Expanding The Capabilities Of Scanning Ion Conductance Microscopy

Scanning ion conductance microscopy (SICM) is an electrochemical technique that is conventionally used to measure topography at the nanoscale. Patrick R. Unwin and coworkers at the University of Warwick, in England, have now extended the capabilities of this method to measure other properties, an advance that may enhance nanoscale analysis of chemical and biological phenomena (J. Am. Chem. Soc. 2014, DOI: 10.1021/ja506139u). They position an electrolyte-filled nanopipette near a surface in contact with an electrolyte solution. The apparatus includes two quasi-reference counter electrodes, one inside and one outside the nanopipette. By applying a bias between the two electrodes, the device measures a current, which is sensitive to surface charge. Modulating the distance of the tip from the surface induces an alternating current that is also sensitive to the surface charge. By measuring the ion current as a function of position and distance modulation, the researchers are able to simultaneously record surface maps showing ion current, topography, and phase. Measuring phase is key to recording the other two maps simultaneously. “I don’t know of any other way to determine in situ surface charge at this scale,” says Lane A. Baker, a chemistry professor at Indiana University.