Integrating Ionic Gate and Rectifier Within One Solid-State Nanopore via Modification with Dual-Responsive Copolymer Brushes

A dual-functional nanofluidic device is demonstrated that integrates the ionic gate and the ionic rectifier within one solid-state nanopore. The functionalities are realized by fabricating temperature-and pH-responsive poly(N-isopropyl acrylamide-co-acrylic acid) brushes onto the wall of a cone-shaped nanopore. At ca. 25 degrees C, the nanopore works on a low ion conducting state. When the temperature is raised to ca. 40 degrees C, the nanopore switches to a high ion conducting state. The closing/opening of the nanopore results from the temperature-triggered conformational transition of the attached copolymer brushes. Independently, in neutral and basic solutions, the conical nanopore rectifies the ionic current. While in acid solutions, no ion rectifying properties can be found. The charge properties of the copolymer brushes, combined with the asymmetrical pore geometry, render the nanopore a pH-tunable ionic rectifier. The chemical modification strategy could be applied to incorporate other stimuli-responsive materials for designing smart multi-functional nanofluidic systems resembling the live creatures in nature.