Biosustainable Flexible Devices with Edible Sensing Material for Real-Time Breath Rate Monitoring

Incorporation of safe and abundant edible materials in devices can be an excellent way to achieve biosustainability, especially in flexible sensors which have become vital components for wearable electronics. In this work, fully decomposable breath rate monitoring sensors are demonstrated with scarcely explored starch-rich rice powder thin film (RPTF) as the sensing element. First, humidity sensing is comprehensively investigated for RPTF prepared by a low-cost drop-casting method using solutions of rice powder with concentration varying from 0.25 to 2.5 wt % in deionized (DI) water. Devices were fabricated with RPTF on Ag interdigitated electrodes screenprinted on paper. It is found that devices with ∼0.56 μm thick RPTF performed better than others, with excellent breath rate sensing for both nose and mouth breathing with fast response/recovery times of 1.1/0.6 and 1.1/1.0 s, respectively. A ∼20% increase in response was observed for mouth breathing due to an increase in humidity from nose to mouth (74–95% RH). Real-time breath rate monitoring was demonstrated by fixing these devices inside a typical surgical mask integrated with an IoT module. Finally, the excellent decomposability of these devices in wet soil in ∼15 days is demonstrated, indicating this strategy to be an effective one for biosustainable electronics.