Fabrication Of Core/Shell Quantum Dots Nanocomposites And Its Visual Fluorescent Recognition Studies

Currently, the fabrication and applieations of the composite nanostructures withdual-emission fluorescence is of great interest。Combining the unique fluoreseenceproperties of Quantum dots （QDs）, the QDs nanocomposites with dual-emissiondemonstrate great potentials in fluorescence molecular imaging, dual-fluorescenceratio sensor, and visual fluorescence detection. In this thesis, controllable fabricationof QDs with different fluorescence color and Au nanopartieles has been investigated,and then Core/Shell QDs nanocomposites have been faeilely fabrieated, we have alsoinvestigated the visual fluorescent recognition of such nanoeomposites in the field ofbiotechnology and the environment. The main points are as follows:1. The fabrication of STPP-stabilized CdS QDs and the determination of traceiron by fluorescence quenching method. The uniform dispersion of water-soluble CdSQDs stabilized by STPP was successfully synthesized in an alkaline medium. Theemission peaks of CdS QDs were tunable, and the half peak width is about25nm.The fluorescence spectral properties of CdS QDs at different pH values, thiourea,STPP and reaction time were investigated. A fluorescence quenching method for thedetermination of trace iron （Ⅱ） was developed, and the factors involving pH, buffersolution, and coexistence ion were investigated. Under the optimum conditions, thevalues of F0/F at483nm are linearly proportional to the concentration of Fe²⁺from0.02-1.2μM. The detection limit of the developed method was6.7nM for Fe²⁺.Mineral water samples were analyzed with the recovery of95.0%-105.0%.2. The fabrication of the CdSe/CdS@SiQ2core/shell nanocomposites and thedetermination of trace Cu²⁺by fluorescence quenching method. Water-soluble CdSeand CdSe/CdS core/shell quantum dots were successfully syntheticed in presence ofSTTP as a stabilizer. CdSe/CdS@SiQ2core-shell nano composites were obtained viathe hydrolysis of Tetraethyl silicate （TEOS）. The fluorescence spectra,ultraviolet-visible absorption spectroscopy （UV）, TEM and XRD were used toquantify the structure and characteristions of CdSe/CdS@SiQ2nanocomplexes. Dueto Cu²⁺can cause fluorescent quenching of CdSe/CdS@SiQ2nanocomplexes selectively, we set up a new method for the determination of Cu2⁺in water samples.The linear range from0.02to0.6μM and the detection limitation is10nM.3. The fabrication of the mesoporous ZnO/CdS@SiO₂Core/Shell nanostructureand visual fluorescence detection of Ag⁺. A new method for the preparation ofmesoporous ZnO/CdS@SiO₂Core/Shell nanostructure has been developed. Themesoporous silica shells allow Ag⁺to enter into the interior of the nanostructures tocontact with ZnO/CdS core, accordingly causes the quenching of its band edgeemission along with a simultaneous enhancement of red emission at around595nm.So, a novel visual fluorescence detection strategy for Ag⁺ion is proposed based on acommon Core/Shell Quantum dots nanostructure. Under optimal conditions, theenhanced fluorescence intensity at595nm increased linearly with the concentrationof Ag⁺ion ranging from0.03μM to0.24μM with a detection limit （3σ） of3.3nM.4. The fabrication of the CdTe@SiO₂/Au nanocomposites and visualmulti-colored fluorescent detection of Hg²⁺. By chitosan as a stabilizer and reducingagent, the tunable surface plasmon resonance absorption peak of gold nanoplate hasbeen successfully fabricated. It was observed that the linear chains of Au nanosphereswere formed by the addition of L-Cysteine in CTS-stabilized Au nanospheressolution. After that, highly fluorescent Au clusters with dual-emission （blue and red）have been synthesized by lysozyme as stabilized and reducing agents. The structureand morphology of the three types of crystals was characterized via scanning electronmicroscopy （SEM）, transmission electron microseopy （TEM） and X-ray diffraction（XRD）. The formation of Au nano-structure was determined by the use of UV-vis,dynamic light scattering as well as resonance light scattering and fluorescence spectra.The growth mechanism of gold nano-structure was discussed. The CdTe@SiO₂/Aunanocomposite with three-color fluorescence （red, green and blue, RGB） under asingle excitation wavelength was synthesized when the Au CNs with dual-emission（blue and red colors） and CdTe@SiO₂with green fluorescent were mixed. Thethree-color fluorescence quenching of CdTe@SiO₂/Au nanocomposite by addingHg²⁺was studied. It was shown that the fluorescent color of the nanocompositechanged from red-organe, yellow and green to blue with increase of the concentrationof Hg²⁺. Therefore, the visual mode with multi-color fluresence was established and the content of Hg²⁺was able to evaluate by naked-eyes.