A biosensor for the determination of ammonium ion using flow injection amperometric system

An ammonium ion biosensor was constructed using a screen-printed carbon electrode based on alanine dehydrogenase immobilized on core shell Fe3O4@Au nanoparticles which were attached to the electrode surface by an external magnet. The amperometric current response in a flow injection analysis system depending on the oxidation of NADPH was proportional to the amount of ammonium ion consumed during the catalytic reaction of the alanine dehydrogenase enzyme. The designed biosensor was evaluated with a linear response range from 5 to 250 mM with a sensitivity of 0.2 mu A mM(-1) cm(-2), a detection limit of 2.1 mM, and a quantification limit of 6.3 mM. Moreover, the repeatability (ten measurements) and the reproducibility (three sensors) were estimated as 2.6%RSD and 3.0%RSD, respectively. The proposed biosensor was applied successfully to the determination of ammonium ion concentration in concentrated latex samples.