Estudo eletroquímico e morfológico do copolímero polianilina-4-aminofenol para detecção do hormônio triiodotironina.

Abstract

In Brazil about 15% of the population suffers from dysfunctions in the thyroid gland, although half are unaware of this condition (IBGE). Thyroid hormones synthesized by the thyroid gland are excreted in the bloodstream, however, because they are highly hydrophobic, they circulate bound to plasma proteins, rendering them inactive, so that the free portion of these hormones for action on the metabolism of the cells is very low. Among the methodologies that can be used to detect thyroid disorders are biosensors, which are presented as a promising alternative, presenting the advantage of a simple, fast and low-cost diagnosis. In immunosensors the success of the immunological reaction depends on the immobilization step of the probe biomolecule, where the development of copolymers may present a differential, by combining the properties of different monomers. In this work, the poly(aniline-4-aminophenol) copolymer (1:1 molar ratio) was electropolymerized on the surface of graphite electrodes using monomeric solution (1,0 mmol L-1). Polyaniline and poly(4-aminophenol) were also electropolymerized under the same conditions for comparison. For the immobilization of the biomolecule probe, aiming the development of a biosensor, the Anti-T3 antibody was incorporated to the surface of the electrodes modified with the different polymeric films. In sequence, the modified electrodes containing the probe were placed in contact with serum containing the T3 target. Differential Pulse Voltammetry (DPV) measurements were performed to detect the different surfaces by monitoring the Fe2+ oxidation peak from K4Fe(CN)6. Anti-T3 antibody immobilization with the use of EDC-NHS on the surface of the poly(aniline-4-aminophenol) copolymer, as well as the detection of the T3 target present in the serum, evidenced by the decrease of the intensity of Fe2+ oxidation peak current at each biofunctionalization stage, with a 25% reduction in the presence of the probe and 23% after the target probe interaction. This fact was much more pronounced on the poly(aniline-4-aminophenol) copolymer, which presented the greatest reduction of peak current when compared to the others: polyaniline and poly(4-aminophenol) suggesting that a higher amount of anti-T3 on the surface of the poly(aniline-4-aminophenol) electrode. The synergistic effect on the copolymer was shown to be promising for application of the material in the quantitative diagnosis of the T3 target in patient serum, since the addition of crosslinking reagents was not required to promote immobilization of the antibody, and no other nanomaterial to reach the target concentration of the hormone T3 in the serum sample, which is usually in the order of picograms/mL. The morphological characterization of the immunosensor showed significant changes in the roughness values, consistent with the electrochemical studies.