Battery-free, wireless, and flexible electrochemical patch for in situ analysis of sweat cortisol via near field communication.

Wearable and flexible biosensing devices have been widely developed for in situ detections. Cortisol is a vital biomarker which plays crucial regulatory role in numerous physiological processes of the human body. Here, a wireless, battery-free, and flexible integrated patch is developed for real-time on-body sweat cortisol detection. The patch integrated with all-printed flexible electrochemical immunosensor, which was used to detect cortisol through differential pulse voltammetry (DPV). The near field communication (NFC) module on the patch enables wireless power harvesting and data interaction with an NFC-enabled smartphone, which makes the patch get rid of rigid batteries and realize epidermal on-body testing. Multiple in situ detections on volunteers' sweat on the surface of skin showed that the flexible integrated patch could reflect the circadian rhythm of the body's sweat cortisol level changes in relaxed mood or under stress, which could be confirmed with the enzyme linked immunosorbent assay (ELISA) kit. In this way, the patch provides a rapid-detecting, convenient, and non-invasive sensing solution for in situ analysis of sweat cortisol, which can be applied for the personalized mental health management.