Ultralinear Glucose Sensing Device with Membrane Supported Complementary Split-ring Resonator on SIW

Abstract

The linearity of a glucose sensor is one of the most important indicators for ensuring measurement accuracy, system stability and post-measurement data processing efficiency. As yet, this issue has not been seriously investigated in the field of glucose sensing. In this work, the use of a substrate-integrated-waveguide (SIW) together with a specially tailored membrane-supported resonator (CSRR) is proposed for realizing an ultralinear glucose sensor. Method: An SIW waveguide with two coplanar ports were realized on an FR4 substrate. On one side of the SIW waveguide, a CSRR was fabricated at the central region, which also served as the sensing region. On the other side of the SIW waveguide, the substrate at the central sensing region was thinned down to a negligible thickness using a nail grinder, thereby forming a circular recess with a membrane-thick bottom for holding a glucose-loaded test solution. The glucose concentration was determined by obtaining the resonant frequency shift in the reflection coefficient (i.e. S11). Results: The proposed glucose sensor has exhibited a highly linear correlation between the glucose concentration and the resonant frequency, with a Pearson correlation coefficient (r) reaching 0.99, even though the magnitudes of S11 minima were subjected to ambient electromagnetic interference. The sensitivity was found to be 1.6 MHz/(mg/dL). The resonant frequency was very weakly dependent on the volume of the test solution. Conclusion: Overall, the proposed glucose sensor has exhibited not only a high sensitivity but also a highly linear characteristics even in the presence of external electromagnetic interference.