Preparation And Surface-enhanced Fluorescence Property Of Nanosilver-based Composite Microspheres

Fluorescence technology was applied to a wide range in chemical, biological and medical science. Surface-enhanced fluorescence (SEF) based on noble metal nanoparticles can increase fluorescence intensity obviously, achieving an enhanced fluorescence detection sensitivity, and thus shows extensive application prospects for cellular imaging and single-molecule detection. Currently, the design and assembly of nanostructure based on the primitives of noble metal nanoparticles have become the important way and research tendency to improve the enhancement factor of SEF. In this work, silver nanoparticles (AgNPs) were assembled onto the surfaces of polystyrene (PS) beads, then silica spacers were fabricated on these surfaces, and the fluorescence enhancement properties of this structure to fluorochrome was preliminarily discussed. The main contents are as follows:(1) Optimization of the fabrication process of composite microspheres. Monodisperse polystyrene (PS) beads were used as templates, and the key controlling conditions of the loading of AgNPs and the fabrication of silica shell were studied. The influences of AgNO3 concentration, polyvinylpyrrolidone (PVP) concentration, ammonia content and tetraethoxysilane (TEOS) content on the morpholoies of the composite microspheres were investigated, obtaining an optimized condition (0.075 mol/L of AgNO3,0.03g/ml of PVP,0.3 ml of ammonia,240μl of TEOS). Under the optimized conditions, silver-loaded composite microspheres (PS@AgNPs@SiO2) with the size about 3-4μm were successfully fabricated, which have a good monodispersity, uniform diameter and compact shell. When the organic templates were removed through calcinations, AgNPs@SiO2 hollow spheres with silver loaded onto the interior surfaces were obtained.(2) The SEF effect of silver-loaded composite microspheres. The influences of composite microspheres on fluorescence properties of rhodamine B, rhodamine 6G and fluorescein isothiocyanate (FiTC) were researched, and the SEF of composite microspheres with different structures were also discussed. The silver-loaded composite microspheres can enhance the fluorescence intensity of different fluorophores in varying degrees. The enhancements of rhodamine B and FiTC were more significant, and their fluorescence intensity is increased about 12.4 times and 4.1 times respectively. The AgNPs@SiO2 hollow spheres show more remarkable enhancement on the fluorescence intensity. The fluorescence intensity of FiTC absorbed on the AgNPs@SiO2 hollow spheres is about as 13.7 times high as that on PS@AgNPs@SiO2 composite microspheres.