On Induced Surface Charge in Solid-State Nanopores

Abstract

Solid-state nanopores constitute a versatile platform for study of ion transport in nanoconfinement. The electrical double layer (EDL) plays a vital role in such nanoconfinements, but effects of induced surface charge on the EDL in the presence of an external transmembrane electric field are yet to be characterized. Here, the formation of induced charge on the nanopore sidewall surface and its effects, via modulation of the EDL and electroosmotic flow, on the ionic current are elucidated using a novel experimental setup with solid-state truncated-pyramidal nanopores. This study consists of three complementary approaches, i.e., an analytical model for induced surface charge, numerical simulation of induced surface charge, electroosmotic flow, and ionic current, and experimental validation with respect to the ionic current. The induced surface charge is generated by polarization in the dielectric membrane as a response to the applied electric field. This charge generation results in a nonuniform density of surface charge along the nanopore sidewall. It further causes ions in the electrolyte to redistribute, leading to a massive accumulation of single-polarity ions in the EDL and their counterions near the smaller opening of the nanopore. It also alters electrohydrodynamic properties in the nanopore, giving rise to the formation of electroosmotic vortexes in the vicinity of the smaller opening of the nanopore. Finally, the pattern of the electroosmotic flow can significantly influence the transport properties of the nanopore.

Nonlinear ion transport mediated by induced charge in ultrathin nanoporous membranes

“…Mao et al noted the IC effect in their continuum simulations of nanochannels in a thin silica membrane, but focused primarily on the fluid flow field rather than the I-V characteristics [31]. Further, the role of induced charges has been investigated in terms of membrane stability [32,33] and for conduction through conical nanopores [34]. Based on these previous studies, the IC effect appears especially relevant for membranes in the atomically thin limit.…”

Nanopore design for exceptional rectification of DNA translocation

“…The slight non-linear I-V characteristics result from the asymmetric pore geometry and the inhomogeneous surface charge distribution. The latter is mainly generated by the ISC effect 31 , especially near the tip of the smallest restriction of the BNP.…”

“…This invariance in position and ow direction of the vortexes after reversing the polarity of external bias is of signi cant implications for DNA translocation shown below. The root cause for the intriguing vortex formation is the surface charge imparity primarily due to the effect of ISC 31 near the smallest restriction where the membrane remains ultrathin for an extended stretch (Fig. S1b, S2 in Supporting Information).…”

Electroosmosis in nanopores: Computational methods and technological applications

“…The tangential component of the electric field at the wall, E t , moves the accumulated charges. h) Continuum simulation results for a negatively charged truncated-conical nanopore [30], showing the distribution of the net charge concentration and corresponding electroosmotic velocity field at negative bias ∆V = −5 V. i) Induced charge selectivity and EOF in an uncharged cylindrical nanopore [31], exploiting symmetry breaking due to a lateral cavity surrounding the nanopore. The simultaneous inversion of ionic selectivity and electric field direction causes a unidirectional parabolic EOF.…”