AMPEROMETRIC ENZYME ELECTRODE BIOFOULING AND PASSIVATION IN BLOOD - CHARACTERIZATION OF WORKING ELECTRODE POLARIZATION AND INNER MEMBRANE EFFECTS

Signal drift of an H2O2-based glucose enzyme electrode following exposure to whole blood has been studied in relation to the inner membrane barrier used to separate the oxidase enzyme from the working electrode as well as working electrode polarisation. Variation of the inner membrane has been found to have a strong influence on signal drift, confirmed as being due to the passage of some diffusible solutes to the working electrode. The subsequent passivation and loss of current output of up to 70% was observed in 120 min, at a polarisation voltage of +800 mV vs. Ag\AgCl with a 2% w/v cellulose acetate membrane. Signal drift was substantially reduced using less permeable inner membranes, which included microporous polycarbonate of 0.01, 0.03, 0.1 and 1 mum pore radii as well as non-porous cellulose acetate membranes (2% w/v and 5% w/v). Signal drift has also been shown to be critically dependent upon working electrode polarisation; higher over-potentials gave higher losses ranging from 10% at +200 mV to 70% at +800 mV vs. Ag\AgCl after 120 min (for 2% w/v cellulose acetate). There is some indication that, in addition to its permeability, the dielectric properties of the inner membrane may influence the sensor drift.