Study Of The Refractive Index Sensing Performances Of Au Nanopaticles Based On The Plasmonic Quadrupole Resonance

Localized surface plasmon resonance(LSPR)is an optical nanoscale phenomenon that can enhance the electromagnetic field interaction of nanoparticles,meanwhile,can lead to a sharp peak in absorption and scattering spectrum when the collective oscillation of free electron at metal-dielectric interface is excited by an incident light at a particular wavelength and polarization state.For its excellent properties in label-free detection,LSPR has been widely used in electronics,photonics,photocatalysis and biosensing,etc.In recent years,gold nanoparticles(Au NPs),such as gold nanorods(GNRs),gold nanobipyramids(GBPs)and gold nanocubes,have attracted great interests due to their high sensing sensitivity and super chemical stability.Currently,gold nanoparticles are mainly obtained by chemical synthesis,but chemically synthesized gold nanoparticles are randomly oriented in a colloidal solution or when deposited on a substrate.In the experiment,the random distribution of asymmetric gold nanoparticles with different horizontal and vertical structures will average the transverse LSPR component and the longitudinal LSPR component,which will greatly reduce the figure of merit(FOM)of the assembled synthesized asymmetric gold nanoparticles.Therefore,it can be predicted that the periodically arranged gold nanoparticles have important application prospects in improving the FOM of the LSPR sensor.Optical processing methods can be used to manufacture gold nanoparticle arrays with periodic structures on the surface of the substrate,thereby forming supersurfaces with super sensing performance.Gold nanoparticles prepared using current nano processing technology generally have larger sizes.As the size of gold nanoparticles increasing,the superposition of their dipole mode resonances and higher order mode resonances increases the plasmon resonance line width of the particles.However,for the asymmetric Au nanorod and Au nanopyramid,their higher-order resonance(especially the quadrupole resonance)will produce a narrower line width than the dipole resonance.Therefore,with the aim to further improve the FOM of LSPR sensor,this paper systematically studied the optical sensing characteristics of plasmon quadrupole resonance of gold Nanocuboids and Nanorhombohedrons,which can be obtained by optical manufacturing.The main work of this article is asfollows:1.The characteristics of surface plasmon resonance and its applications in different fields were given briefly.The research history and development status of surface plasmon resonance of gold nanoparticles were summarized.And the basic theory and calculation methods of local surface plasmon resonance were introduced.2.The optical properties and the refractive index sensing performances of gold nanocubes have been systematically studied.The results show that the full width at half maximum(FWHM)of quadrupole resonance is much smaller than that of dipole resonance for large asymmetric Au nanoparticles.When the ends of nanoparticles become angular(quadrate ends),the quadrupole resonance wavelength will occur“red shift”,and the quadrupole resonance would possess higher FOM,and the RI sensing properties of Au nanocuboid arrays at quadrupole resonance are both no less than the respective parameters of single particle.3.The optical properties and the refractive index sensing performances of gold Nanorhombohedrons were systematically studied,and these properties were compared with that of the gold Nanocuboids in all aspects.