DNA-Crosslinked 2D Photonic Crystal Hydrogels for Detection of Adenosine Actuated by an Adenosine-Binding Aptamer

Cleavable Strand-Fusing Cross-Linkers as Additives for Chemically Deconstructable Thermosets with Preserved Thermomechanical Properties

Permanently cross-linked polymer networks-thermosets-are often difficult to chemically deconstruct. The installation of cleavable bonds into the strands of thermosets using cleavable comonomers as additives can facilitate thermoset deconstruction without replacement of permanent cross-links, but such monomers can lead to reduced thermomechanical properties and require high loadings to function effectively, motivating the design of new and optimal cleavable additives. Here, we introduce "strand-fusing cross-linkers" (SFCs), which fuse two network strands via a four-way cleavable cross-link. SFCs enable deconstruction of model polydicyclopentadiene (pDCPD) thermosets with as little as one-fifth of the molar loading needed to achieve deconstruction using traditional cleavable comonomers. SFCs function under traditional oven curing as well as low-energy frontal ring-opening metathesis polymerization (FROMP) conditions and lead to improved thermomechanical properties, for example, glass transition temperatures, compared to prior cleavable comonomer designs. This work motivates the development of increasingly improved cleavable additives to enable thermoset deconstruction without compromising material performance.

A Recent Review on Stimuli-Responsive Hydrogel Photonic Materials

The unique optical properties of structural colors found in nature garner significant attention. Inspired by these natural phenomena, scientists develop a variety of stimuli-responsive hydrogel photonic materials with periodic structures that can adjust their structural colors in response to environmental changes. In recent years, the emergence of these materials continue to grow, showcasing potential in various advanced applications. This article reviews the latest advancements in stimuli-responsive hydrogel photonic materials, focusing on their classification, manufacturing methods, and practical applications. It provides detailed descriptions of photonic materials across different dimensions and highlights the unique optical properties derived from their periodic microstructures. Additionally, the article outlines innovative technologies that are employed in creating diverse photonic structures. These materials demonstrate sensitivity to a range of external stimuli, including temperature, humidity, pH, light exposure, and mechanical force, allowing for dynamic adjustments in both structure and performance. Furthermore, the article discusses typical applications of stimuli-responsive hydrogel photonic materials in areas such as visual sensing, anti-counterfeiting technology, and drug delivery. Last, it examines the current challenges faced in the field and offers forward-looking insights regarding the future manufacturing and application of stimuli-responsive hydrogel photonic materials.

Molecularly Responsive Aptamer-Functionalized Hydrogel for Continuous Plasmonic Biomonitoring

Continuous in vivo monitoring of small molecule biomarkers requires biosensors with reversibility, sensitivity in physiologically relevant ranges, and biological stability. Leveraging the real-time, label-free detection capability of surface plasmon resonance (SPR) technology, a molecularly responsive hydrogel film is introduced to enhance small molecule sensitivity. This advanced biosensing platform utilizes split-aptamer-cross-linked hydrogels (aptagels) engineered using 8-arm poly(ethylene glycol) macromers, capable of directly and reversibly detecting vancomycin. Investigation through SPR and optical waveguide mode, along with quartz crystal microbalance with dissipation (QCM-D) monitoring, reveals that the reversible formation of analyte-induced ternary molecular complexes leads to aptagel contraction and significant refractive index changes. Optimization of aptamer cross-link distribution and complementarity of split-aptamer pairs maximizes conformational changes of the aptagel, demonstrating a detection limit of 160-250 nM for vancomycin (6-9 fold improvement over monolayer counterpart) with a broad linear sensing range up to 1 mM. The aptagel maintains stability over 24 h in blood serum and 5 weeks in diluted blood plasma (mimicking interstitial fluid). This structurally responsive aptagel platform with superior stability and sensitivity offers promising avenues for continuous in vivo monitoring of small molecules.

