Measurement of ion currents through porous membranes with scanning ion conductance microscopy.

Scanning ion conductance microscopy (SICM) was used to interrogate ion currents emanating from nanometer-scale pores of a polymer membrane. The transport activity of individual pores was measured by examining ion current images and corresponding topographic images recorded simultaneously. Localized ion currents over individual nanopores were generated by introducing a concentration difference between the upper and lower chambers of a diffusion cell. To better estimate these localized ion currents, Goldman-Hodgkin-Katz (GHK) theory was used to model ion current through a permeable membrane under gradients of both concentration and applied potential. Experimental ion current profiles over a single pore fit well with theoretical plots calculated from the GHK model. On the basis of this analysis, nanoscale transport properties can be measured with SICM.