An Accurate Model for the Ion Current-Distance Behavior in Scanning Ion Conductance Microscopy Allows for Calibration of Pipet Tip Geometry and Tip-Sample Distance.

The scanning ion conductance microscope (SICM) is an emerging tool for noncontact topography imaging and multiphysical investigation of soft samples in aqueous environments such as living cells. Despite the increasing popularity of SICM, several aspects of the imaging process are still unknown; for example, there is still no accurate description of the behavior of the ion current for a varying tip-sample distance. To predict this ion current-distance behavior, we provide a new numerical model based on finite element modeling. The model allows, for the first time, accurately determining the tip-sample distance during an SICM experiment. Furthermore, we present a nondestructive method for calibrating the pipet tip geometry by fitting the numerical model to the experimental ion current-distance data and verify this method using pipets with opening radii between 30 and 300 nm.