Amperometric Biosensors for the Determination of Tetracycline

Amperometric biosensors based on an immobilized tyrosinase enzyme and planar graphite electrodes modified with multiwalled carbon nanotubes (MWCNTs) in chitosan, reduced graphene oxide (RGO), and gold nanoparticles (Au NPs) in chitosan and nanocomposites based on them are developed for rapid and accurate determination of tetracycline. It is found that tetracycline is a tyrosinase inhibitor, which makes it possible to determine it using a tyrosinase biosensor in a range of concentrations of 1 nmol/L to 1 μmol/L. It is found on the basis of the results of kinetic studies of the reaction of enzymatic conversion of phenol that uncompetitive inhibition is observed on the tyrosinase biosensor in the presence of tetracycline. A combination of carbon nanomaterials with metal nanoparticles can form a nanocomposite with a synergistic effect. The use of carbon nanomaterials and metal nanoparticles as modifiers of the electrode surface makes it possible to improve the analytical characteristics of the developed sensors: to expand the range of determined concentrations and to decrease the limit of quantification (50 pmol/L for a biosensor with MWCNTs/Au NPs, 0.7 nmol/L for a biosensor with RGO/Au NPs). The relative standard deviation of the obtained using biosensors results does not exceed 0.08. Procedures for the determination of tetracycline using the proposed biosensors in milk and a cosmetic product are tested. The compounds present in these samples which are structurally unrelated to tetracycline do not interfere with its determination.