VOLTAMMETRIC AND AMPEROMETRIC BEHAVIOR OF URIC-ACID AT BARE AND SURFACE-MODIFIED SCREEN-PRINTED ELECTRODES - STUDIES TOWARDS A DISPOSABLE URIC-ACID SENSOR

Systematic voltammetric and amperometric studies have been undertaken to examine the electrochemical behaviour of uric acid at bare and surface-modified screen-printed electrodes. The precision of the electrode manufacture was determined by cyclic voltammetry with a 1.0 x 10(-4) mol dm-3 uric acid solution and was calculated to be 6.0% (n = 5). Several strategies were investigated in an attempt to eliminate interference from ascorbic acid. These involved coating the electrode surface with Nafion, or the enzyme L-ascorbic acid oxidase. The latter was immobilized using one of two methods: either by a simple adsorption process, or by cross-linking with bovine serum albumin and glutaraldehyde. The amperometric response at the surface-adsorbed enzyme electrode for uric acid was linear over the concentration range from 5.08 x 10(-6) to 1.51 x 10(-4) mol dm-3; the limit of detection was 2.54 x 10(-6) mol dm-3 using a full-scale deflection of 0.5-mu-A. This modified electrode exhibited no response to ascorbic acid at levels up to 0.53 mmol dm-3. The electrode modified by cross-linking the enzyme to the surface showed no response to ascorbic acid concentrations of up to 0.093 mmol dm-3.