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In the field of DNA nanotechnology, it is commonly believed that charge transport occurs through the pi-stacked bases of double-stranded DNA. However, recent experimental findings by Zhuravel et al. [Nat. Nanotechnol. 15, 836 (2020)] suggest that electronic transport occurs through the backbone channels rather than pi-pi interactions of the nitrogen bases. This experimental insight warrants further investigation. To address this, we analyze the charge transport properties of three distinct double-stranded DNA sequences (periodic GC, periodic AT, and random ATGC sequences) within a tight-binding framework where the backbones serve as the primary conduction channels. Using the Green's function method, we examine the single-particle density of states and localization properties of DNA in the presence of discontinuities ("nicks") along the backbone channels. Additionally, we explore the impact of these nicks on the current-voltage response using the Landauer-Büttiker formalism for a two-terminal setup with the source electrode connected to one backbone strand and the drain to the other. Our findings reveal that the periodic DNA sequence of GC bases exhibits metallic behavior, whereas the periodic AT sequence and the random ATGC sequence are insulating. Notably, the presence of nicks has intriguing effects on the transport properties of the periodic GC sequence: a single nick on the upper backbone has no impact on electronic transport, but adding a second nick on the lower backbone completely suppresses the current flow. This behavior remains consistent across variations in nick positions and electrode configurations. Analysis of the position-dependent probability distribution of the zero-energy electronic wave function suggests that the insulation mechanism arises from quantum interference of the electronic wave function from the two nicks. Identical conclusions are obtained for the periodic AT and random ATGC sequences in their conducting regimes (obtained above a threshold voltage). In this way, our study opens the door towards further experimental and theoretical investigations in DNA nanotechnology. |