On-line glucose monitoring by using microdialysis sampling and amperometric detection based on 'wired' glucose oxidase in carbon paste

In-vitro on-line glucose monitoring is described, based on microdialysis sampling and amperometric detection operated in a flow-injection system. Samples were injected into a two-electrode microcell containing an Ag/AgCl quasi-reference electrode and a glucose enzyme electrode as the working electrode, operated at +0.15 V vs. Ag/AgCl. The enzyme electrode is constructed by mixing the 'wired' glucose oxidase into carbon paste. {Poly[1-vinylimidazole osmium(4,4'-dimethylbipyridine)(2)Cl)]}(+/2+) was used to 'wire' the enzyme. The non-coated electrodes, cross-linked with poly(ethylene glycol) diglycidyl ether, responded linearly to glucose concentrations up to 60 mM, and were characterized by a sensitivity of 0.23 mu A mM(-1) cm(-2), when operated in flow injection mode and of 5.4 mu A mM(-1) cm(-2) in steady-state conditions. This sensitivity of the resulting enzyme electrode was 50% lower than that of similarly prepared but non-cross-linked electrodes. However, the cross-linked electrodes showed superior operational and storage stabilities, which were further improved by coating the electrodes with a negatively charged Eastman AQ film. An in-house designed microdialysis probe, equipped with a polysulphone cylindrical dialysis membrane, yielded a relative recovery of 50-60% at a perfusion rate of 2.5 mu l/min(-1) in a well stirred glucose solution. The on-line set up effectively rejected common interferences such as ascorbic acid and 4-acetaminophen wizen present at their physiological concentrations.