Low hysteresis relative humidity sensing characteristics of graphene oxide-gold nanocomposite coated langasite crystal microbalance

We propose a relative humidity (RH) sensor made of langasite crystal microbalance (LCM) coated with graphene oxide (GO)-gold nanocomposite and report its excellent hysteresis and sensitivity characteristics. LCM has recently emerged as an alternative to the popular quartz crystal microbalance (QCM). However, only a few attempts have been reported that explore and elaborate the sensing characteristics of LCM. GO has extraordinary humidity sensing capability, yet it suffers from high hysteresis. In this work, we overcame this deficiency by employing an Au-GO nanocomposite as the sensing medium on the LCM electrode. We present the resonance frequency characteristics of the modified LCM under varying RH values in the range of 10% - 80% in nitrogen. Our results suggest that the mass loading effect caused by water molecules altered the resonance frequency of the LCM linearly with a sensitivity of 3.64 Hz/% RH. More importantly, the sensor exhibited low hysteresis with an average value of 3.45% RH, and maximum and minimum hysteresis values of 5.6% RH, and 0.6% RH, respectively. Finally, the proposed Au-GO-LCM sensor displayed very high sensitivity to RH when tested for cross-sensitivity with a range of volatile organic compounds (VOCs).