Nanofiber-based humidity sensor for non-invasive real-time breath analysis

Abstract We report the development of an ultrafast internet of things (IoT)-enabled humidity sensor using a nanofibrillar surface composed of cellulose and graphene oxide nanocomposite embedded with polyaniline and gold nanorods (Au NRs). The results uncover that, as compared to the conventional flat surface sensors, the usage of the physiochemically heterogeneous nanofiber surface embedded with Au NRs and conducting polymers elucidate excellent sensing linearity, fast response time, marginal hysteresis, and repeatability. In particular, the usage of the nanofibers escalates the surface to volume ratio of the sensor significantly to exhibit a remarkable sensitivity across a wide range of humidity levels leading to a variation in the voltage output progressively increasing from the ∼26 mV to ∼73 mV in the range of relative humidity (RH) from a very low (∼11%) to a very high (∼96%). With an optimal loading of Au NRs and conducting polymer, the nanofibrillar composite has also demonstrated the ability to monitor humidity in real-time within the 11%–96% range, with a response time of 45 s and a recovery time of 136 s. The results showed a linear range of 11%–96% RH, a sensitivity of 0.687 mV/%RH, and a limit of detection of 11% RH. Remarkably, during the experiments performed for the measurements of multiple humidity cycles in real-time, the sensor shows a very low relative standard deviation (∼1%). Integration of the IoT platform in the form of a WiFi module (ESP8266) with the proposed humidity-sensing unit enables real-time monitoring of the humidity levels, which can be suitable for point-of-care applications.