. Flow-chart for the fabrication of planar GO humidity sensors

. Schematic illustration of the working principle of GO humidity sensors

. Morphologies of GO humidity sensor Top view SEM image with inset showing an enlarged view of GO; (b) Side view SEM image; (c) Schematic illustration of the GO humidity sensor

. Correlation between the induced voltage of GO humidity sensor and the electrode spacing Photographs of the electrodes with the spacing D (a) 170 µm, (b) 330 µm, (c) 500 µm, (d) 1000 µm. (e) Induced voltage vs relative humidity for sensors with varied electrode spacing. (f) Sensitivity of sensors with varied electrode spacing

. Characteristics of humidity sensors with varied length (a) Induced voltage vs relative humidity; (b) Sensitivity vs length; (c) Response at different relative humidity; (d) Response time vs length

. Respiratory frequency detected with GO humidity sensors

. Recycling and long-term stability of GO humidity sensors (a) Recycling stability; (b) Enlarged view of the curves between 3040 s and 3100 s in (a); Stability of the sensors before (c) and after (d) storage for three months in a cabinet