Fabrication of Single Cylindrical Au-Coated Nanopores with Non-Homogeneous Fixed Charge Distribution Exhibiting High Current Rectifications

We have designed and characterized a cylindrical nanopore that exhibits high electrochemical current rectification ratios at low and intermediate electrolyte concentrations. For this purpose, the track-etched single cylindrical nanopore in polymer membrane is coated with a gold (Au) layer via electroless plating technique. Then, a non-homogeneous fixed charge distribution inside the Au-coated nanopore is obtained by incorporating thiol-terminated uncharged poly(N-isopropylacrylamide) (PNIPAM) chains in series to poly(4-vinyl pyridine) (PVP) chains, which are positively charged at acidic pH values. The functionalization reaction is checked by measuring the current–voltage (I–V) curves prior to and after the chemisorption of polymer chains. The experimental nanopore characterization includes the effects of temperature, adsorption of chloride ions, electrolyte concentration, and pH of the external solutions. The results obtained are further explained in terms of a theoretical continuous model. The combination of well-established chemical procedures (thiol and SAM formation chemistry, electroless plating, ion track etching) and physical models (two-region pore and Nernst-Planck equations) permits to obtain a new nanopore with high current rectification ratios. The single pore could be scaled up to multipore membranes of potential interest for pH sensing and chemical actuators.
P.R., V.G., and S.M. acknowledge the financial support from the Generalitat Valenciana (Project PROMETEO/GV/0069), Ministry of Science and Innovation of Spain, Materials Program (Project MAT2012-32084), and FEDER. M.A., S.N., and W.E. thank Prof. C. Trautmann and crew (GSI, Department of Materials Research) for support with irradiation experiments.