Screen-printed graphene-carbon ink based disposable humidity sensor with wireless communication

Humidity sensing is crucial for several industrial, environmental, and healthcare applications, many of which require sensors in flexible form factors and with features such as disposability and facile fabrication processes. Herein, we present a flexible, cost-effective, and disposable humidity sensor developed on paper substrate. The screen-printed graphene-carbon (G-C) ink-based humidity sensor demonstrates good sensing performance in terms of change in resistance (∼12.4 Ω/%RH) in humidity ranging from 25%RH to 91.7%RH. The sensor displays high flexibility (studied at bending radiuses 40 mm, 30 mm, 25 mm, and 20 mm), appreciable stability (> 4 months), high repeatability (> 100 cycles), short response/recovery time (∼4 s/∼6 s towards respiration rate monitoring) and good reproducibility (minor variations ∼ ± 1 Ω/%RH). The efficacy of fabricated humidity sensor is evaluated for spatial humidity monitoring, respiration rate monitoring, and soil moisture monitoring. Finally, the real time monitoring of humidity is also demonstrated via wireless transmission of data to a smartphone to display the potential of the fabricated sensor for environmental, agricultural, and healthcare applications.