Fano Resonances in Complex Plasmonic Necklaces Composed of Gold Nanodisks Clusters for Enhanced LSPR Sensing

Plasmonic nanoparticles in complex clusters and in specific molecular orientations are able to support strong plasmon and Fano resonances in their nanoscale geometries. In this paper, we examine the spectral response of a symmetric necklace shape nanostructure composed of Au nanodisk heptamers that are located in a close proximity to each other. Determining the appropriate geometrical parameters for the proposed necklace, we analyzed the effect of geometrical variations on the Fano resonance position and quality by calculating the scattering cross-sectional profile, numerically. Considering the strong localization of surface plasmon resonances (LSPR) in the heptamer clusters, the LSPR sensitivity for the studied necklace has been determined. Moreover, we evaluated the performance of the structure for different medium conditions by plotting corresponding figure of merit (FoM). To this end, we measured the plasmon resonance energy differences (Δ E eV) over the refractive index (n) alterations, we quantified the corresponding FoM for the final necklace as 13.7, which can be utilized in designing precise and highly sensitive sensors. Ultimately, we proved that highly complex structures composed of metal nanoparticles clusters yield high sensitivity to the environmental perturbations.