Surface-Treated Nanofibers as High Current Yielding Breath Humidity Sensors for Wearable Electronics

As wearable electronics have gained momentum in the past few years, there is a dire need for smart, responsive, and, most importantly, affordable sensors for biological monitoring. One such noninvasive method to gauge body metabolism is via breath analysis. In a successful attempt to sense and record relative humidity levels (%RH) in nasal and oral breath, this work presents an economical route to fabricate a wearable humidity sensor with high sensitivity and a response time of ∼1 s. The sensor consists of a flexible backbone of electrospun poly(vinylidene fluoride)/reduced graphene oxide (PVDF/rGO) nanofibers which have been selectively sensitized to humidity via surface polymerization of aniline using the inexpensive successive ionic layer adsorption and reaction (SILAR) technique. We report a high sensitivity and a full response range (0-95% RH) supported by a low working voltage and minimalistic circuitry as an attractive feature for integration into wearable electronics. Moreover, as the device sensitivity is adequate even up to 95% RH, it is conducive to detect nasal breath and saturated humidity conditions accurately. As the method utilizes electrospinning, this work involves the preparation of such humidity sensors on a large scale (up to 400 units using 8 mg of rGO) with the benefit of having affordable and cost-effective devices.