High-performance hexagonal cavity-based plasmonic MIM waveguide biosensor for sensitive and label-free detection of carcinoembryonic antigen (CEA).

In this research, a plasmonic metal-insulator-metal (MIM) biosensor is proposed and numerically analyzed for label-free and highly sensitive refractive index detection. The design incorporates a hybrid configuration consisting of a hexagonal resonant cavity coupled with a narrow rectangular slit along its lower boundary. This particular arrangement, which has not been previously reported, enables the excitation of two distinct resonance modes that contribute to improved spectral resolution and sensing precision relative to conventional MIM structures. Finite-difference time-domain (FDTD) simulations were employed to investigate the optical response and optimize the geometrical parameters of the device. The optimized sensor demonstrates strong electromagnetic field confinement, achieving a sensitivity of 770.27 nm/RIU and a figure of merit (FoM) of 160.47, both of which surpass values reported in related studies. Owing to its compact geometry and compatibility with nanoimprint lithography, the proposed design can be fabricated with high practicality. These findings suggest that the device offers an efficient and scalable platform for real-time, label-free detection of carcinoembryonic antigen (CEA) and other biomarkers relevant to early-stage disease diagnostics.