title: Novel, reagentless, amperometric biosensor for uric acid based on a chemically modified screen-printed carbon electrode coated with cellulose acetate and uricase.
abstract: Amperometry in stirred solution has been used for the systematic evaluation of modified screen-printed carbon electrodes (SPCEs) with a view to developing a reagentless biosensor for uric acid. The developed system consists of a base cobalt phthalocyanine (CoPC) electrode tailored to the electrocatalytic oxidation of H2O2 by means of a cellulose acetate (CA)-uricase bilayer. Uricase was immobilized by drop-coating the enzyme onto the CA membrane covering the CoPC-SPCE. The device exploits the near-universal H2O2-generating propensity of oxidases, the permselectivity of the CA film towards H2O2 and the electrocatalytic oxidation of this product at the CoPC-SPCE. The electrochemical oxidation of the resulting Co+ species was used as the analytical signal, facilitating the application of a greatly reduced operating potential when compared with that required for direct oxidation of H2O2 at unmodified electrodes. The time required to achieve 95% of the steady-state current (t95i(ss)) was 44 s [relative standard deviation = 7.5% (n = 10)]. Amperometric calibrations were linear over the range from 13 x 10(-6) to 1 x 10(-3) mol dm-3, with the former representing the limit of detection. The CA membrane extended the linear range of the biosensor by over two orders of magnitude, when apparent Michaelis-Menten constants (Km') of immobilized and free enzymes are compared. This suggests that the process is diffusion-controlled and not governed by the kinetics of the enzyme. The precision of electrode fabrication was determined by cyclic voltammetry to be 4.9% (n = 6).(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Faculty of Applied Sciences, University of the West of England, Bristol, UK.
authors.forename: M A
authors.initials: MA
authors.lastname: Gilmartin
authors.forename: J P
authors.initials: JP
authors.lastname: Hart
mesh_terms: D000328:Adult; D015374:Biosensing Techniques; D002482:Cellulose / Q000031:analogs & derivatives; D004563:Electrochemistry; D004800:Enzymes, Immobilized; D005260:Female; D006801:Humans; D008297:Male; D014503:Urate Oxidase / Q000737:chemistry*; D014527:Uric Acid / Q000032:analysis*
chemical_list: D004800:Enzymes, Immobilized; D014527:Uric Acid; C005062:acetylcellulose; D002482:Cellulose; D014503:Urate Oxidase