A Gas Sensor Based on Electrically Coupled Quartz Crystal Microbalances Coated with ZIF-8

This paper reported a gas sensor based on two quartz crystal microbalances (QCM) weakly coupled through a capacitor (electrically). By coating one of the two QCMs with zeolitic imidazolate framework-8 (ZIF-8), the coated QCM could adsorb/desorb gas molecules, e.g., ethanol molecules, thus breaking the mass symmetry of the coupled system. The mass change due to gas absorption and desorption was measured through the amplitude ratio and the frequency shift of coupled QCMs. The gas sensor operated in an open-loop and closed-loop configuration whose performances were compared. Three orders of magnitude improvement was achieved by using the amplitude ratio change as the output compared to using the frequency shift as the output in the closed-loop configuration. Besides, the closed-loop configuration improved the amplitude ratio sensitivity by 50.2% compared with the open-loop configuration.