Photonic Hydrogel Sensing System for Wearable and Noninvasive Cortisol Monitoring

Wearable biosensors have emerged as an increasingly important tool in personalized health monitoring and are even envisioned to renovate the traditional centralized diagnosis method to home diagnosis. Here, we introduce two types of wearable devices with sandwich structures that utilize photonic crystal hydrogel biosensors with structural color for the detection of cortisol in human sweat. The integrated biosensors exploit molecular imprinting and antibody–antigen competitive binding techniques, which are tailored to different storage and detection requirements for use. By using a smart phone to analyze the color change of the hydrogel, the dynamic fluctuations of endogenous cortisol in sweat during the diurnal cycles were monitored. The detection limit reached the nmol/L level, meeting the detection requirements in body fluids. Furthermore, the Trier Social Stress Test and exercise for specific periods of time were used to verify the relevance of cortisol as a stress biomarker and the sensitivity of the developed biosensors. The development of wearable devices for noninvasive and naked eye detection in this study offers a personalized approach to stress self-management.