Compact dual-band MIM plasmonic sensor with enhanced sensitivity for biochemical sensing

This study investigates a novel dual-band plasmonic refractive index (RI) sensor, to our knowledge, based on an air-silver metal-insulator-metal waveguide configuration, incorporating a circular cavity featuring a centrally embedded elliptical notch. The sensor design was modeled using COMSOL Multiphysics (version 6.2) and optimized through a two-dimensional finite element method analysis. The proposed sensor exhibits dual-band resonance behavior in the ranges of 800-1200 nm and 1300-1900 nm. It demonstrated remarkable sensitivities ranging from 1137 to 1970<i>n</i><i>m</i>/<i>R</i><i>I</i><i>U</i>^-1 for lead nitrate [<i>P</i><i>b</i>(<i>N</i><i>O</i>₃)₂] detection and from 682 to 1136.4 nm/RIU for thyroxine (T4) sensing, alongside a high figure of merit (FoM) reaching 76 and a quality factor (Q.factor) of approximately 83. The structure also achieved a maximum transmission of ∼88<i>%</i> and a narrow full-width at half-maximum of 24.8 nm, underscoring its suitability for high-resolution detection.