A flexible and wearable NO₂ gas detection and early warning device based on a spraying process and an interdigital electrode at room temperature

Flexible sensors used to detect NO₂ gas generally have problems such as poor repeatability, high operating temperature, poor selectivity, and small detection range. In this work, a new spraying platform with a simple structure, low cost, and good film-forming consistency was designed and built to make a sensitive film (rGO/SnO₂) for NO₂ gas sensors. The relationship between the solid content of rGO and SnO₂ nanoparticles, annealing temperature, and sensor performance was studied. The results show that the interdigital electrode-sensitive film formed by spraying 0.25 ml of a 0.4 wt% rGO/SnO₂ mixture and annealing at 250 °C exhibited the best comprehensive performance for NO₂ detection. The sensor's response value for 100 ppm NO₂ gas was 0.2640 at room temperature (25 °C), and the response time and recovery time were 412.4 s and 587.3 s, respectively. In the range of 20–100 ppm, the relationship between the response and NO₂ concentration was linear, and the correlation coefficient was 0.9851. In addition, a soft-monitoring node module with an overlimit warning function for NO₂ gas was designed and manufactured based on flexible electronics. Finally, the flexible sensor and node module were embedded into woven fabric that could be used to make a mask or a watch that could detect NO₂ gas, realizing the practical application of flexible NO₂ gas sensors in the field of wearable electronics.