Microfabricated passive resonator biochip for sensitive radiofrequency detection and characterization of glucose

Passive sensors provide a new route for the characterization of concentration-dependent radiofrequency parameters with high reproducibility in real time. We propose a microfabricated resonator realized using integrated passive device technology for the sensitive detection and characterization of glucose. Experimental results verify the high performance of the proposed biosensor, because radiofrequency parameters such as resonance frequency (from 0.541 to 1.05 GHz) and reflection coefficient (from -34.04 to -24.11 dB) linearly vary in response to deionized water and subsequent iterative measurements of different glucose concentrations (from 50 to 250 mg dL^-1). The biosensor has a very low limit of detection of 8.46 mg dL^-1, a limit of quantitation of 25.63 mg dL^-1, a minimum frequency sensitivity of 29 MHz, and a minimum magnitude sensitivity of 0.22 dB. Moreover, the coupling coefficient consistently decreases with the increasing glucose concentration. We also used the measured radiofrequency parameters to determine the unknown permittivity of glucose samples through mathematical modeling. A decreasing trend in the loss tangent and an increasing trend in the characteristic wave impedance were observed with the increase of glucose concentration. The reproducibility of the sensor was verified through iterative measurements on the same sensor surface and subsequent study of surface morphology.