L-Cysteine-coated CdSe/CdS core-shell quantum dots as selective fluorescence probe for copper(II) determination
Yao-hai Zhanga, Hua-shan Zhanga, Xiao-feng Guoa and Hong Wang
Department of Chemistry, Wuhan University, Wuhan 430072, China
Received 19 September 2007;
accepted 27 January 2008.
Available online 2 February 2008
Abstract
Quantum dots (QDs) or semiconductor nanocrystals have been receiving great interest in the last few years. In this paper, L-cysteine-coated CdSe/CdS core-shell QDs (λem = 585 nm) have been prepared, which have excellent water-solubility. The full width at half maximum (FWHM) of the photoluminescence of these nanocrystals is very narrow (about 30 nm), and the quantum yield (QY) is 15% relative to Rhodamine 6G in ethanol (QY = 95%). With excess free L-cysteine in the solution, the fluorescence intensity of L-cysteine-coated CdSe/CdS QDs showed improved stability. It was found that the fluorescence of L-cysteine-capped CdSe/CdS QDs could be quenched only by copper (II) ions and was insensitive to other physiologically important cations, such as Ca2+, Mg2+, Zn2+, Al3+, Fe3+, Mn2+ and Ni2+ etc. Based on this finding, the quantitative analysis of Cu2+ with L-cysteine-capped CdSe/CdS QDs has been established. The linear range was from 1.0 × 10− 8 to 2.0 × 10− 7 mol L− 1 and the limit of detection (LOD) was 3.0 × 10− 9 mol L− 1 (S/N = 3). The proposed method has first been applied to the determination of Cu2+ in vegetable samples with recoveries of 99.6–105.8%.
Keywords: L-Cysteine-coated CdSe/CdS quantum dots; Spectrofluorimetry; Copper; Vegetable samples
Article Outline
1. Introduction
2. Experimental
2.1. Apparatus
2.2. Chemicals and solutions
2.3. Synthesis of L-cysteine-coated CdSe/CdS core-shell QDs
2.4. Determination of Cu2+
2.5. Sample preparation
3. Results and discussion
3.1. Optical property of QDs
3.2. Determination of Cu2+ with L-cysteine-coated CdSe/CdS QDs
3.2.1. Effect of the ratio between the concentration of L-cysteine and L-cysteine-coated CdSe/CdS QDs on the stability of the whole system
3.2.2. Effect of the concentration of L-cysteine-coated CdSe/CdS QDs
3.2.3. Effect of the buffer
3.2.4. Effect of the reaction time and the temperature
3.2.5. Effect of foreign substances
3.3. Linear equation and detection limit
3.4. Quenching mechanism
3.5. Sample analysis
4. Conclusions
Acknowledgements
References
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