Flexible sensors used to detect NO₂ gas generally have problems such as poor repeatability, high operating temperature, poor selectivity, and small detection range. This work designed and built a new spraying platform to make a sensitive film (rGO/SnO₂) for NO₂ gas sensors. The study found that a sensor with 0.25 ml of a 0.4 wt% rGO/SnO₂ mixture annealed at 250 °C exhibited the best performance, with a response value of 0.2640 at 25°C for 100 ppm NO₂. A linear relationship between response and NO₂ concentration (20–100 ppm) was observed (correlation coefficient 0.9851). A soft-monitoring node module with an overlimit warning function was integrated with the flexible sensor into woven fabric for wearable applications.
