The Effect of Axial Concentration Gradient on Electrophoretic Motion of a Charged Spherical Particle in a Nanopore

Abstract

The electrophoretic motion of a charged spherical nanoparticle along the axis of a nanopore connecting two fluid reservoirs, subjected to an axial electric field and electrolyte concentration gradient, has been investigated using a continuum model. The model consists of the Poisson and Nernst-Planck equations for the electric potential and ionic concentrations and the Stokes equations for the hydrodynamic field with zero gravity. In addition to the electrophoresis generated by the externally imposed electric field, the particle also experiences diffusiophoresis arising from the externally imposed concentration gradient. The effects of the diffusiophoresis on the axial electrophoretic motion are examined with changes in the ratio of the particle size to the thickness of the electric double layer (EDL), and the imposed concentration gradient. Since the EDL thickness, the particle size, and the nanopore size are of the same order of magnitude, the diffusiophoresis is dominated by the induced electrophoresis driven by the generated electric field arising from the doublelayer polarization (DLP). For a relatively small κa p , the ratio of the particle size to the EDL thickness, the diffusiophoresis is dominated by the induced electrophoresis from the type II DLP, which propels the particle toward regions with lower salt concentration. Depending on the magnitude and direction of the externally imposed concentration gradient, the electrophoretic motion can be accelerated, decelerated, and even reversed by the diffusiophoresis.

Diffusiophoresis of an Elongated Cylindrical Nanoparticle along the Axis of a Nanopore

“…[21, 22, 25-31, 37, 38, 40, 42] Experiments show that DNAs are often elongated or stretched during the translocation through a nanopore. [54] Motivated by the use of the diffusiophoresis to regulate DNA translocation through a nanopore for the nanopore-based DNA sequencing technology, we extend our previous analysis on diffusiophoresis of a spherical nanoparticle [44][45][46] to that of an elongated cylindrical nanoparticle along the axis of a nanopore driven by the induced electrophoresis and chemiphoresis under various conditions. The results presented are very useful in controlling the electrophoretic translocation of DNA molecules by diffusiophoresis in a nanopore-based DNA sequencing technique.…”

“…[35,41,47] The possible control of the electrophoretic motion of a spherical nanoparticle in a nanopore by the diffusiophoretic control has been theoretically demonstrated. [45,46] Recently, the regulation of DNA nanoparticle electrophoretic translocation through a nanopore by the induced diffusiophoresis has also been experimentally demonstrated, [49,50] and seems especially attractive in a nanopore-based DNA sequencing method, which is called the third-generation DNA sequencing, with cost sufficiently low to revolutionize genomic medicine. [51][52][53] However, compared to the extensively studied electrophoresis for micro/nanofluidic applications, the existing study on diffusiophoresis is relatively limited, and is subjected to several restrictions, such as thin EDL, low zeta potential or surface charge on the particle, and only marginally non-uniform solute concentration.…”

Diffusiophoretic mobility of charge‐regulating porous particles

“…This migration is known as diffusiophoresis [1][2][3][4][5][6] and provides a mechanism in various practical applications such as particle characterization, transport, manipulation, separation, and deposition in microfluidic and other devices [7][8][9][10]; DNA translocation and sequencing [11][12][13]; pattern formation [14,15]; and autonomous motions of micro/nano-motors [16][17][18]. For a charged particle in an ionic fluid, the particle-ion interaction is in the range of the reciprocal of the Debye screening parameter .…”

Electrophoretic motion of a nanorod along the axis of a nanopore under a salt gradient

“…Diffusiophoresis has also been analyzed for additionally controlling the electrophoretic motion of a spherical nanoparticle in a nanopore [50][51][52]. Regulation of DNA nanoparticle electrophoresis through a nanopore by the diffusiophoresis has been experimentally demonstrated [56,57].…”

“…More rigorous studies on the diffusiophoresis are performed by the authors for a spherical nanoparticle [50][51][52]. In order to mimic stretched DNAs translocating in a nanopore [61], our theoretical study was extended to an elongated cylindrical nanoparticle [55].…”