| Fluorescence emission of the fluorophores around the noble metal nanopaticles could be enhanced obviously, which is called metal-enhanced fluorescence (MEF). With the wide application of the fluorescence spectrum technology, MEF effect can realize the enhancement of the fluorescence intensity and improve the sensitivity of fluorescence detection sensitivity, drawing more and more attention. It has broad prospect of application in many fields, such as single molecule fluorescence detection, DNA sequencing, cell imaging.Ag nanocube (Ag NC) was selected as fluorescence enhancer due to its larger scattering areas and remarkable enhancement effect, and SiO2 interlayer was utilized to justify the distance between the metal core and fluorophore. A novel multilayer core-shell Ag-nanocube@SiO2@PMOs was synthesized, and the outer wall was periodic mesoporous organosilicas (PMOs) which incorporated rhodamine derivative fluorophore. This thesis included synthesis, exploring the mechanism of MEF, the detection for Cu2+, and so on.The synthesis of Ag-nanocube@SiO2@PMOs nanocomposite was through four steps:Firstly, monodispersed Ag NCs with well-controlled sizes were synthesized successfully via ethylene glycol (EG) reduction process. In addition, we investigated the vital role of capping agent—poly (vinyl pyrrolidone) (PVP) and NaHS that created nanocrystallites in the synthesis process. Different colors of silver colloidal solution were corresponding to different reaction stages, and Ag NCs with different size, could be produced by controlling the reaction time. Secondly, the rigid silica spacer shell (10 nm) was coated onto the surface of Ag NC by the hydrolysis and condensation of tetraethyl orthosilicate (TEOS) via classical stober method to separate the metal core and fluorophore, and Ag-nanocube@SiO2 naoparticles were prepared. Thirdly, bis(rhodamine Schiff-base derivative) bridged organosilicon precursor was synthesized by a series of steps. Fourthly, the outer periodic mesoporous organosilicas (PMOs) were constructed on the sueface of Ag-nanocube@SiO2 nanoparticle via a sol-gel approach by using hexadecyltrimethylammonium bromide (CTAB) surfactant as template and TEOS and organosilicon precursor as silicon source, and Ag-nanocube@SiO2@PMOs nanocomposites were obtained.We evaluated the effect of the Ag core on fluorescence emission and explored the origin of MEF in this Ag-nanocube@SiO2@PMOs system. The fluorescence intensity of Ag-nanocube@SiO2@PMOs was 3-fold higher than that of control sample without Ag NC core. There were two dominated way for MEF process:Firstly, the excitation rate of the fluorophore could be increased by the enhanced local electric field around the metal NPs. Secondly, the fluorescence quantum yield was increased and lifetime was decreased, which was due to the acceleration of radiative decay by the excitation-plasmon interaction.The designed Ag-nanocube@SiO2@PMOs nanocomposite could be a sensitive and selective sensor to detect the Cu2+ due to outer shell-periodic mesoporous organosilicas (PMOs) which incorporated the bis(rhodamine Schiff-base derivative) groups. Based on "OFF-ON" model of spirolactam in rhodamine moieties, little fluorescence emission of nanocomposites was observed due to the existence of spirolactam. However, upon the addition of Cu2+, the fluorescence emission intensity increased dramatically, which resulted from ring-opening of the spirolactam in the rhodamine derivative. Upon the addition of other competitive metal ions, the fluorescence intensities showed no discernible changes. The LOD for Cu2+was 3×10-7 M. It was conceivable that the MEF-based method might bring out the lower LOD for Cu2+ than the control sample without Ag core. |
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