Broad Refractive Index Range SPR Sensor for Cholesterol Detection Utilizing Si 3 N 4 / Fe 2 O 3 Coatings

A theoretical study of a high-performance surface plasmon resonance (SPR) biosensor based on Kretschmann configuration (BK7 prism/Ag/Si 3 N 4 /Fe 2 O 3 ) is presented for label-free detection of cholesterol. The surface plasmonic waves are excited via the attenuated total reflection (ATR) phenomenon. The optical characteristics of the sensor are analyzed using the transfer matrix method (TMM), allowing precise calculation of reflectance curves and resonance angle shifts. The inclusion of Si 3 N 4 and Fe 2 O 3 layers improves electromagnetic field confinement and interaction with cholesterol molecules at the sensing interface. The variation of the refractive index of the sensing medium, corresponding to different cholesterol concentrations, is used to evaluate the performance of the sensor. Key parameters like sensitivity (S), full width at half maximum (FWHM), detection accuracy (DA), and figure of merit (FoM) are investigated. The proposed sensor features improved sensitivity of 326.14°/RIU, making it suited for rapid and accurate cholesterol detection in biomedical diagnostics. The proposed designs performance is also evaluated in the wide RI range of 1.30 to 1.40.