Electrochemical enzymatic biosensor for tyramine based on polymeric matrix derived from 4-mercaptophenylacetic acid

In this paper, we investigated a novel functionalized polymeric film derived from 4-mercaptophenylacetic acid (MPAA). The polymerization was carried out through cyclic voltammetry (CV). Electrochemical, spectroscopic, and morphological analyses were used for characterization. Only acidic medium provided an efficient electrode modification as the electrochemical and morphological profiles obtained from treatment in alkaline solution resembles the unmodified electrode. The electrostatic repulsion between the carboxylate anions in the polymer and ferricyanide probe was verified by the current decrease in CV profiles and by the resistance of charge transfer increase through electrochemical impedance spectroscopy (EIS). Scanning electron microscopy (SEM) images showed a complete and homogeneous coverage with a splinter-like morphology. The polymer presents stability under storage conditions until 35days with no lixiviation during washing steps or loss of activity. The FT-IR measurements confirm the presence of the carboxyl group in the polymer suggesting a polymerization through the sulfur atom, which led to a mechanism proposal. The immobilization of enzyme tyrosinase over this platform and the detection of tyramine were performed successfully. 50U of the enzyme for 18h at pH 7.2 was the optimum parameters leading to a limit of detection and limit of quantification of 3.16molL and 10.52molL, respectively. With K-m(app) of 62.11molL and a recovery rate of 110.84% in a wine sample, the novel, stable, functionalized material formed over a low-cost electrode is suitable for further electrochemical applications exploiting the chemical reaction of carboxyl groups for biosensor purposing.