A High-resolution metal-insulator-metal plasmonic biosensor with concentric ring resonators for carcinoembryonic antigen detection.

High-resolution optical sensors are vital for detecting subtle refractive index variations associated with biomolecular interactions, such as changes in carcinoembryonic antigen (CEA) concentration. This work presents a compact metal-insulator-metal (MIM) plasmonic sensor with two concentric ring resonators, numerically investigated using finite-difference time-domain simulations. Structural parameters are optimized to maximize field confinement and resonant mode coupling, yielding a sensitivity of 1035 nm/RIU, a resonance linewidth of 3.75 nm, and a figure of merit of 276 RIU⁻¹. The sensor demonstrates precise spectral shifts corresponding to minute refractive index changes linked to CEA, while the influence of surface-bound layers and fabrication tolerances is also assessed to ensure robustness under practical conditions. These results highlight the sensor's potential as a high-resolution, label-free platform for monitoring CEA in biological samples.