High-figure-of-merit waveguide-based plasmonic MIM biosensor utilizing fano resonance for the detection of mycobacterium tuberculosis

Abstract

This study introduces a high-performance plasmonic sensor based on a metal–insulator–metal waveguide structure, specifically optimized for the detection of Mycobacterium tuberculosis (TB). By employing Fano resonance, the sensor incorporates ladder-shaped steps that produce multiple sharp and asymmetric resonance peaks, significantly enhancing sensitivity to refractive index variations. Finite-difference time-domain simulations demonstrate that increasing the number of steps from one to five introduces additional resonance modes, with the five-step configuration achieving a maximum sensitivity of 806.47 nm/RIU and an outstanding figure of merit (FOM) of 126.20 RIU⁻¹. The sensor’s performance was evaluated using refractive indices representative of healthy blood and various TB strains, exhibiting clear wavelength shifts proportional to biological changes. Key geometrical parameters were optimized to improve field confinement and resonance sharpness. Electric field distribution analysis confirmed step-specific field localization, supporting multimodal detection capabilities. Compared to recent designs, the proposed sensor demonstrates superior resolution and detection limits, establishing its potential for label-free, real-time biomedical diagnostics. Its compact footprint and high sensitivity make it a promising candidate for point-of-care TB detection and broader biosensing applications. Future research will focus on fabrication methods and clinical validation to advance its practical implementation.