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Researchers at the have shown that naturally occurring channels within a common clay mineral can respond to pressure, voltage and pH, offering possibilities for controlling the movement of ions through extremely small, confined spaces. The study, published in , focuses on vermiculite, a naturally abundant layered clay whose structure contains channels only a few angstroms high, providing naturally confined pathways through which ions can move.

Biological ion channels, which have angstrom-scale constrictions, can respond to multiple signals from their surroundings and regulate the movement of ions across cell membranes. Inspired by this principle, researchers investigated whether naturally occurring angstrom-scale channels in vermiculite could also exhibit responsive ion transport when exposed to different external stimuli, e.g., mechanical, electrical and chemical signals.

Depending on the conditions applied, the channels altered both the amount and direction of ion flow, showing behaviours similar to the ion gating behaviour in biological channels.

The clay channels naturally favour positively charged ions. The team found that by changing the acidity of the surrounding solution, they were able to influence this selectivity. Pressure and electrical voltage also altered how ions travelled through the channels, revealing a complex interplay between the different stimuli.

Dr Raj Kumar Gogoi, first author of the study added, 鈥淲e observed that applying pressure and voltage together could change the behaviour of the flowing ions in ways not seen when either stimulus was applied alone. Under certain conditions, the direction of the pressure-driven current could even reverse, highlighting the sensitivity of the system to multiple environmental inputs.鈥�

To understand these observations, the researchers combined laboratory experiments with computational modelling. Prof Narayana R Aluru, from University of Texas-Austin, said "The experimental observations could not be fully explained using conventional models. We introduce a modified surface-charge regulation model, where pressure, voltage and ion concentration influence the distribution of ions inside the channels and modify the charge at the channel surface, which in turn affects ion transport.鈥�

Unlike conventional models, which typically consider surface charge as a function of ion concentration alone, the new approach incorporates the combined effects of voltage, pressure and concentration, to describe how these coupled factors influence ion transport in highly confined channels The findings suggest that naturally layered materials could offer a versatile platform for studying and controlling ionic transport at extremely small scales. The authors say future applications could include adaptive nanofluidic systems, energy conversion devices and bioelectronic platforms, though these applications were not explored in the present study.

The research was conducted by scientists from the Department of Physics and Astronomy, National Graphene Institute and Photon Science Institute at The University of Manchester; the Department of Mechanical Science and Engineering and Beckman Institute for Advanced Science and Technology at the University of Illinois Urbana-Champaign; and the Walker Department of Mechanical Engineering at The University of Texas at Austin.