Probing Access Resistance of Solid‐State Nanopores with a Scanning‐Probe Microscope Tip

Abstract

An apparatus that integrates solid-state nanopore ionic current measurement with a Scanning Probe Microscope has been developed. When a micrometer-scale scanning probe tip is near a voltage biased nanometer-scale pore (10–100 nm), the tip partially blocks the flow of ions to the pore and increases the pore access resistance. The apparatus records the current blockage caused by the probe tip and the location of the tip simultaneously. By measuring the current blockage map near a nanopore as a function of the tip position in 3D space in salt solution, we estimate the relative pore resistance increase due to the tip, ΔR/R0, as a function of the tip location, nanopore geometry, and salt concentration. The amplitude of ΔR/R0 also depends on the ratio of the pore length to its radius as Ohm’s law predicts. When the tip is very close to the pore surface, ~10 nm, our experiments show that ΔR/R0 depends on salt concentration as predicted by the Poisson and Nernst-Planck equations. Furthermore, our measurements show that ΔR/R0 goes to zero when the tip is about five times the pore diameter away from the center of the pore entrance. The results in this work not only demonstrate a way to probe the access resistance of nanopores experimentally, they also provide a way to locate the nanopore in salt solution, and open the door to future nanopore experiments for detecting single biomolecules attached to a probe tip.

Effects of access resistance on the resistive-pulse caused by translocating of a nanoparticle through a nanopore

“…Early studies [23][24][25][26][27] on AR were mainly about the nanopores embedded in biological membranes, where the AR contributes 10-30% to the total resistance. In the recent years, the AR of solid-state nanopores [28][29][30][31][32] has also been highly concerned. Compared with biological nanopores, the articial nanopores drilled in solid membranes provide the ability to fabricate a wide range size of the nanopore with subnanometre precision.…”

Characterization of Protein Unfolding with Solid-state Nanopores

“…If we idealize a nanopore as a cylinder with diameter D p and length H eff , assuming a protein molecule occupies a volume Λ(t) in the pore at time t (the instantaneous excluded volume), and further we assume that a translocating protein molecule in a nanopore driven by an applied voltage Ψ obeys Ohm’s law, the relationship between ΔI b (t) and Λ(t) can be written as [31–34]: $$\mathrm{normal\Delta }{I}_{b}false(tfalse)=-I_0\frac{\mathrm{normal\Lambda }false(tfalse)}{H_{\mathit{\text{eff}}}{A}_p}false[1+ffalse(d_m/D_p,l_m/H_{\mathit{\text{eff}}}false)false]\approx -I_0\frac{\mathrm{normal\Lambda }false(tfalse)}{V_p}$$ Where I o =Ψ/ R 0 is the open pore current, R 0 = H eff σ/ A p is the pore resistance, σ is the solution conductivity, H eff is the effective thickness of the pore taking into account the access resistance region on both sides of the nanopore [35–37], A p is the area of the pore with an average diameter D p , V p = H eff A p the volume of the pore, and d m and l m are the diameter and length of the protein molecule. f (d m /D p , l m /H eff ) is a correction factor for the relative size and shape of the pore and the protein molecule and is often ignored for simplicity.…”

Dielectrophoretic stretching of DNA tethered to a fiber tip

“…The combination of DEP DNA stretching and SPM technique provide a useful tool to manipulate and control DNA molecules for studying DNA’s properties and functions. As a result, Our group has already developed a SPM working with a solid-state nanopore system in order to control DNA translocation speed through a nanopore by immobilizing DNA on a SPM tip [3, 40]. …”