Structure And Properties Of Nanomaterials Based On Fluorescent Quantum Dots

Quantum dots（QDs）have been extensively studied in the fields of biomolecular detection,ion detection,immunoassay,biofluorescence imaging and optoelectronic devices due to their unique optical and physicochemical properties.Generally,quantum dots with high luminescence efficiency are prepared directly in organic phase by high temperature injection method,and have a series of advantages,such as good crystallinity,ultra-narrow half-peak width,higher stability and so on.However,the hydrophobic oil-soluble ligands on the surface of these quantum dots greatly limit their wide application,and the oil-soluble surface ligands synthesized generally do not have functionalized functional groups,which cause great trouble for the practical application of quantum dots.The fluorescence and stability of quantum dots synthesized directly in aqueous phase are much worse than those synthesized in organic phase.Therefore,oil-soluble quantum dots are generally modified to give them water-solubility while maintaining their excellent fluorescence properties,and to carry further modified functional groups.It has important theoretical significance and practical application value for its research in bioimaging,medical diagnosis,biomedicine,analysis and detection.Based on the modification of sulfhydryl ligands on the surface of quantum dots and oil-soluble quantum dots were coated with silica,the effect of the surface structure of quantum dots on their fluorescence properties was investigated.The main contents of this paper include the following three aspects:（1）A series of oil-soluble alloy quantum dots,ranging from red（625 nm）,orange（582 nm）,green（522 nm）to blue（489 nm）,have been synthesized by high temperature injection method.The emission peak is narrow and the quantum yield is as high as 78%.In order to obtain water solubility,thiol ligands with different functional groups and chain lengths were used to exchange their ligands.The fluorescence properties of QDs were greatly affected by the surface ligands of QDs by fluorescence emission spectroscopy.Especially for quantum dots with different thiol ligands,the temperature sensitivity of fluorescence was studied.（2）By sol-gel method,cetyltrimethylammonium bromide（CTAB）was used as the stabilizer and template of the oil soluble quantum dots.Under the catalysis of ammonia,tetraethyl orthosilicate（TEOS）was hydrolyzed.The surface of the oil soluble alloy quantum dots was coated with silica to obtain water solubility while maintaining the fluorescence properties of the original quantum dots,and the quantum yield of the product was as high as 56%.By controlling the reaction process,such as the concentration of TEOS,ammonia and CTAB,the thickness of silica shell on the surface of QDs and the number of QDs coated can be controlled.The results show that QDs@SiO₂ has good heat resistance,alkali resistance and time stability.（3）The fluorescence resonance energy transfer（FRET）system of QDs@SiO₂-RhB was constructed by using QDs@SiO₂ as energy donor and RhB as energy acceptor.The effects of donor-acceptor concentration,pH value,salt ion concentration and particle size of QDs@SiO₂ on energy transfer efficiency were investigated.The FRET system was used to study the visualization detection of cadmium ions.