Health monitoring of human breathing by graphene oxide based sensors

Monitoring of human health is of high importance to enable early detection of illness and improve the quality of life from diseases such as lung cancer or sleep apnea. Breath monitoring is highly interesting in this regard. Graphene oxide is one of the most studied materials for sensing applications and has exceptional properties like large surface area, mechanical stability, and tunable electrical properties. In this paper, we introduce a breath sensor made of a graphene oxide film. Graphene oxide dispersion was deposited on silver interdigitated electrode on flexible substrate, which was then thermally annealed to partially reduce the graphene oxide. The breathing signal was acquired by a digital oscilloscope and the data saved using a LabVIEW interface. The sensors show ultra low response time of less than one second and excellent repeatability. Impedance spectroscopy measurements were carried out at different humidity levels to characterize the sensor. The sensor impedance shows a high decrease by several orders of magnitudes by increasing the relative humidity. Sensitivity to humid air results from the high hydrophilicity of the graphene oxide due to its oxygen functional groups. The change of transport mechanism from Nyquist plot shows the change of the sensor impedance from the capacitive behavior to a semicircle of parallel resistance and capacitance. The high sensitivity of GO to humid air as well as the ultrafast response makes it suitable as a noninvasive and flexible breath-monitoring sensor