Ion Transport in pH-Regulated Double-Barreled Nanopores

Abstract

Single-molecule detection and characterization with nanopores is a powerful technique that does not require labeling. Multinanopore systems, especially double nanopores, have attracted wide attention and have been applied in many fields. However, theoretical studies of electrokinetic ion transport in nanopores mainly focus on single nanopores. In this paper, for the first time, a theoretical study of pH-regulated double-barreled nanopores is conducted using three-dimensional Poisson–Nernst–Planck equations and Navier–Stokes equations. Four ionic species and the surface chemistry on the walls of the nanopores are included. The results demonstrate that the properties of the bulk salt solution significantly affect nanopore conductivity and ion transport phenomena in nanopores. There are two ion-enriched zones and two ion-depleted zones in double-barreled nanopores. Due to the symmetry of the double-barreled nanopore structure and surface charge density, there is no ionic rectification effect in double-barreled nanopores. The ion selectivity is similar to that of conventional single pH-regulated nanopores.

Dynamic and Asymmetrical Ion Concentration Polarization in Dual Nanopipettes

“…To save the simulation time, a simplified 2D model was built with the commercial software COMSOL Multiphysics 5.4. The mass transport process in the solution can be described by the modified Nernst–Planck equation: , J i = prefix− D i ∇ c i − z i F R T D i ∇ c i ∇ normalØ where J i is the total flux; D i , c i , and z i are the diffusion coefficient, concentration, and valence of ionic species i , respectively; F is the Faraday constant; R is the gas constant; T is the temperature; and Ø is the solution potential. The Poisson equation is used to calculate the potential distribution: ∇ 2 normalØ = − F ε ε 0 false ∑ i z i c i where ε is the relative permittivity of water, and ε 0 is the vacuum permittivity.…”

“…40,41 The ion concentration polarization processes in the two channels at different solution pH values have also been elucidated by the simulation. 42 Though great efforts have been made to reveal the fundamental ion transport processes in dual nanopipettes, the dynamic and asymmetrical ion transport processes in the dual nanopipettes are still much less studied.…”

“…To save the simulation time, a simplified 2D model was built with the commercial software COMSOL Multiphysics 5.4. The mass transport process in the solution can be described by the modified Nernst−Planck equation: 41,42…”

“…The mass transport processes would thus be more complicated in the dual nanopipettes as two channels are involved in the mass transport processes. Different ICR phenomena have been observed and controlled in the dual nanopipettes by tailoring the surface charge polarity in the two channels and the separating glass walls. , The ion concentration polarization processes in the two channels at different solution pH values have also been elucidated by the simulation . Though great efforts have been made to reveal the fundamental ion transport processes in dual nanopipettes, the dynamic and asymmetrical ion transport processes in the dual nanopipettes are still much less studied.…”

Ion Transport in Multi-Nanochannels Regulated by pH and Ion Concentration

“…Thus, the nanochannels and reservoirs harbored four types of ions, namely, H + , OH − , K + , and Cl − , with C j and j = 1, 2, 3, and 4 being their volumetric molar concentrations, respectively. Electroneutrality gives C 1 = 10 −pH , C 2 = 10 −(14−pH) , C 3 = C KCl , and C 4 = C KCl + 10 −pH − 10 −(14−pH) for pH ≤ 7; C 3 = C KCl − 10 −pH + 10 −(14−pH) and C 4 = C KCl for pH > 7, 42,43 where C KCl represents the background salt concentration composed of potassium chloride. We adopted a fully coupled continuum-based model to thoroughly explore the intricacies of ion transport within these nanochannels.…”