Electroosmosis-Driven Nanofluidic Diodes

Fundamental understanding of ion transport in a fluidic channel is of critical importance for realizing iontronics. Here we report on asymmetric ion transport in a low thickness-to-diameter aspect ratio nanopore. Under uniform salt concentration conditions, the cross-pore ionic current showed ohmic characteristics with no bias polarity dependence. In stark contrast, despite the weak ion selectivity expected for the relatively large nanopores employed, we observed diode-like behavior when a salt gradient was imposed across the thin membrane. This unexpected result was attributed to the electroosmotic flow that served to modulate the access resistance through dragging the condensed ions into or out of the nanopore orifices. The simple mechanism was also revealed to be effective in fluidic channels of various size from micro- to nanoscale enabling rectification of the property engineering by the pore geometries. The present findings allow for novel designs of artificial ion channel building blocks.