Desenvolvimento da plataforma de grafite funcionalizada com poli(ácido-4hidroxifenilacético) sobre óxido de grafeno reduzido: nanopartículas de ouro, para detecção do hormônio triiodotironina

Abstract

Biosensors show many advantages such as high sensitivity, possibility of point of care detection, small sample volume and low cost, which makes them a versatile tool for the specific diagnosis of diseases and metabolic disorders. This research had as main objective the development of an electrochemical immunosensor for the diagnosis of the thyroid hormone triiodothyronine - T3, in a platform constructed by modifying graphite electrodes with the 4-hydroxyphenylacetic acid polymeric film [poly(4-HPA)] onto a nanocomposite prepared with reduced graphene oxide and gold nanoparticles (RGO-AuNP). RGO was synthesized in laboratory by the oxidation-exfoliation-chemical reduction method, starting from the graphite, and was incorporated into the surface of graphite electrodes by physical adsorption. AuNP were synthesized electrochemically onto electrode containing RGO forming a nanocomposite. The poly(4-HPA) was electropolymerized onto the nanocomposite, and on that the probe biomolecule Anti-T3 was immobilized by covalent bond. Glycine was used as blocking molecules prior to the contact with target T3. The detection measures were obtained by differential pulse voltametry and electrochemical impedance spectroscopy. Characterizations by infrared spectroscopy show the reduction of oxygens groups in RGO, resulting from the synthesis process, while atomic force microscopy and scanning electron microscopy images reveal the characteristic morphology of the more grouped sheets. The incorporation of RGO and the AuNP electrodeposition onto the surface of graphite electrodes show a significant increase in electrical conductivity and electron transfer, besides facilitating the electropolymerization process of poly(4-HPA). The combination of this nanocomposite with poly(4-HPA) leads to the formation of a larger amount of film, highlighting the presence of three redox pairs. This greater amount of film formed increases the probability of immobilization of biomolecules. The best results in Anti-T3 immobilization process by covalent bond and with target T3 interaction are obtained with 1 e 2 pg mL-1 concentration, respectively. The results obtained by electrochemical impedance spectroscopy corroborate with the other analysis, proving the increase in resistance at each stage of imunossensor development. The morphological characterization of the immunosensor shows significant changes in roughness values that are concomitant with the explanations of the results in electrochemical study. Dilution detections of Target T3 show that the proposed immunosensor has a detection limit less than 2 10- g mL- , it being possible to construct an analytical curve of T3 concentration in the order of 1.0 to 5.0 pg mL-1, increasing the prospect of application in real samples of patients, since it include the T3 concentration range present in the blood.