| Heavy metal contaminations are a serious threat to the environment and humanhealth. The development of efficient methods for the selective detection of heavymetal ions with high sensitivity is of great importance. To date, several approachesare available for their detection. Sophisticated apparatus can offer exact detection butare inconvenient for on-line and/or handy monitoring. Quantum dots (QDs), becauseof their unique physicochemical properties, are developed for responding metal ionswith high sensitivity and improved facility. Accordingly, great progress has beenachieved using QDs to selectively detect heavy metal ions, though several problemsstill need to be solved for further development of QDs-based sensors. Theseproblems include compatibility with metal ions, selectivity for specific ions, colloidalstability of the QDs, and so forth. In this paper, we aim to develop the environment-friendly aqueous synthesis approach of QDs and investigate the growth mechanism,fabricate the assembly of QDs superparticles (SPs) and integrate the functionality.Then the prepared QDs and SPs are used to detect and discriminate the metal ions.In the second chapter, we investigate the aqueous synthesis of transition-metaldoped ZnSe QDs stored in the room temperature. The experimental variable-dependent photoluminescence (PL) evolution of transition-metal doped ZnSe QDs isanalyzed by combining the redox reaction and the electrostatics of aqueous QDs.Bulk doping of NCs involves two steps-surface adsorption of the metal impuritiesand the followed internal doping. The former relates to the electrostatics of aqueous NCs, whereas the latter relates to a redox reaction between the impurities andmercapto-ligands. We also choose the simple amines, such as ammonia (NH3) andhydrazine (N2H4), are deliberately added to the growing system of aqueous CdTeQDs to promote their growth at room temperature. Systematical investigations revealthat QD growth is the combination of kinetics-favored agglomeration growth andthermodynamics-favored diffusion equilibrium (or decomposition).In the third chapter, we focus on the aqueous CdTe QDs with diversified surfacefunctionalities are applied to discriminate between heme (Fe(II)) and hemin(Fe(III))/Cr (III) and Cr (VI) by virtue of their difference in quenching QDfluorescence. In aqueous media, the interaction between QDs and heme/hemin orQDs and Cr (III)/Cr (VI) mainly involves electrostatic interaction, which is greatlydetermined by the surface functionalities of the QDs. Thus, by combining thedifferent fluorescence quenching behavior of carboxyl-and/or hydroxyl-functionalized QDs, heme/hemin and Cr (III)/Cr (VI) are discriminated. Moreover,the concentration of heme/hemin can be quantified because the relative PL intensityshows a linear correlation with the concentration of heme/hemin. In comparison tothe discrimination using QDs with single surface functionality, the current methodhas improved reliability and accuracy.In the fourth chapter, we mainly demonstrate fluorescent CdTe QDs-based SPsare fabricated using oil droplets in microemulsion as templates. By controlling theexperimental variables, the current approach is flexible in tuning the NP componentof the as-prepared SPs, generating unitary CdTe SPs with different PL emissions,binary CdTe SPs with composite emissions, and binary CdTe/Fe3O4SPs with bothfluorescence and magnetism.The as-prepared SPs are dispersible in water andapplicable in the detection of Cu2+and Ag+, which possess the advantages of lowdetection limit, short detection time, and broad detection range. In particular, theCdTe/Fe3O4SPs with both fluorescence and magnetism overcome the problem of theseparation of SPs in the detection system. These CdTe-based SPs show an improveddetection of Cu2+and Ag+and greatly promote the practical detection applications ofluminescent QDs. |
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