Electrochemical Sensors for Cortisol: A Review

Cortisol, also known as the "stress hormone," is secreted under the control of the hypothalamic-pituitary-adrenocortical (HPA) axis in response to psychobiological stress. Real-time and continuous monitoring of the cortisol levels throughout the day can provide the information necessary to identify any abnormalities in cortisol's circadian rhythm that may disrupt the several processes that cortisol is involved in in the body. This review presents a systematic search of the literature on electrochemical cortisol sensing techniques that allow real-time measurement of cortisol in human biofluids. Several structural and performance-related parameters of sensors are being discussed, including the sensor stack layers, the limit of detection (LoD), dynamic range, sensitivity, selectivity, reusability, redox probe usage, and the electrochemical detection technique used. The sensors here are primarily categorized based on the type of bioreceptors used: antibodies, molecularly imprinted polymers (MIPs), and aptamers. According to this review, cortisol aptasensors and the MIP-based sensors present, in general, superior stability and sensitivity over immunosensors. They also promise reversible binding, albeit limited research exists on sensors deploying such bioreceptors. Additionally, notable advancements in the field and their impact on the development of point-of-care (PoC) and wearable devices are discussed.