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.

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The SICM can also sample and map the local ion currents above the surface. This is useful in imaging ion currents through membrane channels.

This scanning technique can be used on living tissues, whereas traditional SEM imaging necessitated killing the sample. Biological processes can now be observed whilst in action.

SICM is part of the larger family of scanning probe microscopy (SPM), and was specially designed for the sub-micrometer resolution scanning of soft non-conductive materials that are bathed in electrolyte solution.

References

• http://www.sciencemag.org/cgi/content/abstract/243/4891/641
• http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10777763&dopt=Abstract
• http://www1.imperial.ac.uk/medicine/about/divisions/medicine/experimental_genetics/cell_mol_endo/microscopy/