Single Cylindrical Nanopore Electrodes: Surface Functionalization, Unusual Voltammetry, and Size‐Exclusion Properties

Abstract

AbstractNanopore electrodes have been proved useful tools for fundamental electrochemical research and real applications. In this work, single cylindrical gold nanopore electrodes (SCAuNEs) were fabricated through a laser‐assisted pulling and electrochemical etching method, and then characterized by scanning electron microscopy, cyclic voltammetry, and finite‐element simulations. Our results showed that the electrochemical response of the nanopore electrode corresponds to the diffusion of redox species passing through the nanopore to the underlying gold electrode: surface functionalization of the interior nanopore led to the conversion of surface charge, which could introduce pH‐dependent ion selectivity by electrostatic interaction between redox species and surface functional groups inside the nanopores. It is interesting to find the unusual voltammetric behavior at low concentrations of supporting electrolyte by using single cylindrical nanopore electrodes: the voltammetric limiting current was increased significantly with decreasing supporting electrolyte concentration, but the shift of E1/2 was dependent on the charge change of the redox species. In addition, the distinct size exclusion of two biomolecules, ferritin (ca. 12 nm) and cytochrome C (ca. 3 nm), passing through nanopores at different diameters could be obtained by monitoring the direct electrochemical signals of two biomolecules. This work is important for fundamental electrochemistry and the real applications for counting or separating biomolecules inside cylindrical nanopores.