Wearable Sensors for Breath Monitoring Based on Water‐Based Hexagonal Boron Nitride Inks Made with Supramolecular Functionalization

Abstract Wearable humidity sensors are attracting strong attention as they allow for real‐time and continuous monitoring of important physiological information by enabling activity tracking as well as air quality assessment. Amongst 2Dimensional (2D) materials, graphene oxide (GO) is very attractive for humidity sensing due to its tuneable surface chemistry, high surface area, processability in water, and easy integration onto flexible substrates. However, strong hysteresis, low sensitivity, and cross‐sensitivity issues limit the use of GO in practical applications, where continuous monitoring is preferred. Herein, a wearable and wireless impedance‐based humidity sensor made with pyrene‐functionalized hexagonal boron nitride (h‐BN) nanosheets is demonstrated. The device shows enhanced sensitivity towards relative humidity (RH) (>10¹⁰ Ohms/%RH in the range from 5% to 100% RH), fast response (0.1 ms), no appreciable hysteresis, and no cross‐sensitivity with temperature in the range of 25–60 °C. The h‐BN‐based sensor is able to monitor the whole breathing cycle process of exhaling and inhaling, hence enabling to record in real‐time the subtlest changes of respiratory signals associated with different daily activities as well as various symptoms of flu, without requiring any direct contact with the individual.