Study On Relationship Of Sensing Properties And Near-filed Distribution Of Localized Surface Plasmon Resonance Of Metal Nanosructures

Localized surface plasmon resonance (LSPR) characteristics of metal nanoparticles and its applications is one of the hot contents of the current optical research. On suitable light field excitation a metal nanopartical occurs LSPR, due to the characteristics, which is resonance wavelength is shifted when surrounding refractive index is changed. Therefore, it can be applied to the biosensor. In the application of biosensing, the relationship between sensing performance and the distribution of near-field of LSPR resonance has always been an interesting subject. However, there hasn’t been deeply study. In this paper, we had systematically researched the relationship of sensing characteristics of single/double metal nanostructures and near-field distribution by utilizing3D-FDTD method and creating two refractive index change model.This paper introduces the overview, the basic theory and numerical methods of localized surface plasmon resonance of metal nanoparticles, and then using the layer model and samples sampling model, we investigate the relationship of localized near-field distribution and surface sensing property of LSPR of monomers and dimers. We obtain the relationship of near-field distribution property and sensing performance for different shapes of monomer and dimer nanostructures. Finally, according to the analysis results, a single and a double metal nanostructure are optimized design.The results show that:1) Using the layer model, when the metallic nanostructures excite LSPR, we numerically analysis the relationship of the near-field distribution and surface refractive index sensitivity of three kinds of monomers (single triangle, unilateral column, single disk) metallic nanostructures. We get the relationship that the surface refractive index sensitivity changes as a function of the film thickness increases exponentially fitting relationship. We analyze the relationship of the near-field penetration depth, surface refractive index sensitivity, and bulk refractive-index sensitivity. For the film model, the near-field distribution has good correspondence to the surface refractive index sensitivity. The surface refractive index sensitivity is proportional to the film thickness in the near-field penetration depth. Near-field penetration depths are different for the different metal nanoparticles. The surface refractive index sensitivity is quite different in the same layer-thickness, but the bulk Refractive index sensitivity is alike under the same reference wavelength.2) We researched the relationship between the local refractive index sensitivity and the near-field distribution of monomer nanostructures with the sample model. Only when the most of near-field penetration area was covered by the refractive index change region, it occurs the sensing response. The local refractive index sensitivity is quite low, because of the near-field energy distribution of monomers are relatively dispersed.3) We researched the relationship of surface refractive index sensitivity, local refractive index sensitivity and near-field distribution of dimer metal nanostructures (double triangle, double square prism, double disk). It showed that field energy was concentrated in the dimer nanostructures. Due to coupling between the dimers, it generates the sensing response in a small surface layer. If there is more concentrated field energy, there will be higher refractive index sensitivity in the same surface layer. The surface refractive index sensitivity of three kinds of dimers descending order is double triangles, double disc, double square prisms.4) The local refractive index sensitivity of dimers is better than the monomer in the sample model. The sensing area was concentrated in the coupling region. The near-field energy is concentrated in the pitch area. When the distance was covered by the refractive index changing area, the surface refractive index sensitivity was half of the bulk refractive index sensitivity for double triangular prisms.5) We know that the bulk refractive index sensitivity is same in the same reference wavelength. In order to improving the bulk refractive index sensitivity, the effective method is that makes the resonance wavelength redshift. Using this characteristic, we propose the program of optimized design for the single triangle. An optimization single triangle nanostructure with bulk refractive index sensitivity of594nm/RIU and figure of merit of5.3is presented. In order to improving the surface sensing ability of local area, the effect method is that makes the field energy concentrating in the detection region. Using this characteristic, we propose the program of optimized design for the dimers. When the reference wavelength is787nm, an optimization double triangle nanostructures with the bulk refractive index sensitivity of154nm/RIU and figure of merit of1.18is presented in the area of20nm×20nm×20nm. The local refractive index sensitivity of double triangles is about4times as many as the double disks.