Spurious Resonance of the QCM Sensor: Load Analysis Based on Impedance Spectroscopy

Abstract

A research topic of equal importance to technological and application fields related to quartz crystal is the presence of unwanted responses known as spurious resonances. Spurious resonances are influenced by the surface finish of the quartz crystal, its diameter and thickness, and the mounting technique. In this paper, spurious resonances associated with fundamental resonance are studied by impedance spectroscopy to determine their evolution under load conditions. Investigation of the response of these spurious resonances provides new insights into the dissipation process at the QCM sensor surface. The significant increase of the motional resistance for spurious resonances at the transition from air to pure water is a specific situation revealed experimentally in this study. It has been shown experimentally that in the range between the air and water media, spurious resonances are much more attenuated than the fundamental resonance, thus providing support for investigating the dissipation process in detail. In this range, there are many applications in the field of chemical sensors or biosensors, such as VOC sensors, humidity sensors, or dew point sensors. The evolution of D factor with increasing medium viscosity is significantly different for spurious resonances compared to fundamental resonance, suggesting the usefulness of monitoring them in liquid media.

Hydrophobic MOF/PDMS-Based QCM Sensors for VOCs Identification and Quantitative Detection in High-Humidity Environments

“…In the next step, a 10 mm diameter hole was created using a hole puncher at the center of a thermal-release tape (HOTFILM-HM, SUNANO) with a release temperature of 90 to 100 °C. The patterned tape was then gently attached to the cleaned QCM surface with the opening hole concentrically aligned to the center of the QCM disc, ensuring a symmetric patterned adsorption layer that effectively suppresses spurious modes in the resonant signals . After that, a 20 μL suspension containing 0.2% w/v MOF NPs dispersed in ethanol solution was drop-coated onto the open area of the QCM disc 6 times.…”