Effect of nanoscale water media confinement on the approach curve in SICM

The features of the ion current dependence on distance when a glass nanopipette with an aperture diameter of ∼100 nm approaches the surface of a solid dielectric in a scanning ion conductivity microscope have been studied. A characteristic peak in the approach curve has been observed when the electrode in the nanopipette with an electrolyte is negatively biased relative to electrode in the bath, while a monotonic current decline occurs with a positive bias. To explain this unusual behavior of the ion current, the model accounting for the overlap of electric double layers and water confinement phenomenon in nanochannels and nanogaps have been proposed. The model demonstrates good agreement with the experimental data and provides a basis for quantitative assessment of surface charge at electrolyte–solid interfaces with nanometer-scale spatial sensitivity.