Scanning ion conductance microscopy with distance-modulated shear force control

A scanning ion conductance microscope (SICM) is based on a tapered nanopipette as a nanoscale conductance probe that is scanned over a sample submerged in an electrolyte solution. In conventional SICM scanning the ion current through the pipette aperture is at the nano- and picoampere level and is influenced by both sample topography and local conductance. Here we present an SICM with integrated shear-force distance control that allows measuring the ion current independently of sample topography. The nanopipette is hereby transversally vibrated and the shear forces that arise are detected optically with the help of two periscopes that are partially submerged in the electrolyte. We also present a new imaging mode designed to facilitate shear-force imaging of soft samples. This mode is based on a periodic modulation of the pipette–sample distance combined with triggered sampling, reducing the probability for sample and pipette damage and increasing the image quality. We apply this imaging mode to polycarbonate membranes and mammalian cells.