Studies On Determination For Ions Based On Quantum Dots Fluorescence Probes

Quantum Dots or semiconductor nanoparticles are comprised ofhundreds of atoms and the range of the nanoparticles is from 1 to 100nm.QDs would show especial physicochemical and photoelectriccharacterizations if the diameters are smaller than their Bohr diameters.Therefore, QDs were widely used as sensors, fluorescence probes, photoluminescenceand electroluminescence devices.At present, many kinds of QDs have been synthesized and applied toassay for organic and inorganic molecoles, drug molecoles, biomolecoles,metal cations and some anions. In the present work, water-soluble CdS andCdTe QDs were synthesized and used as fluorescence probes to determineiodate, iodide and bromate anions as well as copper( ) and mercury(ⅡⅡ)ions in aqueous solution. The main contents are as follows:Water-soluble QDs capped with sodium carboxymethylcellulose whichare green and environmentally friendly were synthesized and characterizedby optical spectrum. The interaction between CdS QDs and iodate wasinvestigated and the mechanism of reaction was also researched. Influencefactors including pH, the concentration of the buffer solution, theconcentration of QDs and the reacting time were investigated and theoptimum conditions were determined. Under the optimum conditions, therelative fluorescence intensity of CdS quantum dots was linearlyproportional to the concentration of iodate in the range from 1.0×10^-8mol/L to 1.0×10^-5 mol/L, with a determination limit of 6.0 nmol/L. Thecorrelation coefficient is 0.9987. The presented method was applied todetect iodine in table salt with satisfactory results.Using CMC-CdS QDs as fluorscence probes, a novel method fordetermining iodide was estblished based on fluorescence enhancing ofCMC-CdS QDs caused by CuI. The linear range is from 1.0×10^-9 to 1.0×10^-7 mol/L, the correlation coefficient is 0.9997 and the LOD is 0.8 nmol/L.We have found that bromate can quench the fluorescence of CdS QDs,so we proposed a novel method for detection of trace bromate in drinkingwater. The interaction between CdS QDs and bromate was also investigated.The optimum conditions were determined through the investigation of the factors which have influence on the quenching fluorescence of CdS QDs.Under optimum conditions, the relative fluorescence intensity of QDs waslinearly proportional to the concentration of bromate in the range from 1.0×10^-9 to 1.0×10^-3 mol/L with a correlation coefficient of 0.9972.The interaction between CdS QDs and copper(Ⅱ) ions was alsoinvestigated. We found copper(Ⅱ) ions could quench the fluorescenceintensity of CdS QDs sharply and some trace coexisting cations couldhardly quench the fluorescence of QDs. Therefore, a method with highselectivity for copper(Ⅱ) assay in tap water was estblished.TGA-capped CdTe QDs were prepared by refluxing in boilling waterused NaHTe as precursor synthesized with TeO₂ and NaBH₄. The optimumconditions of synthesis of CdTe QDs were determined and CdTe QDs werecharacterized by UV/Vis spectrum, fluorescence spectrum and FT-IRspectrum. The quantum yield of CdTe was 60%. We found that the fluorescenceintensity of CdTe QDs would enhance when QDs was modified withBSA. A novel method for trace mercury(Ⅱ) assay was proposed based onthe quenching of fluorescence of BSA-CdTe QDs caused by Hg²⁺. Therelated mechanism was also discussed.