Rectification in synthetic conical nanopores

The theoretical description of ionic transport processes in nanoporous materials is a very interesting topic, since these materials have promising technological applications e.g. in sensing and filtration of molecules with size comparable to the pore diameter, and especially single pores may serve as model systems for biological ion channels. By the track-etching method [1], it is possible to produce single conical pores with nanometer sized openings on one side, showing transport properties similar to biochannels such as ionic current fluctuations [2], rectification [2], flux inhibition by divalent cations [3] and selectivity [4]. We proposed a theoretical model based on the PoissonNernst-Planck formalism [5] able to describe experiments on such nanopores prepared in 12 μm thick PET film (irradiation at GSI with 11.4 MeV/u U, etching from one side with 9 M NaOH at 23 C). Subject of the study was the concentration dependence of the rectification recorded under symmetric electrolyte conditions, 0.01 – 1 M KCl. It was demonstrated experimentally and is also assumed in our model that rectification results from electrostatic interactions of the mobile ions with fixed charges on the pore wall, which are created during the etching process. The model used here makes it possible to reproduce the experimental results using the surface charge as the only free parameter.