Nanoflower-like titanium dioxide modified ethyl cellulose-based QCM humidity sensor with low-hysteresis for wearable respiratory monitoring

There is a growing demand for reliable and portable humidity detection in both medical and industrial applications. The quartz crystal microbalance (QCM) is a high-performance sensor for gas and moisture detection and has been extensively studied in recent years. In this study, titanium dioxide with nanoflower-like structure was synthesized and doped with ethyl cellulose to modulate the microstructure of ethyl cellulose/titanium dioxide composite, and constructed ethyl cellulose/titanium dioxide composite thin-film QCM humidity sensor. A vector network analyzer was utilized to evaluate the mechanical stability of the sensor devices. The EC/TiO 2 QCM humidity sensor demonstrated low hysteresis (2.49% RH), and exhibit good stability, repeatability, selectivity, and short response/recovery time (18.8   s/2.2   s). Furthermore, the nanoflower-like structure of TiO 2 is an important factor influencing the humidity sensitivity of the QCM sensor. The water molecule adsorption process on the QCM sensor was analyzed using the Langmuir adsorption isotherm model. This work confirmed that the EC/TiO 2 QCM humidity sensor holds strong potential for use in wearable respiratory monitoring and non-contact triggering applications.