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Broadband dielectric spectroscopy measurements of biological materials within RF/microwave range can reveal cellular information, which is of important value in biological and medical researches. Here we present a platform that combines a miniaturized coplanar waveguide (CPW) transmission line (TL) sensor and a special CPW fed interdigitated capacitor (IDC), which allows us to measure the complex permittivity of cell cultures from 300 kHz to 50 GHz. The CPW-TL sensor and the CPW-IDC sensor are integrated with an SU-8 microfluidic channel, enabling measurements of microliter or even nano-liter volumes of liquids and suspensions. Due to the accurate alignment of the SU-8 polymer and the reliable lift-off fabrication procedure, we are able to minimize the measurement errors caused by the sensors' dimension tolerance. To ensure accurate complex permittivity extraction of the tested material, related calibrations and de-embedding processes are explained. With the measurement of deionized water as a validation, the platform is used to measure the complex permittivity of both a yeast cell culture and a mammalian cell culture. We elaborate on the interesting findings and discuss future possibilities.

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The dielectric spectroscopy measurement is an attractive noninvasive method to reveal the intrinsic information of biological materials and cell cultures. However, the presence of a double layer due to electrode polarization (EP) within the lower RF and microwave range significantly affects the accurate analysis of dielectric properties of ionic liquids. In this work, we measure the broadband dielectric spectroscopy of five saline solutions with a microfluidic coplanar waveguide (CPW) transmission line sensor across the frequency range from 40 kHz to 110 GHz. Derived from a parallel plate structure that is transformed from the quasi-TEM CPW sensor through a conformal mapping technique, a broadband spectroscopy modeling method is proposed, where a Cole-Cole function or a constant phase element formula is used depending on the ionic concentrations and the measurement window. Validation analysis on the five saline solutions demonstrates the capability of the modeling method in separating relaxation properties of the bulk sample from the double layer effects.