First millimeter-wave animal in vivo measurements of L-Glucose and D-Glucose: Further steps towards a non-invasive glucometer

The authors present the first in vivo measurements of L-Glucose and D-Glucose concentrations using millimeter waves. Employing direct injection of solutions into the rat jugular vein, we have been able to correlate immediate changes in blood glucose readings with transmission loss through the ears of anesthetized rats at Ka band (27-40 GHz). The sensed changing D-glucose levels are shown to track blood values, but with a delay of approximately 10-15 minutes, which may be due to cellular glucose uptake. Surprisingly, levels of L-glucose, the non-bioactive enantiomer (L-isomer) are also tracked by millimeter-wave transmission through the ear, suggesting that we are looking at the direct chemical presence of glucose or products of its breakdown in the tissue, rather than metabolism. Both isomers of glucose are gradually removed from the bloodstream after injection of insulin, consistent with the observed changes in the millimeter-wave absorption. These results represent a major step towards the realization of a non-invasive glucose monitor based on millimeter-wave transceivers.