Noninvasive in Vivo Evaluation of Mouse-Blood Glycemia with a Microwave Spiral Sensor

Noninvasive in vivo measurements of glycemia in 8 living non anesthetized mice were done using a microwave spiral sensor (MSS). The D-glucose concentration in the blood of the animals was measured in the 80-350 mg/dL concentration range using microwaves of frequencies from 4-5 GHz. Aqueous D-glucose solution with concentrations from 0 to 6% was orally injected into the mice and the change in the total glycemia was monitored in real time. In particular, two sets of measurements were done. In the lower frequency regime, using a resonance of about 4.1 GHz, for a 6% blood glucose concentration, there was a frequency shift of 48 MHz and a reflection coefficient S-11 change of 15 dB, while in the higher frequency regime, about 5 GHz, the frequency shift was 59 MHz with a S-11 change of 1.6 dB. These in vivo results show a signal-to-noise ratio (SNR) of 24 dB and a minimum detectable glucose level was determined to be 10 mg/dL. This is in contrast with in vitro measurements, using the same spiral sensor, which show 32 dB SNR and a minimum detectable glucose level of 5 mg/dL. The results show the utility and sensitivity of the MSS for noninvasive biological investigations of glycemia in living animals.