Single-Walled Carbon Nanotubes: Mimics of Biological Ion Channels

Abstract

Here we report on the ion conductance through individual, small diameter single-walled carbon nanotubes. We find that they are mimics of ion channels found in natural systems. We explore the factors governing the ion selectivity and permeation through single-walled carbon nanotubes by considering an electrostatic mechanism built around a simplified version of the Gouy–Chapman theory. We find that the single-walled carbon nanotubes preferentially transported cations and that the cation permeability is size-dependent. The ionic conductance increases as the absolute hydration enthalpy decreases for monovalent cations with similar solid-state radii, hydrated radii, and bulk mobility. Charge screening experiments using either the addition of cationic or anionic polymers, divalent metal cations, or changes in pH reveal the enormous impact of the negatively charged carboxylates at the entrance of the single-walled carbon nanotubes. These observations were modeled in the low-to-medium concentration range (0.1–2.0 M) by an electrostatic mechanism that mimics the behavior observed in many biological ion channel-forming proteins. Moreover, multi-ion conduction in the high concentration range (>2.0 M) further reinforces the similarity between single-walled carbon nanotubes and protein ion channels.

Enhanced water permeability and tunable ion selectivity in subnanometer carbon nanotube porins

“…At low salt concentrations, we observed a C 1/2 dependence (Fig. 3D, inset) that is different from the C 1/3 scaling reported for larger 7-to 28-nm-diameter CNTs at low concentrations (26), although similar to the C 1/2 dependence recently reported for very long 1.3-to 1.5-nm-diameter CNTs (27).…”

Voltage‐Gated Nanoparticle Transport and Collisions in Attoliter‐Volume Nanopore Electrode Arrays

“…capabilities to mediate analyte transport into the nanopore, where chemical signals can be generated. [8][9][10][11] Some biomimetic nanopores behave like ionic diodes, allowing ions or molecules to flow in one direction while suppressing motion in the reverse direction. [12][13][14][15][16] By modifying the inner nanopore wall with bioreceptors or molecular recognition motifs, target molecules can be selectively detected in high-sensitivity assays.…”

“…The recent rapid development of solid‐state nanopores represents a robust and durable sensing platform to perform single biomolecule detection, DNA sequencing, and proteomic profiling . Synthetic nanopores not only approach the small size of biological ion channels, but can also be designed to incorporate voltage‐gating properties and biorecognition capabilities to mediate analyte transport into the nanopore, where chemical signals can be generated . Some biomimetic nanopores behave like ionic diodes, allowing ions or molecules to flow in one direction while suppressing motion in the reverse direction .…”

Nanofluidics: A New Arena for Materials Science

“…Because the probed transport phenomena are averaged behaviors across numerous nanochannels in the CNT membrane, more recently there is a trend to experimentally study transport in isolated single CNTs to unveil detailed fluidic characteristics in CNTs. Some groups have built single‐CNT nanofluidic platforms by overcoming the great challenge to embed single CNTs in micro‐/nanodevices via various approaches . These platforms offer great potentials to utilize CNTs as building blocks to flexibly build devices with complex nanofluidic networks in the future.…”