Development of a conductometric nitrate biosensor based on Methyl viologen/Nafion® composite film

A conductometric biosensor for nitrate analytical determination was developed using nitrate reductase (NR) from Aspergillus niger immobilized on a thin-film electrode by cross-linking with bovine serum albumin in the presence of glutaraldehyde, Nafion® cation-exchange polymer and methyl viologen mediator. The process parameters for the fabrication of the enzyme electrode and various experimental variables were investigated with regard to their influence on sensitivity, limit of detection, dynamic range, operational and storage stability. The biosensor can reach 95% of steady-state conductance value in about 13 s. Linear calibration in the range of 0.02 and 0.25 mM with detection limits of 0.005 mM nitrate was obtained with a signal-to-noise ratio of 3. When stored in 5 mM phosphate buffer (pH 7.5) at 4 °C, the sensor showed good stability over two weeks. The electrode is suitable for use in real samples.