A flexible magnetic DNA biosensor composed of AgNWs/hydrogel/PS/Fe3O4 for the detection of ASFV P72 protein gene fragment

African swine fever virus (ASFV) is a highly infectious and pathogenic DNA virus with a mortality rate of nearly 100%. Here, we developed a flexible biosensor based on a AgNWs/hydrogel/PS(polystyrene)/Fe3O4 composite film for the detection of ASFV P72 protein gene fragments. A large number of carboxyl groups in the hydrogel provide modification sites for capture probes (cp) simplifying the preparation process of the biosensor. Combined with the excellent magnetic properties of Fe3O4, the excellent electrical conductivity of silver nanowires (AgNWs) and the unique optical properties of two-dimensional photonic crystals (2DPC), the flexible biosensor can convert biological signals into optical signals and electrical signals, and the micro-deformation of the film can be verified by simple optical methods. In order to improve the sensitivity, we introduce Fe3O4 and apply an external magnetic field to amplify the thin film micro-deformation. The concentration of P72 protein gene fragment and the relative change rate of resistance showed a good linear relationship, and the linear equation is y = - 0.00126x - 0.31729; the detection limit (LOD) is as low as 0.208 μM. The composite film was used to detect real serum samples, and the recovery of the composite film fluctuated in the range 91.89 to 103.19%, indicating that the composite film has practical application potential in clinical detection of ASFV. In addition, the biosensor also shows good biocompatibility, stability, and specificity.

Physical stimuli-responsive DNA hydrogels: design, fabrication strategies, and biomedical applications

Physical stimuli-responsive DNA hydrogels hold immense potential for tissue engineering due to their inherent biocompatibility, tunable properties, and capacity to replicate the mechanical environment of natural tissue, making physical stimuli-responsive DNA hydrogels a promising candidate for tissue engineering. These hydrogels can be tailored to respond to specific physical triggers such as temperature, light, magnetic fields, ultrasound, mechanical force, and electrical stimuli, allowing precise control over their behavior. By mimicking the extracellular matrix (ECM), DNA hydrogels provide structural support, biomechanical cues, and cell signaling essential for tissue regeneration. This article explores various physical stimuli and their incorporation into DNA hydrogels, including DNA self-assembly and hybrid DNA hydrogel methods. The aim is to demonstrate how DNA hydrogels, in conjunction with other biomolecules and the ECM environment, generate dynamic scaffolds that respond to physical stimuli to facilitate tissue regeneration. We investigate the most recent developments in cancer therapies, including injectable DNA hydrogel for bone regeneration, personalized scaffolds, and dynamic culture models for drug discovery. The study concludes by delineating the remaining obstacles and potential future orientations in the optimization of DNA hydrogel design for the regeneration and reconstruction of tissue. It also addresses strategies for surmounting current challenges and incorporating more sophisticated technologies, thereby facilitating the clinical translation of these innovative hydrogels.

Single-tube detection of a foodborne bacterial pathogen using user-friendly portable device

Timely and reliable detection of foodborne bacterial pathogen is crucial for reducing disease burden in low- and middle-income countries. However, laboratory-based methods are often inaccessibility in resource-limited settings. Here, we developed a single-tube assay and a low-cost palm-sized device for on-site detection of the representative foodborne bacterial pathogen, Salmonella Enteritidis. Our assay incorporates the advantages of protein-nucleic acid signal transduction, EXPonential Amplification Reaction (EXPAR), and clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated 12a (Cas12a). After systematically investigating the compatibility of these components, we developed a "three-in-one" integration reaction, termed ST-EXPAR-CRISPR assay. This assay requires only one tube, one controlled temperature (39 °C) and simple operation, eliminating the need for bacterial isolation, nucleic acid extraction, or washing steps. ST-EXPAR-CRISPR assay is capable of detecting as few as 37 CFU/mL of target bacterium. Using our kit and portable device, untrained volunteers successfully detected contamination in food samples outdoors. The simplicity of the detection process and minimal hardware requirements make our assay highly promising for application in point-of-care and on-site scenarios. Moreover, the ST-EXPAR-CRISPR assay can be easily modified to detect other targets by changing the nucleic acid sequence with low research and development cost, potentially reducing the global disease burden.

