Α‐co(oh)2‐based Quartz Crystal Microbalance Humidity Sensor for Real‐Time Monitoring of Respiration

Respiration is an important physiological process of the human body and can assess an individual's health status. Humidity detection is an effective method for real‐time breath monitoring. Herein, the α‐Co(OH)2‐based quartz crystal microbalance humidity sensor (Co‐QCM sensor) is prepared via the hydrothermal method. The Co‐QCM sensor is characterized by scanning electron microscopy, Fourier‐transform infrared, and X‐ray diffraction. The α‐Co(OH)2 with hierarchical nanostructure and hydroxy functional groups leads to good humidity‐sensing performance. The Co‐QCM sensor exhibits high sensitivity (23.1 Hz/% relative humidity), fast response and recovery times (within 3 and 4 s, respectively), high linearity (R2 = 0.994), and long‐term stability (≈30 days) in the humidity range of 4–73.3%. In addition, different human breathing signals, including free breathing, shallow breathing, and deep breathing, can be detected and distinguished by this humidity sensor, showing the potential application in human respiratory detection.