Circuit theory for electrical transport through nanopores: Effect of DNA base pair dipoles

We study the electrical transport through nanopores affected by the presence of DNA translocations. The current through the pore depends not only on the base pair inside the pore but also on what the neighbouring base pair outside of the pore is, because the neighbouring base pair possesses an electric dipole moment that exerts an electric field at the nanopore with a magnitude which is comparable to the externally applied electric field. This physical effect has not been included in previous studies, which focused on the blockage of the current by the bases inside the pore. There is much interest in extracting the base information from the current through the pore and to sequence the DNA. This extraction including our effect requires an analytical study of the phenomena so that the inverse problem is tractable. To study the electrical transport quantitatively and analytically, we formulate a rigorous analytical circuit theory for the interaction of a conducting medium with the electromagnetic field in the presence of a nanopore. We found that the base pair dipolar field only affects the total current when another base pair is in the pore and blockage occurs. It does not change the current otherwise. The effect of these dipoles is through a change of the diffusion induced by a change at the nanopore of the local charge carrier density and not by a change of the local conductivity. In addition to the effect of the dipoles, we clarify how the large capacitive response affects the current and when it will not do so.