Real-Time Noninvasive Measurement of Glucose Concentration Using a Microwave Biosensor

We measured the glucose concentration by using the real-time electromagnetic interaction between probe-tip and glucose solution using a microwave biosensor. The microwave biosensor, consisting of a dielectric resonator coupled to the probe-tip, allows observation of the small variation of the glucose concentration changes in the ranges of 0–300 mg/ml by measuring the microwave reflection coefficient S11. We could observe the concentration of glucose with a detectable resolution up to 1 mg/ml at an operating frequency of about f=4-5 GHz. The change of the glucose concentration is directly related to the change of the reflection coefficient due to the electromagnetic interaction between the microwave resonator and the glucose solution. The operational principal is explained by the plane-wave solution model. The measured signal-to-noise ratio was about 37 dB, and the minimum detectible signal was about 0.003 dB/(mg/ml). A glucose biosensor using a microwave resonator with probe provides a unique approach for glucose real-time monitoring.