- 1-Supporting Information Fabrication of Stable Single Nanochannels with Controllable Ionic Rectification

The fabricationof artificial nanochannels is becominga focus of attentionbecause, comparedwith theirbiological counterparts, they offer flexibility in terms of shape, size, and surface properties for real-world applications. At present, there are several approaches to building single nanochannels (nanopores), such as ion-beam sculpting of Si3N4 membranes, [3] Si/ SiO2 membrane shrinking in transmission electron microscopy, electrochemical etching of glass membranes, and chemical etching of single-track polymer membranes. Because the nanochannel is small enough for interactions between the channel surface and chemical species in the solution, the chemical modification of the nanochannel surface confers great flexibility in developing functional nanochannel materials. Even though several solution methods of coating nanochannels with functional molecules, which enable the size and ion-transport properties of the nanochannels to be easily tuned, have been developed during the past few years, how to endow nanochannels with asymmetric chemical properties is still a challenging task. The chemical properties and chemical modification of artificialnanochannels arecritical components in theadvance of smart functional nanochannels that are tunable by ambient stimuli, such as specific ions, applied force, light, pH, and compression. Recently, the ionic-current rectification of a single nanochannel prepared by the ion-track-etching technique has been studied in comparison with the properties of various ion channels. In those studies, the surface properties of the nanochannel wall are significant for the