Emergence of selectivity and rectification phenomena in voltage-gated nanopores from axial field-induced interfacial gradients.

Gate-modulated nanopores have emerged as a promising platform for achieving ion selectivity and ionic current rectification (ICR) with the advantage of active field-based control. However, the origin of these experimentally reported nanoscale phenomena, arising from electrostatic coupling between the prescribed radial pore surface potential and the axial transmembrane electric field, remains insufficiently understood. Here, we decompose the complex surface condition on the nanopore walls to the superposition of contributions from a fixed surface charge (FSC), a Stern layer-like, and fixed surface potential (FSP) conditions. Using coupled Poisson-Nernst-Planck-Stokes simulations supported by asymptotic analysis for the ionic current and electroosmotic flow, we show that a uniform surface potential inherently interacts with the axial driving field to generate a three-dimensional, axially nonuniform electric double layer (EDL). This field-induced EDL heterogeneity effectively mimics a linear axial variation in zeta potential, breaking translational symmetry within an otherwise uniform pore. As a result, the system exhibits coupled electrokinetic responses, including ion selectivity, ionic current rectification, and non-canonical electroosmotic flow, all governed by a single asymmetry parameter α derived from the EDL structure. Critical transitions occur at specific values of α. At α = 0, the EDL undergoes an axial antisymmetry transition that reverses ion selectivity and electroosmotic-flow direction while generating internal vortical structures. Meanwhile, ionic current rectification persists over a much broader range of α, and a peculiar negative electroosmotic-flow rectification emerges for negative α for |V0/VG| > 2. These findings establish axial symmetry breaking as the fundamental nanoscale mechanism for enhancing transport functionality in asymmetric nanopores, providing a unified mechanistic framework that extends beyond voltage-gated nanopores to conical, chemically patterned, and other asymmetrically engineered nanopore architectures.