Gas-breathing polymer film for constructing switchable ionic diodes

Abstract

Carbon dioxide (CO₂), as one of the major byproducts of cellular metabolism, mediates many fundamental behaviors, and its detection is associated with the activation of protein ion channels expressed on olfactory sensory neurons. Inspired by this biological phenomenon, we developed an extraordinary gas-sensitive ion channel, reconfigurable ionic diode and bionic ion pump on the basis of the growth of a gas-responsive polymer film, which can be rendered hydrophilic with CO₂ stimulus and hydrophobic with N₂ stimulus. In particular, by alternatively purging CO₂/N₂ into the solutions which are placed on both sides of the channel embedded in the polymer membrane, the smart polymer-coated channel can be either closed or opened, which is independent of voltage polarity. Most intriguingly, under asymmetric stimulation with pH pairs (pH 6.5‖pH 9.0) or with gas inputs (CO₂‖N₂) on both sides of the channel, a change in voltage polarity can switch the channel between a closed status and open status, leading to the construction of a reconfigurable fluidic diode. Furthermore, by combination of gas inputs and voltage polarity, each of the gates of the channel can be individually manipulated, which is a very important prerequisite for the construction of a bionic ion pump that can be operated under physiologically mild conditions. It is envisaged that this new progress in the bionic pore/channel field will hold great prospects for the application of this kind of biomimetic device for energy storage, sample filtration and seawater desalinization.