Ultra-highly sensitive humidity sensing by polydopamine/graphene oxide nanostructure on quartz crystal microbalance

[Display omitted] •Polydopamine (PDA)-graphene oxide (GO) nanofilm coated QCM humidity sensor was fabricated at first time.•The PDA-GO film based QCM sensor has fast response/recovery time, stable repeatability and excellent stability.•The sensor exhibits potential applications for the detection of humidity evaporation on skin and human breath.•The sensing mechanism and bimodal exponential kinetic adsorption model of the sensor was discussed. Accurate and reliable humidity measurement is very important in a variety of practical applications. High-performance humidity sensors have always been a hot spot in scientific research in industrial environments and in everyday life. This study proposes a solution to coat polydopamine (PDA)-graphene oxide (GO) nanocomposite films on quartz crystal microbalances (QCM). The elemental composition, morphology and nanostructure of PDA/GO nanocomposites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), FT-IR spectroscopy, and X-ray photoelectron spectroscopy (XPS). The PDA/GO film-coated QCM sensor exhibits the best dynamic response with the ratio of PDA to GO is 2:3 and the spray amount is 5 μL. The overall frequency offset is 9786 Hz (0–97% RH). In addition, the PDA-GO nanocomposite-based QCM sensors have fast response/recovery time (18 s/2 s), stable repeatability, and excellent stability. In particular, the sensor can sensitively detect the proximity of fingers, sliding and human breathing, as well as subtle changes caused by coughing and speaking, demonstrating its potential in a variety of applications. Finally, the adsorption kinetic of water molecules was studied in combination with the bimodal exponential kinetic adsorption model.