A Liquid Metal Based Capacitive Microsensor

Capacitive microsensor is a widely used detection technique for the analysis and assays in biochemistry, biomedicine, environmental monitoring and force measurement in MEMS. In this study, a liquid-metal based capacitive microsensor is proposed. A pair of high aspect ratio polydimethylsiloxane (PDMS) microchannels were fabricated symmetrically and vertically to both sides of detection channel. These two microchannels were filled with room temperature liquid-metal to form two electrodes. These two liquid-metal microchannels worked as two polar plates of a micro parallel-plate capacitor with the detection channel going between them. When the fluid changes in the detection channel, the capacitance of the micro parallel-plate capacitor will also change. Thus, by measuring the change in the capacitance of the micro capacitor, the fluid in the detection channel can be therefore detected. The capacitive microsensor can provide a wide range of applications in microfluidic technologies, such as detection of droplets, cells, particles or biological macromolecules. For better understanding of the capacitive microsensor, theoretical model was developed to reveal the working principle. To evaluate the capacitive microsensor, experiments were also performed to measure the microparticle concentration in deionized water by measuring its dielectric constant.