STAINLESS-STEEL ELECTRODES IN ENZYME-BASED POTENTIOMETRIC AND PH-STAT BIOSENSORS

Surface-oxidised stainless steel electrodes are pH sensitive and can form the basis of low-cost, robust potentiometric biosensors. The potential at pH 7 varies from day to day and is sensitive to oxidising and reducing agents, but the response to pH change is stable for at least 3 months. Urea biosensors were constructed by immobilising a urease/gelatin film on such electrodes. The dependence of the response of these sensors on the buffer characteristics of the medium could be reduced by coupling the response to the electrolytic generation of acid or base near the enzyme layer. In such a ''pH-stat'' configuration, the amount of electrolytic current required to maintain the working pH is proportional to the urea concentration.