Multichannel Monolithic Quartz Crystal Microbalance Gas Sensor Array

Multichannel Monolithic Quartz Crystal Microbalance (MQCM), in which an array of electrodes is fabricated on a monolithic quartz wafer, is a very attractive approach for miniaturization using Micro-Electro-Mechanical Systems (MEMS) technology for high throughput chemical or biological sensor systems. In this paper, we demonstrate and validate a monolithic QCM sensor array for gas detections. The monolithic QCM sensor array chip was fabricated using a simple, straightforward method. Four pairs QCM electrodes on a single AT-cut 10 MHz quartz plate were fabricated in both symmetric and asymmetric designs. Their resonance and sensing properties were thoroughly characterized and compared with a single regular QCM under the same conditions by using parallel multichannel QCM instruments. It is confirmed that each QCM in the MQCM behaves like an independent oscillator that responds to mass and/or viscosity change. Various factors that may affect the MQCM performance, such as the fabrication design, the numbers of oscillated electrodes in one MQCM, and the concentration of target analytes, were studied. Finally, the MQCM electrodes were selectively coated with an assortment of sensing films (ionic liquids (BMICS, BMIBF4) and conductive polymer poly(vinyl ferrocene) (PVF)). Their applications capabilities for classification and detection of Volatile Organic Compounds (VOCs, i.e., ethanol, CH2Cl2, hexane) and water were studied. Our results show that the single-chip, multichannel QCM is a feasible and promising technology for a miniaturized, highly sensitive multianalysis system that can lead to substantial reductions in cost, analysis time, and sample volume.