Ion transport and selectivity in nanopores with spatially inhomogeneous fixed charge distributions

Abstract

Polymeric nanopores with fixed charges show ionic selectivity when immersed in aqueous electrolyte solutions. The understanding of the electrical interaction between these charges and the mobile ions confined in the inside nanopore solution is the key issue in the design of potential applications. The authors have theoretically described the effects that spatially inhomogeneous fixed charge distributions exert on the ionic transport and selectivity properties of the nanopore. A comprehensive set of one-dimensional distributions including the skin, core, cluster, and asymmetric cases are analyzed on the basis of the Nernst-Planck equations. Current-voltage curves, nanopore potentials, and transport numbers are calculated for the above distributions and compared with those obtained for a homogeneously charged nanopore with the same average fixed charge concentration. The authors have discussed if an appropriate design of the spatial fixed charge inhomogeneity can lead to an enhancement of the transport and selectivity with respect to the homogeneous nanopore case. Finally, they have compared the theoretical predictions with relevant experimental data.

The current-voltage relation of a pore and its asymptotic behavior in a Nernst-Planck model

“…In some lipid pores the I-V curve is linear from approximately −150 to +150 mV, and the I-V relation becomes non-linear when |V|>150 mV [19]. At intermediate pH values of the bathing solution, in polymeric-synthetic nanopores (double-conical pore) the I-V curve deviates from the linear behavior in a similar fashion with our model [4]. In a synthetic conical nanopore, the current-voltage curve shows a mild linear slope for "inverse current" and a steeper slope for "direct current", the milder slope for the "direct current" being less visible for the chosen voltage scale, but more visible for 20 mM KCl [20].…”

“…The effects of asymmetry are now used in nanofluidic diodes [3,4], for example, and in nanoslits [24]. The energy asymmetry can be obtained from the geometrical asymmetry of the pore, like in synthetic conical pores [25] or intentional misalignment in nanoslits [24], and from surface charges due to manufacturing processes [3,20,26].…”

“…The current-voltage relation of a pore is essential for studying ion channels [1,2], or for designing synthetic nanopores or nanodevices [3][4][5][6]. The current-voltage relation of a porous membrane is useful in understanding the way in which epithelia function, especially the skin's epidermal stratum corneum [7] or for describing and predicting electroporation [8,9].…”

Resistive-pulse and rectification sensing with glass and carbon nanopipettes

“…The combined effects of the applied voltage and excess surface charge thus lead to the high and low ion currents at the negative and positive bias, respectively. Besides the surface charge [60] and geometry [61], the ICR was shown to depend on other factors, including electrolyte concentration [49,62], pressure [63], applied voltage and scan rate [62,64]. Such dependences are potentially useful for designing rectification sensors.…”

The averaged potential gradient approach to model the rejection of electrolyte solutions using nanofiltration: Model development and assessment for highly concentrated feed solutions

“…(2) the fixed-charge density is considered to be homogeneous. Even though previous theoretical works have stressed the impact of inhomogeneous charge distributions on membrane rejection [46,[50][51][52][53], this approximation remain a reliable way to predict the behaviour of a wide range of commercial membranes [54].…”