Interference of ascorbic and uric acids on dopamine behavior at graphene composite surface: An electrochemical, spectroscopic and theoretical approach

Graphene materials are widely used in the area of dopamine (DA) detection, but, in spite of the extensive work and the good reported results, the development of commercial graphene-based sensors for DA detection is still challenging. Actually, a lot of studies related to dopamine detection are conducted only for the development of new graphene materials, but the processes and transformations occurred at graphene electrode surface are not considered. In this work, the capacity of a nanocomposite, based on graphene and gold, platinum nanoparticles, to adsorb dopamine and the changes occurred during the DA electrooxidation process were investigated by electrochemistry, Raman spectroscopy and DFT methods. These studies were realized in the absence and the presence of two interfering agents, ascorbic (AA) and uric (UA) acids. Different molecular structures have been found for the species adsorbed on the graphene surface, before and after the electrooxidation process. The DA current density increased in the presence of AA even if neither the diffusion process nor the homogeneous catalysis were involved. The DA detection in the presence of UA appears to be influenced by larger adducts formed at the graphene surface. The DQ presence on the graphene surface was revealed when the procedure involved an electrochemical treatment with DA free in solution, more than five DPVs measurements and higher levels of DA concentration. The Raman investigations of the graphene-based electrodes indicated that the shifts of D frequency from graphene can be easily correlated with the electronic properties of adducts that have been adsorbed to the graphene surface (red shift for a graphene - electron-rich system interaction and a blue shift for graphene – electron-deficient adduct interaction). These results should be taken into consideration in the DA detection procedures or to the stategies to minimise the electrochemical fouling of DA when the graphene composites are used for electrode preparation.