Substrate Integrated Waveguide Cavity Resonator-Based Differential RF Biosensor for Glucose Detection in Blood Serum

The detection of low levels of analyte concentration in biomedical fluids such as whole blood, blood serum, platelets, etc., is quite challenging for medical diagnostics and sensing applications. The difficulty mainly arises due to the fact that these biofluids usually exhibit high permittivity with significantly high dielectric losses, thereby posing challenges for their accurate dielectric testing using microwave sensors. Additionally, environmental factors like temperature, humidity, etc., and internal noises can also introduce errors in the measurement limiting the use of these types of sensors for low analyte concentrations. To address these challenges, a novel differential microwave sensor based on a microstrip line-fed Wilkinson power divider and combiner, along with a pair of identical substrate integrated waveguide (SIW) resonant cavities is proposed. The proposed differential configuration achieves low limit of detection (LoD), high quality factor (Q), and high sensitivity by effectively nullifying common-mode errors caused by environmental fluctuations and internal noises. The parameters of the proposed differential RF sensor are first optimized using the CST microwave studio for a better performance. The sensor performance is verified utilizing the dielectric testing of industrial liquids and medical grade solvents such as acetone, acetonitrile, chloroform and deionized (DI) water, with a maximum error of ±2.69%. The designed sensor is then utilized for blood glucose concentration measurement with a minimum LoD of 5 mg/dL in the heat-inactivated fetal bovine serum (FBS) to emulate the dielectric characteristics of blood. The proposed RF sensor can be potentially developed as a standalone real-time glucose concentration monitoring system.