VOLTAMMETRIC ENZYME SENSOR FOR UREA USING MERCAPTOHYDROQUINONE-MODIFIED GOLD ELECTRODE AS THE BASE TRANSDUCER

A voltammetric urea-sensing electrode was prepared by combining a lipi d-attached urease layer with a 2,5-dihydroxythiophenol-modified gold e lectrode. A self-assembled monolayer of dihydroxythiophenol was prepar ed on the gold surface by soaking the electrode into an ethanolic solu tion containing the modifier. A layer of the lipid-attached enzyme and that of acetyl cellulose overcoat were successively made on the dihyd roxythiophenol-modified electrode by applying a dip-coating procedure. The addition of urea in a test solution (10 mM phosphate buffer, pH 7 .0) brought about an increase of pH near the urease layer. The pH shif t accompanied a negative shift of the anodic peak, which corresponded to the electro-oxidation of dihydroxyphenol moiety to form quinone, on the linear sweep voltammograms for the urease/dihydroxythiophenol ele ctrode. The concentration of urea (0.2-5 mM) could be determined by me asuring the electrode current at -0.05 V versus Ag/AgCl from the volta mmogram. The electrode was applied to the determination of urea in hum an urine: the measurement of electrode current at such a low potential provided the urea determination without any electrochemical interfere nce from L-ascorbic acid and uric acid. (C) 1997 Elsevier Science Limi ted.