A sensitive and stable amperometric nitrate biosensor employing Arabidopsis thaliana nitrate reductase.

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.