High-Property Refractive Index and Bio-Sensing Dual-Purpose Sensor Based on SPPs

A high-property plasma resonance-sensor structure consisting of two metal-insulator-metal (MIM) waveguides coupled with a transverse ladder-shaped nano-cavity (TLSNC) is designed based on surface plasmon polaritons. Its transmission characteristics are analyzed using multimode interference coupling mode theory (MICMT), and are simulated using finite element analysis (FEA). Meanwhile, the influence of different structural arguments on the performance of the structure is investigated. This study shows that the system presents four high-quality formants in the transmission spectrum. The highest sensitivity is 3000 nm/RIU with a high FOM of 9.7 × 10⁵. In addition, the proposed structure could act as a biosensor to detect the concentrations of sodium ions (Na), potassium ions (K), and the glucose solution with maximum sensitivities of 0.45, 0.625 and 5.5 nm/mgdL^-1, respectively. Compared with other structures, the designed system has the advantages of a simple construction, a wide working band range, high reliability and easy nano-scale integration, providing a high-performance cavity choice for refractive index sensing and biosensing devices based on surface plasmons.