Wearable resistive graphene-based sensor for human behavioral and mental monitoring

Abstract

The current responses of flexible wearable sensors made of thin layers of a graphene:PEDOT:PSS composite (printed on paper or applied to fishing lines) were studied under continuous signal reading conditions. A number of relatively fast peaks on the response curve were found, which lasted for 1–10 min (width at half height) and were associated with the reaction of the nervous system of a person to various external events. Dynamic changes in the psycho-emotional state were associated with physical and emotional stressors of different natures and the intensity of impact: moderate physical activity, telephone conversations, anticipation of eating sweets for a diabetic, or finger pricking for measurement of blood glucose levels. The increased sensor conductivity can presumably be associated with a number of biologically active substances (adrenaline or cortisol, defamine or other hormones) secreted by sweat glands in response to psycho-emotional stimuli. The analysis of data showed that the height of the signal peak carries information about the stress level of a person. The application of a thin (up to 10 nm) porous Nafion film, which is permeable to sweat and provides isolation of the sensor layer from the skin surface, led to a decrease in the signal amplitude with precise preservation of its shape. Therefore, the main contribution to the sensor response comes from the interaction with sweat and not skin resistance. At the same time, shunting of the sensor by the skin is not a factor defining the sensor response, and the use of Nafion increases the service life of the sensor. This study constitutes the first step towards developing a personal health system for stress detection.