Subcutaneous implantation of a ferrocene-mediated glucose sensor in pigs

Miniature, amperometric glucose sensors were constructed using entrapped 1,1'-dimethylferrocene to mediate electron transfer between immobilised glucose oxidase and a carbon base electrode. Electrodes were calibrated in buffered glucose solutions and then implanted in the subcutaneous tissue of anaesthetised, non-diabetic pigs. Subcutaneous tissue glucose concentrations, as measured by the sensor, were about 20% of blood glucose values, measured by a conventional glucose oxidase assay. After an intravenous 0.07 mol bolus glucose injection, electrode responses increased with almost no time lag, but the subsequent rates of rise and fall of electrode-measured tissue glucose concentrations were slower than that of the blood values. After an intravenous 0.2 U/Kg bolus short-acting insulin injection the electrode response was also rapid, but decreased at a slower rate than the blood glucose concentrations. We conclude that this is a feasible technology for future development as an implantable glucose sensor for use in diabetic man.