Design And Applications Of Turn-on Fluorescent Probe Based On The Surface Structure Of Quantum Dots Modulated Using Suitable Chemical Agents

In this dissertation, the design strategy of turn-on fluorescent probe for selective and sensitive determination of designated analyte is proposed based on the quantum dots (QDs) modulated by using suitable chemical agents. And the applications in the quick measurements of trace cadmium in aqueous media and ascorbic acid from human unrine are discussed. The dissertation consists of the following four chapters.In the preface, the essential properties, preparation and characteristic method of QDs are described. The applications of QDs as a kind of fluorescent probe are summarized. Finally, the research aims, significance and methods in this article are proposed.In chapter 2, a new kind of turn-on fluorescent sensor for the selective detection of cadmium ion in aqueous media is developed basing on fluorescent recovery of sodium diethyldithiocarbamate (DDTC)-modified acetylcysteine-capped CdTe quantum dots (CdTe-Ac-Cys QDs). In the presence of Cd2+, the fluorescence of CdTe-Ac-Cys QDs that has been quenched by DDTC is found to be efficiently recovered. The experimental results showed that Cd2+ modulated quenching behavior of DDTC toward the fluorescence luminescence of CdTe-Ac-Cys QDs, and a good linear relationship between the fluorescent intensity recovery (△F) and the concentration of Cd2+ can be obtained in the aqueous media of Tris-HCl buffer solution (pH=9.1) with a detection limit of 0.03μmol/L. The calibration equation is△F = 29.56 c(Cd) + 15.06 with a correlation coefficient(r) of 0.9951. The method has been used to determine cadmium in samples of Ling lakes, Ling river and tap water with (0.32-0.33)% RSD.In chapter 3, the sulfosalicylic acid-modified glutathione-capped CdTe quantum dots as a turn-on fluorescent probe for determination of cadmium is designed. The experimental results showed that the detection limit is 0.16μmol/L in the presence of 60.0μmol/L Ssal. The calibration equation isΔF = 2.79 + 10.46 c(Cd) with a correlation coefficient (r) of 0.9936 and a linear range of 0.3 ~ 8.0μmol/L. The method have been applied to determine cadmium in four water samples with (97-102)% recovery.In chapter 4, a simple chemical redox strategy for modulating the surface chemistry of the QDs to develop a QD-based turn-on fluorescent probe is reported. The principle of the strategy is demonstrated by employing glutathione-capped CdSe quantum dots (CdSe-GSH QDs) with KMnO4 as the quencher and ascorbic acid as the target analyte. Therefore, a rapid, simple and sensitivity turn-on fluorescent probe using ASA-modu- lated quenching behavior of KMnO4 toward the fluorescent luminescence of CdSe-GSH QDs is developed for determination of ASA in human urine. The experimental results showed that the good linear relationship between the fluorescence recovery and the concentration of ASA is obtained in the concentration range of 0.12 ~7.50μmol/L. The correlation coefficient(r) is 0.9963 with a detection limit of 0.06μmol/L. The method has been applied to determination of ASA in human urine with (0.44-0.54)% RSD.