Studies On Quantum Dots As Selective Fluorescent Probes And Their Applications In Biochemical Analysis

As a result of quantum confinement (1-10nm), quantum dots (QDs) have unique optical and electronic properties. In the dissertation, the surface-modified QDs have been synthesized as fluorescent probes for the application in biochemical analysis. The dissertation is divided into three sections.In the first section, studies of quantum dots are reviewed with the emphasis on its properties and applications on bioassays and in ultra sensitive optical detection and imaging.In the second section, the core-shell CdSe/CdS QDs were synthesized in a non-TOP/TOPO system. To make the synthesized CdSe/CdS QDs soluble in basic aqueous solution, they were further reacted with 2-mercaptoacetic acid to finish the exchange of surface ligand. A sensitive and selective sensor for L-cysteine was established based on the recovered fluorescence (FL) of the chitosan capped CdSe/CdS quantum dots (QDs)-Ag (I) system. Fluorescence of chitosan-QDs could be quenched greatly by Ag (I) and in the presence of L-cysteine, however, Ag (I) preferred to react with L-cysteine to form the Ag-S bond because of the strong affinity with the thiols of L-cysteine rather than quenching the fluorescence of the chitosan-QDs. Thus, the fluorescence of chitosan-QDs was recovered. The restoration ability was due to the decreased steric hindrance effect. Under the optimized conditions, a good linear relationship was obtained from 0.039 to 1.25μmol/L (R2=0.994) for L-cysteine with a detection limit of 0.017μmol/L. In addition, the method showed a high selectivity for L-cysteine among the other 19 amino acids. Furthermore, human serum samples were analyzed by the methodology and the results were satisfying.In the third section, an attempt is made to develop an analytical method for the determination of CD40. QDs-CD40L conjugates are synthesized, and used as the probe of CD40. A good linear relationship is obtained between the extents of fluorescence enhancing and the concentration of cells in the range of 20×10~4~100×10~4. However, it can not meet the requirement when the serum samples are detected.