Chromogenic Photonic Crystal Detectors for Monitoring Small Molecule Diffusion at Solid-Solid Interfaces Using Stimuli-Responsive Shape Memory Polymers

In situ monitoring of small molecule diffusion at solid-solid interfaces is challenging, even with sophisticated equipment. Here, novel chromogenic photonic crystal detectors enabled by integrating bioinspired structural color with stimuli-responsive shape memory polymer (SMP) for detecting trace amounts of small molecule interfacial diffusion are reported. Colorless macroporous SMP membranes with deformed macropores can recover back to the "memorized" photonic crystal microstructures and the corresponding iridescent structural colors when triggered by diffused small molecules. Systematic experimental and theoretical investigations using various microscopes, optical spectroscopy and modeling, spatio-resolved energy-dispersive X-ray spectroscopy, and theoretical diffusion calculations confirm the diffusion-induced shape memory and chromogenic mechanisms. Importantly, proof-of-concept sensing of temporospatial-resolved diffusion of bioactive ingredients used in drug delivery, including anti-inflammatory methyl salicylate in pain relieving patches and vitamin E barriers loaded in contact lens, and phthalates plasticizers in commercial PVC products has been demonstrated. These innovative detectors are inexpensive, reusable, and easy to operate and deploy for both qualitative and quantitative analyses, promising for opening new avenues in biomedical research, threat detection, and monitoring of plastics, food, and environmental safety. Moreover, reconfigurable photonic crystals with micrometer-scale resolution, which are of great importance in tunable and integrated nanooptics, can be fabricated by diffusion-enabled microcontact printing.

Application of smart-responsive hydrogels in nucleic acid and nucleic acid-based target sensing: A review

In recent years, nucleic acid-related sensing and detection have become essential in clinical diagnostics, treatment and genotyping, especially in connection with the Human Genome Project and the COVID-19 pandemic. Many traditional nucleic acid-related sensing strategies have been employed in analytical chemistry, including fluorescence, colorimetric and chemiluminescence methods. However, their key limitation is the lack of understanding of the interaction during analysis, particularly at the 3D matrix level close to biological tissue. To address this issue, smart-responsive hydrogels are increasingly used in biosensing due to their hydrophilic and biocompatible properties. By combining smart-responsive hydrogels with traditional nucleic acid-related sensing, biological microenvironments can be mimicked, and targets can be easily accessed and diffused, making them ideal for nucleic acid sensing. This review focuses on utilizing smart-responsive hydrogels for nucleic acid-related sensing and detection, including nucleic acid detection, other nucleic acid-based analyte detection and nucleic acid-related sensing platforms applying nucleic acid as sensing tools in hydrogels. Additionally, the analytical mechanisms of smart-responsive hydrogels with the combination of various detection platforms such as optical and electrochemical techniques are described. The limitations of using smart-responsive hydrogels in nucleic acid-related sensing and proposed possible solutions are also discussed. Lastly, the future challenge of smart-responsive hydrogels in nucleic acid-related sensing is explored. Smart-responsive hydrogels can be used as biomimetic materials to simulate the extracellular matrix, achieve biosensing, and exhibit great potential in nucleic acid-related sensing. They serve as a valuable complement to traditional detection and analytical methods.

