Preparation Of Water Soluble CdSe Quantum Dots And Their Application In Ion Recognition

The thesis consists of six chapters and is listed as follow:Chapter 1:Introduction. We include a brief discussion on the attractive optical properties of QDs and on the importance of adequate control of the synthesis and surface modification of the luminescent QDs, in order to achieve the desired selectivity and sensitivity for sensing target analytes.Chapter 2:The preparation and Characterization of highly luminescent CdSe QDs with a diameter form 3 to 7nm in a mixture of ODE and Ole.Chapter 3:Water-soluble luminescent CdSe quantum dots surface-modified with triethanolamine (TEA-CdSe-QDs) were prepared with high stability. The fluorescence of the TEA-CdSe-QDs was greatly quenched only when Hg2+ and I- coexisted in the solution, whereas addition of either Hg2+ or I- individually has no noticeable effect on the fluorescence emission. Such a unique quenching effect could be used for reciprocal recognition of mercury (Ⅱ) ions and/or iodide anions in aqueous solution with rather high selectivity and sensitivity. The adequate experiments showed that iodine (Ⅰ) anions could bridge between TEA-CdSe-QDs and Hg2+ to form a stable complex (QDs-I--Hg2+) and the following effective electron transfer from the QDs to the Hg2+ could be responsible for the fluorescence quenching of QDs.Chapter 4:A facile method was developed for the preparation of water soluble P-Cyclodextrin (β-CD)-modified CdSe QDs (β-CD-QDs) by directly replacing the Oleic acid ligands on the QDs surface withβ-CD in an alkaline aqueous solution. The as-prepared QDs show good stability in aqueous solution for several months. Oxoanions, including phosphoric acid ion, sulfite acid ion and carbonic acid ion, affect the fluorescence ofβ-CD-QDs. Among them, H2PO4- exhibited the largest quenching effect. For the polyprotic acids (HO)3AO, the effect of acidic anions on the fluorescence ofβ-CD-QDs was in the order monoanion (HO)2AO2>dianion (HO)AO32->>trianion AO43-. After photo activation for several days in the presence of anions at alkaline pH, theβ-CD-QDs exhibited strong fluorescence emission. The effect of various heavy and transition metal ions on the fluorescence properties of the P-CD-QDs was investigated further. It was found that Ag+, Hg2+ and Co2+ have significant quenching effect on the fluorescence of theβ-CD-QDs. The Stern-Volmer quenching constants increased in the order Hg2+<Co2+<Ag+. The adsorption model of metal ions on P-CD-QDs was explored.Chapter 5:CdSe QDs have been prepared and modified with MSA. They are water-soluble and biocompatible. To improve their fluorescence intensity and stability in water solution, Cd2+ was absorbed onto their surface. Based on the quench of fluorescence signals of the functionalized CdSe QDs by Ag+ ions and Cu2+ ions at pH 7.2, a simple, rapid and specific method for Ag+ and Cu2+ determination was proposed.Chapter 6:This chapter highlights the overlap between QD and analytical chemistry and speculates on future research directions.