Nanopore Electrodrying Enables Precise Impedance Control for Iontronic Devices

Controlling ion flow within nanoscale spaces is central to the rapidly developing field of iontronics, offering new possibilities for sensing and device technologies. Giovanni Di Muccio, from Sapienza Università di Roma and NY-MaSBiC, along with Gonçalo Paulo and Lorenzo Iannetti, also from Sapienza Università di Roma, lead a team that has discovered a counter-intuitive method for manipulating ion flow within nanopores. Their research demonstrates ‘electrodrying’, a process where voltage is applied not to wet, but to dry hydrophobic nanopores, effectively switching off conduction and providing precise control over ion flow. This breakthrough, supported by detailed modelling and simulations from colleagues including Adina Sauciuc and Giovanni Maglia at the Groningen Biomolecular Sciences and Biotechnology Institute, reveals a new type of memristive behaviour and opens exciting avenues for designing advanced iontronic devices, validated through experiments on engineered nanopores led by Alberto Giacomello from Sapienza Università di Roma.

Iontronics represents a developing field that utilises ions in solution as information carriers for sensing and computing, for example in neuromorphic devices. This fundamentally different operating principle compared to electronics necessitates new approaches and concepts to control the impedance of nanoscale fluidic circuit elements, such as nanopores. The present study investigates an alternative, counterintuitive mechanism, employing voltage to dry hydrophobic nanopores and consequently terminate conduction, termed “electrodrying”. This concept provides precise, bidirectional control over nanopore conductance, demonstrating hysteresis in the current-voltage curve, a characteristic feature of memristors. Employing an analytical model and free-energy molecular dynamics simulations, the research team investigates this phenomenon and explains the physical mechanism underlying electrodrying, providing clear design criteria for solid-state and biological nanopores with bidirectional control over conductance.

Electrodrying nanopores exhibit unique electrical behaviour, including a memristive response with a shifted hysteresis loop, a previously unreported characteristic, and a broad voltage range displaying negative differential resistance. These properties were successfully implemented in a short-term memory task and an iontronic oscillator circuit, highlighting their potential for advanced applications. Researchers acknowledge that further investigation is needed to fully explore the limits of this mechanism across diverse nanopore configurations and electrolyte conditions, but the findings suggest a pathway to mimic the gating properties of biological ion channels without requiring complex structural rearrangements, potentially impacting our understanding of fluid behaviour in both biological and synthetic nanopores and driving innovation in neuromorphic and iontronic devices.

CytK Channel Exhibits Unusual Electrodrying Behaviour

This research details an extensive investigation into the CytK potassium channel, focusing on its structure, function, and the effects of specific genetic modifications. The team combined molecular dynamics simulations, experimental conductance measurements, and genetic engineering to understand how the channel’s pore and gating mechanisms operate. A key finding is that the CytK channel exhibits unusual electrodrying behaviour, where its response to voltage is asymmetric, influenced by both mutations and the surrounding ionic environment. Researchers engineered several mutations in the CytK channel to investigate how specific amino acid changes affect the channel’s conductance, gating, and electrodrying behaviour. Molecular dynamics simulations were used to model the channel’s structure, electrostatic potential, and the effects of mutations and ionic conditions, revealing an unexpected inversion of the intrinsic potential within the channel under certain conditions.

The research reveals that the CytK channel exhibits an electrodrying behaviour, meaning its response to applied voltage is asymmetric. Single-channel conductance recordings were performed to measure the channel’s activity and how it’s affected by mutations and voltage. The researchers investigated the role of ionic strength and screening effects on the channel’s behaviour, finding that high ionic strength can mask the electrodrying behaviour. The channel’s behaviour resembles a memristor, a type of electronic component with memory, and provides insights into the complex mechanisms governing potassium channel function and gating, demonstrating the possibility of tailoring channel properties for specific applications.

Electrodrying Dynamically Tunes Nanopore Conductance

This research introduces the concept of electrodrying, a counterintuitive phenomenon where an applied voltage reduces water occupancy within hydrophobic nanopores, effectively switching them from a conductive to a non-conductive state. By combining electrostatic theory, molecular dynamics simulations, and experiments using engineered nanopores, scientists have established a comprehensive framework for dynamically tuning nanopore conductance with precise electrostatic control. This bidirectional control significantly expands upon conventional electrowetting techniques, which are limited to switching currents on.

The team demonstrated that the interplay between an intrinsic dipole within a nanopore and an applied voltage reliably controls the pore’s state. This mechanism offers a pathway to mimic the gating properties of biological ion channels without requiring complex structural rearrangements, potentially impacting our understanding of fluid behaviour in both biological and synthetic nanopores and driving innovation in neuromorphic and iontronic devices.