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

Electricity-Wettability Controlled Fast Transmission of Dopamine in Nanochannels

Achieving fast transmembrane transmission of molecules in organisms is a challenging problem. Inspired by the transport of Dopmine (DA) in organisms, the DA transporter (DAT) binds to DA in a way that has a ring recognition (the recognition group is the tryptophan group). Herein, D-Tryptophan-pillar[5]arene (D-Trp-P5) functionalized conical nanochannel is constructed to achieve fast transmission of DA. The D-Trp-P5 functionalized nanochannel enables specific wettability recognition of DA molecules and has great cycle stability. With the controlling of voltage to wettability, the transport flux of DA is up to 499.73 nmol cm^-2 h^-1 at -6 V, 16.88 times higher than that under positive voltages. In response to these results, a high-throughput DA transport device based on controlled electricity-wettability is provided.

Bioinspired Photo-Responsive Liquid Gating Membrane

Stomata in the plant leaves are channels for gas exchange between the plants and the atmosphere. The gas exchange rate can be regulated by adjusting the opening and closing of stoma under the external stimuli, which plays a vital role in plant survival. Under visible light irradiation, the stomata open for gas exchange with the surroundings, while under intense UV light irradiation, the stomata close to prevent the moisture loss of plants from excessive transpiration. Inspired by this stomatal self-protection behavior, we have constructed a bioinspired photo-responsive liquid gating membrane (BPRLGM) through infusing the photo-responsive gating liquid obtained by dissolving the azobenzene-based photo-responsive surfactant molecules (AzoC8F15) in N,N-Dimethylacetamide (DMAC) into nylon porous substrate, which can reversibly switch the open/closed states under different photo-stimuli. Theoretical analysis and experimental data have demonstrated that the reversible photoisomerization of azobenzene-based surfactant molecules induces a change in surface tension of the photo-responsive gating liquid, which eventually results in the reversible variation of substantial critical pressure for gas through BPRLGM under alternating UV (PCritical (off)) and visible (PCritical (on)) light irradiations. Therefore, driven by a pressure difference ΔP between PCritical (on) and PCritical (off), the reversible switches on the open/closed states of this photo-responsive liquid gating membrane can be realized under photo-stimuli. This bioinspired membrane with switchable open/closed liquid gating performance under photo-stimuli has the opportunity to be used in the precise and contactless control of microfluidics.

Light-Controlled Ionic/Molecular Transport through Solid-State Nanopores and Nanochannels

Biological nanochannels perfectly operate in organisms and exquisitely control mass transmembrane transport for complex life process. Inspired by biological nanochannels, plenty of intelligent artificial solid-state nanopores and nanochannels are constructed based on various materials and methods with the development of nanotechnology. Specially, the light-controlled nanopores/nanochannels have attracted much attention due to the unique advantages in terms of that ion and molecular transport can be regulated remotely, spatially and temporally. According to the structure and function of biological ion channels, light-controlled solid-state nanopores/nanochannels can be divided into light-regulated ion channels with ion gating and ion rectification functions, and light-driven ion pumps with active ion transport property. In this review, we present a systematic overview of light-controlled ion channels and ion pumps according to the photo-responsive components in the system. Then, the related applications of solid-state nanopores/nanochannels for molecular sensing, water purification and energy conversion are discussed. Finally, a brief conclusion and short outlook are offered for future development of the nanopore/nanochannel field.

Interfacial Superassembly of Mesoporous Titania Nanopillar-Arrays/Alumina Oxide Heterochannels for Light- and pH-Responsive Smart Ion Transport

Stimuli-responsive nanochannels have attracted extensive attention in various fields owing to their precise regulation ability of ionic transportation. However, the poor controllability and functionality as well as responding to only one type of external stimulus still impede the development of the smart nanochannels. Here, we demonstrate a novel heterogeneous membrane composed of ordered mesoporous titania nanopillar-arrays/anodic aluminum oxide (MTI/AAO) using an interfacial superassembly strategy, which can achieve intelligent light and pH multimodulation ion transport. The MTI/AAO membranes are generated through the self-assembly of templates, followed by interfacial superassembly of micelles on AAO, and then the nanostructure and phase transformation of titania. The presence of the MTI layer with anatase crystal endows the heterogeneous membrane with an excellent light-responsive current density of 219.2 μA·cm^-2, which is much higher than that of a reported traditional light-responsive nanofluidic device. Furthermore, the MTI/AAO heterogeneous membranes with an asymmetric structure exhibit excellent rectification performance. Moreover, pH-regulated surface charge polarity leads to a reversal of current rectification polarity. This light and pH multiresponsive membrane realizes efficient, sensitive, and stable ion regulation, extending the traditional nanochannel from single modulation to smart multimodulation.

Photoresponsive Solid Nanochannels Membranes: Design and Applications

Light stimuli have notable advantages over other environmental stimuli, such as more precise spatial and temporal regulation, and the ability to serve as an energy source to power the system. In nature, photoresponsive nanochannels are important components of organisms, with examples including the rhodopsin channels in optic nerve cells and photoresponsive protein channels in the photosynthesis system of plants. Inspired by biological channels, scientists have constructed various photoresponsive, smart solid-state nanochannels membranes for a range of applications. In this review, the methods and applications of photosensitive nanochannels membranes are summarized. The authors believe that this review will inspire researchers to further develop multifunctional artificial nanochannels for applications in the fields of biosensors, stimuli-responsive smart devices, and nanofluidic devices, among others.

Porphyrin Derivative Based Tandem Response Nanochannels Triggered by Zn2+ and NO

We describe tandem response solid nanochannels tailored with a porphyrin derivative that show Zn2+ and NO gating behaviors with good selectivity, stability, and reversibility. EXAFS and fluorescence experiments showed that...

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.

