Mass transport properties and applications of nanochannels

Abstract

With the development of materials science, micro/nano processing technologies, and mass transport theories at the micro/nano scale, nanochannel-based technology has been receiving increasing attention. Nanochannels can be classified as biological and artificial. The size of a nanochannel is typically 1-100 nm, which greatly enhances the interaction between the channel surface and substances inside the channel, inducing several special mass transport properties such as ion selectivity, ionic current rectification, and resistive current pulse. Ion selectivity is caused by the electrostatic interaction between ions and the surface charge of the nanochannel, ionic current rectification arises from the asymmetric distribution of the electrochemical potential inside the nanochannel, and a resistive current pulse is generated by the blocking of the nanochannel during the transport of ions/molecules. By taking advantage of these mass transport properties, nanochannels can be applied to various fields. For example, gated ion transport can be realized by modifying the surface of the nanochannel with functional groups; single-molecule sensing can be realized using sub-nanoscale channels; the separation of ions, molecules, or nanoparticles can be realized by regulating the interaction between the nanochannel and transport substances; and various forms of energy, such as light, heat, and salt gradient, can drive charge separation within the nanochannel and be converted into electricity by harnessing the ion selectivity of the nanochannel. However, despite the achievements in nanochannel-based technology, in-depth exploration of the mass transport properties at the nanoscale and further expansion of its application remain to be realized. For the development of this technology, four major issues need to be addressed: fabrication of a single-atom-thick nanochannel/nanopore membrane, precise control of the nanochannel structure, effective regulation of the surface properties of the nanochannel, and enrichment and development of mass transport theories. Nanochannel-based technology requires interdisciplinary efforts at the intersection of chemistry, materials science, and nanotechnology, and shows good promise for solving basic problems in biology, environment, and energy. Herein, we briefly describe the mass transport properties of nanochannels and some emerging developments and applications, and finally provide a brief outlook on this field.