A Resonant Reflection Type Microwave Reference Sensor for Testing of Small Biomolecules

Electromagnetic analysis of small biomolecules, such as amino-acids, is important in development of new methods for biomedical therapy and diagnostics based on the dielectric properties of biomolecular solutions. The dielectric behavior of amino-acid solutions is especially interesting in microwave band, because they possess their dielectric signature at around few GHz. We apply our biophysical insights from the rotational dynamics of a particular amino-acid to rationally select the operation frequency and, therefore, to design a microwave reference sensor resonating at the operation frequency of interest. The proposed sensor is based on a coplanar waveguide (CPW) terminated with flares to impedance-match the line at the operating frequency of the complementary split ring (CSRR) sensing element on the other side of the substrate. The unique design of sensing element gives freedom in testing of water-based bio-molecular solution without disturbing the electromagnetic field of CPW. The proposed sensor is comprised of two sensing elements operating at the same frequency, while one of them works as the reference sensor. Our results contribute to the label-free microwave based technologies for the analysis of the biomolecular components of proteins - main nanomachines executing life processes.