Theoretical insight on dopamine, ascorbic acid and uric acid adsorption on graphene as material for biosensors

In the present work, the interaction of dopamine (DA), ascorbic acid (AA) and uric acid (UA) molecules with graphene, with and without divacancies, has been theoretically studied within the framework of Density Functional Theory (DFT), in particular, paying attention on those surface properties relevant for field effect transistor (FET) and electrochemical biosensor applications. Several adsorption modes for these molecules were examined, and the main sources of adsorbate-substrate bonding were considered. The electric dipole moment for these molecules, when adsorbed, suffers in some cases large modifications due to conformational changes. The perpendicular component of dipole moment has a main molecular contribution molecule and another from the adsorbate-substrate polarization. The proposed reaction models of DA, AA and UA oxidations, show a good agreement with the oxidation potential ordering obtained in electrochemical experiments, i.e., UA > DA > AA. A spreading of reaction energies is observed due to the heterogeneity in adsorption modes.