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.
Highlights
The determination of ammonia (NH3) in the environmental samples has become increasingly important
The applications of diaphorase coupled with tetrazolium salts, which produce highly colored formazan dyes upon NADH oxidation, have been used as chromogenic reagents for quantification of NADH as detection signal [15]
We explored the use of dual enzymes system glutamate dehydrogenase (GLDH)/Diaphorase in combination with MTT for the determination of ammonium in aqueous solutions
Summary
The determination of ammonia (NH3) in the environmental samples has become increasingly important. Various approaches have been developed to detect dissolved ammonia in aqueous environment employing either electrochemical or optical methods [4,5,6]. These methods are time consuming and often require skill personnel to operate the sample preparation. Several papers have been published on the determination of dissolved ammonia employing enzyme system. The reaction involved the use of enzyme glutamate dehydrogenase (GLDH), which requires the cofactor βnicotinamide adenine dinucleotide (NADH) and ammonium ( NH+4 ) in the enzymatic conversion of 2-oxoglutarate to L-glutamate [8,9,10]. Quick indication on the presence of analyte of interest based on the color changes by using dual enzymes
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