An ultra-high response humidity sensor based on porous boron nitride nanofibers: For respiratory monitoring and non-contact sensing

Abstract

Advanced humidity sensors with high response and fast response/recovery time are crucial for environmental and real-time respiratory monitoring applications. Porous boron nitride nanofibers (BNNFs), characterized by high specific surface area, small diameters, non-toxicity, and excellent thermal and chemical stability, have emerged as a promising material for developing advanced humidity sensors. Herein, a humidity sensor utilizing porous BNNFs as a novel humidity-sensitive material has been demonstrated. The sensor exhibits ultra-high response (seven orders of magnitude change), wide humidity detection range (11 % to 93 % RH), fast response/recovery time (1.03 s/4.67 s) (measured as the relative humidity is changed between 11 % and 93 %), and excellent repeatability and selectivity. The porous BNNFs possess high specific surface area and abundant micro/mesopores, which provide active sites and transport channels for efficient water molecules transfer and dispersion. Concurrently, their hydrophilic functional groups enable rapid adsorption through hydrogen bonding, collectively contributing to enhanced sensor performance. Given the remarkable sensing properties, the porous BNNFs humidity sensor has been successfully applied in respiratory monitoring and non-contact sensing. The test results demonstrate that the sensor can accurately achieve real-time monitoring of 63 min⁻¹ high-frequency breaths and distinguish between different breathing patterns under varying physiological states. Additionally, the sensor exhibits a pronounced responsiveness to millimeter-scale variations in fingertip distance. These results highlight its potential for non-contact health monitoring systems and next-generation high-precision respiratory monitoring sensors.