Selectivity enhancement for glutamate with a Nafion/glutamate oxidase biosensor

Response properties and selectivity are reported for glutamate biosensors constructed with a film of Nafion between the platinum anode and a layer of immobilized glutamate oxidase. The effects of enzyme loading, sample pH and temperature are established. Operation at pH 7.8 and 37 degrees C results in linearity up to 800 muM and a limit of detection of 0.3 muM. Nafion enhances selectivity for glutamate over test species that include ascorbic acid, uric acid and acetaminophen. Selectivity enhancement was greater over the anionic interferences because of electrostatic repulsion and the extent of this enhancement depends on the thickness of the Nafion layer. Even under ideal conditions, some interfering signal is observed when glutamate levels are ten-times less than ascorbate.