Azathioprine Electrochemical Adsorption onto the Reduced Graphene Oxide Sheets in Absence and in the Presence of Polyaniline

The azathioprine (AZA) electrochemical adsorption onto the screen-printed carbon electrodes (SPCE) modified with the reduced graphene oxide (RGO) sheets in the absence and in the presence of polyaniline–emeraldine salt (PANI-ES) is reported in this work. Using cyclic voltammetry (CV), in the case of the SPCE modified with the RGO sheets non-functionalized and functionalized with PANI-ES, respectively, an irreversible process at the electrode/electrolyte interface is highlighted to take place. In the case of the SPCE modified with the non-functionalized RGO sheets (SPCERGO), the oxidation-reduction processes induce an up-shift of the AZA Raman lines from 856 and 1011 cm^-1 to 863 and 1020 cm^-1, respectively. These variations indicate an AZA adsorption onto the surface of the SPCE modified with the RGO sheets that takes place throught the imidazole and pyrimidine cycles of mercaptopurine, when the generation of the π–π ^* bonds between the mercaptopurine structure and hexagonal carbon cycles of RGO occurs. The electrochemical functionalization of the RGO sheets with PANI-ES is proved by the appearance of the Raman lines at 1165, 1332-1371, 1496 and 1585 and 1616 cm^-1. The oxidation-reduction processes induced at the interface of the SPCE modified with PANI-ES functionalized RGO sheets and the electrolyte consisting into a phosphate buffer (PB) and AZA lead to the generation of new positive charges onto the PANI macromolecular chain and the adsorption of the drug on the working electrode surface that takes place via the π–π ^* bonds established between the benzene/quinoide rings of PANI and the imidazole/ purine cycles of AZA. These results indicate that the SPCE modified with the PANI-ES functionalized RGO sheets shows potential applications in the field of sensors for AZA detection.