Visual Chemical Detection Mechanism by a Liquid Gating System with Dipole-Induced Interfacial Molecular Reconfiguration

Visual Biosensing with Specific Liquid-Based Interface Behaviors

Liquid-based interface behaviors at micro/nano or even smaller scales induced by biomolecules take us into a fascinating realm, fostering a deeper understanding and innovation in visual biosensing. This biosensing technology, grounded in specific liquid-based interface behaviors, redefines how diseases can be detected, monitored, and diagnosed in resource-limited settings, providing rapid, cost-effective, and self-testing solutions to the current healthcare landscape. To date, the technology has witnessed significant advancements in visual sensing, driven by diverse liquid-based materials, advanced nanomanufacturing techniques, and a profound understanding of interface-material interactions. In this Perspective, we discuss and elucidate the interface biosensing mechanisms arising from three types, including liquid-solid, liquid-liquid, and liquid-gas interfaces, and we provide insights into the challenges and future development of visual biosensing applications.

Nano-Structural Superwetting Surfaces for Highly Reliable On-Site Detection of Bisphenol A

In the domain of big data geographic screening for environmental pollutants, the expeditious dissemination of testing results to environmental investigation professionals is pivotal in facilitating comprehensive analysis and the implementation of more efficacious strategies for managing environmental issues. However, this endeavor can prove to be particularly arduous when conducting examinations in remote, resource-scarce rural areas and field environments, where deficient infrastructure often emerges as the principal impediment to unimpeded environmental monitoring. Therefore, the development of a reliable and portable monitoring strategy with the ability to analyze large amounts of data is highly required. Here, a deep-learning (DL)-assisted portable sensing strategy was developed based on thermal and pH dual-responsive nano-structural superwetting surfaces, for highly reliable, quick, and field monitoring of environmental pollutants. In our experiment, bisphenol A (BPA) was selected as the representative pollute. The achieved limit of detection, attaining a remarkably low value of 1.05 μM, unequivocally adhered to stringent international testing standards for evaluating the migration of BPA in thermal paper. Based on a DL image classification algorithm, highly precise predictions regarding the migration of BPA concentration were achieved, with an accuracy rate exceeding 99%. Furthermore, it successfully facilitated automated and exceedingly reliable monitoring of the migration of BPA from thermal paper within the principal provinces of thermal paper production in China. This strategy engenders the potential to establish correlations between environmental pollutant concentrations in specific regions and the prevalence of certain human ailments.

Dilational Rheology of Extended Surfactants at the Air/Water and Oil/Water Interfaces: Effect of Propylene Oxide Group Numbers

In this paper, the interfacial properties of extended surfactants with different oxypropylene (PO) groups were comprehensively investigated by using interfacial dilational rheology. The differences in molecular orientation, spatial configuration, and relaxation process were compared at the gas-water interface and oil-water interface. The influences of the PO groups on the interface viscoelasticity were analyzed, providing important theoretical support for the wide application of extended surfactants. Experimental results show that the lower number of PO groups in extended surfactants does not cause differences in their presence states on the interface; however, once it increases, the longer PO segment will spiral up in the direction perpendicular to the interface, forming a spatial configuration like a thin cylinder. Compared with air, the PO group has better solubility in the oil phase. The chain segment can still maintain a helical extension from the beginning to the end as a result. However, the upper layer of the thin cylinder will collapse to a certain extent at the surface. Moreover, the orientation of the hydrophobic side has a dynamic process of "tilting to upright" with the increase of adsorption amount or in response to interfacial dilation and compression. The increase of PO number or the insertion of oil molecules has little effect on dilational modulus, and the interfacial film strength is generally relatively low. That is to say, the better emulsifying and solubilizing ability of PO-containing extended surfactants may be more attributed to the matching steric effect at interface or better packing action in bulk phase than to higher film strength.

