Biological ion channels have prominent rectification and ion selectivity. Recent work published in Nature Materials by Huanting Wang and colleagues discloses that subnanochannels constructed by metal–organic frameworks (MOFSNC) can achieve monovalent metal ion selectivity and permeability with ultrahigh and pH-tunable features. The mechanism of ultra-high ion selectivity may be that the interaction between ions and carboxyl groups substantially reduces the energy barrier of monovalent cations passing through MOFSNC.