The Research And Application Of Metal-enhanced Fluorescence Based On Core-shell Nanoparticles

SiO₂-coated Au ?Au@SiO₂? core-shell nanoparticles ?NPs? have received intensive attention for decades because of their unique optical properties, biocompatability, and versatility of surface functionalization. For example, the plasmon of the Au NPs can create a giant near field around their suface,which is essential for metal-enhanced fluorescence ?MEF?. Whiles, the outer, thickness-tuanable SiO₂ shell can separate the fluorescence molecule from direct contacting with the Au metal. Therefore, Au@SiO₂ core-shell NPs may serves as an indeal platform for MEF applications, The research interests of this thesis, thus, are to improve the MEF intensity, and to functionalize the Au@SiO₂ core-shell NPs to enable fluorescence detection of Hg2+ ions with improved sensitivity, achieved by engineering the structure of the Au@SiO₂ core-shell NPs. The main contents and results achieved are outlined as follows:1. Synthesis of SiO₂-coated Au nanoshell ?SiO₂@Au@SiO₂? dimers with a high yield and tunning their MEF. To improve the Au seed density, we have developed an approach of salt-derived densification, thereby enabling the growth of a continious Au shell on the surfaes of the SiO₂ spheres, forming SiO₂@Au nanoshells. The dimers of SiO₂@Au nanoshells were produced by precisely controlling the aggregation of the Au nanoshells, realized via finely changing the concentration and chain length of PVP. Because SiO₂ coating is critically dependent on the number of the core particles ?here the SiO₂@Au dimers? introduced, its thickness ?9,18,28 and 40 nm? can be tunned controlling the amount of the silica source ?TEOS? and the number of the SiO₂@Au dimers. These steps enable the systhesis of the final SiO₂@Au@SiO₂ dimers. After their synthesis, a newly synthesized ICG-like molecule ?named compound 1? was labled onto the surface of SiO₂@Au@SiO₂ dimers via electrostatic adsorption. Experimental and theoretically simulated results reveal that in the thickness range examined, the maximum MEF enhancement is 69-fold, achieved on the SiO₂@Au@SiO₂ dimers with a 9 nm external SiO₂ shell.2. MEF-assisted fuoresecence detection of Hg2+ with improved sensitivity. Thin SiC>2 shell-coated Au ?Au@SiO₂? NPs were synthesized by chemical deposition of a ultrathin SiO₂ shell ??4 nm? on Au seeds synthesized according to the Frens method. By carefully controlling reaction parameters such as pH, reaction time, temperature, and the amount of silica source fed, this method allows coating the Au NPs with a continious, pinhole-free SiO₂ shell. With such a unique core-shell configuration, the fluorescence enhancement is 8.2 times achieved on the Au@SiO₂ nanoparticles with a 80 nm core and a 4 nm-thick SiO₂ shell. To demonstrate application of this MEF platform, fluorescence probed was anchored on the surfaces fo the Au@SiO₂) NPs with a 4 nm external SiO₂ shell. The optimized detection limit achieved was 5.0×10-11 M, which was about two orders of magnitude lower than that ?8.5×10-9 M? achieved for free fluorescence probe.