Theoretical study of electric current in DNA base molecules trapped between nanogap electrodes

Recent advances in bionanotechnology have resulted in the development of single-molecule detection techniques. In particular, high-resolution electric current measurement promises major breakthroughs in the frontier of deoxyribonucleic acid (DNA) sequencing. It is expected to be possible to probe single base molecules using nanogap electrodes by introducing a DNA fragment into a nanopore in a microfluidic device. In the present study, we develop a theoretical model for the behavior of electrons that flow across a nanogap and interact with a DNA base. The electronic motion in this model is described by electrodynamics. Electrons pass through electrostatic potentials computed by ab initio methods. Their trajectories are strongly affected by the trapped molecule. In this process, momentum transport and impulses produced by applied electric fields are balanced in non-equilibrium steady states. We then obtain current–voltage characteristics with respect to differences between DNA bases. We find that interactions between almost free electrons and a molecule, which acts as a scattering center, generates a constant current. This permits the conductances of DNA bases to be evaluated. They are found to be in reasonable agreement with experimental results. In particular, electrons injected perpendicular to molecular surfaces are predicted to have a higher output than those injected parallel to the surfaces.