Backbone-mediated electrical transport in double-stranded DNA

In the field of DNA nanotechnology, it is common wisdom that charge transport occurs through the π stacked bases of double-stranded DNA. However, recent experimental findings by Zhuravel et al. [Nat. Nanotechnol. 15, 836 (2020)1748-338710.1038/s41565-020-0741-2] suggest that electronic transport happens through the backbone channels instead of π-π interaction of the nitrogen bases. This experimental insight calls for a detailed investigation. In keeping with this, we examine charge transport properties of three characteristic double-stranded DNA sequences (periodic GC, periodic AT, and random ATGC sequences) within a tight-binding framework where backbones form the main conduction channels. Using techniques based on the Green's function method, we inspect the single-particle density of states and localization properties of DNA in the presence of discontinuities ("nicks") along the backbone channels. We also investigate the effect of these nicks on current-voltage response using the Landauer-Büttiker formalism for a two-terminal geometry where the source electrode is attached to one backbone strand and the drain to the other. We observe that the periodic DNA sequence of GC bases is metallic in nature, while the periodic AT sequence and the random ATGC sequence are insulating. Further, the effects of nicks on the transport properties of the periodic GC sequence is interesting: while a single nick on the upper backbone does not affect electronic transport, the addition of a second nick on the lower backbone causes the current to vanish altogether. This is found to be robust against changes in the positions of the nicks, as well as the alternation of the source and drain electrodes. Analysis of the position dependence of the probability distribution of the zero-energy electronic wave function leads us to conclude that the insulation mechanism arises from a quantum interference of the electronic wave function from the two nicks.