Transfer Matrix Modelling of an MgAl ₂ O ₄ /Antimonene-Enhanced SPR Sensor for Label-Free Quantitative Carcinoembryonic Antigen Detection: A Simulation-Based Study

Cancer screening, early detection, and clinical diagnostics require highly sensitive identification of biomarkers such as Carcinoembryonic Antigen (CEA), motivating the development of advanced label-free biosensing platforms. In this study, an ultra-sensitive SPR biosensor is computationally designed using a multilayer Kretschmann configuration comprising a BK7 prism, silver (Ag) plasmonic layer, magnesium aluminate (MgAl 2 O 4 ) dielectric film, antimonene nanolayer, and a CEA-containing sensing medium. The sensor operates by monitoring resonance-angle shifts induced by refractive-index variations associated with different CEA concentrations. Numerical simulations demonstrate that increasing the CEA concentration from 0 to 5 ng/mL changes the refractive index from 1.3300 to 1.3485, resulting in a resonance-angle shift from 79.35° to 83.50°. The optimized sensor achieves a maximum sensitivity of 229.73°/RIU, a minimum FWHM of 3.65°, a detection accuracy of 0.273° -1 , and a FoM of 51.624 RIU -1 . Enhanced plasmonic coupling provided by the MgAl 2 O 4 and antimonene layers contributes to strong field confinement and improved sensing performance. These findings demonstrate that the proposed SPR design can be efficient for CEA biomarker screening, early cancer detection and future point-of-care healthcare applications.