An amperometric biosensor was constructed by immobilization of enzyme, tyrosinase, in an electrochemically synthesized phosphate ion-doped polypyrrole film on a Pt disk electrode. The tyrosinase maintains its bioactivity well within the polypyrrole thin film. A clearly defined reduction current proportional to the phenolic compounds concentration was observed in cyclic voltammetry, which attributed to the reduction of enzymatically produced quinone at the electrode surface.
Phenolic compounds were quantitatively estimated in aqueous medium by the direct electrochemical reduction of enzymatically liberated quinone species at −0.05 V by chronoamperometry. For the all six phenolic compounds analyzed, the kinetics of the enzymatic reaction fitted into a Michaelis–Menten type kinetics, as demonstrated by the h parameter close to 1 obtained from the Hill's plot.
The sensitivity followed the decreasing order catechol > phenol > 2-bromophenol > 2-chlorophenol > 2-iodophenol > 2-fluorophenol. The greater value of Imax and the lowest was found for catechol.
The detection limits were in the range of 0.84–8.54 μM. The lowest detection limits were found for catechol and the highest for 2-fluorophenol.
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