The Study of Interfacial Adsorption Behavior for Hydroxyl-Substituted Alkylbenzene Sulfonates by Interfacial Tension Relaxation Method

In order to explore the interface adsorption mechanism of hydroxyl-substituted alkylbenzene sulfonates, the interfacial tension relaxation method was used to investigate the dilational rheology properties of sodium 2-hydroxy-3-octyl-5-octylbenzene sulfonate (C₈C₈OHphSO₃Na) and sodium 2-hydroxy-3-octyl-5-decylbenzene sulfonate (C₈C₁₀OHphSO₃Na) at the gas-liquid interface and oil-water interface. The effect of the length of the hydroxyl para-alkyl chain on the interfacial behavior of the surfactant molecules was investigated, and the main controlling factors of the interfacial film properties under different conditions were obtained. The experimental results show that for the gas-liquid interface, the long-chain alkyl groups adjacent to the hydroxyl group in the hydroxyl-substituted alkylbenzene sulfonate molecules tend to extend along the interface, showing strong intermolecular interaction, which is the main reason why the dilational viscoelasticity of the surface film is higher than that of ordinary alkylbenzene sulfonates. The length of the para-alkyl chain has little effect on the viscoelastic modulus. With the increase in surfactant concentration, the adjacent alkyl chain also began to extend into the air, and the factors controlling the properties of the interfacial film changed from interfacial rearrangement to diffusion exchange. For the oil-water interface, the presence of oil molecules will hinder the interface tiling of the hydroxyl-protic alkyl, and the dilational viscoelasticity of C₈C₈ and C₈C₁₀ will be greatly reduced relative to the surface. The main factor controlling the properties of the interfacial film is the diffusion exchange of surfactant molecules between the bulk phase and the interface from the beginning.

Non-Newtonian fluid gating membranes with acoustically responsive and self-protective gas transport control

Control of gas transport through porous media is desired in multifarious processes such as chemical reactions, interface absorption, and medical treatment. Liquid gating technology, based on dynamically adaptive interfaces, has been developed in recent years and has shown excellent control capability in gas manipulation-the reversible opening and closing of a liquid gate for gas transport as the applied pressure changes. Here, we report a new strategy to achieve self-protective gas transport control by regulating the dynamic porous interface in a non-Newtonian fluid gating membrane based on the shear thickening fluid. The gas transport process can be suspended and restored via modulation of the acoustic field, owing to the transition of particle-to-particle interactions in a confined geometry. Our experimental and theoretical results support the stability and tunability of the gas transport control. In addition, relying on the shear thickening behaviour of the gating fluid, the transient response can be achieved to resist high-impact pressure. This strategy could be utilized to design integrated smart materials used in complex and extreme environments such as hazardous and explosive gas transportation.

Membranes for the life sciences and their future roles in medicine

Since the global outbreak of COVID-19, membrane technology for clinical treatments, including extracorporeal membrane oxygenation (ECMO) and protective masks and clothing, has attracted intense research attention for its irreplaceable abilities. Membrane research and applications are now playing an increasingly important role in various fields of life science. In addition to intrinsic properties such as size sieving, dissolution and diffusion, membranes are often endowed with additional functions as cell scaffolds, catalysts or sensors to satisfy the specific requirements of different clinical applications. In this review, we will introduce and discuss state-of-the-art membranes and their respective functions in four typical areas of life science: artificial organs, tissue engineering, in vitro blood diagnosis and medical support. Emphasis will be given to the description of certain specific functions required of membranes in each field to provide guidance for the selection and fabrication of the membrane material. The advantages and disadvantages of these membranes have been compared to indicate further development directions for different clinical applications. Finally, we propose challenges and outlooks for future development.

Carbon Dioxide Chemically Responsive Switchable Gas Valves with Protonation-Induced Liquid Gating Self-Adaptive Systems

Carbon dioxide (CO₂ ) capture and storage technologies are promising to limit CO₂ emission from anthropogenic activities, to achieve carbon neutrality goals. CO₂ capture requires one to separate CO₂ from other gases, and therefore a gas flow system that exhibits discernible gating behaviors for CO₂ would be very useful. Here we propose a self-adaptive CO₂ gas valve composed of chemically responsive liquid gating systems. The transmembrane critical pressures of the liquid gate vary upon the presence of CO₂ , due to the superamphiphiles assembled by poly(propylene glycol) bis(2-aminopropyl ether) and oleic acid in gating liquids that are protonated specifically by CO₂ . It is shown that the valve can perform self-adaptive regulation for specific gases and different concentrations of CO₂ . This protonation-induced liquid gating mechanism opens a potential platform for applications of CO₂ separators, detectors, sensors and beyond.

