Caracterização estrutural do poli(ácido 4-hidroxifenilacético) eletropolimerizado sobre eletrodo de grafite e sua aplicação no desenvolvimento de imunossensor amperométrico para diagnóstico de leishmaniose visceral

Abstract

In this work was developed an electrochemical immunosensor that can detect label free specific antibody for visceral leishmaniasis using graphite electrode modified with poly(4-HPA) as a platform and DPV as electrochemical technique support. Therefore, investigations of main structural characteristics, thermal and electrochemical poly(4-HPA), obtained by electropolymerization of acid 4-HPA, were conducted using the following techniques: FTIR, UV-vis and Fluorescence. The FTIR spectra showed that the functional groups present in the monomer are preserved and that new groups are formed after electropolymerization, and the obtained polymer is 1,2,4,5-tetra-substituted, with strong evidences that these two new substituents are diphenyl ethers and ring-ring bonds, which justifies the increase in the extension of conjugation and the presence of new chromophore groups observed in UV-vis and Fluorescence studies. Thus, it was possible to discuss about the structure of poly(4-HPA), as well as propose the possible reaction mechanisms involved in its formation. These studies were of great importance in the search for a better understanding and discussion of the results. The thermal stability of the polymer, evaluated by TGA shows that the poly(4-HPA) presents a complex and heterogeneous structure and do not exhibits good thermal stability after 100 ° C. It was also investigated the growth of polymer in function of the number of potential scans. Through of this investigation it was possible obtained a profile for the increased electrochemical response of this material in relation to the time of electropolymerization, and such profile showed that the number of potential scans used in electrosynthesis is a good parameter to be used at the studies of this material. For the immunosensor development, the immobilization of the rK39 antigen, specific for visceral leishmaniasis, onto EG/poly(4-HPA) was confirmed through electrochemical studies. A electrochemical detection of IgG+ was conducted using CV and DPV techniques, using Coomassie Brilliant Blue G-250 and ruthenium hexamine II chloride as possible indicators of the formation of Antigen-Antibody complex. The Coomassie was efficient to indicate the surface modification of EG/poly(4-HPA) with rK39, however, did not show satisfactory sensitivity for IgG+, as well as selectivity for the non-complementary target (IgG-, negative control). However, the ruthenium hexamine II chloride, showed high efficiency to indicate the surface modification of EG/poly (4-HFA) with rK39 and good sensitivity for IgG+ and selectivity towards IgG-; enabling the development of the electrochemical immunosensor proposed in this work.