A sensitive and stable amperometric nitrate biosensor employing Arabidopsis thaliana nitrate reductase.
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Nitrate reductase (NR) from the plant Arabidopsis thaliana has been employed in the development of an amperometric nitrate biosensor that functions at physiological pH. The anion anthraquinone-2-sulfonate (AQ) is used as an effective artificial electron transfer partner for NR at a glassy carbon (GC) electrode. Nitrate is enzymatically reduced to nitrite and the oxidized form of NR is electrochemically reduced by the hydroquinone form of the mediator (AQH2). The GC/NR electrode shows a pronounced cathodic wave for nitrate reduction and the catalytic current increases linearly in the nitrate concentration range of 10-400 µM with a correlation coefficient of 0.989. Using an amperometric method, a low detection limit of 0.76 nM (S/N = 3) was achieved. The practical application of the present electrochemical biosensor was demonstrated by the determination of nitrate concentration in natural water samples and the results agreed well with a standard spectroscopic method.