SICM – High-resolution imaging of the surface of living cells

Scanning Ion Conductance Microscopy (SICM) is a contact-free scanning probe technique that allows to map the surface of a sample in electrolyte solution at room temperature. In SICM, the probe is a glass micro- or nanopipette and the ionic current through the opening of the pipette is used to determine the distance between probe tip and sample. 

SICM has been developed by Hasma and colleagues in 1989 [1] and its application to image living cells was introduced by Korchev and colleagues in 1997 [2,3]. It has been used to investigate various cell physiologic questions, some of which are detailed in a publically available review [4].

Operating principle

REM image of glass nanopipette

Scanning electron microscope image of typical a glass nanopipette used in SICM.

SICM utilizes the current through the opening of a glass micro- or nanopipette (as shown in the image) to determine the distance between probe tip and sample. At distances far away from the sample, the current is nearly constant, and thus the normalized current, that is the current normalized to the current at an infinite distance, is one. At smaller distances, the current asymptotically approaches zero. The shape of the current-distance relation is determined  by the geometry of the glass micro- or nanopipette [5] as well as the angle between sample and tip [6].

Since the current reduces before physical contact between tip and sample is formed, SICM allows to sense the sample without biasing it. In most applications, a threshold current drop – for example a drop by 1% – is selected that is used to image the sample.

SICM approach curve

Current-distance relation in SICM. A threshold drop of 1% (resulting in a remaining current of 99%) and the corresponding imaging distance are depicted as dashed lines,

Example recording

SICM von HeLa-Zellen

Example image of HeLa cells. Recording taken from ref [7]. 

Copyright: The Royal Society of Chemistry. Reproduction covered by the author rights of the license to publish. 

Literature

  1. Hansma et al., Science, 1989. DOI: 10.1126/science.2464851
  2. Korchev et al., Journal of Microscopy, 1997. DOI: 10.1046/j.1365-2818.1997.2430801.x
  3. Korchev et al., Biophysical Journal 1997. DOI: 10.1016/S0006-3495(97)78100-1
  4. Happel et al., Sensors (Basel) 2012. DOI: 10.3390/s121114983
  5. Rheinlaender and Schäffer, Analytical Chemistry, 2017. DOI: 10.1021/acs.analchem.7b03871
  6. Thatenhorst et al., Analytical Chemistry, 2014. DOI: 10.1021/ac5024414
  7. Gesper et al., Nanoscale, 2017. DOI: 10.1039/C7NR04306F

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