A planar one-port microwave microfluidic sensor for microliter liquids characterization

This paper describes the design, fabrication, and assessment of an on-wafer measurement platform for noninvasive quantitative characterization of small volumes of liquids over the frequency range from 500 kHz to 1 GHz. The platform, integrated with amicrometer scale SU-8 microfluidic channel, allows accurate placement of very small liquid volumes at a well-defined location. For the first time, a miniaturized one-port interdigital capacitor (IDC) sensor is used for dielectric spectroscopy measurements at RF/lower microwave frequency range. Three-dimensional simulation on the IDC sensor with the finite element method (FEM) verifies the complex permittivity extraction model. A validation of this platform is performed using water-isopropanol mixtures, and then, it is utilized for liquid temperature measurement and baker's yeast cell concentration detection. An observation over 5 min is also carried out on a cell suspension, which has shown the capability of this platform in monitoring dynamic process in chemical or biological fields.