A GLUCOSE SENSOR, INTERFERENCE FREE FOR ASCORBIC-ACID

An improved glucose sensor was fabricated by entrapping the enzyme glu cose oxidase during polymerization of pyrrole onto a platinum electrod e (1 mm diameter). In a flow-injection system the glucose responses we re measured amperometrically at a potential of +0.7 V vs. SCE to detec t hydrogen peroxide, generated by the enzyme in the presence of oxygen . The study includes: (1) preparation and characterization of polypyrr ole-modified electrodes using both potentiostatic and amperostatic ele ctrochemical techniques; (2) demonstration that polypyrrole-modified e lectrodes are stable for several weeks and (3) testing of the interfer ence from ascorbic acid (5 mM). The best results were obtained using a current of 1 nA for 5 min (galvanostatic mode), in the presence of 0. 3 M pyrrole and glucose oxidase dissolved in 10 mM HEPES pH 7. Experim ents were carried out using glucose oxidase concentrations of 100, 150 and 200 U/ml. The stability of these electrodes for glucose (100 mM) was tested for several weeks. It turns out that the stability is quite satisfying. The selectivity for ascorbic acid was also tested. When m easured in time, the electrodes are quite stable and give very small r esponses. Electrodes with higher glucose oxidase concentrations show l ess interference from ascorbic acid.