Rational Design of DNA Hydrogels Based on Molecular Dynamics of Polymers

In recent years, DNA has emerged as a fascinating building material to engineer hydrogel due to its excellent programmability, which has gained considerable attention in biomedical applications. Understanding the structure-property relationship and underlying molecular determinants of DNA hydrogel is essential to precisely tailor its macroscopic properties at molecular level. In this review, the rational design principles of DNA molecular networks based on molecular dynamics of polymers on the temporal scale, which can be engineered via the backbone rigidity and crosslinking kinetics, are highlighted. By elucidating the underlying molecular mechanisms and theories, it is aimed to provide a comprehensive overview of how the tunable DNA backbone rigidity and the crosslinking kinetics lead to desirable macroscopic properties of DNA hydrogels, including mechanical properties, diffusive permeability, swelling behaviors, and dynamic features. Furthermore, it is also discussed how the tunable macroscopic properties make DNA hydrogels promising candidates for biomedical applications, such as cell culture, tissue engineering, bio-sensing, and drug delivery.

Direct Detection of Tobacco Mosaic Virus in Infected Plants with SERS-Sensing Hydrogels

The impact of plant pathogens on global crop yields is a major societal concern. The current agricultural diagnostic paradigm involves either visual inspection (inaccurate) or laboratory molecular tests (burdensome). While field-ready diagnostic methods have advanced in recent years, issues remain with detection of presymptomatic infections, multiplexed analysis, and requirement for in-field sample processing. To overcome these issues, we developed surface-enhanced Raman scattering (SERS)-sensing hydrogels that detect pathogens through simple contact with a leaf. In this work, we developed a novel reagentless SERS sensor for the detection of tobacco mosaic virus (TMV) and embedded it in an optimized hydrogel material to produce sensing hydrogels. To test the diagnostic application of our sensing hydrogels, we demonstrate their use to detect TMV infection in tobacco plants. This technology has the potential to shift the current agricultural diagnostic paradigm by offering a field-deployable tool for presymptomatic and multiplexed molecular identification of pathogens.

Bionic ordered structured hydrogels: structure types, design strategies, optimization mechanism of mechanical properties and applications

Natural organisms, such as lobsters, lotus, and humans, exhibit exceptional mechanical properties due to their ordered structures. However, traditional hydrogels have limitations in their mechanical and physical properties due to their disordered molecular structures when compared with natural organisms. Therefore, inspired by nature and the properties of hydrogels similar to those of biological soft tissues, researchers are increasingly focusing on how to investigate bionic ordered structured hydrogels and render them as bioengineering soft materials with unique mechanical properties. In this paper, we systematically introduce the various structure types, design strategies, and optimization mechanisms used to enhance the strength, toughness, and anti-fatigue properties of bionic ordered structured hydrogels in recent years. We further review the potential applications of bionic ordered structured hydrogels in various fields, including sensors, bioremediation materials, actuators, and impact-resistant materials. Finally, we summarize the challenges and future development prospects of bionic ordered structured hydrogels in preparation and applications.

Self-regulating bioinspired supramolecular photonic hydrogels based on chemical reaction networks for monitoring activities of enzymes and biofuels

Inspired by the way many living organisms utilize chemical/biological reactions to regulate their skin and respond to stimuli in the external environment, we have developed a self-regulating hydrogel design by incorporating chemical reaction networks (CRNs) into biomimetic photonic crystal hydrogels. In this hydrogel system, we used host-guest supramolecular non-covalent bonds between beta-cyclodextrin (β-CD) and ferrocene (Fc) as partial crosslinkers and designed a CRN involving enzyme-fuel couples of horseradish peroxidase (HRP)/H₂O₂ and glucose oxidase (GOD)/d-glucose, by which the responsive hydrogel was transformed into a glucose-driven self-regulating hydrogel. Due to the biomimetic structural color in the hydrogel, the progress of the chemical reaction was accompanied by a change in the color of the hydrogel. Based on this principle, the designed supramolecular photonic hydrogel (SPH) can not only achieve naked-eye detection of H₂O₂ and glucose concentrations with the assistance of a smartphone but also monitor the reactions of HRP and GOD enzymes and determine their activity parameters. The sensitivity and stability of the sensor have been proven. In addition, due to the reversibility of the chemical reaction network, the sensor can be reused, thus having the potential to serve as a low-cost point-of-care sensor. The SPH was ultimately used to detect glucose in human plasma and H₂O₂ in liver tumor tissue. The results are comparable with commercial assay kits. By redesigning the chemical reaction network in the hydrogel, it is expected to be used for detecting other enzymes or fuels.

