Single Solid‐State Ion Channels as Potentiometric Nanosensors

Abstract Single solid‐state nanopores are powerful tools for resistive pulse sensing (RPS), but fabricating nanopores to selectively detect the smallest analytes, such as inorganic ions, remains challenging. This problem is tackled by introducing chemically functionalized single gold nanopores (GNPs) as solid‐state ion channels with potentiometric transduction. The “selectivity filter” is established by modifying the nanopore interior with a mixed self‐assembled layer containing perfluoroalkane, ion exchanger, and ionophore. The hydrophobic nanopore interior excludes bulk electrolyte and “routes” the ion transport to the functionalized inner surface, which provides ion selectivity. The combination of low resistivity and suppression of active component loss overcomes key barriers to the extreme miniaturization of conventional ionophore‐based ion‐selective electrodes. Here, the proof of concept is shown for selective silver ion sensing with functionalized nanopores of only 10 nm radius. The new “selectivity filter” provided Ag + selectivities exceeding those of biological ion channels, enabling robust ion measurements with unprecedented miniaturization, but without the need for subnanometer pore size control. The versatility of nanopore functionalization paves the way for fabricating single GNPs tailored to sensing and transporting other ions, while also advancing the mechanistic understanding of selective ion transport in functional nanoporous materials.