A Fluoride-Driven Ionic Gate Based on a 4-Aminophenylboronic Acid-Functionalized Asymmetric Single Nanochannel

Fluorine is one of the human body's required trace elements. Imbalanced fluoride levels severely affect the normal functioning of living organisms. In this article, an anion-regulated synthetic nanochannel is described. A fluoride-driven ionic gate was developed by immobilizing a fluoride-responsive functional molecule, 4-aminophenylboronic acid, onto a single conical polyimide nanochannel. When the ionic gate was in the presence of fluoride, the boron bound F-, and the hybridization of the boron center changed from sp2 to sp3. Thus, negatively charged monofluoride adduct (RB(OH)2F-), difluoride adduct (RB(OH)F2-), and trifluoride adduct (RBF3-) modified surfaces with different wettability would be formed successively by increasing the concentration of F-. On the basis of the variation of surface charge and wettability, the nanochannel can actualize reversible switching between the "off" state and the "on" state in the absence and presence of F-, respectively. As an anion-regulated synthetic nanochannel, this fluoride-driven ionic gate was characterized by measuring ionic current, which possesses high sensitivity, fine selectivity, and strong stability. Thus, this gate may show great promise for use in biosensors, water quality monitoring, and drug delivery.