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

Methylamine dehydrogenase (MADH) has been immobilized in a polypyrrole (PPy ) film on an electrode surface and used as an amine sensor for the determin ation of primary amines. Its response to histamine has been characterized i n detail. The PPy film containing MADH was formed electrochemically on a go ld minielectrode (1-mm diameter) in the presence of ferricyanide. The him w as then coated with Nafion. This enzyme electrode did not require any addit ional cofactors and was not sensitive to oxygen. It exhibited a maximum res ponse 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. Th e immobilized MADH on the electrode exhibited Michaelis-Menten behavior sim ilar to that of the free enzyme in solution with a K-m value of 1.3 mM. Thi s sensor could be used to reliably detect histamine over a concentration ra nge from approximately 25 mu M to 4 mM. This is the first example of a bios ensor that uses an immobilized enzyme that possesses the tryptophan tryptop hylquinone prosthetic group.