Smart DNA Hydrogel Integrated Nanochannels with High Ion Flux and Adjustable Selective Ionic Transport

Improved Ion Transport and High Energy Conversion through Hydrogel Membrane with 3D Interconnected Nanopores

To mimic and use the functions of the ion transport system that are central to biological processes, bioinspired ion-selective membranes are developed and show great potential in a variety of fields. However, the practical applications of them are now limited due to low pore density, low conductivity, or scale-up difficulty. Herein, we demonstrate a 2-hydroxyethyl methacrylate phosphate (HEMAP) hydrogel membrane with 3D interconnected nanopores and space charged through simple photopolymerization. The HEMAP hydrogel membrane exhibits high conductance and outstanding ion selectivity, and the membrane-based osmotic power generator shows the excellent output power density up to 5.38 W/m². Both experimentally and theoretically, the 3D interconnected structure is revealed to play a key role in enhancing charge-governed ion transport and energy conversion. This work highlights the advantages of 3D interconnected nanopores in ion diffusion and shows the potential of our designed hydrogel membrane in osmotic energy conversion, water desalination, and sensors.

Robust sulfonated poly (ether ether ketone) nanochannels for high-performance osmotic energy conversion

The membrane-based reverse electrodialysis (RED) technique has a fundamental role in harvesting clean and sustainable osmotic energy existing in the salinity gradient. However, the current designs of membranes cannot cope with the high output power density and robustness. Here, we construct a sulfonated poly (ether ether ketone) (SPEEK) nanochannel membrane with numerous nanochannels for a membrane-based osmotic power generator. The parallel nanochannels with high space charges show excellent cation-selectivity, which could further be improved by adjusting the length and charge density of nanochannels. Based on numerical simulation, the system with space charge shows better conductivity and selectivity than those of a surface-charged nanochannel. The output power density of our proposed membrane-based device reaches up to 5.8 W/m2 by mixing artificial seawater and river water. Additionally, the SPEEK membranes exhibit good mechanical properties, endowing the possibility of creating a high-endurance scale-up membrane-based generator system. We believe that this work provides useful insights into material design and fluid transport for the power generator in osmotic energy conversion.

Stimuli-Responsive Biomolecule-Based Hydrogels and Their Applications

This Review presents polysaccharides, oligosaccharides, nucleic acids, peptides, and proteins as functional stimuli-responsive polymer scaffolds that yield hydrogels with controlled stiffness. Different physical or chemical triggers can be used to structurally reconfigure the crosslinking units and control the stiffness of the hydrogels. The integration of stimuli-responsive supramolecular complexes and stimuli-responsive biomolecular units as crosslinkers leads to hybrid hydrogels undergoing reversible triggered transitions across different stiffness states. Different applications of stimuli-responsive biomolecule-based hydrogels are discussed. The assembly of stimuli-responsive biomolecule-based hydrogel films on surfaces and their applications are discussed. The coating of drug-loaded nanoparticles with stimuli-responsive hydrogels for controlled drug release is also presented.

Ultrasensitive detection of ochratoxin A based on biomimetic nanochannel and catalytic hairpin assembly signal amplification

In this paper, an ultrasensitive nanochannel sensor has been proposed for label-free Ochratoxin A (OTA) assay in combination with graphene oxide (GO) and catalyzed hairpin assembly (CHA). The high-performance sensor is segmented into two parts. One is composed of graphene oxide (GO) and DNA probes. In the presence of target OTA, OTA works as a catalyst to trigger the self-assembly pathway of the two probes and initiate the cycling of CHA circuits, which results in numerous double-stranded DNAs (dsDNA) in solution. The excess ssDNA probes are removed by GO. The other part is composed of biomimetic nanochannel coated with polyethyleneimine (PEI) and Zr⁴⁺, which can quantify the concentration of OTA by detecting the dsDNA in solution. The nanofluidic device has a detection limit of as low as 6.2 pM with an excellent selectivity. The nanochannel based assay was used to analyse food samples (red wine) with satisfied results. Thus, the proposed analytical method will provide a new approach the detection of OTA and can be applied for quality control to ensure food safety.

Biocatalytic reversible control of the stiffness of DNA-modified responsive hydrogels: applications in shape-memory, self-healing and autonomous controlled release of insulin

The enzymes glucose oxidase (GOx), acetylcholine esterase (AchE) and urease that drive biocatalytic transformations to alter pH, are integrated into pH-responsive DNA-based hydrogels. A two-enzyme-loaded hydrogel composed of GOx/urease or AchE/urease and a three-enzyme-loaded hydrogel composed of GOx/AchE/urease are presented. The biocatalytic transformations within the hydrogels lead to the dictated reconfiguration of nucleic acid bridges and the switchable control over the stiffness of the respective hydrogels. The switchable stiffness features are used to develop biocatalytically guided shape-memory and self-healing matrices. In addition, loading of GOx/insulin in a pH-responsive DNA-based hydrogel yields a glucose-triggered matrix for the controlled release of insulin, acting as an artificial pancreas. The release of insulin is controlled by the concentrations of glucose, hence, the biocatalytic insulin-loaded hydrogel provides an interesting sense-and-treat carrier for controlling diabetes.

