Surface enhanced fluorescence effect of SiO2 coated silver nanoparticles and clusters

Abstract

Composite Ag@SiO2 nanoparticles are prepared for investigating a metal-enhanced fluorescence effect. Due to the competition between enhanced electromagnetic field intensity and fluorescence emission decay, the distance between the molecules and metal surface is an important surface-enhanced fluorescence factor for enhancing or quenching. This distance can be controlled by the size of the separation-layer, and thus the surface-enhanced fluorescence enhancement can be controlled. To avoid fluorescence quenching and obtain a considerable fluorescence enhancement, SiO2 shell is used to separate the molecules from the metal surface. The surface modification of metallic nanoparticles by SiO2 can not only improve the dispersibility and stability of metal particles, but also expanding its application effectively in the biological field. For fluorophores located around metal nanostructures, many factors would affect a fluorescence enhancement effect. Investigation of the enhancement mechanism usually becomes difficult and complicated due to too many variables and factors involved in the enhancement process. In order to systematically study the influence of these factors on fluorescence intensity, single polymer nanoparticles are chosen to be an enhanced substrate. The particle distribution is labeled through electron beam lithography and the surface-enhanced fluorescence spectroscopy of single nanoparticle or cluster is achieved by in - situ measurement method. The influence of metal particle size, cluster property and excitation polarization on the surface enhanced fluorescence is studied by using Rh6G as the probe molecule. Obvious fluorescence enhancement effect of Rh6G molecules at the surface of Ag@SiO2 is observed with nanocomposite, and the enhancement effect is controlled by the metal core particle size, aggregation property, and the polarization direction of the excitation light.