Amperometric glucose-sensing electrode based on carbon paste containing poly (ethylene glycol)-modified glucose oxidase and cobalt octaethoxyphthalocyanine

An amperometric enzyme electrode for glucose was prepared by incorporating poly (ethylene glycol)-modified glucose oxidase and cobalt octaethoxyphthalocyanine [CoPc(OEt)8], a new mediator, into a carbon paste matrix. The polymer-modified enzyme exhibited a higher activity than the native enzyme in the hydrophobic carbon paste medium. CoPc(OEt)8 could oxidize the enzyme at more negative potentials than unsubstituted cobalt phthalocyanine (CoPc). Further, the CoPc(OEt)8-mediated enzyme electrode showed a high stability: the electrode response to glucose did not decrease for at least 4 weeks (or for 700 assays), whereas the glucose response from a CoPc-mediated enzyme electrode fell to half of the initial value within 2 weeks (or after 300 assays). CoPc(OEt)8, a paraffin-oil soluble derivative of CoPc, incorporated in the bulk of carbon paste, diffused towards the electrode surface so as to renew continuously the electrode surface, which resulted in the high stability of the new mediator-based enzyme electrode.