Surface Enhanced Fluorescence Effect Of SiO 2 Coated Noble Metal Nano-single Particles And Multimers

Fluorescence spectroscopy technology,which has a high sensitivity,is widely used in the qualitative and quantitative measurement,medical diagnosis,bio-imaging and other fields.Metal-enhanced fluorescence is a method used to enhance fluorescence.Surface plasmon generated by the metal nano-substrates under the excitation of the incident light,will affect the fluorescence emission of the nearby fluorescent molecules.This method provides a new channel to improve the signal sensitivity.The surface-enhanced fluorescence effect is affected by various factors,like the enhanced substrate,luminescent material and excitation light source,etc.According to the existing study,the element composition,surface morphology,size,spacing,distribution of the metal substrate,and the number of molecules,the distance between the fluorescent molecules and the substrate,the wavelength of the excitation light can affect the surface-enhanced fluorescence.It has a great significance to study the influence factors of the fluorescence intensity of fluorescent molecules that adsorbed on nanoparticlesIn this paper,gold and silver alloy nanoparticles with good dispersibility and unifonn morphology,as well as silver nanoparticles with large size and easy labeling are used as enhanced substrate.The surface of the two kinds of metal nanoparticles can be modified by coating a layer of silica which is thickness-controllable and biocompatible and optically transparent.The rhodamine 6G with a broad absorption peak was used as probe molecule.The effects of the distance between molecules and the sxurface of metal sulbstrate,the size of metal particles,the properties of clusters,and the polarization of excitation light on the surface-enhanced fluorescence were systematically studied.The research of this paper is divided into the following two parts:The first part:the effects of the distance between molecules and the metal nanoparticles on surface enhanced fluorescence.Au-Ag alloy@SiO2 with good monodispersity was used as the enhanced substrate.By changing thick:ness of the silica layer with 2,5,8,15,20 and 35 nm,respectively.The effect of the distance between the organic molecules and the metal substrate on the surface-enhanced fluorescence effect was studied.The experimental results show that the thickness of the shell layer has a significant effect on the surface enhanced fluorescence,and the fluorescence enhancement effect increases first and then decreases with the increase of the distance.When the thickness of the shell layer is about 8nm,the result is the best,which leads to the strongest fluorescence enhancement.The second part:the effect of the size of metal substrate,cluster properties and polarization on the surface-enhanced fluorescenceSilver nanoparticles were prepared by using ethylene glycol as reducing agent under high temperature.Ag@SiO2 composite nanoparticles were prepared by coating a silica layer of about 8 nm on the surface of the silver nanoparticles and their clusters using a modified Stober method.The Ag@SiO2 composite nanoparticles and their clusters were successffully labeled by electron beam etching on the substrate surface.The effects of particle size,cluster properties,and polarization on the surface-enhanced fluorescence are systematically studied.The results show that Ag@SiO2 nanocomposite substrate has an obvious fluorescence enhancement effect on Rh6G,and the enhancement effect can be affected by the size,polymerization degree,polymerization state of the metal particles and polarization angle of the excitation light.