Electroimmobilization of MAO into a Polypyrrole Film and Its Utilization for Amperometric Flow Detection of Antidepressant Drugs

The preparation of a biosensor based on the enzymatic immobilization in polypyrrole polymer for the detection of antidepressant drugs is described. The enzyme monoamine oxidase (MAO) was immobilized by electropolymerization of pyrrole around a platinum electrode, at a constant potential of +0.75 V (vs. Ag/AgCl) in such a way to obtain a membrane thickness, which was constant and equal to 100 mC/cm2. The biosensor was obtained from a 0.1 M KCl saline solution containing pyrrole at a concentration equal to 0.4 M and 2.5 mU/mL of MAO. The biosensor was adapted to a continuous flow injection analysis system (FIA) with the amperometric detection of hydrogen peroxide produced by enzymatic reaction carried out at a potential of +0.7 V (vs. Ag/AgCl), pH 7.4 and temperature of 37 °C. In optimized flow conditions, the biosensor presented an analytical response for fluoxetine in the interval between 0.67 and 4.33 mM, with a detection limit of 0.10 mM. The analytical use of the biosensor developed was evaluated through analysis of commercial pharmaceutical products containing fluoxetine, available on the Portuguese market. The amperometric flow results obtained do not differ significantly from the values resulting from analysis of the same products by the method proposed by the US Pharmacopeia, with sampling rates of 20–25 samples/hour.