An optical biosensor employing tiron-immobilised polypyrrole films for estimating monophenolase activity in apple juice

A method is described for the incorporation of tiron as a substrate for tyrosinase enzyme into a polypyrrole film deposited on indium titanium oxide (ITO) glass. The presence of tiron in the polypyrrole film is verified by cyclic voltammetry (CV). The enzyme activity using the polypyrrole–tiron film is confirmed by the catalytic conversion of immobilised substrate to quinones by the enzyme. The use of both potentiometric and optical methods for the detection of the catalytic activity of the polypyrrole–tiron film and their potential use for the determination of monophenolase activity of apple polyphenol oxidase is described. This is the first report of this kind whereby tiron has been immobilised in a polypyrrole matrix for the enzyme activity determination.