Michael V. Pishko

Amperometric biosensor for in vivo glucose sensing based on glucose oxidase immobilized in a redox hydrogel

A potentially implantable glucose sensor, based on glucose oxidase immobilized in a redox hydrogel, is considered. The redox hydrogel consisted of glucose oxidase immobilized in a cross-linkable poly(vinylpyridine) complex of [Os(bis-bipyridine)2Cl]+1/+2 that communicates electrically with the flavin adenine dinucleotide (FADH2) redox centres of the glucose oxidase. The implantable electrode consisted of a Teflon insulated platinum wire (0.25 mm diameter) which was coated at the tip with a cross-linked redox polymer/glucose oxidase film and covered with a thin layer of polycarbonate. In a three-electrode system at +400 mV (Ag/AgCl) the response to increasing glucose concentrations in isotonic phosphate buffer and human plasma was approximately 0.2-0.3 nA/mM, linear in the range between 0 and 15 mM glucose. No oxygen dependence was observed. To determine the in vivo performance, the electrode was implanted into the subcutaneous tissue of a dog. The sensor currents after an oral glucose load paralleled the plasma glucose measurements, with a time lag of 10 min. Three-day implantations in cultured cells showed that the electrode did not affect the growth and differentiation of cell monolayers.

Electrical Communication Between Graphite Electrodes and Glucose Oxidase/Redox Polymer Complexes

Abstract Redox polymers can fold along the glycoproteins of glucose oxidase (MW 160,000) at low electrolyte concentrations and thereby penetrate the enzyme. Upon penetration, the distance between the redox centers of the polymer and the FADH2 centers of the reduced enzyme is reduced sufficiently for electrons to be transferred and, therefore, for the mediated electro-oxidation of glucose on conventional electrodes. At high (1M) electrolyte (NaCl) concentrations the redox polymers coil. Such coiling prevents the penetration of the enzyme by the redox polymers. Consequently, electron transfer does not take place and glucose is not electro-oxidized. When an appropriate polycationic redox polymer is covalently bound to the enzyme, the electro-oxidation of glucose occurs even at high electrolyte concentrations. Electron transfer from the enzymes FADH2 centers to copolymers of poly(N-methyl-4-vinylpyridinium) chloride with either poly(vinylferrocene), E° = 0.25V (SCE), or with poly(4-vinylpyridine) complexes o...