Low-Cost and Highly Sensitive Reflective-Mode Phase-Variation Sensor for Bacteria Detection

This paper presents a reflective-mode planar microwave biosensor based on phase-variation allowing for the detection of low bacteria concentration. The sensor is a one-port coplanar waveguide (CPW) structure implemented by means of a pair of weakly coupled step-impedance resonators (SIRs). The high sensitivity needed for bacteria detection is obtained by modulating (reducing) the coupling level between the pair of resonators, which simply requires separating such resonators enough. A sensor demonstrator is developed to operate in K-band, resulting in a compact structure manufactured using a single-layer metal-on-glass technology. An experimental study is conducted on an example of detection of various concentrations of E. coli bacteria, where the phase variation at single frequency is an indicator of the bacteria presence. The measurement results show that as low as 100 colony-forming-unit in 1 ml (100 CFU/ml) of bacteria suspension can be easily detected with sensitivity of 3.24° per order of concentration, indicating potential to go even lower with detection threshold, which is superior to many state-of-the-art E. coli microwave biosensors.