Low-Potential
Amperometric Enzyme Biosensor for Xanthine
and Hypoxanthine
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Abstract
The bacterial xanthine dehydrogenase
(XDH) from Rhodobacter capsulatus was
immobilized on an edge-plane
pyrolytic graphite (EPG) electrode to construct a hypoxanthine/xanthine
biosensor that functions at physiological pH. Phenazine methosulfate
(PMS) was used as a mediator which acts as an artificial electron-transfer
partner for XDH. The enzyme catalyzes the oxidation of hypoxanthine
to xanthine and also xanthine to uric acid by an oxidative hydroxylation
mechanism. The present electrochemical biosensor was optimized in
terms of applied potential and pH. The electrocatalytic oxidation
response showed a linear dependence on the xanthine concentration
ranging from 1.0 × 10<sup>–5</sup> to 1.8 × 10<sup>–3</sup> M with a correlation coefficient of 0.994. The modified
electrode shows a very low detection limit for xanthine of 0.25 nM
(signal-to-noise ratio = 3) using controlled potential amperometry