A GLUCOSE SENSOR, INTERFERENCE FREE FOR ASCORBIC-ACID

An improved glucose sensor was fabricated by entrapping the enzyme glucose oxidase during polymerization of pyrrole onto a platinum electrode (1 mm diameter). In a flow-injection system the glucose responses were measured amperometrically at a potential of +0.7 V vs. SCE to detect hydrogen peroxide, generated by the enzyme in the presence of oxygen. The study includes: (1) preparation and characterization of polypyrrole-modified electrodes using both potentiostatic and amperostatic electrochemical techniques; (2) demonstration that polypyrrole-modified electrodes are stable for several weeks and (3) testing of the interference 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. Experiments 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 measured in time, the electrodes are quite stable and give very small responses. Electrodes with higher glucose oxidase concentrations show less interference from ascorbic acid.