Host-guest liquid gating mechanism with specific recognition interface behavior for universal quantitative chemical detection

Universal visual quantitative chemical detection technology has emerged as an increasingly crucial tool for convenient testing with immediate results in the fields of environmental assessment, homeland security, clinical drug testing and health care, particularly in resource-limited settings. Here, we show a host-guest liquid gating mechanism to translate molecular interface recognition behavior into visually quantifiable detection signals. Quantitative chemical detection is achieved, which has obvious advantages for constructing a portable, affordable, on-site sensing platform to enable the visual quantitative testing of target molecules without optical/electrical equipment. Experiments and theoretical calculations confirm the specificity and scalability of the system. This mechanism can also be tailored by the rational design of host-guest complexes to quantitatively and visually detect various molecules. With the advantages of versatility and freedom from additional equipment, this detection mechanism has the potential to revolutionize environmental monitoring, food safety analysis, clinical drug testing, and more.

In field, visual, chemical detection is of use for a wide range of possible applications. Here, the authors report on the creation of a host-guest liquid gating mechanism where detection of the target host triggers gate opening allowing for gas through the liquid gate, which can be used for visual detection.

Liquid Gating Meniscus-Shaped Deformable Magnetoelastic Membranes with Self-Driven Regulation of Gas/Liquid Release

Liquid gating membranes have been demonstrated to show unprecedented properties of dynamicity, stability, adaptivity, and stimulus-responsiveness. Most recently, smart liquid gating membranes have attracted increasing attention to bring some brand-new properties for real-world applications, and various environment-driven systems have been created. Here, a self-driven system of a smart liquid gating membrane is further developed by designing a new sytem based on a liquid gating magnetoelastic porous membrane with reversible meniscus-shaped deformations, and it is not subject to the complex gating liquid restriction of magnetorheological fluids. Compared with other systems, this magnetic-responsive self-driven system has the advantage that it provides a universal and convenient way to realize active regulation of gas/liquid release. Experiments and theoretical calculations demonstrate the stability, the nonfouling behavior, and the tunability of the system. In addition, this system can be used to perfectly open and close gas transport, and the gating pressure threshold for the liquid release can be reduced under the same conditions. Based on the above capabilities, combined with the fast and 3D contactless operation, it will be of benefit in fields ranging from visible gas/liquid mixture content monitoring and energy-saving multiphase separation, remote fluid release, and beyond.

Terraced and Three-dimensional Pyramid-shaped Polymer Single Crystal via low temperature-Assisted Microfluidic Technology

Three-dimensional pyramidal polymer single crystals provide spatial gradient variations within the crystal molecules, and these variations facilitate the study of the relationship between structure and properties within the molecules of various complexes with anisotropic structures. As described herein, we propose a low-temperature-assisted microfluidic pore channeling approach to prepare structurally ordered polymer single crystals. A mixture of dichloromethane and dimethyl sulfoxide was used as a prepolymer, and a liquid microfluidic technique was employed to grow the end-functionalized polymers into three-dimensional polymer single crystals. Through the ordered growth of single crystals, a personalized pyramidal pattern with a homogeneous structure was formed. To evaluate the mesh node density, low-temperature growth time and substrate type were also investigated. Rectangular, pyramidal, and dendritic patterns were synthesized via low-temperature single crystal growth. This work shows that low temperature-assisted microfluidics provides a novel means to tune the three-dimensional structure of polymer single crystals. This article is protected by copyright. All rights reserved.

