Enzyme electrode‐based differential potentiometric cell with enhanced substrate sensitivity

A novel approach for enhancing the substrate sensitivity of ion‐selective electrode‐based enzyme probes is described. The concept involves the use of two working enzyme electrodes in a differential potentiometric cell arrangement. One of the enzyme probes is prepared by immobilizing a suitable enzyme or enzymes at the surface of a cation‐selective electrode, while the second working electrode contains the same or different enzymes immobilized on an appropriate anion‐selective electrode. Enzymatic substrate conversion at the surface of each electrode yields a detectable cation and anion, respectively. Since each sensor selectively responds to the same substrate, but in opposite directions, the potential difference between the two working enzyme electrodes is greater than that obtained when each enzyme probe is measured alone versus a standard reference electrode. As examples, differential cells for measuring urea and arginine are reported in which urease or urease plus arginase is immobilized on the surfaces of ammonium‐ and carbonate‐selective electrodes prepared with asymmetric cellulose acetate membranes.