Diffusional Motion of a Particle Translocating through a Nanopore

The influence of diffusional motion on the capture and release of individual nanoparticles as they are driven through a conical-shaped glass nanopore membrane (GNM) by pressure-induced flow is reported. In these experiments, one to several hundred particles are driven through the orifice of the nanopore. Following the initial translocation, the pressure is reversed and the particles are driven through the GNM orifice in the reverse direction. The resistive-pulse technique is used to monitor the temporal sequence of particle capture and release translocations. The size of the particles (120–160 nm) and the direction of translocation can be determined from the pulse amplitude and shape. The stochastic influence of diffusion on particle trajectories has been investigated, including instantaneous transfer rate, release probability, and cumulative release success rate. We demonstrate that the sequence of particle translocations in the capture step (<i>a</i>, <i>b</i>, <i>c</i>... where the letters represent different particles) is largely preserved and can be read out by resistive-pulse signature during the release translocations (...<i>c</i>, <i>b</i>, <i>a</i>). The observed stochastic events are in good agreement with a convective diffusion model of particle trajectory within the confined geometry of the nanopore. The pressure-reversal technique opens new avenues for chemical analysis of particles using resistive-pulse methods

Effect of Surface Charge on the Resistive Pulse Waveshape during Particle Translocation through Glass Nanopores

This paper describes a fundamental study of the effect of electrostatic interactions on the resistive pulse waveshape associated with translocation of charged nanoparticles through a conical-shaped, charged glass nanopore. In contrast to single-peak resistive pulses normally associated with resistive-pulse methods, biphasic pulses, in which the normal current decrease is preceded by a current increase, were observed in the current–time recordings when a high negative potential (lower than −0.4 V) is applied between the pore interior and the external solution. The biphasic pulse is a consequence of the offsetting effects of an increased ion conductivity induced by the surface charge of the translocating particle and the current decrease due to the volume exclusion of electrolyte solution by the particle. Finite-element simulations based on the coupled Poisson–Nernst–Planck equations and a particle trajectory calculation successfully capture the evolution of the waveshape from a single resistive pulse to a biphasic response as the applied voltage is varied. The simulation results demonstrate that the surface charges of the nanopore and the particle are responsible for the voltage-dependent shape evolution. Additionally, the use of high ionic strength solution or high pressures to drive particle translocation was found to eliminate the biphasic response. The former is due to the screening of the electrical double layer, while the latter results from the solution flow preventing formation of an equilibrium double layer ion distribution within the nanopore, similar to the previously reported elimination of ion current rectification when solution flows through a nanopore

Tunable Negative Differential Electrolyte Resistance in a Conical Nanopore in Glass

Liquid-phase negative differential resistance (NDR) is observed in the <i>i–V</i> behavior of a conical nanopore (∼300 nm orifice radius) in a glass membrane that separates an external <i>low-conductivity</i> 5 mM KCl solution of dimethylsulfoxide (DMSO)/water (v/v 3:1) from an internal <i>high-conductivity</i> 5 mM KCl aqueous solution. NDR appears in the <i>i–V</i> curve of the negatively charged nanopore as the voltage-dependent electro-osmotic force opposes an externally applied pressure force, continuously moving the location of the interfacial zone between the two miscible solutions to a position just inside the nanopore orifice. An ∼80% decrease in the ionic current occurs over less that a ∼10 mV increase in applied voltage. The NDR turn-on voltage was found to be tunable over a ∼1 V window by adjusting the applied external pressure from 0 to 50 mmHg. Finite-element simulations based on solution of Navier–Stokes, Poisson, and convective Nernst–Planck equations for mixed solvent electrolytes within a negatively charged nanopore yield predictions of the NDR behavior that are in qualitative agreement with the experimental observations. Applications in chemical sensing of a tunable, solution-based electrical switch based on the NDR effect are discussed