Flexible Electrochemical Biosensor for Non-Invasive, on-Site Cortisol Monitoring in Sweat and Saliva.

Chronic stress is a critical public health concern with strong links to both mental and physical health. Excessive stress alters brain architecture and stimulates the adrenal gland to release cortisol, a key biomarker of stress. Conventional cortisol measurements rely on invasive, laboratory-based methods that are unsuitable for real-time, point-of-care testing. This study reports the development of a noninvasive, flexible electrochemical biosensor for the selective detection of cortisol in human sweat and saliva. The sensor was fabricated on a polyethylene terephthalate (PET) substrate coated with indium tin oxide (ITO) and functionalized with gold nanoparticles (AuNPs) to enhance conductivity and surface area. AnteoBind chemistry was employed for oriented immobilization of monoclonal anticortisol antibodies. The device was integrated with a microfluidic platform to enable controlled sweat analysis. Electrochemical measurements demonstrated a linear response over the range of 0.5-150 ng/mL, with a detection limit of 0.58 ng/mL. The sensor retained 80% of its signal over 30 days, with reproducibility across batches (RSD ∼ 3.2%). Real sample analysis showed recovery values of 95.5-104% in sweat and saliva samples. These findings underscore the potential of this biosensor for noninvasive monitoring of stress markers in wearable applications, supporting early stress detection and personalized health management.