Preparation And Application Of The Fluorescent Probes And Fluorescent Bar Codes Based On QDs And Au Nanoclusters

This thesis is involved in the preparation and application of the fluorescent probes and fluorescent bar codes based on the quantum dots (QDs) and Au nanoclusters (Au NCs). It consists of five chapters.In Chapter one, it presented the general introduction including the property, synthesis method, modifing method and the application of the QDs and Au NCs; the researching hotpoint and the application field of the multifunctional hybrid materials based on QDs and Au NCs. Additionally, the aim and significance of this thesis were also briefly summarized.In Chapter two, for the first time, without the help of any amphiphilic polymers or polymerizable surfactants,3-mercaptopropionic acid (MPA) capped CdTe QDs could be one-pot copolymerized into poly(N-isopropylacrylamide)(PNIPAM) microspheres during the monomer polymerization process just by controlling the synthesis temperature at two different polymerization stages. Compared with the original CdTe QDs, the CdTe/PNIPAM microspheres exhibited a temperature-dependent fluorescence properties. Around the lower critical solution temperature (LCST), when the temperature increasing, the fluorescence intensity decreased sharply; when cooling the solution, the fluorescence intensity would restore. Moreover, after repeatedly heating and cooling recycles, the photoluminescence (PL) quenching and enhancement processes were fully reversible around the region of LCST.In Chapter three, chemically denatured ovalbumin (dOB) was used to modify the surface of3-mercaptopropionic acid (MPA) stabilized CdTe QDs, which resulted in a great enhancement of the synchronous fluorescence intensity. Moreover, dOB shell layer can effectively prevent the binding of other cations onto the QDs core and enhance the selective binding ability of Hg2+to dOB coated CdTe QDs (CdTe-dOB QDs). A simple method with high sensitivity and selectivity was developed for the determination of Hg2+with the CdTe-dOB QDs as fluorescence probe based on the merits of synchronous fluorescence spectroscopy (SFS). Compared with general fluorescence methods, the proposed method, which combined the advantages of high sensitivity of synchronous fluorescence and specific response of Hg2+to CdTe-dOB, had a wider linear range and higher sensitivity. Furthermore, the proposed method was applied to the determination of trace Hg2+in water samples with satisfactory results.In Chapter four, a core-satellite CdTe/Silica/Au NCs hybrid sphere was synthesized by covalently linking the separately synthesized highly fluorescent bovine serum albumin (BSA) stabilized gold nanoclusters (Au@BSA NCs) to the surface of the amino functionalized CdTe@SiO2spheres by using the EDC chemistry. The synthesized dual-emission hybrid spheres were further characterized and developed as ratiometric fluorescence probe for the determination of Cu2+with high sensitivity and selectivity. Furthermore, the ratiometric fluorescent probe was successfully applied in the determination of Cu2+in vegetable samples with satisfactory results.In Chapter five, the QDs-Silica-Au NCs hybrid spheres in which the solid silica core contained QDs while the mesostructure silica shell contained Au NCs were fabricated by a two step synthesis procedure. The hybrid spheres were further characterized to confirm the formation of the ternary hybrid structure. The as-prepared ternary hybrid spheres showed an interesting fluorescence spectrum variation behavior and further be developed as precursor of fabricating multicolor fluorescence bar codes by using L-cysteine (L-Cys) as an effective post-encoding adjuster. A small variation of the concentration of L-Cys led to a prominent change of the precursor’s fluorescence intensity ratio, which could correspond to a series of distinguishable multicolor fluorescent bar codes.