Touch‐Based Stressless Cortisol Sensing

Tracking fluctuations of the cortisol level is important in understanding the body's endocrine response to stress stimuli. Traditional cortisol sensing relies on centralized laboratory settings, while wearable cortisol sensors are limited to slow and complex assays. Here, a touch‐based non‐invasive molecularly imprinted polymer (MIP) electrochemical sensor for rapid, simple, and reliable stress‐free detection of sweat cortisol is described. The sensor readily measures fingertip sweat cortisol via highly selective binding to the cortisol‐imprinted electropolymerized polypyrrole coating. The MIP network is embedded with Prussian blue redox probes that offer direct electrical signaling of the binding event to realize sensitive label‐free amperometric detection. Using a highly permeable sweat‐wicking porous hydrogel, instantaneously secreted fingertip sweat can be conveniently and rapidly collected without any assistance. By eliminating time lags, such rapid (3.5 min) fingertip assay enables the capture of sharp variations in cortisol levels, compared to previous methods. Such advantages are demonstrated by tracking cortisol response in short cold‐pressor tests and throughout day‐long circadian rhythm, along with gold‐standard immunoassay validation. A stretchable epidermal MIP sensor is also described for directly tracking cortisol in exercise‐induced sweat. The rapid touch‐based cortisol sensor offers an attractive, accessible, stressless avenue for quantitative stress management.