Analytes Induced Fluorescence Quenching Of Quantum Dots And Applications

Quantum dots(QDs) developed in recent years as a kind of fluorescent nanomaterials. The research of QDs has become popular, and is widely applied to inorganic ion detection, drug analysis and biological field. In this paper, the water-soluble Cd S quantum dots and carbon(CDs) dots were synthesized which were applied to detection of PFOA, Fe3+, H2O2 and EDTA.The major research works are as follow:Firstly, it was observed that the addition of Perfluorooctanoic acid strongly quenched the fluorescence emission of the mercaptoacetic acid capped Cd S QDs because the adsorption of PFOA promotes the aggregation of Cd S QDs through a fluorine-fluorine affinity interaction. Under optimum conditions, the fluorescence intensity was observed to decrease linearly with an increase in the concentration of PFOA from 0.5 to 40 mmol L-1, with a detection limit of 0.3 mmol L-1. This new method was successfully implemented for the analysis of textile samples, with recoveries ranging from 95% to 113%.Then, using phenylboronic acid as precursor, synthesized CDs. Fluorescence quenching was observed between Fe3+ and the CDs in HAc-Na Ac buffer solution(p H 4.0), whereas many other metal ions could not quench its fluorescence. When Fe3+ ions are added into the CDs solution, they can be quickly adsorbed onto the surface of the negatively charged CDs through the electrostatic attractions. Because the outer electronic structure of Fe3+ is 4s23d5 and the 3d orbits are halffilled, the electrons at the conductive band of CDs will be easily transferred to the half-filled 3d orbits of Fe3+. Meanwile, Fe3+ had strong interaction with OH, it caused CDs aggregation. These two processes lead to the significant fluorescence quenching of CDs. Under optimum conditions, the relative fluorescence intensity ln[F/F0] was linearly proportional to the Fe3+ concentration in the range from 1 to 250 mmol L-1, with a detection limit of 0.4 mmol L-1. The proposed method was successfully applied to determine iron in milk powder. Besides, we found that Fe2+ didn't quench the fluorescence of CDs, and H2O2 could oxidate Fe2+ to be Fe3+. Based on Fenton reaction, we developed a new system for H2O2 detection. Under optimum conditions, the relative fluorescence intensity ln[F/F0] was linearly proportional to the H2O2 concentration in the range from 0.7 to 500 mmol L-1, with a detection limit of 0.2 mmol L-1. The proposed method has been applied to the determination of H2O2 in throwaway chopsticks. The addition of EDTA in CDs-Fe2+ system caused a significant quenching of the CDs fluorescence intensity. Based on this phenomenon, we developed a new system for EDTA detection. Under optimum conditions, the relative fluorescence intensity ln[F/F0] was linearly proportional to the EDTA concentration in the range from 1.0 to150 mmol L-1, with a detection limit of 0.5 mmol L-1. The proposed method has been applied to the determination of EDTA in tap water and lake water with the recoveries of 95.2% to 106.5%.