Ultrahigh-Sensitivity Mediator-Free Biosensor Based on a Microfabricated Microwave Resonator for the Detection of Micromolar Glucose Concentrations

Abstract

This paper presents a miniaturized microwave-resonator-based ultrahigh sensitivity mediator-free biosensor for determining the level of glucose in deionized-water glucose solutions and human sera using integrated passive device technology on a gallium–arsenide substrate. The proposed glucose biosensor, which consists of cross-coupled stepped-impedance resonators (SIRs), strongly concentrates electromagnetic energy between the coupling regions at a central frequency of 6.53 GHz. The changes in effective permeability $(\mu_{\rm eff})$ and permittivity $(\varepsilon_{\rm eff})$ , which correlate with the variations in the glucose concentration, effectively change the equivalent series inductance and shunt capacitance of the biosensor resonator. This concept was used for the first time to develop an ultrahigh-sensitivity biosensor based on a low $-$ Q microwave resonator. The length of each SIR was meandered width wise, and a meandered-line stub-load was embedded inside the SIR to utilize the equivalent high series inductance and shunt capacitance, respectively. The newly designed present biosensor, which linearly detected glucose level within a wide range of concentration, exhibited an ultrahigh sensitivity (978.7 ${\hbox{MHz/mgmL}}^{-1}$ for sera) at least 4.918 times higher than that of previously reported microwave-resonator-based glucose biosensors, a lower detection limit of 0.01928 $\mu{\hbox{M}}$ , and a rapid detection time of less than 5 s. Supported by S-parameter-based effective-medium-parameter analysis and a sensitivity enhancement principle, the detection accuracy of the proposed biosensor was increased using its glucose-level-dependent spreading of propagation constant $(\gamma)$ and self-resonances of impedance $(Z)$ .