Ionic Signal Enhancement by the Space Charge Effect through the DNA Rolling Circle Amplification on the Outer Surface of Nanochannels

DNA species are recognized as a powerful probe for nanochannel analyses to address the issues of specific target recognition and highly efficient signal conversion due to their programmable and predictable Watson-Crick bases. However, in the conventional view, abundant sophisticated DNA structures synthesized by DNA amplification strategies are unsuitable for use in nanochannel analyses owing to their low probability to enter a nanochannel restricted by the smaller opening of the nanochannel, as well as the faint ion signal produced by the steric effect. Here, we present an integrated strategy of nanochannel analyses that combines the target recognitions by encoded rolling circle amplification (RCA) in solution and the ionic signal enhancement by the space charge effect through the immobilization of highly negative-charged RCA amplicons on the outer surface of the nanochannels. Owing to the highly negative-charged RCA amplicons with 100 nm sizes, a sharp increase of ionic current up to 7454% has been achieved. The RCA amplicon triggered by mRNA-21 on the outer surface of the poly(ethylene terephthalate) membrane with a single nanochannel realized the single-base mismatch detection of mRNA-21 with a sensitivity of 6 fM. The DNA amplicon endows the nanochannel with high sensitivity and selectivity that could extend to other applications, such as DNA sequencing, desalination, sieving, and water-energy nexus.

Liquid-Based Adaptive Structural Materials

Structural materials are used to provide stable mechanical architectures and transmit or support forces, and they play an important role in materials science and technology. During the long process of the exploitation of structural materials, the functionality of structural materials has gained prominence. Adaptive structures responding to external stimuli have come to the fore with significant advantages in structural materials. However, many solid adaptive structural materials still suffer from their single function and the lack of dynamic performance, such as issue around fouling and energy consumption, defects present everywhere in materials at the microscale, etc. To meet the increasing demands, more and more researchers have started turning their attention to liquid-based materials owing to their intrinsic spontaneous, dynamic, and functional properties. Liquid-based adaptive structural materials (LASMs) have been proposed and developed. Building upon both dynamic liquids and fixed solids, LASMs have been demonstrated to possess both dynamic adaptivity (from the active liquid part) and stable mechanical structure (from the fixed solid part), which are desired in many applications such as 3D printing, droplet manipulation, omniphobic surfaces, microfluidics, mass separation, etc. A unifying view of the recent progress of LASMs is presented, including liquid with particles, liquid with surfaces, as well as liquid with membranes. In addition, the discussion of the prospects and challenges are provided for promoting the development of LASMs.

Solid-Liquid Host-Guest Composites: The Marriage of Porous Solids and Functional Liquids

Composite materials can provide remarkable improvements over the individual constituents. Especially, with a liquid component introduced into a solid porous host, solid-liquid host-guest composites have recently come to the forefront with exceptional functions that promise them for a wealth of applications. Combining the unprecedented dynamic, transparent, omniphobic, self-healing, diffusive and adaptive nature of functional liquid with inherent solid host's property, solid-liquid host-guest composites can realize the ease of fabrication, long-term stability, and a broad spectrum of enhanced properties, which cannot be fully met by conventional solid-solid composites or liquid-liquid composites. This review presents the state-of-the-art progress in solid-liquid host-guest composites. Initially, the concept, classification, design strategy, as well as fabrication methods as a path forward to develop the composites are unraveled, and further it is elaborated on how the functionality of porous solid and functional liquid can be harnessed to create composites with a broad range of unique properties, especially, the optical, thermal, electric, mechanical, sorption, and separation properties. With these fascinating properties, a myriad of emerging applications such as optical devices, thermal management, electromagnetic-interference shielding, soft electronics, gas capture and release, and multiphase separations are touched upon, inspiring more frontier researches in materials science, interfacial chemistry, membrane science, engineering, and multidisciplinary. Finally, this review provides the perspective on the future directions of solid-liquid host-guest composites and assesses the challenges and opportunities ahead.

