Simulation and analysis of 2D material/metal carbide based fiber optic SPR probe for ultrasensitive cortisol detection

Cortisol, a steroid hormone, plays a vital part in regulating various activities such as metabolism and immune response. It is a well-known stress biomarker and should be measured with as high precision as possible. In this work, a non-invasive fiber optic surface plasmon resonance (FOSPR) based sensor probe is proposed for detection of salivary cortisol at the w avelength (lambda) of 830 nm. Proposed sensor design consists of chalcogenide glass core, polymer clad, silver (Ag) layer with two-dimensional (2D) materials such as conventional (graphene, WS2 and MoS2) and transition metal carbides (MXenes) based layered materials considered one at a time. Angular and intensity interrogation methods have been envisaged for simulation and analysis purpose. The sensing performance analysis is carried out in terms of figure of merit (FOM) and combined performance factor (CPF). A comprehensive analysis of all the probe variants reveals that among all the sensor design variants, the Ti3C2O2-based probe is able to provide superior overall sensing performance including a detection limit as fine as 15.7 fg/mL, which is finer compared to existing cortisol sensors based on diverse techniques.