| Quantum dots(QDs) or semiconductor nanocrystals is a specific kind of nanoparticles newly developed in recent years because of their unique optical properties such as broader excitation spectrum,narrower emission spectrum,longer lifetime.CdSe QDs has often been investigated among theⅡ-Ⅵsemiconductor nanocrystals due to its unique size-dependent fluorescence tunable across the visible spectrum.It is possible to synthesize differently sized CdSe nanocrystals that emit from blue to red with very pure color.CdSe semiconductor nanocrystals exhibit great potential as a new type of labeling material for chemical research.Heavy metals are very widely used in the oil industry,chemical industry, aviation and aerospace industry.The analysis of heavy metals is a challenging task,so the detection of heavy metals based on QDs as flurescent probe has been one of the most popular analytical methods.Our focus is on the synthesis of water-soluble QDs and it application to the analysis of heavy ions.The dissertation includes four chapters.Chapter 1 is the detailed review about the synthesis and application of QDs.Chapter 2-4 are the experimental sections.Chapter 1,the review about quantum dots,including definition,structure, character and luminescence,mainly focuses on the synthesis and modification of QDs. The application of luminescence quantum dot in biology and chemistry is also discussed.Chapter 2,In the capter,CdSe quantum dots(QDs) modified with L-cysteine is prepared by two steps.The transmission electron microscopy and fluorescence spectrum was adopted to verify these synthesized QDs.The fluorescence of the water-soluble QDs can be quenched only by Pb2+ in Kolthoff buffer solution,so CdSe QDs has been used as a sensitive sensor for the detection of lead ion.The optimum experimental conditions were as follows:pH=8.0,8.0×10-4 mol/L L-cysteine,3 min of reaction time and 293 K of reaction temperature.The fluorescence intensity of CdSe QDs was linearly proportional to Pb2+ concentration from 1.00×10-7 to 1.00×10-6 mol/L with a limit of detection of 8.4×10-8 mol/L.Possible fluorescence quenching mechanism is also studied.The proposed method has been successfully applied to detect the content of Pb2+ in green tea,and the recoveries were found to be 102.9-108.3%with standard addition method.Chapter 3,By a one-pot approach,CdSe quantum dots have been obtained directly in aqueous solution using citric acid as stabilizing agent at room temperature under open air,and then characterized by fluorescence spectroscopy and UV-Visible, respectively.Elucidating interaction mechanism between CdSe quantum dots and citric acid was attempted using Fourier transform infrared spectra(FTIR).This method could be applied to the determination of vitamin B1,the results obtained by this method was the higher sensitivity and wider linear range.Chapter 4,CdSe QDs stabilized by citric acid was synthesized directly in aqueous solution according to the one-pot approach developed in Chapter 3.Based on the characteristic fluorescence quenching of the CdSe QDs by copper ion,a selective quantification method for Cu2+ is proposed.Effects of reaction time,the kinds of buffer solution and buffer pH,detection temperature and the concentration of CdSe QDs on the quantification of Cu2+ were carefully examined.The mechanism of reaction was also discussed.Under the optimum conditions,a linear relationship was observed between 1.00×10-8 and 1.00×10-7 mol/L with a correlation coefficient of 0.9953 for Cu2+ determination and the detection limit was 8.99×10-9 mol/L.
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