Inkjet-printed wireless passive humidity sensor with ultrahigh sensitivity using ZnO/Ti₃C₂T x MXene nanocomposite

Abstract This study presents a highly sensitive, wireless passive humidity sensor that employs a ZnO/Ti₃C₂T x MXene nanocomposite, synthesized using the hydrothermal method. The sensor circuit was created on pre-cut polyethylene terephthalate substrates via inkjet printing, allowing for scalable production. Material characterization techniques such as x-ray diffraction, scanning electron microscopy, x-ray photoelectron spectroscopy, and Brunauer–Emmett–Teller verified the intercalation of ZnO nanoparticles within the MXene layers. This resulted in mesoporous structures with a surface area of 21.53 m 2 g −1 and a plethora of active sites. Operating on the principles of inductor–capacitor (LC) resonance, changes in humidity-dependent permittivity cause shifts in resonant frequency that can be detected wirelessly. The sensor exhibits an ultra-high sensitivity of 138 kHz/%RH in low humidity ranges (10%–60% RH) and 2734 kHz/%RH in high humidity ranges (60%–95% RH), maintaining stable performance over a 15 d period. This remarkable dual-range sensitivity is attributed to the synergistic proton conduction through the MXene’s functional groups and the oxygen vacancy-mediated dissociation of ZnO. Overall, the inkjet-printed LC sensor offers a cost-effective, robust solution for wireless humidity monitoring in sealed environments.