Construction of hybridization chain reaction induced optical signal directed change of photonic crystals-DNA hydrogel sensor and its visual determination for aflatoxin B1

Herein, we have introduced hybridization chain reaction (HCR) into the photonic crystals (PhCs) hydrogel, for the first time, realizing HCR for inducing the change of the optical signal of PhCs hydrogel and using this hydrogel as a sensor for determination of the aflatoxin B1 (AFB1). By using specific sequences as the cross-linker, the extension of the cross-linker by HCR drives the swelling of the hydrogel, and the optical property of 2D PhCs array converts this swelling into a change of the Debye diffraction ring. Moreover, by further selecting the aptamer to construct the cross-linker, the hydrogel is also endowed with a unique capability for AFB1, making the hydrogel a novel sensor based on the signal amplification strategy. The results show that the designed hairpin DNAs can effectively trigger the HCR and cause the swelling of hydrogel, and the hydrogel sensor has a good determination performance and high specific recognition for AFB1.

Design and application of stimuli-responsive DNA hydrogels: A review

Deoxyribonucleic acid (DNA) hydrogels combine the properties of DNAs and hydrogels, and adding functionalized DNAs is key to the wide application of DNA hydrogels. In stimuli-responsive DNA hydrogels, the DNA transcends its application in genetics and bridges the gap between different fields. Specifically, the DNA acts as both an information carrier and a bridge in constructing DNA hydrogels. The programmability and biocompatibility of DNA hydrogel make it change macroscopically in response to a variety of stimuli. In order to meet the needs of different scenarios, DNA hydrogels were also designed into microcapsules, beads, membranes, microneedle patches, and other forms. In this study, the stimuli were classified into single biological and non-biological stimuli and composite stimuli. Stimuli-responsive DNA hydrogels from the past five years were summarized, including but not limited to their design and application, in particular logic gate pathways and signal amplification mechanisms. Stimuli-responsive DNA hydrogels have been applied to fields such as sensing, nanorobots, information carriers, controlled drug release, and disease treatment. Different potential applications and the developmental pro-spects of stimuli-responsive DNA hydrogels were discussed.

Multi-Factors Cooperatively Actuated Photonic Hydrogel Aptasensors for Facile, Label-Free and Colorimetric Detection of Lysozyme

Responsive two-dimensional photonic crystal (2DPC) hydrogels have been widely used as smart sensing materials for constructing various optical sensors to accurately detect different target analytes. Herein, we report photonic hydrogel aptasensors based on aptamer-functionalized 2DPC poly(acrylamide-acrylic acid-N-tert-butyl acrylamide) hydrogels for facile, label-free and colorimetric detection of lysozyme in human serum. The constructed photonic hydrogel aptasensors undergo shrinkage upon exposure to lysozyme solution through multi-factors cooperative actuation. Here, the specific binding between the aptamer and lysozyme, and the simultaneous interactions between carboxyl anions and N-tert-butyl groups with lysozyme, increase the cross-linking density of the hydrogel, leading to its shrinkage. The aptasensors’ shrinkage decreases the particle spacing of the 2DPC embedded in the hydrogel network. It can be simply monitored by measuring the Debye diffraction ring of the photonic hydrogel aptasensors using a laser pointer and a ruler without needing sophisticated apparatus. The significant shrinkage of the aptasensors can be observed by the naked eye via the hydrogel size and color change. The aptasensors show good sensitivity with a limit of detection of 1.8 nM, high selectivity and anti-interference for the detection of lysozyme. The photonic hydrogel aptasensors have been successfully used to accurately determine the concentration of lysozyme in human serum. Therefore, novel photonic hydrogel aptasensors can be constructed by designing functional monomers and aptamers that can specifically bind target analytes.