Microwave Measurement of Bovine Serum Albumin Solutions Based on High-Q/High-Resolution Resonator

Progressive techniques that enable reagent-free detection and analysis of low-concentration and low-volume chemical samples are of great interest for scientific and technological investigations in biochemical and physiological areas. Highly sensitive microwave-based sensors are promising approaches among such techniques. In this work, we present a novel microwave-based noncontact sensing method to determine the concentration of standard bovine serum albumin (BSA) solution. It is demonstrated that the modal suppression technique can excite a split-ring resonator by two independent microstrip lines with reversed phase, resulting in high quality factor and resolution. The quality factor exceeding $5.5\times 10^{5}$ with lossy-liquid loaded can be achieved at $\sim 4.3$ GHz. The obtained high resolution in frequency is $\sim 20$ kHz for the concentration of BSA from 0 to 1 mg/mL. The measured concentration level ranges from 1 to 200 mg/mL in 0.9% sodium chloride, which covers most commercial standard BSA solutions. An equivalent circuit model is built to study and explain its working principle. Using the fit premeasurement data of standard solutions, the concentration and permittivity of an unknown BSA solution can be estimated.