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H. Jaegfelt, A. B. C. Torstensson, L. Gorton and G. Johansson, “Catalytic Oxidation of Reduced Nicotina-mide Adenine Dinucleotide by Graphite Electrodes Modi- fied with Adsorbed Aromatics Containing Catechol Functionalities,” Analytical Chemistry, Vol. 53, No. 13, 1981, pp. 1979-1982. doi:10.1021/ac00236a007

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• TITLE: An Optical Based Biosensor for the Determination of Ammonium in Aqueous Environment

  AUTHORS: Nur Ellina Azmi, Jaafar Abdullah, Musa Ahmad, Hamidah Sidek, Lee Yook Heng, Samsulida Abd Rahman

  KEYWORDS: Optical Biosensor; Glutamate Dehydrogenase; Diaphorase; Ammonium

  JOURNAL NAME: American Journal of Analytical Chemistry, Vol.3 No.5, May 29, 2012

  ABSTRACT: A simple and rapid optical biosensor for the determination of ammonium was developed by immobilization of gluta-mate dehydrogenase (GLDH) and diaphorase (Dph) in chitosan film coated on a glass slide employing thiazolyl blue tetrazolium bromide (MTT) as a color indicator. The developed biosensor displays a purple color formation of formazan attributed to the unreacted NADH in the reaction system in the presence of ammonium. The color intensity was found to decrease proportionally with the increase of ammonium concentrations after 10 min exposure. The linearity of the biosensor towards ammonium was in the range of 16.8 – 70 μM (R2 = 0.9955) with detection limit of 11 μM. A good agreement (R2 = 0.9984) with indothymol method was obtained in the measurement of fish pond water samples. The effect of potential interferences such as metals ion has also been evaluated.