SFFO Cortisol Biosensor: Highly Sensitive S-Flex Fiber Optic Plasmonic Biosensor for Label-Free Cortisol Detection

In this study, a localized surface plasmon resonance (LSPR)-based S-flex fiber optic (SFFO) sensor is designed and developed for the qualitative as well as quantitative measurement of cortisol. The SFFO configuration allows the generation of highly effective evanescent fields, which are used to excite LSPR phenomena of precious metal nanoparticles (NPs) on the surface of the probe. In this experiment, gold NPs (AuNPs) are utilized as precious metal NPs owing to their favorable attributes of facile manufacturing and enduring physical and chemical properties. In order to enhance the sensing performance of the sensing probe, MoS2-NPs are utilized to modify the proposed sensor. The optimization and enhancement of sensor performance by MoS2-NPs are verified through comparative experiments. Different levels of cortisol solutions are detected using: 1) probe 1 (AuNPs) and 2) probe 2 (AuNPs/MoS2-NPs) based on different NP modifications. The logarithmic sensitivity and detection limits of the sensing probes are probe 1 (1.34 nm/log(ng/mL) and 147.9 pg/mL) and probe 2 (3.07 nm/log(ng/mL) and 148.5 pg/mL), respectively. The experimental results reveal the significant contribution of MoS2-NPs to the performance of the sensor. Furthermore, performance metrics such as reproducibility, reusability, selectivity, and stability of probe 2 are also investigated and und satisfactory. The sensors presented in this study exhibit significant potential for utilization within various application scenarios, such as aerospace, clinical medicine, and aquaculture.