Retina‐Inspired Nanofluidic Membranes for Underwater Visual Imaging Based on Active Ion Transport

Abstract2D semiconductor heterostructures exhibit broad application prospects. However, regular nanochannels of heterostructures rarely caught the researcher's attention. Herein, a metal–organic framework (i.e., Cu3(HHTP)2) and transition metal dichalcogenides (i.e., MoS2)‐based multilayer van der Waals heterostructure (i.e., Cu3(HHTP)2/MoS2) realized band alignment‐dominated light‐driven ion transport and further light‐enhanced ionic energy generation. High‐density channels of the heterostructure provide high‐speed pathways for ion transmembrane transport. Upon light illumination, a net ionic flow occurs at a symmetric concentration, suggesting a directional cationic transport from Cu3(HHTP)2 to MoS2. This is because Cu3(HHTP)2/MoS2 heterostructures containing type‐II band alignment can generate photovoltaic motive force through light‐induced efficient charge separation to drive ion transport. After introducing into the ionic power generation system, the maximum power density under illumination can achieve notable improvement under different concentration differences. In addition to the photovoltaic motive force, type‐II band alignment and material defect capture‐induced surface charge increase also raise ion selectivity and flux, greatly facilitating ionic energy generation. This work demonstrates that 2D semiconductor heterostructures with rational band alignment can not only be a potential platform for optimizing light‐enhanced ionic energy harvesting but also provide a new thought for biomimetic iontronic devices.

Enhanced Ionic Power Generation via Light‐Driven Active Ion Transport Across 2D Semiconductor Heterostructures

Zhang,

Wang,

Bian

et al. 2024

Nanofluidic Membrane‐Assisted Organic Electrochemical Transistors for Bioinspired Gustatory Sensation Based on Selective Cation Transport

Zhang,

Ma,

Wang

et al. 2024

Natural organisms have evolved precise sensing systems relying on unique ion channels, which can efficiently perceive various physical/chemical stimuli based on ionic signal transmission in biological fluid environments. However, it is still a huge challenge to achieve extensive applications of the artificial counterparts as an efficient wet sensing platform due to the fluidity of the working medium. Herein, nanofluidic membranes with selective cation transport properties and solid‐state organic electrochemical transistors (OECTs) with amplified signals are integrated together to mimic human gustatory sensation, achieving ionic gustatory reagent recognition and a portable configuration. Cu‐HHTP nanofluidic membranes with selective cation transport through their uniform micropores are constructed first, followed by assembly with OECTs to form the designed nanofluidic membrane‐assisted OECTs (nanofluidic OECTs). As a result, they can distinguish typically ionic gustatory reagents, and even ionic liquids (ILs), demonstrating enhanced gustatory perception performance under a wide concentration range (10−7–10−1 m) compared with those of conventional OECTs. The linear correlations between the response and the reagent concentration further indicate the promising potential for practical application as a next‐generation sensing platform. It is suggested that nanofluidic membranes mediated intramembrane cation transport based on the steric hindrance effect, resulting in distinguishable and improved response to multiple ions.

Ultrathin Ionic Diodes with Electrostatically Heterogeneous Hybrid Interfaces of Nanoporous SiO₂ Nanofilms and Polymer Layer‐by‐Layer Multilayers

Ishizaki‐Betchaku,

Kumakura,

Yamamoto

et al. 2024

Nanofluidic ionic diodes have attracted much attention due to their unique functions as unidirectional ion transportation ability and promising applications from molecular sensing, and energy harvesting to emerging neuromorphic devices. However, it remains a challenge to fabricate diode‐like nanofluidic systems with ultrathin film thickness <100 nm. Herein the formation of ultrathin ionic diodes from hybrid nanoassemblies of nanoporous (NP) SiO2 nanofilms and polyelectrolyte layer‐by‐layer (LbL) multilayers is described. Ultrathin ionic diodes are prepared by integrating polyelectrolyte multilayers onto photo‐oxidized NP SiO2 nanofilms obtained from silsesquioxane‐containing block copolymer thin films as a template. The obtained ultrathin ionic diodes exhibit ion current rectification (ICR) properties with high ICR factor = ≈20 under low ionic strength and asymmetric pH conditions. It is concluded that this ICR behavior arises from effective ion accumulation and depletion at the interface of NP SiO2 nanofilms and LbL multilayers attributed to high ion selectivity by combining the experimental data and theoretical calculations using finite element methods. These results demonstrate that the hybrid nano assemblies of NP SiO2 nanofilms and polyelectrolyte LbL multilayers have potential applications for (bio)sensing materials and integrated ionic circuits for seamless connection of human‐machine interfaces.