the decreased fluorescence intensity is in proportion to the concentration of rosmarinic acid in the range of 0.36～11.52μg·mL-1 (1×10-6～3.2×10-5 M). The linear equation is F0/F = (0.93174±0.0137) + (0.12892±0.0023)×c (μg·mL-1) with an excellent 0.9982 correlation coefficient. The detection limits (S/N=3) are 0.16μg·mL-1. The relative standard deviation of ten replicate measurements for 2.16μg·mL-1 rosmarinic acid is 2.80%. The possible synchronous fluorescence quenching mechanism was also proposed.