Amperometric detection of histamine with a methylamine dehydrogenase polypyrrole-based sensor

Methylamine dehydrogenase (MADH) has been immobilized in a polpyrrole (PPy) film on an electrode surface and used as an amine sensor for the determination of primary amines. Its response to histamine has been characterized in detail. The PPy film containing MADH was formed electrochemically on a gold minielectrode (1-mm diameter) in the presence of ferricyanide. The film was then coated with Nafion. This enzyme electrode did not require any additional cofactors and was not sensitive to oxygen. It exhibited a maximum response current to histamine at applied potentials of 0.24-0.33 V and at pH 7.5-8.5. This MADH-PPy sensor exhibited a response time of less than 3 s. The immobilized MADH on the electrode exhibited Michaelis-Menten behavior similar to that of the free enzyme in solution with a Km value of 1.3 mM. This sensor could be used to reliably detect histamine over a concentration range from approximately 25 microM to 4 mM. This is the first example of a biosensor that uses an immobilized enzyme that possesses the tryptophan tryptophylquinone prosthetic group.