Brain Wave-Like Signal Modulator by Ionic Nanochannel Rectifier Bridges.

Smart modulation of bioelectric signals is of great significance for the development of brain-computer interfaces, bio-computers, and other technologies. The regulation and transmission of bioelectrical signals are realized through the synergistic action of various ion channels in organisms. The bionic nanochannels, which have similar physiological working environment and ion rectification as their biological counterparts, can be used to construct ion rectifier bridges to modulate the bioelectric signals. Here, the artificial smart ionic rectifier bridge with light response is constructed by anodic aluminum oxide (AAO)/poly (spiropyran acrylate) (PSP) nanochannels. The output ion current of the rectifier bridge can be switched between "ON" and "OFF" states by irradiation with UV and visible (Vis) light, and the conversion efficiency (η) of the system in "ON" state is ≈70.5%. The controllable modulation of brain wave-like signal can be realized by ionic rectifier bridge. The ion transport properties and processes of ion rectifier bridges are explained using theoretical calculations based on Poisson-Nernst-Planck (PNP) equations. These findings have significant implications for the understanding of the intelligent ionic circuit and combination of artificial smart ionic channels to organisms, which provide new avenues for development of intelligent ion devices.

"Ion Pool" Structural Ion Storage Device: A New Strategy to Collect Ions by Nanoconfinement Effects.

Ion storage structure widely exists in organisms, which is used to harvesting energy in environment and converting it into ion concentration gradient to maintain complex life activities. The construction of ion storage structures relies on isolating the biological body fluids by biofilm systems, which can also be regarded as local ions confinement. Mimicking this ions storage process, an "ion pool" structural ion storage device is proposed in this research by artificial ion nanochannels, which can transform the electric power into ion concentration gradient. It is consisted of micrometer-sized ions reservoir and nanosized ions filters. Ions can be isolated within the "pool" and performed ultrahigh ions enrichment or depletion behavior deviated from bulk. Through numerical simulation by Poisson-Nernst-Planck equations, "ion pool" structural device achieves nearly 20 000 rectification ratio with low surface charge. An "ion pool" structural ions storage device is also constructed with block copolymer and polyethylene terephthalate composite membranes, a super high rectification ratio of 3184.0 is achieved from the experiment, which is the highest reported so far. The ion storage efficiency of the device reaches 14.90%, which is an order of magnitude better than non-"ion pool" structural nanofluid devices.

Rod-Cell-Mimetic Photochromic Layered Ion Channels with Multiple Switchable States for Controllable Ion Transport.

The controllable ion transport in the photoreceptors of rod cells is essentially important for the light detection and information transduction in visual systems. Herein, inspired by the photochromism-regulated ion transport in rod cells with stacking structure, layered ion channels have been developed with a visual photochromic function induced by the alternate irradiation with visible and UV light. The layered structure is formed by stacking spiropyran-modified montmorillonite 2D nanosheets on the surface of an alumina nanoporous membrane. The visual photochromism resulting from the photoisomerization of spiropyran chromophores reversibly regulates the ion transport through layered ion channels. Furthermore, the cooperation of photochromism and pH value achieves multiple switchable states of layered ion channels for the controllable ion transport mimicking the biological process of the visual cycle. The ion transport properties of these states are explained quantitatively by a theoretical calculation based on the Poisson and Nernst-Plank (PNP) equations.

Geometric Tailoring of Macroscale Ti3C2Tx MXene Lamellar Membrane for Logic Gate Circuits.

Constructing nanofluidic diode nanochannels with an asymmetric structure for logic gate circuits has attracted extensive research interests. Currently, the preparation of a geometrically asymmetric nanochannel relies on cost-effective material-processing methods and has been hard to scale up, limiting the development of nanofluidic research. Herein, we introduce the idea of geometric tailoring to cut the MXene lamellar membrane in different shapes and investigate the ion transport behavior systematically. The ion rectification can be regulated by adjusting geometric factors such as the asymmetric ratio and height of the trapezoidal membrane. On the basis of the above-mentioned research on rectification characteristics, we further optimized the trapezoidal membrane into a triangular membrane on the macroscopic level and successfully applied it to logic circuits, realizing the logic operations of "AND" and "OR". It is worth mentioning that the shape of a macrocut triangular membrane is exactly the same as the symbol of an electronic diode, and the conduction and cutoff directions of the ionic current are also exactly the same as those of electronic diodes. Our finding provides a facile and general strategy for fabricating a macroscale geometric asymmetry nanochannel-based two-dimensional lamellar membrane and shows the potential applications in complex highly integrated ionic circuits.

