Stimuli-Responsive Ion Transport Regulation in Nanochannels by Adhesion-Induced Functionalization of Macroscopic Outer Surface

Responsive regulation of ion transport through nanochannels is crucial in the design of smart nanofluidic devices for sequencing, sensing, and water-energy nexus. Functionalization of the inner wall of the nanochannel enhances interaction with ions and fluid but restricts versatile chemical approaches and accurate characterizations of fluidic interfaces. Herein, we reveal a responsive regulating mechanism of ion transport through nanochannels by polydopamine (PDA)-induced functionalization on the macroscopic outer surface of nanochannels. Responsive molecules were codeposited with PDA on the outer surface of nanochannels and formed a valve of nanometer thickness to manually manipulate ion transport by changing its gap spacing, surface charge, and wettability under external stimulus. The response ratio can be up to 100-fold by maximizing the proportion of responsive molecules on the outer surface. Laminating the codepositions of different responsive molecules with PDA on the channel's outer surface produces multiple responses. A nearly universal adhesion of PDA with responsive molecules on the open outer surface induces nanochannels responsive to different external stimuli with variable response ratios and arbitrary combinations. The results challenge the primary role of functionalization on the nanoconfined interface of nanofluidics and open opportunities for developing new-style nanofluidic devices through the functionalization of macroscopic interface.