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Fluorescence Enhancement of IgG-FITC Based on Surface Plasmon Resonance of Ag@SiO2 Nanoparticles as Application of Biomarker

Ag@SiO2 nanoparticles with the core-shell structure have been prepared, of which the silver core was about 50 nm and the thickness of silica shell was approximately 10 nm. In slightly alkaline aqueous solution (pH = 8), through electrostatic force between cationic polymer PDDA (i.e., poly-diallyldimethylammonium chloride) and the obtained Ag@SiO2 nanoparticles, PDDA molecules were fixed on the surface of Ag@SiO2 nanoparticles. The prepared Ag@SiO2/PDDA nanoparticles have both rich positive surface charges and rich micro-holes of silica shell. Based on micro-hole adsorption, the small molecule FITC (i.e., fluorescein isothiocyanate) marking on IgG (i.e., immunoglobulin) was adsorbed into the rich microholes of silica shell; at the same time, the negatively charge macromolecule IgG marked by FITC was firmly fixed on the rich positive charges surface of Ag@SiO2/PDDA nanoparticles by electrostatic interaction. And then, Ag@SiO2/PDDA/IgG-FITC fluorescent nanoparticles with the SPR fluorescence enhancement were prepared. The shell-type SiO2/PDDA/IgG-FITC nanoparticles were obtained by dissolving the silver core in the prepared core-shell Ag@SiO2/PDDA/IgG-FITC nanoparticles by using H2O2. Compared with the shell-type nanoparticles, the fluorescence intensity of Ag@SiO2/PDDA/IgG-FITC was enhanced 1.7 times. The prepared Ag@SiO2/PDDA/IgG-FITC nanoparticles have both SPR-based fluorescence enhancement ability and the surface distributing IgG–based obvious advantages including good biocompatibility and easy marking with other biomolecules.