Multiwalled carbonnanotubes enhance the response and sensitivity of the ammonium biosensor based on alanine dehydrogenase

Abstract An amperometric ammonium biosensor based on alanine dehydrogenase of Bacillus subtilis and functionalized multiwalled carbonnanotubes was developed by using screen printed electrodes. The output current of the biosensor was increased around 2.4 times at 100 mM NH 4 + after the addition of functionalized multiwalled carbonnanotubes at the concentration of 0.1 μg/ml along with the enzyme. The biosensor showed much broader linearity range (0.05–500 mM NH 4 + ), better detection limit (0.001 mM NH 4 + ) and response time (30 s) due to the incorporation of the functionalized multiwalled carbonnanotubes. The cyclic voltammogram of enzyme-carbonnanotubes/carbon working electrode showed the output current at the oxidation peak, which was > 2 times higher compared to that of enzyme/carbon working electrode. This suggests the promotion of electron transfer from the enzyme to the working electrode by carbonnanotubes, which may act as electron transducers and rapidly transfer the electrons from the redox centre of the enzyme to the electrode, thereby improving the signal, response time and sensitivity. The sensor retained 89.93% of its initial output current after 119 days. The concentrations of NH 4 + detected by the biosensor were in close agreement with that of standard Nessler's reagent method suggesting the suitability of the present biosensor for the testing of water samples.