Planar single and dual-resonant microwave biosensors for label-free bacteria detection

Abstract Label-free microwave resonator-type biosensors covered with polyclonal anti-Escherichia coli antibodies are presented. The sensors` construction provides high sensitivity on the bacteria detection, whereas the utilization of specific antibodies ensures selective bacteria binding. Two types of biosensors are studied to explore the benefits of microwave sensing: the first one, in which increased sensitivity on the bacteria detection is obtained due to the differential excitation of the resonating conductors, and the second one, in which a multi-resonant character increases the probability for the bacteria detection. The exemplary sensors were designed to operate in the frequency range of 4.4 – 4.8 GHz or 15 – 25 GHz and physically realized on a silicon wafer using standard microelectronic processor using the United Monolithic Semiconductor (UMS) PH25 process on a 100 μm thick GaAs substrate, respectively. The sensors were experimentally validated by measurements of various concentrations of Escherichia coli. Both types of sensors were compared to show their advantages and disadvantages in terms of future use for biomedical applications. Both biosensors were shown to enable bacteria detection at concentrations reaching as low as 103 CFU/ml. Interestingly, a monotonic response for bacteria concentration was observed for a multi-resonant sensor, which can be utilized for estimation of bacteria content using the calibration curve.