Performance of subcutaneously implanted needle-type glucose sensors employing a novel trilayer coating

A miniature, needle-type glucose sensor based on a new trilayer membrane configuration has been prepared and evaluated both in vitro and in vivo. The perfluorinated ionomer, Nafion, was used as a protective, biocompatible, outer coating, and poly(o-phenylenediamine) as an inner coating to reduce interference by small, electroactive compounds. Glucose oxidase immobilized in a bovine serum albumin matrix was sandwiched between these coatings. The entire sensor assembly of Pt working electrode and Ag/AgCl reference electrode was 0.5 mm in diameter and could be inserted subcutaneously through an 18-gauge needle. The sensor current closely followed the plasma glucose level during a glucose tolerance test in active dogs, with a delay of 3 min, corresponding to the known lag time for subcutaneous glucose levels. The sensor remained functional after 1 week of implantation, but failed after 2 weeks due to degradation of the reference electrode. In vitro tests in pH 7.4 buffer or whole blood show the sensors have good selectivity, sensitivity of about 25 nA/mM, precision of 2-5%, and a 90% response time of 33 s. Stabilization following polarization requires 10-30 min in vitro and 30-40 min in vivo.