A novel metal–insulator–metal (MIM) plasmonic sensor has been designed and numerically optimized for highly sensitive detection of glucose concentration via refractive index (RI) modulation. The proposed structure consists of a compact MIM bus waveguide side-coupled to a composite cavity formed by a drop-shaped cavity embedded within an opened ring resonator. This configuration enables the generation of multiple coupled resonance modes with strong electromagnetic field confinement, enhancing light–matter interaction in the sensing region and providing an effective approach for engineering multi-resonance plasmonic responses in compact MIM sensors. Through comprehensive geometric optimization- nine key structural parameters- such as coupling gap, drop-shape cavity dimensions, and ring configuration- were identified as critical factors in enhancing both sensitivity and spectral characteristics. The optimized sensor exhibits multiple sharp resonance modes in the near-infrared region (NIR), with strong electromagnetic field confinement observed within the cavity. Numerical results reveal a high refractive index (RI) sensitivity of 1296.7 n m / R I U for the optimized mode. For refractive index sensing, the calculated Q factors for the two main modes are 41.27 and 24.73, while the corresponding FOM values are 38.46 RIU −1 and 21.43 RIU −1 , with LOD values on the order of 10 −6 RIU. By incrementally varying glucose concentration and converting the values to their corresponding refractive indices, a linear and robust wavelength shift response was achieved, yielding a sensitivity of 0.1857 (nm.L)/g over the concentration range of (0–200 g/L). The proposed plasmonic glucose sensor operates over a wide concentration range, enabling real-time monitoring in industrial applications. Its performance surpasses several recent MIM-based sensors, highlighting the effectiveness of the presented multi-resonance design and the importance of precise geometric engineering in high–performance plasmonic sensors.
Farokhi et al. (Fri,) studied this question.