Electrochemically addressed FET-like nanofluidic channels with dynamic ion-transport regimes

Insight into the transport of ions from salts of moderated solubility through nanochannels: negative incremental resistance assisted by geometry

In this study, the transport of salt with moderate solubility through bioinspired solid-state nanochannels was comprehensively investigated. For this purpose, bullet-shaped channels were fabricated and exposed to KClO4, a monovalent salt with moderate solubility. These channels displayed the typical rectifying behavior characteristic of asymmetrical channels but with one remarkable difference, the iontronic output exhibited a negative incremental resistance phenomenon of high gating efficiency when the transmembrane voltage in the open state was increased enough, giving rise to an inactivated state characterized by a low and stable ion current. The behavior is attributed to salt precipitation inside the channel and remarkably, it is not observed in other geometries such as cylindrical or cigar-shaped channels. Considering the central role of the surface in precipitation formation, the influence of several parameters such as electrolyte concentration, pH, and channel size was studied. Under optimized conditions, this system can alternate among three different conductance states (closed, open, and inactivated) and exhibits gating ratios higher than 20. Beyond its potential application in fields related to electronics or sensing, this study provides valuable insight into the fundamental principles behind ion rectifying behavior in solid-state channels and highlights the implications of surface phenomena at the nanoscale.

Advances in nanofluidic field-effect transistors: external voltage-controlled solid-state nanochannels for stimulus-responsive ion transport and beyond

Ion channels, intricate protein structures facilitating precise ion passage across cell membranes, are pivotal for vital cellular functions. Inspired by the remarkable capabilities of biological ion channels, the scientific community has ventured into replicating these principles in fully abiotic solid-state nanochannels (SSNs). Since the gating mechanisms of SSNs rely on variations in the physicochemical properties of the channel surface, the modification of their internal architecture and chemistry constitutes a powerful strategy to control the transport properties and, consequently, render specific functionalities. In this framework, both the design of the nanofluidic platform and the subsequent selection and attachment of different building blocks gain special attention. Similar to biological ion channels, functional SSNs offer the potential to finely modulate ion transport in response to various stimuli, leading to innovations in a variety of fields. This comprehensive review delves into the intricate world of ion transport across stimuli-responsive SSNs, focusing on the development of external voltage-controlled nanofluidic devices. This kind of field-effect nanofluidic technology has attracted special interest due to the possibility of real-time reconfiguration of the ion transport with a non-invasive strategy. These properties have found interesting applications in drug delivery, biosensing, and nanoelectronics. This document will address the fundamental principles of ion transport through SSNs and the construction, modification, and applications of external voltage-controlled SSNs. It will also address future challenges and prospects, offering a comprehensive perspective on this evolving field.

Ionic Transistors

Biological voltage-gated ion channels, which behave as life's transistors, regulate ion transport precisely and selectively through atomic-scale selectivity filters to sustain important life activities. By this inspiration, voltage-adaptable ionic transistors that use ions as signal carriers may provide an alternative information processing unit beyond solid-state electronic devices. This review provides a comprehensive overview of the first generation of biomimetic ionic transistors, including their operating mechanisms, device architecture development, and property characterizations. Despite its infancy, significant progress has been made in the applications of ionic transistors in fields such as DNA detection, drug delivery, and ionic circuits. Challenges and prospects of full exploitation of ionic transistors for a broad spectrum of practical applications are also discussed.