Bio-inspired Track-Etched Polymeric Nanochannels: Steady-State Biosensors for Detection of Analytes

Bio-inspired polymeric nanochannel (also referred as nanopore)-based biosensors have attracted considerable attention on account of their controllable channel size and shape, multi-functional surface chemistry, unique ionic transport properties, and good robustness for applications. There are already very informative reviews on the latest developments in solid-state artificial nanochannel-based biosensors, however, which concentrated on the resistive-pulse sensing-based sensors for practical applications. The steady-state sensing-based nanochannel biosensors, in principle, have significant advantages over their counterparts in term of high sensitivity, fast response, target analytes with no size limit, and extensive suitable range. Furthermore, among the diverse materials, nanochannels based on polymeric materials perform outstandingly, due to flexible fabrication and wide application. This compressive Review summarizes the recent advances in bio-inspired polymeric nanochannels as sensing platforms for detection of important analytes in living organisms, to meet the high demand for high-performance biosensors for analysis of target analytes, and the potential for development of smart sensing devices. In the future, research efforts can be focused on transport mechanisms in the field of steady-state or resistive-pulse nanochannel-based sensors and on developing precisely size-controlled, robust, miniature and reusable, multi-functional, and high-throughput biosensors for practical applications. Future efforts should aim at a deeper understanding of the principles at the molecular level and incorporating these diverse pore architectures into homogeneous and defect-free multi-channel membrane systems. With the rapid advancement of nanoscience and biotechnology, we believe that many more achievements in nanochannel-based biosensors could be achieved in the near future, serving people in a better way.

Controllable ion transport induced by pH gradient in a thermally crosslinked submicrochannel heterogeneous membrane

Solid-state nanochannels have attracted considerable attention for their similar ion transport properties to biological ion channels. The construction of porous ion channels with good stability at the submicro/micrometer scale is very beneficial to develop large-area ion channel devices. In this manuscript, based on in-situ thermal crosslinking of a small organic molecule containing triphenylamine and styrene groups, we construct a heterogeneous membrane with asymmetrical charge and wettability on cylindrical anodic aluminum oxide (AAO) channels (D ≈ 319 nm). This heterogeneous membrane has typical ion current rectification characteristics with a high rectification ratio of 36.9 and good stability. This work provides an effective strategy for the construction of submicrochannel heterogeneous membranes and also broadens the application range of bionic ion channels.

Bioinspired Solid-State Nanochannel Sensors: From Ionic Current Signals, Current, and Fluorescence Dual Signals to Faraday Current Signals

Inspired from bioprotein channels of living organisms, constructing "abiotic" analogues, solid-state nanochannels, to achieve "smart" sensing towards various targets, is highly seductive. When encountered with certain stimuli, dynamic switch of terminal modified probes in terms of surface charge, conformation, fluorescence property, electric potential as well as wettability can be monitored via transmembrane ionic current, fluorescence intensity, faraday current signals of nanochannels and so on. Herein, the modification methodologies of nanochannels and targets-detecting application are summarized in ions, small molecules, as well as biomolecules, and systematically reviewed are the nanochannel-based detection means including 1) by transmembrane current signals; 2) by the coordination of current- and fluorescence-dual signals; 3) by faraday current signals from nanochannel-based electrode. The coordination of current and fluorescence dual signals offers great benefits for synchronous temporal and spatial monitoring. Faraday signals enable the nanoelectrode to monitor both redox and non-redox components. Notably, by incorporation with confined effect of tip region of a needle-like nanopipette, glorious in-vivo monitoring is conferred on the nanopipette detector at high temporal-spatial resolution. In addition, some outlooks for future application in reliable practical samples analysis and leading research endeavors in the related fantastic fields are provided.

Molecular Design of Solid-State Nanopores: Fundamental Concepts and Applications

Solid-state nanopores are fascinating objects that enable the development of specific and efficient chemical and biological sensors, as well as the investigation of the physicochemical principles ruling the behavior of biological channels. The great variety of biological nanopores that nature provides regulates not only the most critical processes in the human body, including neuronal communication and sensory perception, but also the most important bioenergetic process on earth: photosynthesis. This makes them an exhaustless source of inspiration toward the development of more efficient, selective, and sophisticated nanopore-based nanofluidic devices. The key point responsible for the vibrant and exciting advance of solid nanopore research in the last decade has been the simultaneous combination of advanced fabrication nanotechnologies to tailor the size, geometry, and application of novel and creative approaches to confer the nanopore surface specific functionalities and responsiveness. Here, the state of the art is described in the following critical areas: i) theory, ii) nanofabrication techniques, iii) (bio)chemical functionalization, iv) construction of nanofluidic actuators, v) nanopore (bio)sensors, and vi) commercial aspects. The plethora of potential applications once envisioned for solid-state nanochannels is progressively and quickly materializing into new technologies that hold promise to revolutionize the everyday life.

Engineered Artificial Nanochannels for Nitrite Ion Harmless Conversion

Inspired by the delicate functions of living organisms to transport or transform nitrite ions (NO₂^-), a bioinspired smart nanochannel that can realize harmless conversion of NO₂^- into N₂ is developed by immobilizing a NO₂^--responsive functional molecule, p-phenylenediamine, onto a single conical polyethylene terephthalate nanochannel. Subsequently, the aromatic primary amine groups could be triggered to transform into a phenyldiazonium molecule based on the acid-activated NO₂^--binding process. The nanochannel exhibits specific selectivity and highly ultratrace recognition of NO₂^-. Fascinatingly, the transformed phenyldiazonium molecules could be triggered to generate phenol groups and release N₂ by ultraviolet light activation, achieving NO₂^- harmless conversion. This system could provide inspiration to construct artificial nanofluidic devices for ion-sensing and nitrogen cycle fields.