Nanoscale ion transport is emerging as a key bridge between living systems and artificial computing platforms. Unlike conventional electronics, nanofluidic devices can operate in aqueous environments with high biocompatibility and, in principle, exchange information bidirectionally with biological matter. Although numerous nanofluidic devices have been invented, most of them behave like only one single circuit element—typically a resistor, capacitor, inductor or memristor—and their underlying mechanisms need further explorations. In particular, it remains uncommon for a single nanofluidic architecture to generate multiple hysteresis behaviors arising from distinct physical origins. Meanwhile, the vast diversity of ionic species—arguably the most natural “programmable parameter” in iontronics—has not been systematically exploited to expand device functions.
Recently, Associate Prof. Kai Xiao (Southern University of Science and Technology), together with Dr. Junjun Liu (Shenzhen Polytechnic University), assistant researcher Guoheng Xu (Lanzhou Institute of Chemical Physics CAS), and their collaborators, reported a programmable nanofluidic neuromorphic device whose electrical performance can be adjusted without changing its structure. The core of the system is a confined space formed by stacked gold nanoparticles, which assemble into nanostructured pathways inside a polycarbonate track-etched (PCTE) membrane. The strong confinement environment makes the devices’ performance highly sensitive to electrolyte conditions (the ionic concentration and species).
By intentionally tuning ionic concentration, the team realized the switching between capacitive hysteresis and inductive hysteresis within the same device framework. At low electrolyte concentration, ions behave more like separated point charges. Under confinement, these ions accumulate near the gold surface and form electrical double layers (EDLs), producing an EDL-dominated capacitive response. When the electrolyte concentration increases, the ionic state changes qualitatively. At high concentration, ions are more likely to form Bjerrum pairs, which can dissociate under an applied electric field. This introduces a coupled “chemical” process—pairing and field-assisted dissociation—alongside transport, yielding an inductive hysteresis loop with characteristics resembling a chemical inductor. In other words, the device’s response can shift from predominantly capacitive to effectively inductive as the electrolyte environment drives a change in the dominant microscopic mechanism. Based on the observations, the authors propose a universal criterion that links ionic states to ionic concentration: the transition is governed by the relative relationship between interionic distance and the Bjerrum length. When interionic distances are larger compared with the Bjerrum length, ions behave more independently and EDL effects dominate; when interionic distances shrink, ion–ion correlations and pairing become increasingly significant, enabling inductive-like behavior. This framework provides a practical rule for anticipating which hysteresis mode will appear under a given electrolyte condition.
In addition to the ionic concentration, the ion species are the second parameter to adjust the device responses. Different ions interact with confined nanochannels with different strengths—through size, valence, hydration, and adsorption tendencies—allowing function selection simply by replacing the ionic species. Leveraging these ion–nanochannel interaction differences, the researchers demonstrated programmable unidirectional synaptic plasticity, switching between paired-pulse facilitation (K: PPF) and paired-pulse depression (La: PPD) depending on the chosen ionic species. Furthermore, by connecting devices in series, they demonstrated a high-pass filter (HPF) whose cut-off frequency was tunable via ionic species.
Overall, this work clarifies how confined ionic states map onto device-level electrical performance, achieves multifunctional hysteresis responses within a single nanofluidic architecture, and demonstrates a tunable HPF circuit. These advances help address both long-standing challenges—limited functionality and unclear mechanisms—and point to a new paradigm for neuromorphic and iontronic circuit design driven by ion diversity.
National Science Review
Experimental study