{\it {Ab initio}} Calculations of Electronic Fingerprints of DNA bases on Graphene

We have carried out first principles DFT calculations of the electronic local density of states (LDOS) of DNA nucleotide bases (A,C,G,T) adsorbed on graphene using LDA with ultra-soft pseudo-potentials. We have also calculated the longitudinal transmission currents $T(E)$ through graphene nano-pores as an individual DNA base passes through it, using a non-equilibrium Green's function (NEGF) formalism. We observe several dominant base-dependent features in the LDOS and $T(E)$ in an energy range within a few eV of the Fermi level. These features can serve as electronic fingerprints for the identification of individual bases from $dI/dV$ measurements in scanning tunneling spectroscopy (STS) and nano-pore experiments. Thus these electronic signatures can provide an alternative approach to DNA sequencing.