Fluorescence Enhancement Based On Surface Plasmon Coupling Of Silver Nanocomposites

The coupling of the metallic nanostructures and their application in optoelectric have beendraw wide attention. Recently, the study of coupling among surface plasmon has emerged as an active and important research area. Two kinds of coupling structures are proposed in the thesis involvingsilver nanocomposites. One is the coupling between localized surface plasmon(LSP) and LSP of Fe3O4@Ag core-shell nanostrutures and the other is the coupling between LSP andsurface plasmon propagations(SPP) based on silver nanoparticles(AgNPs) and silver nanowires(AgNWs). Firstly, the optical properties of coupling stuctures were analyzed by UV-vis spectrum and FDTD software. Secondly, the enhanced optical property of the coupling structures was experimentally studied through fluorescence spectrum. Finally, the physical mechanism of the optical phenomena was investigated. Our work has potential significance in the fluorescence imaging and detection of biological molecules.The details of the thesis are listed as followings:Fe3O4 nanoparticle and silver nanoparticlewith well monodispersibility were both synthesized by the chemical oxidation-reduction method,Fe3O4@Ag nanostructures were successfully synthesized via stober method by combing Fe3O4 nanoparticle and silver nanoparticles with MPTS. In addition, AgNPs-AgNWs coupling structure was successfully synthesized via modification method by the media function of PVP.According to the characteristics of couplingstructure,Fe3O4@Ag core-shell nanostructure and AgNPs-AgNW snanostructures were systematically investigated respectively. For Fe3O4@Ag core-shell nanostructure, the surface density was tuned and its coupling was studied via measuring the spectrum of Fe3O4@Ag nanoparticle and calculating the electric field around nanoparticle. The results showed that the surface plasmon coupling of Fe304@Agnanostructure was formed ,when the average distance of nanostructures was less than 19 nm, and the intensity of coupling was enhanced with the narrow of average distance.For AgNPs-AgNWs nanostructure, the surface density of AgNPs on AgNWwas tuned, and the morphology of nanostructure was modified; and the coupling of AgNPs-AgNWs was studied via measuring the spectrum nanostructures and calculating the electric field around nanostructures.The results showed that more "hotspots" was formed when the AgNPs-AgNWs nanostructures was systhesized, and the adsorption of surface plamon resonance was enlarged and the surface electromagnetic field was markly enhanced when the coupling was achived.Surface plasmon enhanced fluorescence by Fe3O4@Ag nanostructure and AgNPs-AgNWs nanostructure were respectively studied. For Fe3O4@Ag nanostructure, the fluorescence intensity of probe molecule changed with the size ofFe3O4@Ag nanostructure, was firstly analyzed, and fluorescence intensity of fluorophore enhanced by coupling structurewassecondly demonstrated.The results showed that the fluorescence of probe molecule was significantly enhanced by Fe3O4@Ag coupling nanostructure, and 5.4 folds enhancement for RB molecules and 15.8 folds enhancement for PpIX moleculeswere achieved,respectively.Finally,theaverage distance of fluorophore and plasmon structures was tuned by PVA dielectric layer, and the mechanism of surface enhanced fluorescence (SEF) was demonstrated. For AgNPs-AgNWsnanostructure, the fluorescence intensity of probe molecule enhanced by AgNPs-AgNWs nanostructure was firstly analyzed, as well as the fluorescence intensity of fluorophore changed with the morphology of coupling structure.The results showed that the fluorescence of probe molecule was significantly enhanced by AgNPs-AgNWs coupling nanostructure, and 9.6 folds enhancement for RB molecules and 10.6 folds enhancement for PpIX molecules were achieved, respectively.Finally, the average distance of fluorophore and plasmon structures was also tuned by PVA dielectric layer, and the mechanism of surface enhanced fluorescence was further demonstrated.Based on the surface plasmon coupling enhanced optical effect, we have appliedthe coupling structuresto fluorescence imaging and molecule detection.The LSP-LSPcoupling structure was applied to the detection of Rodanmine B(RB) molecule,the detectionlimit concentration of RB molecule was 5×10-8mol/L; and the LSP-SPP coupling structure was applied to fluorescence imaging of PpIX molecules.The results showed that the coupling structures were effectively enhanced the fluorophore signal and lower the photobleaching of PpIX probe molecule.