Functionalized CdSe/CdS Quantum Dots As Fluorescent Probes For The Detection Of Heavy Metal Ions

Quantum dots (QDs) are nanoparticles with unique optical properties such as broader excitation spectrum, narrower emission spectrum and longer lifetime. The analysis of heavy metals in samples with complicated matrix and low concentration is still a challenging task. Application of QDs in analytical chemistry and particularly heavy metals analysis has attracted enormous attention recently. The focus in this dissertation is on the synthesis of water-soluble QDs and it application to the analysis of heavy ions.The dissertation includes three chapters. Chapter 1 is the detailed review on the synthesis of QDs and its application. Chapters 2 and 3 are the experimental sections.In Chapter l, a review on quantum dots, including its definition, structure, character and luminescence is presented with the emphasis on the synthesis and modification of QDs. The application of luminescence QDs in chemistry and biology is also discussed.In Chapter 2, a new fluorescent probe for copper ion detection is reported that is based on the quenching of the fluorescence of diethyldithiocarbamate (DDTC)-functionalized quantum dots (QDs) in the presence of copper ions. A linear relationship existed between the extent of quenching and the concentration of copper in the range of 0 - 100μg L^-1, with a detection limit of 0.29μg L^-1 (3σ). The DDTC-QDs showed excellent selectivity for Cu²⁺ over other metal cations. The fluorescent probe was successfully used for the determination of copper in environmental samples. In addition, the quenching mechanism is also described in depth.In Chapter 3, mercaptosuccinic acid (MPS)-functionalized CdSe/CdS quantum dots are synthesized and used as the probe for silver ion detection, which is based on the quenching of the fluorescence in the presence of Ag⁺. Parameters of this simple and rapid approach including reaction time, pH and the amount of MPS-QDs have considerable influence on the fluorescence quenching percentage of MPS-QDs. Under optimal conditions, a linear relationship existed between the extent of quenching and the concentration of silver in the range of 0-100μg L^-1, with a detection limit of 2.30μg L^-1 (3σ).