Numerical Investigation of Selective Near-infrared Fluorescent Enhancement Based on Dual-Band Plasmonic Metasurfaces with Truncated Pyramids

This paper presents a numerical investigation of near-infrared plasmonic metasurfaces formed by periodic arrays of subwavelength truncated pyramids of stacks of silver (Ag) and silica (SiO₂) nanosquares placed on an Ag layer (acting as a reflector). By controlling the difference between the two base lengths of the truncated pyramid, it is possible to design a plasmonic metasurface that generates two distinct resonances. Simulation results using the finite-difference time-domain (FDTD) method reveal that these two resonances are generated by coupling between the localized modes of Ag nanosquares and the propagative surface plasmon mode on the Ag reflecting layer. Looking at the field distribution at the resonances, the strong confinement of incident light localized inside the air-SiO₂ spacer-layer, which has extremely low reflection (close to 0%), corresponded to the absorption of up to 100% and a high quality-factor (Q-factor) of ~ 180. Operating in the near-infrared range, the proposed plasmonic metasurface has low Ohmic loss, it can produce the E-field enhancements of ~ 65 and ~ 400 times at wavelengths of ~ 1372.0 and ~ 1499.0 nm, respectively, and high directivity of ~ 1296. The proposed plasmonic metasurface holds potential applications in fields such as cell imaging, biomarkers for disease diagnostics, and environmental monitoring.