Scanning ion-conductance microscopy

The scanning ion-conductance microscope (SICM) consists of an electrically charged glass micro- or nanopipette probe filled with electrolyte lowered toward the surface of the sample (which is non-conducting for ions) in an oppositely charged bath of electrolyte. As the tip of the micropipette approaches the sample, the ion conductance and therefore current decreases since the gap through which ions can flow, is reduced in size. Variations in the ion current are measured by an amplifier, and are used as a feedback signal by a scanner control unit to keep the distance between pipette tip and sample constant by applying corresponding voltages to the Z-piezo drive during the scanning procedure. Therefore, the path of the tip follows the contours of the surface.