Sensing Investigation For Heavy Metal Ions Based On ZnSe Core-Shell Quantum Dots

Heavy metal ions are one of highly toxic pollutants because of their toxicity to natural environment and living things. Compared with the developed analytical techniques based on sophisticated instruments, a variety of multi-functional nanosensors based on semiconductor core-shell quantum dots (QDs) have been widely studied and applied. However, there are still poor selectivity, low sensitivity and lack of stability existing in practical applications of nanosensor due to negative effects of detection mechanism and nanosensor components. In my dissertation, to overcome these mentioned problems above, several novel QD-based nanosensors were designed and fabricated for sensitive and selective detecting trace amounts of heavy metal ions in water.(1) A novel fluorescence nanosensor was fabricated to sensitively and rapidly detect mercury ions ranging from5to70nM. The limit of detection was2.5nM. In addition, model of detection was proposed through studying chemical properties of the surface of the quantum dots. By means of FT-IR and simulation, the proposed detection model was validated.(2) Based on doping technique Mn-doped ZnSe QDs have been prepared. Effects of amount of oleic acid and oleylamine on diffusion of manganese ions and formation of ZnSe layer during the doping process have been investigated. Furthermore, influences of carbon chain lengths and functional groups of ligands on optical properties of Mn doped ZnSe QDs were studied in detail. Meanwhile, several models of QDs and surface organic ligand exchange process were built by taking advantage of simulation tools, which could be used to explain the enhancement phenomenon of fluorescence during the functionalization process.(3) Two thiol ligand-coated Mn-ZnSe/ZnS QDs have been prepared, which were used to assemble two nanosensors for detecting Hg2+and As3+ions. The nanosensor functionalized by MPA could fast determine trace Hg2+ions within the range of0.1to20nM. There was a good linear correlation within the range of0.1to1.5nM with low limit of detection, up to0.1nM. Another nanosensor was functionalized using glutathione, which was capable to detect As3+ions ranging from5to100nM with limit of detection,5.1nM. Furthermore, Hg2+and As3+ions were analyzed in simulated water, which showed that the nanosensors could be applied in practice in comparison to sophisticated instrument.(4) Ultrasmall Cu-ZnIn2Se4/ZnSe ternary nanocrystals were successfully synthesized by thermal decomposition method. Effects of proportions of zinc/indium and doping concentrations of copper ions on emission peak of ternary nanocrystals have been investigated. Nanosensors based on functionalized ternary nanocrystals were prepared by using surface ligand exchange. The as-synthesized nanosensor was used to detect Hg2+ions in a range of5to140nM. The limit of detection was10nM.In summary, to meet the needs of water safety and quality monitoring, unique optical properties of QDs and related technologies in materials chemistry, biochemistry and computational chemistry were combined for synthesis of QDs and investigation of their functionalizations. Four novel nanosensors have been fabricated for detecting trace heavy metal ions in aqueous solution, which reveals detection mechanism of the obtained nanosensors, clarifying intrinsic interaction between interfacial reaction on the surface of QDs and analysts, thus prompting wide applications of functionalized QDs in the environmental analysis.