Integrated Mental Stress Smartwatch Based on Sweat Cortisol and Hrv Sensors

Abstract

Mental stress, a human’s common emotion that is difficult to recognize and describe can give rise to serious psychological disorders. Skin and sweat are readily available sources of biomarkers and bio-signals that carry information about mental stress. Hence, we developed a smartwatch integrated with a sweat cortisol sensor and a heart rate variation (HRV) sensor, which can simultaneously real-time record the cortisol levels in sweat and HRV index over a long period. The cortisol sensors based on organic electrochemical transistor (OECT) are fabricated by utilizing the Prussian-blue (PB) doped molecular imprinting polymer (MIP) modified gate electrode. The sensor signal current will drop after the combination of the PBMIP and cortisol due to the blocking of PBMIP conductive path showing good sensitivity, selectivity, and stability. The HRV sensor is manufactured by a photoplethysmography method. We have integrated the two sensors into a wearable smartwatch that can match well with the mobile phone APP and the upper computer software. By means of this smartwatch, we find that the cortisol in sweat and HRV index show a negative correlation in short-term stressful environments. Our research presents an great progress in real-time and non-invasive monitoring human’s stress levels, which promotes not only the stress management, but also better psychological research.

Keywords: mental stress, Cortisol, sweat sensors, transistors, HRV