Carbon Nanotube Porins: Biomimetic Membrane Pore Channels for Nanofluidic Studies

Abstract

Living systems control transport of ions or small molecules across biological membranes using ion channels that form pores in lipid bilayers. Although bottom-up synthesis and top-down fabrication could produce pores of comparable size, an unresolved challenge remains to build a simplified nanopore scaffolds that fully replicate transport properties of membrane channels. Membrane pores formed by ultra-short carbon nanotubes (CNTs) of sub-2 nm diameter assembled in the lipid membranes have transport properties that come remarkably close to that goal. The defining features of these nanostructures are their inner pores that have atomically smooth hydrophobic walls, which can confine water on a molecular level, and, in some cases, down to a single-file configuration. We present experimental results that explore the physical origins of efficient transport in CNT porins, and focus on the role that molecular confinement plays in determining the transport characteristics and selectivity for water, protons, and ions. Overall, CNT porins represent a simplified biomimetic system that is ideal for studying fundamentals of nanofluidic transport and transport in biological channels, and for building complex engineered mesoscale structures.