Computational study of transport properties of graphene upon adsorption of an amino acid: importance of including – NH ₂ and –COOH groups

The effects of histidine and its imidazole ring adsorption on the electronic transport properties of graphene were investigated by first-principles calculations within a combination of density functional theory and non-equilibrium Greens functions. Firstly, we report adsorption energies, adsorption distances, and equilibrium geometrical configurations with no bias voltage applied. Secondly, we model a device for the transport properties study: a central scattering region consisting of a finite graphene sheet with the adsorbed molecule sandwiched between semi-infinite source (left) and drain (right) graphene electrode regions. The electronic density, electrical current, and electronic transmission were calculated as a function of an applied bias voltage. Studying the adsorption of the two systems, i.e., the histidine and its imidazole ring, allowed us to evaluate the importance of including the carboxyl (–COOH) and amine (–NH ₂) groups. We found that the histidine and the imidazole ring affects differently the electronic transport through the graphene sheet, posing the possibility of graphene-based sensors with an interesting sensibility and specificity.