Wireless-electrodeless ultrasensitive quartz-crystal-microbalance sensors

A quartz crystal microbalance (QCM) sensor enables the detection of various physical, chemical, and biological targets by monitoring changes in its mechanical resonant frequency. Conventional sensing mechanisms relies on the mass-loading effect, allowing QCM sensors to function as label-free biosensors. Additionally, the adsorption of target gas molecules can induce bending deformation of the resonator, leading to frequency shifts that facilitate gas sensing. A key factor in enhancing sensitivity is reducing the resonator thickness. However, traditional QCM sensors employ heavy metallic electrodes and wiring for electrical connections, which significantly degraded the mass sensitivity. To address this limitation, we have developed a wireless, electrodeless QCM system in which resonator vibrations are excited and detected contactlessly using antennas. Utilizing MEMS fabrication processes, we have achieved significant thinning of the resonator while enabling mass production of packaged sensor chips. The reduced thickness of the resonator not only increases the measurement frequency but also enables battery-free, wireless sensing over long distances exceeding 50 m.