Sandwich "Ion Pool"-Structured Power Gating for Salinity Gradient Generation Devices.

Nanoconfinement ion transport, similar to that of biological ion channels, has attracted widespread research interest and offers prospects for broad applications in energy conversion and nanofluidic diodes. At present, various methods were adopted to improve the rectification performance of nanofluidic diodes including geometrical, chemical, and electrostatic asymmetries. However, contributions of the confinement effects within the channels were neglected, which can be a crucial factor for ion rectification behavior. In this research, we report an "ion pool"-structured nanofluidic diode to improve the confinement effect of the system, which was constructed based on an anodic aluminum oxide (AAO) nanoporous membrane sandwiched between zeolitic imidazolate framework 8 (ZIF-8) and tungsten oxide (WO3) thin membranes. A high rectification ratio of 192 is obtained through this nanofluidic system due to ions could be enriched or depleted sufficiently within the ion pool. Furthermore, this high-rectification-ratio ion pool-structured nanofluidic diode possessed pH-responsive and excellent ion selectivity. We developed it as a pH-responsive power gating for a salinity gradient harvesting device by controlling the surface charge density of the ion pool nanochannel narrow ends with different pH values, and hence, the ionic gate is switched between On and Off states, with a gating ratio of up to 27, which exhibited 8 times increase than ZIF-8-AAO and AAO-WO3 composite membranes. Significantly, the peculiar ion pool structure can generate high rectification ratios due to the confinement effect, which then achieves high gating ratios. Such ion pool-structured nanochannels created new avenues to design and optimize nanofluidic diodes and boosted their applications in energy conversion areas.

Ion Transport Behaviors of Nanofluidic Diode Bichannel Systems in the Independent and Synergistic Cascade Mode.

The nanofluidic diode device was a significant ionic transistor. Its multiple cascades could realize diversified ion transport behaviors and information processing functions. Different cascade modes of channel units will affect the response current properties of multichannel systems. Inspired by independent and synergistic effects in semiconductor transistors, artificial conical nanoporous bichannel systems were investigated in separation and stacking cascade modes to discuss their different ion transport behaviors. The dynamic resistance fitting method was adopted to discuss the properties of each circuit components in the bichannel system for analyzing the circuit properties in different cascade modes. In the stacking mode, electric field interactions at the heterojunctions between channel units dominated the ionic transport properties, and response current of the bichannel system was influenced by the channel unit cascade sequence. In the separation mode, channel units transport ions independently, and the cascade sequence had little effect on response current properties of the system. These promising results provide a new strategy to design and build a series of artificial composite nanochannels with multifunction and intelligence.

Artificial NO and Light Cooperative Nanofluidic Diode Inspired by Stomatal Closure of Guard Cells.

Gas messenger molecule (NO) plays important roles in K+ nanochannels of guard cells by binding directly to the heme-containing enzymes. Inspired by this natural phenomenon, we developed artificial K+ nanochannels modified with ferroporphyrin, where NO triggered the nanochannels to turn "ON" states from the ferroporphyrin blocked "OFF" states. The mechanism relies on the fact that NO has higher affinity with ferroporphyrin compared to carboxyl groups on the nanochannel surface. The synergistic effect of the released carboxyl groups and the conically asymmetric shape leads the ion transportation to be diode-like. However, the nanofluidic diode properties vanished after illumination with light to remove NO from the ferroporphyrin-NO complex. This NO and light cooperative nanofluidic diode possesses excellent stability and reversibility, which shows great promise for use in gas detection and remote control of mass delivery.

Smooth Muscle Cell-Mimetic CO-Regulated Ion Nanochannels.

A CO-regulated ion nanochannel is demonstrated, which is inspired by the living activity of CO-induced smooth muscle vasodilation. The mechanism relies on the fact that CO has a higher affinity with ferroporphyrin compared to carboxyl groups on the surface of the nanochannels. The cooperation effect of the released carboxyl groups and the conical asymmetric shape leads the ion transportation to be diode-like.