Electrophoresis of a Membrane-Coated Cylindrical Particle Positioned Eccentrically along the Axis of a Narrow Cylindrical Pore

Abstract

Although theoretical analyses on electrophoresis are ample in the literature, most of them focused on the one-or two-dimensional problems for a simpler treatment; available results for the three-dimensional case, which may be closer to reality, are extremely limited. The electrophoresis of a soft, finite cylindrical particle positioned eccentrically along the axis of a narrow cylindrical pore is modeled in this study. The type of particle considered is capable of mimicking a wide class of nonrigid entities such as biocolloids and particles covered by an artificial polymer layer in practice. The electrophoretic behaviors of the particle under various conditions are simulated. We show that if the membrane layer of a particle is charged, then its electrophoretic behavior depends largely on its aspect ratio, eccentricity, and relative size, the thickness of double layer, and the thickness of the membrane layer, which might not be the case if that layer is uncharged. In addition, the electrophoretic mobility of a particle in the former may not increase with increasing thickness of the membrane layer, which has not been reported previously. The results gathered provide the theoretical basis for both the design of an electrophoresis apparatus and the interpretation of experimental data.

Influence of membrane layer properties on the electrophoretic behavior of a soft particle

“…In this case, we assume that the surface of the core of a soft particle is maintained at a constant potential of ζ p =25.668 mV, and its membrane layer is uncharged ($n_{{\rm{fix}}0} = 0$ ). This type of particle is often adopted to simulate soft particles having an inorganic core 21, 29, 31, 32, 34–36, 40. Note that in the present case, the surface charge density of the core, σ p , is a function of κ a , ( c/a ), and ε fix .…”

“…In a series attempts to simulate the electrophoretic behavior of biocolloids, Ohshima 20–23 proposed a soft particle model in which a particle comprises a rigid core and a porous membrane layer. This model was used to describe the electrophoretic mobility of natural lattices 24, 25 and biological cells 26–28, to simulate a concentrated dispersion of particles 29, 30, and to model the boundary effect on the electrophoretic behavior of a particle 31–34. Adopting the original nonlinear Poisson–Boltzmann equation, Hill et al 35 examined the polarization effect of the electrophoresis of a single soft particle in an unbounded electrolyte solution.…”

“…This can be unrealistic because the membrane layer near the core region is expected to have a denser structure than that near the membrane–liquid interface. Another usually assumed condition is that the dielectric property of the membrane layer of a soft particle is the same as that of the bulk liquid phase 29–36, which can also be unrealistic. For instance, the relative dielectric constant decreases from ca.…”

Slowing down DNA translocation through a nanopore by lowering fluid temperature

“…Since the size of fluid reservoirs is usually much larger than that of the nanopore, the local electric field within the nanopore is significantly higher than that in the fluid reservoir, resulting in slow particle motion within the fluid reservoir and high translocation velocity inside the nanopore. One of the major challenges in the nanopore-based technique is that DNA nanoparticles translocate through the nanopore too fast to be accurately detected [5,6,[17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. Although one can reduce the voltage bias applied across the nanopore to reduce the electric field inside the nanopore and consequently slow down the DNA translocation, lower voltage bias will simultaneously reduce the capture rate of the nanopore and the magnitude of the current change, leading to lower throughput and read-out accuracy.…”

“…Therefore, a relatively high voltage bias is typically applied across the nanopore in the nanoporebased DNA sequencing applications. To now, several methods have been proposed to slow down the DNA translocation through the nanopore to achieve higher read-out accuracy [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. They include increasing the solvent viscosity to increase the viscous drag force on the particle, lowering the fluid temperature to increase the fluid viscosity, adjusting salt concentration and/or salt type to modify the charge property of the nanopore by chemical functionalization of the nanopore or by an ionic field effect transistor, imposing a salt concentration gradient, utilizing optical tweezers, and conducting nanopores [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36].…”