Bioinspired cation-gated dynamic liquid film nanochannel for controlled transport of ions and molecules

Abstract

Calcium-gated nanochannels in vivo play an important role in many life activities. Inspired by biological ion channels, artificial ion gating has been extensively studied. However, conventional ion gating relies on asymmetric charge structures and fixed nanochannel sizes, resulting in difficult channel blocking and low gating ratios. Herein, a dynamic liquid film nanochannel is constructed by inserting an oil droplet into a carboxylated glass capillary filled with ion solution. The liquid film between the oil and capillary is used as a nanochannel to transport ions and molecules, and the height of the nanochannel can be flexibly controlled by the electrostatic force between the oil–water and water–solid interfaces. The switching of the liquid film nanochannel depends on the ion valence. Compared to monovalent ions, the introduction of multivalent ions yields less negative zeta potential at both the oil–water and water–solid interfaces, which in turn reduces the electrostatic repulsion force between the oil–water and water–solid interfaces, resulting in the nanochannel changing from the “ON” state to the “OFF” state. The system shows good cyclic gating performance and high gating ratios up to ∼1000. Moreover, this cation-gated liquid film nanochannel enables controlled transport of molecules such as rhodamine 6G. In this paper, we present a convenient intelligent nanochannel capable of regulating the transport of ions and molecules within the liquid film simply by adjusting the electrostatic force between the oil–water and water–solid interfaces. This research holds promise for applications in drug delivery, biosensing, species separation, and beyond.