Image formation, resolution, and height measurement in scanning ion conductance microscopy

Abstract

Scanning ion conductance microscopy ͑SICM͒ is an emerging tool for the noncontact investigation of biological samples such as live cells. It uses an ion current through the opening of a tapered nanopipette filled with an electrolyte for topography measurements. Despite its successful application to numerous systems no systematic investigation of the image formation process has yet been performed. Here, we use finite element modeling to investigate how the scanning ion conductance microscope images small particles on a planar surface, providing a fundamental characterization of the imaging process. We find that a small particle appears with a height that is only a fraction of its actual height. This has significant consequences for the quantitative interpretation of SICM images. Furthermore, small and low particles are imaged as rings in certain cases. This can cause small, closely spaced particles to appear with a lateral orientation that is rotated by 90°. Considering both real space and spatial frequency space we find that a reasonable and useful definition of lateral resolution of SICM is the smallest distance at which two small particles can clearly be resolved from each other in an image. We find that this resolution is approximately equal to three times the inner radius of the pipette tip opening.

Scanning ion conductance microscopy for imaging biological samples in liquid: A comparative study with atomic force microscopy and scanning electron microscopy

“…We showed that the lateral resolution of the ARS/hopping SICM mode is about 50 nm, which is comparable to the finding by previous investigators (Novak et al, 2009;Happel and Dietzel, 2009). However, the actual resolution of SICM imaging is still a matter of debate (Rheinlaender and Schaffer, 2009). Theoretical studies of SICM will be required to consider the resolution in relation to the pipette radius and other parameters, although there are a few papers already in this field (Edwards et al, 2009).…”

Size and mobility of lipid domains tuned by geometrical constraints

“…3 A and B, Lower) further show that the membrane is predominately flat in the center of the pore. Of note is that no detailed information about the precise membrane curvature at the pore rims can be extracted, due the finite lateral resolution (∼100 nm to 200 nm, depending on the size of the aperture) of the SICM method (38,39).…”

Characterization of Nanopipettes

“…Method 1 assumes that the ratio between the outer and inner diameter of a nanopipette remains constant to that at the nanopipette opening, 13,41,52 and, as such, the inner nanopipette angle can be calculated by using the relationship:…”