An amperometric biosensor design, where the electrode is directly in contact with the analyte solution and the receptor matrix is separated from the solution by the electrode, such that the substrates must pass through the permeable electrode and then react with the enzyme, is described for an oxidase enzyme reaction both experimentally and theoretically. The response of this sensor was shown to be independent of the thickness of the bioactive matrix under conditions of limiting co-substrate, and it therefore has less stringent manufacturing tolerances. The consumption of co-substrate in the biorecognition matrix is shown to be dependent on the bulk substrate concentration, the rate constants of the reaction and a quantity known as the Thiele modulus.