Near-infrared Optical Properties Research On The Weakened Polarization Dependent Of Nanorod Heterodimers

Gold,silver,platinum and other precious metal nanomaterials have unique local surface plasmon resonance characteristics(LSPR),and exhibit strong extinction properties in the visible near infrared spectrum,giving them broad application prospects in biosensing,imaging,detection,and drug transportation,nano-medicine and other life sciences.The LSPR properties of nanoparticles strongly depends on their structural parameters such as particle size and shape.However,it is difficult to achieve a large redshift of the spectrum only by changing the size of particles with a single structure(for example,spherical gold nanoparticles with a diameter of 50 nm having its extinction curves at 532 nm,and when the particle size is increased to 100 nm,its curves is only red-shifted to 570 nm),and the changes in shape and structure has been proved to have a more sensitive spectrum response,so a variety of shapes and structures have been produced and studiedAmong them,gold nanorods are particularly attractive.As markers for molecular probes,they play an important role in biochemical and clinical basic research.This is because the good near-infrared optical performance of nanorods can effectively avoid water absorption interference and have a deeper penetration depth.Breaking the spherical symmetry,the nanorods form long and short axes in the structure,have more controllable structural parameters,and the adjustment range of broadband spectrum can be obtain only by slightly changing the structural parameters(such as the ratio of the length to the diameter).With the action of incident light,the electric field vector of the light causes dipole resonance on the long and short axes,respectively,exciting two LSPR modes(including low-level and high-level),which appear as two resonance peaks.The spectral curves properties of the near infrared range corresponds to the contribution of the electric field vector on the long axis.In order to obtain the best optical performance in this segment,the electric field vector(polarization direction)of the incident light needs to be parallel to the long axis to generate the optimal locally enhanced electric field.However,when the gold nanorod is used as a probe,it is in a random arbitrary posture in space,which makes it difficult to match the polarization state and subsequent processing.How to reduce or even remove the influence of polarization state to automatically excite the near infrared characteristics of nanorods is very expected in the field of sensing and imaging applications.In order to solve this problem in the application field,the resonance coupling between nanoparticles is used to compensate the near-infrared optical performance of the nanorods in the short axis direction during the simulation study,so as to achieve the near-infrared properties excitation that weakens the influence of polarization state in the near-infrared segment.For non-spherical nanoparticles,the classical analytical solution of Mie scattering is no longer applicable.Therefore,this thesis uses the software of COMSOL Multiphysics to establish a model to numerically solve the research problem,which based on the finite element method.The LSPR resonance coupling of nanoparticles has always been a hot issue in the industry.A large number of studies have been carried out based on molecular orbital theory,most of which have focused on homodimer structure.In order to control the size and ensure the acquisition of the near-infrared spectral segment,this thesis determined that the nanorods and the core-shell particles constitute a heterodimer based on the previous structural screening,because these two structures have the characteristics of excellent near-infrared performance.Although the experimental data of the interaction between nanorods and nanospheres has been reported in the literature,the mechanism of action of such heterodimers is not clear.The experimental data of the interaction between nanorods and nanospheres reported in the literature was used to verify the correctness of the model,and then the interaction law of nanorods and core-shell nanostructured particles was discussed through the model.Based on this law,this thesis proposes to compensate the short axis properties by combining the midpoint of nanorods with the core-shell of nanorod.The simulation data shows that the method has satisfactory results in weakening the influence of the polarization direction.The model shows that when the nanocore-shell particles deviate from the midpoint of the rod,two peaks are generated due to the LSPR of the two.The difference of these peaks corresponds to the joint of the two particles,which has potential for determining the molecular junction.In order to further optimize the performance,based on the interaction law of nanorods and nanocore-shells,this thesis proposes a prospective optimization structure: the nanoshell particle is circled around the midpoint of the rod to form a rod-ring structure to achieve better weakening effect.