Optoplasmonic Enhanced SERS Detection In SiO₂ Microsphere On Au Film

Surface Enhanced Raman Spectroscopy(SERS)refers to that when the analytes molecules are adsorbed on the surface of rough metal or in the form of nano particles as the substrate,when the laser light source irradiates on the surface of precious metal,Local surface plasma excitation is generated by the collective vibration of free electrons on the metal surface,and the signal intensity of surface-enhanced Raman spectrum of molecules adsorb on the surface of precious metals will be greatly enhanced,which is a kind of molecular vibration spectrum.Compared with the very weak signal strength of the traditional Raman spectrum,the intensity of the electromagnetic field could be significantly enhanced through various SERS substrates,and it was based on this enhancement effect that the very weak Raman spectrum signal was enhanced.SERS technique for sample preparation is simple,high sensitivity,low can detect the concentration of the analytes,also has the testing material composition,stability is good wait for a characteristic,it is because of Raman spectroscopy has the excellent performance,it has been widely used in analysis and detection technology used in SERS spectra become a rapid and sensitive analysis testing tools.In this paper is mainly studied by Si O₂ dielectric microspheres and without the light of the nanostructures of Au film of optoplasmonic film,the dielectric microspheres were deposited on Au film of a simple SERS substrate,the molecules is located in the gap between the Au film and microspheres as a probe to study the influence of different dielectric microsphere size and of different laser wavelength of the Raman spectrum signal intensity.The simulation software finite-difference time-domain method(FDTD)was used to explore the coupling system composed of different sizes of single particle Si O₂ dielectric microspheres and Au film,though numerical simulation of electric field distribution and charge distribution show that the synergistic effect of electromagnetic field was stronger than the Raman signal strength of the system composed only of dielectric microspheres or Au film.The simulated electromagnetic field points out the enhancement caused by the optical lens effect of Si O₂ microsphere that high light intensity is generated under the microsphere to excite surface plasmon on Au film.Furthermore,we also simulated the electric field enhancement of different sizes of Si O₂microspheres under different laser wavelengths and the variation trend of energy sum in a specific region.In this experiment,using Methylene Blue(MB)molecule as probe molecule,the optoplasmonic film consists of Si O₂ microsphere and Au film without any nanostructures is investigated.With the help of a microsphere,the intensity of SERS on Au film is highly enhanced(?1000 times)compared to bare Au film.The experimental and theoretical data demonstrates the electric field enhancemeny of the optoplasmonic hybrid structure is greatly influenced by the size of the Si O₂ microsphere and wavelength of incident light.This interesting film with a simple configuration could overcome the challenges in the fabrication and store process induced by nanostructures,which play an important role in SERS application.Our work not only enlarges the knowledge of electromagnetic strength under synergistic effects in the optoplasmonic hybrid structure,but also exhibits excellent application prospective in light harvest field e.g.enhanced spectrum,photocatalysis,optothermal effect,and hot electron generation,etc.