Fabrication of a Biomimetic Nanochannel Logic Platform and Its Applications in the Intelligent Detection of miRNA Related to Liver Cancer

Nanochannel-based analytical techniques have great potential applications for nucleic acid sequencing and high sensitivity detection of biological molecules. However, the sensitivity of conventional solid-state nanochannel sensors is hampered by a lack of effective signal amplification strategies, which has limited its utility in the field of analytical chemistry. Here we selected a solid-state nanochannnel modified with polyethylenimine and Zr⁴⁺ in combination with graphene oxide as the sensing platform. The high-performance sensor is based upon the change of the surface charge of the nanochannel, which is resulted from DNA cascade signal amplification in solution. The target miRNA (miR-122) can be indirectly quantitated with a detection limit of 97.2 aM with an excellent selectivity. Depending on the nucleic acid's hybridization and configuration transform, the designed nanochannel sensing systems can realize the intelligent detection of multiple liver cancer-related miRNA (miR-122 and miR Let-7a) integrating with cascaded INHIBIT-OR logic gate to provide theoretical guidance and technical support for clinical diagnosis and therapeutic evaluation of liver cancer.

Tailoring DNA Self-assembly to Build Hydrogels

DNA hydrogels are crosslinked polymeric networks in which DNA is used as the backbone or the crosslinker. These hydrogels are novel biofunctional materials that possess the biological character of DNA and the framed structure of hydrogels. Compared with other kinds of hydrogels, DNA hydrogels exhibit not only high mechanical strength and controllable morphologies but also good recognition ability, designable responsiveness, and programmability. The DNA used in this type of hydrogel acts as a building block for self-assembly or as a responsive element due to its sequence recognition ability and switchable structural transitions, respectively. In this review, we describe recent developments in the field of DNA hydrogels and discuss the role played by DNA in these hydrogels. Various synthetic strategies for and a range of applications of DNA hydrogels are detailed.

Redox-Switchable Binding Properties of the ATP-Aptamer

In this study, we report on a redox-controllable and reversible complete "ON"/"OFF"-switchable aptamer binding to ATP. A series of methylene blue-modified ATP-aptamers was synthesized, revealing improved binding affinities toward ATP as compared to the nonmodified aptamer. These binding affinities were dependent on the conjugation site of the redox label on the aptamer scaffold. Importantly, we find that the oxidized methylene blue-modified aptamers bind to ATP with micromolar affinity, while the reduced form lacks binding affinity toward ATP, resulting in an unprecedented complete "ON"/"OFF" redox-controllable aptamer switch. We demonstrate the cyclic "ON"/"OFF" binding of ATP to the methylene blue-functionalized aptamer through cyclic oxidation and reduction of the redox label using both chemical and electrochemical means. Molecular dynamics and docking simulations were performed to account for the redox-switchable properties of the conjugated aptamers and to rationalize the enhanced binding affinities of the different aptamer designs.

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.

Quantum-Confined-Superfluidics-Enabled Moisture Actuation Based on Unilaterally Structured Graphene Oxide Papers

The strong interaction between graphene oxides (GO) and water molecules has trigged enormous research interest in developing GO-based separation films, sensors, and actuators. However, sophisticated control over the ultrafast water transmission among the GO sheets and the consequent deformation of the entire GO film is still challenging. Inspired from the natural "quantum-tunneling-fluidics-effect," here quantum-confined-superfluidics-enabled moisture actuation of GO paper by introducing periodic gratings unilaterally is reported. The folded GO nanosheets that act as quantum-confined-superfluidics channels can significantly promote water adsorption, enabling controllable and sensitive moisture actuation. Water-adsorption-induced expansion along and against the normal direction of a GO paper is investigated both theoretically and experimentally. Featuring state-of-the-art of ultrafast response (1.24 cm^-1 s^-1 ), large deformation degree, and complex and predictable deformation, the smart GO papers are used for biomimetic mini-robots including a creeping centipede and a smart leaf that can catch a living ladybug. The reported method is simple and universal for 2D materials, revealing great potential for developing graphene-based smart robots.

