Wetting of nanopores probed with pressure

Abstract

Nanopores are both a tool to study single-molecule biophysics and nanoscale ion transport, but also a promising material for desalination or osmotic power generation. Understanding the physics underlying ion transport through nano-sized pores allows better design of porous membrane materials. Material surfaces can present hydrophobicity, a property which can make them prone to formation of surface nanobubbles. Nanobubbles can influence the electrical transport properties of such devices. We demonstrate an approach which uses hydraulic pressure to probe the electrical transport properties of solid state nanopores. We demonstrate how pressure can be used to wet pores, and how it allows control over bubbles in the nanometer scale range normally unachievable using only an electrical driving force. Molybdenum disulfide is then used as a typical example of a 2D material on which we demonstrate wetting and bubble induced nonlinear and linear conductance in the regimes typically used with these experiments. We show that by using pressure one can identify and evade wetting artifacts due to nanobubbles.

Pressure Induced Enlargement and Ionic Current Rectification in Symmetric Nanopores

“…To study how hydrostatic pressure and potential differences influence the ion transport through a solid state nanopore we use a sealed, pressure-tight chamber (See Materials and Methods and figure 1a) as described previously. 15 After a sample consisting of a membrane with an 80 nm diameter nanopore is mounted into the chamber, the system is wetted with a degassed 1 M KCL buffered solution under 7 bar compression pressure. Pres- sure P is applied on the sample membrane using a microfluidics pressure controller.…”

“…Taking into account that the non-linearity in conductance is almost negligible (figure 1b), we perform a Taylor expansion of the conductance G(V, P ) ≈ G 1 (P ) + G 2 (P )V , with G 1 and G 2 corresponding to the linear and first nonlinear contribution. 15 The conductance term G 1 has contributions from the pore interior, and the access region resistance and obeys…”

“…All AC measurements are performed using a sinusoidal voltage at a frequency of f = 1 Hz, where the resistance matches the DC measured value and no signal leakage through parasitic chip capacitance is present. 15 We use a phase sensitive amplifier, which can independently measure both G 1 and G 2 by averaging out any components of the measured current which are not at the base measurement frequency f or one of its multiples. Thus the current measured with the AC voltage does not have the streaming contribution included, and we obtain the total current which has two independently measured components…”

“…9 The combination of hydrostatic pressure gradients with nanopores has so far been mostly used to study analyte translocations, [10][11][12][13] the surface charge of the pore, 14 or as a tool to control wetting. 15 . It has been shown that pressure can strongly influence the ion transport properties of a nanopore or nanochannel depending on the system's resistance to hydraulic fluid flow, and modulate ion transport.…”