Computational study of transport properties of graphene upon adsorption of an amino acid: importance of including -NH2 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 (-NH2) 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.