Simultaneous scanning ion conductance and atomic force microscopy with a nanopore: Effect of the aperture edge on the ion current images

Abstract

Scanning ion conductance microscopy (SICM) is a technique for high-resolution non-contact imaging, particularly powerful for live cell studies. Despite debates on its lateral resolution, consensus is that a probe presenting a tip with small opening aperture, large opening angle, and large outer-to-inner radius ratio will offer a SICM current signal more sensitive to tip-sample separation, ultimately impacting the image resolution. We report here the design of such a probe, integrating a nano-opening (<20 nm opening diameter) with increased outer-to-inner radius ratio and a wide opening angle through microfabrication and ion milling. The probe consists of a microfluidic atomic force microscopy (AFM) cantilever offered by the Fluid Force Microscope (FluidFM) technology, able to act as an SICM and AFM probe. Such a combination allows investigating the implications of the new probe geometry on the SICM imaging process by simultaneously recording currents and forces. We demonstrate through experiments on well-defined samples as well as corresponding simulations that by integrating a nanopore onto the FluidFM, nanoscale features could be successfully imaged, but the increased sensitivity of the probe current to sample distance comes with higher sensitivity to an inherent SICM wall artefact.

Localized detection of ions and biomolecules with a force-controlled scanning nanopore microscope

“…Moreover, the wide opening angle of the fabricated pores provides higher ionic sensitivity compared to the conical glass pores. 21,22 The nanopore AFM enables nano-confinement of biomolecules between the apex and the underlying surface. Pre-confinement of biomolecules results in slower translocation speeds through the nanopore, which in general provides longer times for the sequence-based read-out.…”

Multiscale Additive Manufacturing of Metal Microstructures

“…[25,26] In the latter case, the apertures were milled by focused ion beam (FIB) to form square-shaped openings with sides of 100 nm, 1, and 2 μm (Figure 2c-e, see Experimental Section). The choice of the smallest aperture dimension of 100 nm was conditioned to avoid potential complications in filling the probes with electrolyte, [27] whereas 2 μm was the maximum size possible due to the limit set by the presence of the apex of the inner pyramid (discernable in Figure 2e).…”

Effect of Substrate Permeability on Scanning Ion Conductance Microscopy: Uncertainty in Tip–Substrate Separation and Determination of Ionic Conductivity

“…Simulation has generally been an underutilized tool for SICM measurements with early analytic and semianalytical models that described the system in terms of resistors in series. , More recently numerical simulations, specifically the finite element method (FEM) have significantly improved the understanding of the current response with respect to the probe dimensions and surface features with quantitative agreement with experimental data. − The recent interest in numerical simulation has been spurred by the emergence of new implementations of SICM allowing for topography mapping as well as surface charge mapping, − electrochemical flux quantification − or both simultaneously . With new scanning methods and potentially obtainable information comes an expanded material scope, in which lies, for example, industrially relevant electrode materials such as energy storage materials − where an active material is embedded in a conductive particle and polymer matrix to form a heterogeneous, porous structure.…”