Publication date: 22nd July 2026
This study reports the first experimental demonstration of the confinement of gramicidin, a biological ion-channel peptide with a β-helical structure, inside a single-walled carbon nanotube (SWCNT). The main objective is to determine whether such a biological ion channel can be stably integrated into a solid nanochannel while preserving its function-like biological structure – an essential step toward the development of artificial conductive nanochannels with high ion permeability and selectivity for applications such as iontronics, desalination, and blue energy harvesting [1–3].
Two sets of SWCNTs, i.e., e-DIPS (Meijo Nano Carbon Co., Ltd., Japan), whose diameters range from 1.8 to 2.5nm, have been studied. The gramicidin used is provided by Aldrich (ref.G5002) and is made of 80-85% gramicidin A, 6-7% B, 5-14% C, and <1% gramicidin D. Its native form, gramicidin A (gA) is a “head-to-head” dimer of β-helices that selectively conducts monovalent cations while blocking divalent ions. [4] Its outer diameter, close to 2 nm, closely matches the inner diameter of the SWCNTs selected in this study.
The SWCNTs are impregnated with gA in pure ethanol. First, it is observed that gA acts as a surfactant, promoting the stable dispersion of SWCNTs. The resulting gA–SWCNT hybrid system is characterized using a combination of techniques: small-angle X-ray and neutron scattering, Raman spectroscopy, high-resolution Transmission Electron Microscopy, and water sorption isotherms. All results obtained with these techniques are consistent and demonstrate a strong interaction between gA and SWCNTs: gA adsorbs onto the surface and inserts into the tube’s channel.
In conclusion, this work provides the first experimental evidence that a β-helical biological ion channel can be confined within SWCNTs of compatible diameter. The results open promising perspectives for the design of bio-inspired hybrid materials that combine the exceptional mechanical and electronic properties of carbon nanotubes with the high selectivity and efficiency of biological ion channels.
References:
[1]. Xin, W., Fu, J., Qian, Y. et al. (2022) Biomimetic KcsA channels with ultra-selective K+ transport for monovalent ion sieving. Nat Communю 13, 1701.
[2]. Ye, T., Hou, G., Li, W. et al. (2021) Artificial sodim-selective ionic device based on crown-ether crystals with subnanometer pores. Nat Commun. 12, 5231.
[3]. Chen Q. (2025). Understanding Protein Adsorption on Carbon Nanotube Inner and Outer Surfaces by Molecular Dynamics Simulations; Langmuir 41, 6, 4318.
[4]. Kelkar D.A., Chattopadhyay A. (2007) The gramicidin ion channel: A model membrane protein. Biochimica et Biophysica Acta-Biomembranes. 1768(9), 2011.
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