Revealing Ionic Signal Enhancement with Probe Grafting Density on the Outer Surface of Nanochannels

Probe-modified nanopores/nanochannels are one of the most advanced sensors because the probes interact strongly with ions and targets in nanoconfinement and create a sensitive and selective ionic signal. Recently, ionic signals have been demonstrated to be sensitive to the probe-target interaction on the outer surface of nanopores/nanochannels, which can offer more open space for target recognition and signal conversion than nanoconfined cavities. To enhance the ionic signal, we investigated the effect of grafting density, a critical parameter of the sensing interface, of the probe on the outer surface of nanochannels on the change rate of the ionic signal before and after target recognition (β). Electroneutral peptide nucleic acids and negatively charged DNA are selected as probes and targets, respectively. The experimental results showed that when adding the same number of targets, the β value increased with the probe grafting density on the outer surface. A theoretical model with clearly defined physical properties of each probe and target has been established. Numerical simulations suggest that the decrease of the background current and the aggregation of targets at the mouth of nanochannels with increasing probe grafting density contribute to this enhancement. This work reveals the signal mechanism of probe-target recognition on the outer surface of nanochannels and suggests a general approach to the nanochannel/nanopore design leading to sensitivity improvement on the basis of relatively good selectivity.

Liquid gating technology

Recent years have witnessed the emergence of liquid gating technologies that employ liquids as structural materials to provide dynamic gating control. Such technologies have attracted considerable attention globally owing their antifouling, energy-saving, reversible, and reconfigurable characteristics. This study considers a new perspective to discuss advancements in liquid gating technologies, including the concept, mechanisms, development, designs, and emerging applications. Moreover, recommendations are provided for the selection of the gating liquid and porous matrix, preparation processes, technical parameters, and theoretical modelling to guide related research. Emerging applications of liquid gating technologies, such as microscale flow control, multiphase separation, chemical detection, and biomedical catheters, are reported. Finally, the challenges currently faced by these technologies are discussed and potential directions for further research are explored to promote the use of these technologies in future applications.

Light-responsive and corrosion-resistant gas valve with non-thermal effective liquid-gating positional flow control

Safe and precise control of gas flow is one of the key factors to many physical and chemical processes, such as degassing, natural gas transportation, and gas sensor. In practical application, it is essential for the gas-involved physicochemical process to keep everything under control and safe, which significantly relies on the controllability, safety, and stability of their valves. Here we show a light-responsive and corrosion-resistant gas valve with non-thermal effective liquid-gating positional flow control under a constant pressure by incorporating dynamic gating liquid with light responsiveness of solid porous substrate. Our experimental and theoretical analysis reveal that the photoisomerization of azobenzene-based molecular photoswitches on the porous substrate enabled the gas valve to possess a light-responsive and reversible variation of substantial critical pressure of non-thermal effective gas flow switch. Moreover, the chemically inert gating liquid prevented the solid substrate from corrosion and, by combining with the high spatiotemporal resolution of light, the gas valve realizes a precisely positional open and close under a steady-state pressure. The application demonstrations in our results show the potentials of the new gas valve for bringing opportunities to many applications, such as gas-involved reaction control in microfluidics, soft actuators, and beyond.

Reconfiguring confined magnetic colloids with tunable fluid transport behavior

Collective dynamics of confined colloids are crucial in diverse scenarios such as self-assembly and phase behavior in materials science, microrobot swarms for drug delivery and microfluidic control. Yet, fine-tuning the dynamics of colloids in microscale confined spaces is still a formidable task due to the complexity of the dynamics of colloidal suspension and to the lack of methodology to probe colloids in confinement. Here, we show that the collective dynamics of confined magnetic colloids can be finely tuned by external magnetic fields. In particular, the mechanical properties of the confined colloidal suspension can be probed in real time and this strategy can be also used to tune microscale fluid transport. Our experimental and theoretical investigations reveal that the collective configuration characterized by the colloidal entropy is controlled by the colloidal concentration, confining ratio and external field strength and direction. Indeed, our results show that mechanical properties of the colloidal suspension as well as the transport of the solvent in microfluidic devices can be controlled upon tuning the entropy of the colloidal suspension. Our approach opens new avenues for the design and application of drug delivery, microfluidic logic, dynamic fluid control, chemical reaction and beyond.