Biomolecule-Functionalized Solid-State Ion Nanochannels/Nanopores: Features and Techniques

Solid-state ion nanochannels/nanopores, the biomimetic products of biological ion channels, are promising materials in real-world applications due to their robust mechanical and controllable chemical properties. Functionalizations of solid-state ion nanochannels/nanopores by biomolecules pave a wide way for the introduction of varied properties from biomolecules to solid-state ion nanochannels/nanopores, making them smart in response to analytes or external stimuli and regulating the transport of ions/molecules. In this review, two features for nanochannels/nanopores functionalized by biomolecules are abstracted, i.e., specificity and signal amplification. Both of the two features are demonstrated from three kinds of nanochannels/nanopores: nucleic acid-functionalized nanochannels/nanopores, protein-functionalized nanochannels/nanopores, and small biomolecule-functionalized nanochannels/nanopores, respectively. Meanwhile, the fundamental mechanisms of these combinations between biomolecules and nanochannels/nanopores are explored, providing reasonable constructs for applications in sensing, transport, and energy conversion. And then, the techniques of functionalizations and the basic principle about biomolecules onto the solid-state ion nanochannels/nanopores are summarized. Finally, some views about the future developments of the biomolecule-functionalized nanochannels/nanopores are proposed.

DNA-Based Hydrogels Loaded with Au Nanoparticles or Au Nanorods: Thermoresponsive Plasmonic Matrices for Shape-Memory, Self-Healing, Controlled Release, and Mechanical Applications

Gold nanoparticles (AuNPs) or gold nanorods (AuNRs) are loaded in polyacrylamide hydrogels cooperatively cross-linked by bis-acrylamide and nucleic acid duplexes or boronate ester-glucosamine and nucleic acid duplexes. The thermoplasmonic properties of AuNPs and AuNRs are used to control the stiffness of the hydrogels. The irradiation of the AuNP-loaded (λ = 532 nm) or the AuNR-loaded (λ = 808 nm) hydrogels leads to thermoplasmonic heating of the hydrogels, the dehybridization of the DNA duplexes, and the formation of hydrogels with lower stiffness. By ON/OFF irradiation, the hydrogels are switched between low- and high-stiffness states. The reversible control over the stiffness properties of the hydrogels is used to develop shape-memory hydrogels and self-healing soft materials and to tailor thermoplasmonic switchable drug release. In addition, by designing bilayer composites of AuNP- and AuNR-loaded hydrogels, a reversible thermoplasmonic, light-induced bending is demonstrated, where the bending direction is controlled by the stress generated in the respective bilayer composite.

Stepping gating of ion channels on nanoelectrode via DNA hybridization for label-free DNA detection

Natural ion channels on cell membrane can gate the transport of ions and molecules by the conformational alteration of transmembrane proteins to regulate the normal physiological activities of cells. Inspired by the similarity of the conformation change under specific stimuli, here we introduce an ion channel gating model on a single nanoelectrode by anchoring DNA-gated switches on the very nanotip of gold nanoelectrode to mimic the response-to-stimulus behaviors of ion channels on bio-membranes. The surface-tethered DNA ion channels can be switched on by the Watson-Crick base pairing, which can alter the conformation of the tethered DNA from lying state to upright state. And these conformational alterations of the anchored DNA switches can effectively gate the transport of potassium ferricyanide onto the electrode interface. By continuously initiating the gates with DNA of different concentrations, we achieved the stepping gating of ion channels on a single nanoelectrode. Further, we demonstrated that the ion gating system on nanoelectrode showed excellent sensing performance. For example, the response kinetic was very fast with the signal saturation time of ~1 min, the reproducibility of the OFF/ON switch was robust enough to sustain for two cycles, and simultaneously, the specificity was high enough to distinguish complementary DNA and noncomplementary DNA. When used for label-free DNA detection, the limit of detection can be as low as 10 pM. This study provides a promising avenue to achieve label free and real-time detection of multiple biomolecules.

DNA Quadruple Helices in Nanotechnology

DNA has played an early and powerful role in the development of bottom-up nanotechnologies, not least because of DNA's precise, predictable, and controllable properties of assembly on the nanometer scale. Watson-Crick complementarity has been used to build complex 2D and 3D architectures and design a number of nanometer-scale systems for molecular computing, transport, motors, and biosensing applications. Most of such devices are built with classical B-DNA helices and involve classical A-T/U and G-C base pairs. However, in addition to the above components underlying the iconic double helix, a number of alternative pairing schemes of nucleobases are known. This review focuses on two of these noncanonical classes of DNA helices: G-quadruplexes and the i-motif. The unique properties of these two classes of DNA helix have been utilized toward some remarkable constructions and applications: G-wires; nanostructures such as DNA origami; reconfigurable structures and nanodevices; the formation and utilization of hemin-utilizing DNAzymes, capable of generating varied outputs from biosensing nanostructures; composite nanostructures made up of DNA as well as inorganic materials; and the construction of nanocarriers that show promise for the therapeutics of diseases.

