Cortisol Biosensors: From Sensing Principles to Applications

Stress detection and monitoring have attracted substantial research interests due to stress being a risk factor for health disorders and economic burdens. In particular, the steroid hormone cortisol plays an important role both as an indicator of stress and a coordinator of downstream physiological responses. Recent years have witnessed a flourishing of cortisol biosensors and bioassays based on various physical principles. In this review, we first provide an overview of cortisol function and its presence in different biological matrices. Next, we discuss the existing range of cortisol biosensors, from their sensing principles (i.e. chromogenic, nanoparticle-based colorimetric and fluorometric, surface-enhanced Raman spectroscopy, surface plasma resonance spectroscopy, and electrochemical sensors), performances (sensitivity, selectivity, portability, etc.), and applications. We particularly correlate the sensing performances and their suitability for point-of-care diagnostics with sensor principles and the use of different affinity ligands, such as antibodies, aptamers, molecular imprint, and even 2D materials such as MXenes. Finally, we discuss the challenges and perspectives of future high-performing cortisol sensors for a wider range of applications in human and animal stress monitoring.