Sequential recognition of zinc and pyrophosphate ions in a terpyridine-functionalized single nanochannel

A highly selective recognition system for zinc(II) and pyrophosphate ions is constructed using a single conical nanochannel covalently functionalized with N'-(4-[(2,2':6',2''-terpyridine)-4-yl]benzyl)ethane-1,2-diamine (TPYD). The immobilized TPYD acts as a specific coordination site for Zn²⁺ to form TPYD-Zn²⁺ complexes in preference over other metal ions, and subsequently, the resulting Zn²⁺-coordinated nanochannel can be used as a selective recognition element for the pyrophosphate ion based on the coordination reaction between hydroxyl oxygen atoms of pyrophosphate and Zn²⁺. Ion recognition is monitored by measuring the current-voltage curves of the solutions. The ionic current of the TPYD-functionalized system at -2.0V undergoes a clear decrease after exposure to Zn²⁺ ions and is followed with an obvious increase after subsequent treatment with a pyrophosphate solution. The change of ionic current can be primarily attributed to the variation of charge density of the nanochannel. This functionalized single nanochannel might provide a simple and universal means to recognize other targets by modifying different functional molecules onto the inner surfaces of nanochannels.