Modeling of pH-Switchable Ion Transport and Selectivity in Nanopore Membranes with Fixed Charges

Ramı́rez, Patricio; Mafé, Salvador; Alcaraz, A.; Cervera, Javier

doi:10.1021/jp035778w

Cited by 70 publications

(58 citation statements)

References 45 publications

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“…͑16͒ yields X Ϸ 2 / Fa for m small, that is, the volume fixed charge concentration contained in differential conical slabs of radius a. 37,38 The boundary values for the average ionic concentrations and electric potential at the pore borders r = r L and r = r R are obtained assuming that the external and pore solution average concentrations are related through the Donnan equilibrium conditions,…”

Section: ͑12͒mentioning

confidence: 99%

Ionic conduction, rectification, and selectivity in single conical nanopores

Cervera

Schiedt²,

Neumann³

et al. 2006

The Journal of Chemical Physics

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399

539

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Modern track-etching methods allow the preparation of membranes containing a single charged conical nanopore that shows high ionic permselectivity due to the electrical interactions of the surface pore charges with the mobile ions in the aqueous solution. The nanopore has potential applications in electrically assisted single-particle detection, analysis, and separation of biomolecules. We present a detailed theoretical and experimental account of the effects of pore radii and electrolyte concentration on the current-voltage and current-concentration curves. The physical model used is based on the Nernst-Planck and Poisson equations. Since the validity of continuum models for the description of ion transport under different voltages and concentrations is recognized as one of the main issues in the modeling of future applications, special attention is paid to the fundamental understanding of the electrical interactions between the nanopore fixed charges and the mobile charges confined in the reduced volume of the inside solution.

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Section: ͑12͒mentioning

confidence: 99%

Ionic conduction, rectification, and selectivity in single conical nanopores

Cervera

Schiedt²,

Neumann³

et al. 2006

The Journal of Chemical Physics

Self Cite

399

539

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“…For the surface charge density, we have considered the values r = -0.1 and -0.5 e/nm 2 , which are equivalent to fixed charge concentrations X : -2r/FR p = 0.11 and 0.55 M. These values are typical of nanopores (Westermann-Clark and Christoforou 1986; Apel and Pretzsch 1986;Manzanares et al 1991;Ramírez et al 2003b;Chun et al 2006;Ku et al 2007). The external electrolyte concentrations have been assigned values between 0 and 0.8 M. The radii ratio R i /R p assumes values ranging from 0 (point ions) to 0.1 (R i = 0.3 nm).…”

Section: Theoretical Modelingmentioning

confidence: 99%

Incorporating ionic size in the transport equations for charged nanopores

Cervera

Ramı́rez

Manzanares

et al. 2009

Microfluid Nanofluid

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Nanopores with fixed charges show ionic selectivity because of the high surface potential and the small pore radius. In this limit, the size of the ions could no longer be ignored because they occupy a significant fraction of the pore and, in addition, they would reach unrealistic concentrations at the surface if treated as point charges. However, most models of selectivity assume point ions and ignore this fact. Although this approach shows the essential qualitative trends of the problem, it is not strictly valid for high surface potentials and low nanopore radii, which is just the case where a high ionic selectivity should be expected. We consider the effect of ion size on the electrical double layer within a charged cylindrical nanopore using an extended Poisson-Boltzmann equation, paying special attention to (non-equilibrium) transport properties such as the streaming potential, the counter-ion transport number, and the electrical conductance. The first two quantities are related to the nanopore selectivity while the third one characterizes the conductive properties. We discuss the nanopore characteristics in terms of the ratio between the electrolyte and fixed charge concentrations and the ratio between the ionic and nanopore radii showing the experimental range where the point ion model can still be useful. Even for relatively small inorganic ions at intermediate concentrations, ion size effects could be significant for a quantitative estimation of the nanopore selectivity in the case of high surface charge densities.

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“…The effect of the membrane bulk nonuniformity on ion transport characteristics has been studied in a number of papers [7][8][9][10][11][12][13][14]. It was shown that the membrane transport properties, such as the electrical conductivity, diffusion, hydraulic permeability, and permselectivity, including the competition between ions with the same sign of charge, are determined by the inner membrane morphology.…”

Section: Introductionmentioning

confidence: 99%