Application of polytetrafluoroethylene (PTFE) membranes to control interference effects in a glucose biosensor

The implantable feedback-controlled insulin delivery system provides the greatest potential for the control of certain types of diabetes mellitus. The development of an implantable glucose sensor is thus a prerequisite. A glucose biosensor using the enzyme glucose oxidase immobilized on fine carbon powder has been developed. Its in-vitro behavior is investigated in the presence of interfering substances commonly encountered in human blood and other body fluids. Here, in-vitro interference tests carried out on this sensor with polytetrafluoroethylene (PTFE) membranes are described. The authors used PTFE membranes (pore size 0.02 micron), some of which were coated with positively and negatively charged hydrogel layers. The sensors showed a stable and linear response to glucose concentrations > 300 mg/dL, in the presence of glucose alone in the phosphate buffer medium and in the presence of interferences. The interference effects of ascorbic acid, bilirubin, creatinine, L-cystine, glycine, uric acid, and urea on the amperometric signal of the sensor were studied. The PTFE membrane coated with the negatively charged hydrogel layer provided good protection for the enzyme electrode, especially in the presence of ionic interferants such as ascorbic acid and uric acid.