Scanning ion-conductance microscopy

[1] SICM allows for the determination of the surface topography of micrometer and even nanometer-range[2] structures in aqueous media conducting electrolytes.

It is important to note that the tip is stopped before contacting the sample, thus it does not bend nor damage the surface observed, which is one of the major advantages of SICM.

Rt is the resistance of the current flowing through the tip Rb and Rm depend on the electrolyte conductivity, and the position and shape of the Ag/AgCl electrodes.

Usual approximations are: 1) the voltage drop at the surfaces of the Ag/AgCl electrodes is neglected, it is assumed that it is negligible compared to the voltage drop at the tip, and constant, 2) the fact that the bulk resistance is a function of d is neglected since it depends on the distance between the tip and the electrode in the bulk.

SICM is used in an electrolyte-containing solution, so can be used in physiological media and image living cells and tissues, and monitor biological processes while they are taking place.

In constant-z mode, the micro-pipette is maintained at a constant z (height) while it is moved laterally and the resistance is monitored, its variations allowing for the reconstitution of the topography of the sample.

Hopping mode is slower than the others, but is able to image complex topography and even entire cells, without distorting the sample surface.

[11][12] SICM was used to image a living neural cell from rat brain,[5] determine the life cycle of microvilli,[8] observe the movement of protein complexes in spermatozoa.

[14] A combination of AFM and SICM was able to obtain high resolution images of synthetic membranes in ionic solutions.

Fluorescent particles, coming from the inside of the micro-pipette, provide a light source for the SNOM that is being continuously renewed and prevent photobleaching.