Cu(OH)2 nanowires/graphene oxide composites based QCM humidity sensor with fast-response for real-time respiration monitoring

Respiration is an essential physiological process of human body and acts as a vital sign for personal health. Humidity sensing is a promising way to monitor respiration based on the humidity change when people breathing. Here we demonstrate Cu(OH)(2) nanowires and graphene oxide (GO) based quartz crystal microbalance (QCM) humidity sensor for real-time respiration monitoring. The Cu(OH)(2) nanowires/GO composites humidity-sensitive film was fabricated by the method of in-situ growth and drop-casting. The morphology and structure of the Cu(OH)(2) nanowires/GO composites were characterized by energy dispersive spectrometer (EDS), Raman, Fourier transform infrared (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopic (TEM), high resolution TEM (HRTEM), and energy dispersive X-ray spectroscopy (EDXS). The nanocomposites with large surface area and abundant oxygen-rich functional groups lead to good humidity sensing performance. When changing relative humidity (RH) between 0 and 80%, our device exhibits high sensitivity (52.1 Hz/%RH), fast response and recovery (within 1.9 s and 7.6 s, respectively) and high linearity (R-2 = 0.9968). Different breathing patterns can be distinguished, including normal breathing, apnea, speaking, nose and mouth respiration, and humidity variations before and after water intake, showing potential applications in analyzing human health-status.