Electrochemically mediated gating membrane with dynamically controllable gas transport

The regulation of mass transfer across membranes is central to a wide spectrum of applications. Despite numerous examples of stimuli-responsive membranes for liquid-phase species, this goal remains elusive for gaseous molecules. We describe a previously unexplored gas gating mechanism driven by reversible electrochemical metal deposition/dissolution on a conductive membrane, which can continuously modulate the interfacial gas permeability over two orders of magnitude with high efficiency and short response time. The gating mechanism involves neither moving parts nor dead volume and can therefore enable various engineering processes. An electrochemically mediated carbon dioxide concentrator demonstrates proof of concept by integrating the gating membranes with redox-active sorbents, where gating effectively prevented the cross-talk between feed and product gas streams for high-efficiency, directional carbon dioxide pumping. We anticipate our concept of dynamically regulating transport at gas-liquid interfaces to broadly inspire systems in fields of gas separation, miniaturized devices, multiphase reactors, and beyond.

Highly stretchable and reliable graphene oxide-reinforced liquid gating membranes for tunable gas/liquid transport

The ability of membrane technologies to dynamically tune the transport behavior for gases and liquids is critical for their applications. Although various methods have been developed to improve membrane success, tradeoffs still exist among their properties, such as permeability, selectivity, fouling resistance, and stability, which can greatly affect the performance of membranes. Existing elastomeric membrane designs can provide antifracture properties and flexibility; however, these designs still face certain challenges, such as low tensile strength and reliability. Additionally, researchers have not yet thoroughly developed membranes that can avoid fouling issues while realizing precise dynamic control over the transport substances. In this study, we show a versatile strategy for preparing graphene oxide-reinforced elastomeric liquid gating membranes that can finely modulate and dynamically tune the sorting of a wide range of gases and liquids under constant applied pressures. Moreover, the produced membranes exhibit antifouling properties and are adaptable to different length scales, pressures, and environments. The filling of graphene oxide in the thermoplastic polyurethane matrix enhances the composites through hydrogen bonds. Experiments and theoretical calculations are carried out to demonstrate the stability of our system. Our membrane exhibits good stretchability, recovery, and durability due to the elastic nature of the solid matrix and dynamic nature of the gating liquid. Dynamic control over the transport of gases and liquids is achieved through our optimized interfacial design and controllable pore deformation, which is induced by mechanical stimuli. Our strategy will create new opportunities for many applications, such as gas-involved chemical reactions, multiphase separation, microfluidics, multiphase microreactors, and particulate material synthesis.

Design of Active Interfaces Using Responsive Molecular Components

Responsive interfaces are interfaces that show a defined and reversible change in physical properties in response to external stimuli. Typically, responsive interfaces result from the immobilization of responsive molecular components at the interface that translate a nanoscale signal into a macroscopic effect. Responsive interfaces can also be obtained if the topology of the interface can be reversibly changed using an external stimulus. As the surface of any material is its connection to the environment, responsive interfaces provide opportunities for interactive materials which are not only able to change properties upon demand, but also sense their environment and act autonomously. The application of responsive molecular components at interfaces, however, requires chemical and physical compatibility with the material surface of interest, posing a challenge not least in the retention of the responsive functionality. The state of the art in "active" interfaces which display responsive wettability, permeability, or adhesion is discussed, with a particular emphasis on microscale and nanoscale patterning since patterned interfaces can give rise to unique material properties. Finally, perspectives in the development of responsive interfaces, as well as promising approaches for bypassing the most prominent challenges are discussed.

Soft interface design for electrokinetic energy conversion

The exploitation and utilization of renewable clean energy is of great significance to the sustainable development of society. Electrokinetic energy conversion (EKEC) based on micro/nanochannels is expected to provide immense potential for ocean energy harvesting, self-powered micro/nanodevices, and small portable power supplies through converting environmental energy into electrical energy. Herein, aiming to get a deeper understanding of EKEC based on micro/nanochannels, several classic theoretical models and corresponding calculation equations are introduced briefly. For high efficiency energy conversion, it is essential to clearly discuss the interface properties between the inner surface of the channel and the bulk electrolyte solution. Therefore, we put forward soft interface designs of solid-liquid and liquid-liquid interfaces, and summarize their recent progress. In addition, the different applications of EKEC, harvesting from environmental energy, are further discussed. We hope that this review will attract more scientists' attention to transform the experimental results of EKEC systems in the lab into available products on shelves.

Liquid-based porous membranes

The confluence of available membrane materials and the explorations into fluid behaviors have revolutionized liquid-based porous membranes, which deserve more attention.