Exploration of the Mass Sensitivity of Quartz Crystal Microbalance under Overtone Modes Using Electrodeposition Method

Abstract

With the in-depth application of quartz crystal microbalance (QCM) sensors in the fields of science and engineering, there is an urgent need for QCM sensors with high mass sensitivity. The mass sensitivity of a QCM is closely related to its resonance frequency, and the high resonance frequency leads to improve its mass sensitivity. However, the resonance frequency of a QCM resonator cannot be increased all the time due to the fragility of quartz wafer and the limits of energy trapping effect. Few studies are associated with mass sensitivity of a QCM resonator under overtone modes. Herein, we propose to make a QCM resonator work in its n-th overtone (n = 3, 5, 7, 9 in this study) mode to increase its resonance frequency during operating. Thereby, the purpose of improving QCM mass sensitivity is achieved, and the mass sensitivity of a QCM working in the n-th overtone mode can be called as n-th overtone mass sensitivity. Then, the n-th overtone mass sensitivity of a QCM sensor is measured by an electrodeposition method. The experimental results show that the n-th overtone mass sensitivity of a QCM is a bit more than n times that of the fundamental mass sensitivity, and it is consistent with the theoretical calculation results. The application of overtone mass sensitivity will greatly improve the sensitivity of QCM sensors, which is very attractive for the research fields that require QCM sensors with high sensitivity.

Mass-Fabrication Scheme of Highly Sensitive Wireless Electrodeless MEMS QCM Biosensor with Antennas on Inner Walls of Microchannel

“…The conventional QCM sensor consists of a quartz plate (or resonator) with electrodes on both sides to which wires are connected. The electrodes cause significant inertia resistance at the resonator surfaces due to much larger mass density than that of quartz, deteriorating the mass sensitivity of QCM. , In addition, electric connectors on the quartz resonator for fixation, power supply, and signal detection not only deteriorate the quality factor of the resonator but also limit the use of a resonator with high fundamental resonant frequency (< ∼10 MHz). − To improve the operating frequency and thus the sensitivity of QCM, the wireless and electrodeless QCM has been developed using the microelectro-mechanical-systems (MEMS) processes. − Instead of using the contacting electrodes, excitation and detection of the shear vibration are achieved by noncontacting antennas in the wireless QCM. Although Au films were occasionally used for forming a self-assembled monolayer through the alkanethiol reaction, their thickness was only several nanometers, affecting little QCM’s mass sensitivity.…”