Light-responsive arylazopyrazole-based hydrogels: their applications as shape-memory materials, self-healing matrices and controlled drug release systems

Carboxymethyl cellulose functionalized with nucleic acids, β-cyclodextrin and arylazopyrazole photoisomerizable units self-assembles into stimuli-responsive hydrogels.

Constructing peptide-based artificial hydrolases with customized selectivity

The substrate selectivity of peptide-based artificial enzymes can be customized by combining molecularly imprinted polymers as binding sites with peptide nanofibers as catalytic moieties.

Self-assembly of a magnetic DNA hydrogel as a new biomaterial for enzyme encapsulation with enhanced activity and stability

A rationally designed strategy has been established to construct a magnetic DNA hydrogel for enzyme encapsulation through a programmable one-pot self-assembly approach.

Chemical and photochemical DNA "gears" reversibly control stiffness, shape-memory, self-healing and controlled release properties of polyacrylamide hydrogels

A new class of stimuli-responsive DNA-based polyacrylamide hydrogels is described. They consist of glucosamine-boronate ester-crosslinked polyacrylamide chains being cooperatively bridged by stimuli-responsive nucleic acids. The triggered closure and dissociation of the stimuli-responsive units lead to switchable stiffness properties of the hydrogel. One hydrogel includes glucosamine-boronate esters and K⁺-ion-stabilized G-quadruplex units as cooperative crosslinkers. The hydrogel bridged by the two motifs reveals high stiffness, whereas the separation of the G-quadruplex bridges by 18-crown-6-ether yields a low stiffness hydrogel. By cyclic treatment of the hydrogel with K⁺-ions and 18-crown-6-ether, it is reversibly cycled between high and low stiffness states. The second system involves a photo-responsive hydrogel that reveals light-induced switchable stiffness functions. The polyacrylamide chains are cooperatively crosslinked by glucosamine-boronate esters and duplex nucleic acid bridges stabilized by trans-azobenzene intercalator units. The resulting hydrogel reveals high stiffness. Photoisomerization of the trans-azobenzene units to the cis-azobenzene states results in the separation of the duplex nucleic acid bridges and the formation of a low stiffness hydrogel. The control over the stiffness properties of the hydrogel matrices by means of K⁺-ions/crown ether or photoisomerizable trans-azobenzene/cis-azobenzene units is used to develop shape-memory, self-healing, and controlled drug-release hydrogel materials.

Shape-memory and self-healing functions of DNA-based carboxymethyl cellulose hydrogels driven by chemical or light triggers

Photoresponsive nucleic acid-based carboxymethyl cellulose (CMC) hydrogels are synthesized, and their application as shape-memory and self-healing functional matrices are discussed. One system involves the preparation of a carboxymethyl cellulose hydrogel crosslinked by self-complementary nucleic acid duplexes and by photoresponsive trans-azobenzene/β-cyclodextrin (β-CD) supramolecular complexes. Photoisomerization of the trans-azobenzene to the cis-azobenzene results in a hydrogel exhibiting lower stiffness due to the separation of the azobenzene/β-CD bridging units. The hydrogel is switched between high and low stiffness states by the cyclic and reversible light-induced isomerization of the azobenzene units between the trans and cis states. The light-controlled stiffness properties of the hydrogel are used to develop a shape-memory hydrogel, where the duplex bridging units act as permanent memory in the quasi-liquid shapeless state of the hydrogel. A second system in the study is a carboxymethyl cellulose hydrogel crosslinked by the K+-stabilized G-quadruplex bridging units and by trans-azobenzene/β-CD complexes. The resulting hydrogel includes dual-trigger functionalities, where the trans-azobenzene/β-CD complexes can be reversibly formed and dissociated through the trans and cis photoisomerization of the azobenzene units, and the K+-stabilized G-quadruplexes can be reversibly dissociated and reformed in the presence of 18-crown-6-ether/K+-ions. The signal-responsive crosslinked hydrogel reveals controlled stiffness properties, where the hydrogel crosslinked by the trans-azobenzene/β-CD and K+-ion-stabilized G-quadruplex reveals high stiffness and the hydrogel crosslinked only by the K+-ion-stabilized G-quadruplexes or only by the trans-azobenzene/β-CD complexes reveals low stiffness properties. The controlled stiffness properties of the hydrogel are used to develop shape-memory hydrogels, where the trans-azobenzene/β-CD complexes or the K+-ion-stabilized G-quadruplexes act as permanent memories in the shapeless and quasi-liquid states of the hydrogels. In addition, the hydrogel that includes two types of stimuli-responsive crosslinking units is used as a self-healing matrix, where each of the triggers guides the self-healing processes.