Sb-doped WO3 based QCM humidity sensor with self-recovery ability for real-time monitoring of respiration and wound

Humidity sensing is a promising method for monitoring respiration and diagnosing diseases. However, the fabrication of a semiconductor-based humidity sensor with fast response/recovery times and high sensitivity even under wet conditions remains challenging. In this study, a quartz crystal microbalance (QCM) humidity sensor was fabricated using Sb-doped WO3 nanocrystals via a simple solvothermal method. Sb doping increased the number of oxygen vacancies and led to a narrow band gap. It also restricted the further growth of WO3 and provided more adsorption sites, which resulted in a small particle size and large specific surface area. The device displayed a wide range of relative humidity (0–85%) with fast response and recovery times (10 and 1.6 s, respectively) and good long-term stability. After 100 cycles of wet treatment, the response of the sensor recovered to 92.2%, showing good self-recovery ability. The Sb/WO3-based QCM sensors were applied to the sensitive monitoring not only of respiratory humidity but also of moisture changes of a wound; the latter had never previously been performed using a QCM. This study therefore provides valuable insights for the development of integrated wound-microenvironment monitoring.