Tunable Plasmonic Resonances in the Hexagonal Nanoarrays of Annular Aperture for Biosensing

In this paper, we demonstrate a nanostructure sensor based on hexagonal arrays of annular aperture operating in the near-infrared wavelength range. The strong coupling interaction between propagating surface plasmons (PSP) mode and localized surface plasmons (LSP) mode in the designed structure generates two sharp spectral features under normal incidence. The mode coupling strongly enhances the electromagnetic fields and increases the interaction volume of the analyte and optical field. A high refractive index sensitivity of 623 nm/RIU is demonstrated in a wide refractive index range of 1.33 to 1.40. Due to the excitation of sharp spectral feature, as narrow as 7 nm, high figure of merits of 93 was obtained in the refractive index range, which is nearly 10 times larger than that from hole arrays and disk arrays. Furthermore, sharp spectral feature in the designed structure provides more error margin for structure parameters, which is advantageous for experimental realization of systems without requiring challenging fabrication resolution. The sensor is promising for biosensing applications with high sensitivity and low limit of detection.