Low-Cost and Easy-to-Fabricate Microwave Sensor for Sensitive Glucose Monitoring: A Step Towards Continuous Glucose Monitoring

Basal-bolus insulin therapy is associated with frequent injections, dosing errors, and hypoglycemia risks. Integrating continuous glucose monitoring (CGM) with insulin pumps offers several advantages. However, current CGM systems lack accuracy and have high costs. To overcome these challenges, a CGM system requires sensor with enhanced sensitivity and low cost. In this study, we develop a planar microwave resonator-based sensor for sensitive glucose detection in human serum and whole blood. We track the variation in the transmission coefficient (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$s_{21}$</tex-math></inline-formula>) to deduce changes in glucose concentration. Utilizing combinations of complementary split ring resonators (CSRRs) and complementary electric-LC (CELC) structures, the sensor achieves remarkable sensitivity, notably 37.3 mdB/(mg/dL) for glucose in human serum and 1.557 mdB/(mg/dL) for glucose in whole blood. We also evaluate other performance metrics, linearity (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$R^{2} = 0.985$</tex-math></inline-formula> for serum and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$R^{2} = 0.963$</tex-math></inline-formula> for whole blood), and limit of detection (LOD) of 477.75 μg/dL for serum and 53.84 mg/dL for whole blood. While we initially use an FR-4 rigid substrate in our proof-of-concept demonstration, we also investigate the feasibility of employing a flexible polyimide substrate. Our flexible glucose sensor shows an order of magnitude better performance than our rigid sensor.