Enhanced angular sensitivity of surface plasmon resonance sensor based on Si-Ag-MXene structure for cortisol application

In this study, a surface plasmon resonance (SPR) based sensor is designed and modelled analytically to achieve the maximum sensitivity with improved selectivity. To achieve this, an Ag layer is sandwiched between Si and MXene layers. The Si layer is placed between CaF₂ prism and Ag layer. Because of its higher charge carrier transfer efficiency to the metal interface and superior charge carrier confinement, the Si layer in SPR sensor has significantly improved sensor’s performance. The Si and Ag layer thickness have been characterized to achieve optimized sensing parameters. The analysed designs ensure the maximum sensitivity of 437.5°/RIU and figure of merit (FoM) of 37.99/RIU. The estimation of the electric field distribution is also utilized to analyse the enhancement of the field at the interfaces between multiple layers of the material. A penetration depth (PD) of 273.52 nm, which represents the separation between positions from the maximum electric field intensity to 37% strength, has been attained. As a result, the proposed sensor can also detect the cortisol concentration, achieving the sensitivity and limit of detection (LoD) of 441.91°/RIU and 2.26 × 10^–6 RIU, respectively. The proposed sensor demonstrates the potential for detecting concentration-based cortisol.