A Conductometric Urea Biosensor by Direct Immobilization of Urease on Pt Electrode

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Urease was immobilized on platinum electrode both by chemical binding and electropolymerization.The conductometric urea biosensor thus prepared showed a detection limit of 4.9×10-5 M and linear dynamic range from 4.9×10-5 to 5.8×10-3 M for urea concentration when the enzyme is covalently immobilized on Pt electrodes. Conductometric transducers respond to the changes in ionic strength thereby leading to uncontrolled inaccuracies. Such interferences were effectively suppressed by here the use of differential sensor pairs. It was shown that measurements in diluted fluids are possible with the use of areference sensor having no immobilized enzyme.Specifically, the sensor constructed by covalent binding provided more reproducible responses than that prepared by electropolymerization. Namely the former preserved 80% of its initial activity over a period of 25 days. In order to provide more reproducibility,a method was developed for regeneration of the sensor surface so that, the renewed sensor would responded to urea almost as new.