| Rare earth luminescent materials with unique optical properties are widely used in bioimaging, medical diagnosis, radiation detection, etc. However, it is an urgent problem to fabricate a kind of novel rare earth luminescent material system with efficient accurate and precise identification. Noble metal nanomaterials have the characteristics of plasma resonance, resulting the enhancement of the local electromagnetic field. The emission intensity and efficiency enhancement of rare earth ion will achieve by the metal enhanced fluorescence.In this thesis, nanocomposites with core-spacer-shell structure were fabricated through a layer-by-layer assembly method using Au nanoparticle (Au nanorod and spherical Au nanoparticle) as core, mesoporous silica layer as spacer, and oxide doped with rare earth ions/rare earth complexes/coordination polymer as shell. The emission intensity of the rare earth luminescent materials will be enhanced via the metal enhanced fluorescence through controlling the thickness of mesoporous silica between Au nanoparticle and rare earth luminophore. We discussed the mechanism of the fluorescence enhancement and quenching and explored the application of the as-prepared nanocomposites in Hela cell imaging. The structures and properties of the as-prepared nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, UV-visible absorption spectroscopy, infrared spectroscopy, fluorescence spectroscopy and so on. The main research of this thesis is summarized as follows:(1) The well-defined Aunanorod@mSiO2@Y2O3:Er nanocomposites was synthesized with Au nanorod core, Y2O3 doped with erbium shell, and mesoporous silica as spacer. The thickness of mesoporous silica layer could be simply controlled from 15 to 50 nm by varying the reaction time and the amount of silica precursor. The strongest upconversion fluorescence enhancement is observed when the optimized silica thickness is around 40 nm, resulting in about 10- and 8-fold enhancement for green and red emissions, respectively. The as-prepared nanocomposites exhibit strong green and red fluorescent light when it is used for HeLa cells imaging.(2) The mesoporous silica coated Au nanoparticles (Aunanoparticle@mSiO2) were prepared at first by the one-pot method. Aunanoparticle@mSiO2@Y2O3:Eu nanocomposites are synthesized by coating of Y2O3 doped europium on their surface. The as-preparedAunanoparticle#mSiO2@Y2O3:Eu nanocomposites displayed the red emission intensity enhancement to 6.23 times at 30 nm thickness of the silica spacer between the core of Au nanoparticle and the shell of Y2O3:Eu. According to the observation of fluorescent lifetime and the modeling of local electric field, the metal-enhanced and quenched fluorescence is closely related with the enhancement of excitation and radiative decay rate and the quenching by NRET comes as a result of competition between the distance-dependent mechanism. A bright red fluorescence was observed when the Aunanoparticie@mSiO2@Y2O3:Eu nanocomposite was used in HeLa cells imaging.(3) Aunanoparticie@mSiO2@PABI-Eu nanocomposite is successfully fabricated by grafting the europium complex of PABI-Eu on the surface of Aunanoparticie@mSiO2 nanostruture via the method of chemical modification. The enhancement factor of 4.20 is achieved at an optimal silica thickness about 30 nm in solution. The as-prepared nanocomposite display good hydrophilic property and bright fluorescence in cell imaging.(4) Aunanoparticie@mSiO2@TDA-Eu nanocomposite is fabricated by modifying AunanosParticie@mSiO2 with the coordination polymer of TDA-Eu via a hydrothermal method. The nanocomposite with 30 nm thickness of the spacer layer exhibits the strongest enhancement factor of 6.81. |
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