Role of access resistance in governing conductance in nanopore translocation experiments*

Nanopores are valuable for a variety of applications such as biomolecule detection, sequencing, and fingerprinting applications, among others. Electrical signatures from nanopores provide information about the morphological characteristics of translocating biomolecules. Therefore, careful interpretation of these signatures and accurately modeling the accompanying conductance blockades is critical for practical applications and remains an open question in the field.

The key resistances in the system include access (or convergence) resistance and channel resistance. In addition to their dependence on pore geometry and salt concentration, both quantities are perturbed due to the presence of an analyte inside the pore. 

We numerically solve fully coupled Poisson-Nernst-Planck and Navier Stokes system of equations and predict conductance blockades for a range of geometrical parameters. We find that the state-of-the-art approaches are inaccurate for experimentally relevant conditions – thin pores and size of the analyte comparable to pore diameter. Our results underscore that the usage of the existing models is limited.

We combine computational and analytical modeling and propose a new model for access resistance accounting for the presence of an analyte inside the capture region. The proposed model is validated using computer simulations and experimental data. These results constitute an important step towards accurate, physics-based modeling of conductance in nanopores and ion channels.