Properties And Synthesis Of Core-capped Heterodimer As Optical Probe

The unique localized surface plasmon resonance(LSPR)of noble metal nanomaterials have aroused widespread interest of people,and have broad application prospects in biosensor,imaging,detection,drug delivery and nanomedicine.As an optical probe,noble metal nanoparticles can generate electromagnetic field enhancement several orders of magnitude higher than the incident electromagnetic field,and the performance of large specific surface area and easy surface modification are the main reasons why they replace the traditional probes.In addition,nanoparticles can achieve the resonance frequency tuning by changing their size,shape and other parameters.The main obstacle of optical probe in biomedical application is the absorption of light by liquid tissue environment.However,when the diameter of the nanospheres changes from 10 nm to 100 nm,the resonance wavelength can only produce a red shift of about 40 nm,which is difficult to avoid the absorption of water.Therefore in order to manipulate light in a wide range of wavelengths with small-scale nanostructures and obtain excellent extinction and field enhancement properties,people have prepared various shapes of nanostructures.Among them,the asymmetric structures have more tunable degrees of freedom,which has attracted people's attention.Because of the breaking of the spherical symmetry,the resonance frequency tunability of the core-capped structure is greatly enhanced,and the optical performance shows a unique change.The spectrum of core-capped structure shows two obvious resonance peaks,corresponding to the resonance modes of electric dipole and magnetic dipole.However,due to the asymmetry of the core-capped,its extinction performance is very sensitive to the change of the polarization state.It is difficult to control the polarization direction of the nanoparticles in the free space to achieve the optimal resonance state,which hinders the application of the core-capped structure.In this paper,a heterodimer structure is proposed,which is composed of spherical symmetric structure and core-capped structure.By using the resonance coupling effect between the dimer structures,the dependence of the core-capped structure on the polarization state is improved,and the heterodimer structure has high efficient and stable extinction performance in the visible and near-infrared band.In this paper,the optical properties of the core-capped structure and the proposed heterodimer are systematically calculated by the software of COMSOL Multiphysics.The details are as follows:(1)Based on the simulation results,the optical properties of the core-shell and core-capped structures under linearly polarized plane waves,such as extinction and field enhancement,are discussed.Based on the surface charge density distribution,the change of resonance mode of core-capped with wavelength is discussed.Finally,the performance defects of the core-capped is sensitive to polarization state in the application process are proposed.(2)A new method is proposed to compensate the structural defects of the core-capped by using heterodimer,and the optical properties of the dimer are studied by simulation.(3)The optical properties of heterodimer in the case of core-capped rotation are studied and the dimer is modeled by Simpson-Peterson Approximation(SPA)theory.(4)An innovative method for the preparation of three-dimensional heterodimer with directional connection is proposed,and the dimer is successfully prepared.The feasibility of the compensation method is verified by the simulation and characterization of scanning electron microscope and optical microscope.In this paper,the results show that the optical properties of the core-capped are very sensitive to the change of polarization state due to the breaking of the spherical symmetry,which hinders its application.The core-shell/core-capped heterodimer proposed in this paper has successfully removed the dependence of core-capped on polarization state,greatly improves the self matching of core-capped structure on polarization state,and obtains stable and efficient optical performance.In the case of core-capped structure rotating,SPA theory is used to model the dimer structure that realize a heterodimer plasma ruler,which provides a means of tuning resonance wavelength in a wide range.Based on the synthesis method of our group,the directional connection of three-dimensional heterodimer is successfully synthesized,and the feasibility of compensation method for core-capped structure of heterodimer is verified by experimental characterization and simulation calculation.