Determination of horseradish peroxidase and a peroxidase-like iron porphyrin at a Nafion-modified electrode.

A catalytic coupling reaction between 4-amino antipyrine and a N,N-disubstituted aniline derivative has been exploited in the indirect electrochemical detection of horseradish peroxidase (HRP) and of a biomimetic catalyst, the iron(III) sulfonated tetraphenyl porphyrin. In the presence of hydrogen peroxide and one of the two catalysts a cationic electroactive quinone-iminium dye P+ was formed and detected by linear scan voltammetry using a screen-printed electrode coated with a Nafion film. Detection limits of 10(-12) M for HRP and 4 x 10(-10) M for the iron porphyrin have been achieved. In conclusion the iron porphyrin is considered to be a promising alternative to the HRP label in enzyme immunoassays with electrochemical detection.