DNA hydrogel as a template for synthesis of ultrasmall gold nanoparticles for catalytic applications

Improving DNA nanostructure stability: A review of the biomedical applications and approaches

DNA's programmable, predictable, and precise self-assembly properties enable structural DNA nanotechnology. DNA nanostructures have a wide range of applications in drug delivery, bioimaging, biosensing, and theranostics. However, physiological conditions, including low cationic ions and the presence of nucleases in biological systems, can limit the efficacy of DNA nanostructures. Several strategies for stabilizing DNA nanostructures have been developed, including i) coating them with biomolecules or polymers, ii) chemical cross-linking of the DNA strands, and iii) modifications of the nucleotides and nucleic acids backbone. These methods significantly enhance the structural stability of DNA nanostructures and thus enable in vivo and in vitro applications. This study reviews the present perspective on the distinctive properties of the DNA molecule and explains various DNA nanostructures, their advantages, and their disadvantages. We provide a brief overview of the biomedical applications of DNA nanostructures and comprehensively discuss possible approaches to improve their biostability. Finally, the shortcomings and challenges of the current biostability approaches are examined.

Multimodal Golden DNA Superstructures (GDSs) for Highly Efficient Photothermal Immunotherapy

DNA-templated metallization has emerged as an efficient strategy for creating nanoscale-metal DNA hybrid structures with a desirable conformation and function. Despite the potential of DNA-metal hybrids, their use as combinatory therapeutic agents has rarely been examined. Herein, we present a simple approach for fabricating a multipurpose DNA superstructure that serves as an efficient photoimmunotherapy agent. Specifically, we adsorb and locally concentrate Au ions onto DNA superstructures through induced local reduction, resulting in the formation of Au nanoclusters. The mechanical and optical properties of these metallic nanoclusters can be rationally controlled by their conformations and metal ions. The resulting golden DNA superstructures (GDSs) exhibit significant photothermal effects that induce cancer cell apoptosis. When sequence-specific immunostimulatory effects of DNA are combined, GDSs provide a synergistic effect to eradicate cancer and inhibit metastasis, demonstrating potential as a combinatory therapeutic agent for tumor treatment. Altogether, the DNA superstructure-templated metal casting system offers promising materials for future biomedical applications.

Biomass RNA for the Controlled Synthesis of Degradable Networks by Radical Polymerization

Nucleic acids extracted from biomass have emerged as sustainable and environmentally friendly building blocks for the fabrication of multifunctional materials. Until recently, the fabrication of biomass nucleic acid-based structures has been facilitated through simple crosslinking of biomass nucleic acids, which limits the possibility of material properties engineering. This study presents an approach to convert biomass RNA into an acrylic crosslinker through acyl imidazole chemistry. The number of acrylic moieties on RNA was engineered by varying the acylation conditions. The resulting RNA crosslinker can undergo radical copolymerization with various acrylic monomers, thereby offering a versatile route for creating materials with tunable properties (e.g., stiffness and hydrophobic characteristics). Further, reversible-deactivation radical polymerization methods, such as atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer (RAFT), were also explored as additional approaches to engineer the hydrogel properties. The study also demonstrated the metallization of the biomass RNA-based material, thereby offering potential applications in enhancing electrical conductivity. Overall, this research expands the opportunities in biomass-based biomaterial fabrication, which allows tailored properties for diverse applications.

Templating of catalytic gold and silver nanoparticles by waste plastic PET-derived hydrogel playing a dual role of a reductant and a matrix

The progressive accumulation of discarded plastic in the environment demands further development of waste management of plastic waste and conversion technologies of such waste to value-added materials. Recently, the conversion of plastic waste to functional materials via chemical recycling has attracted considerable attention. In this report, plastic waste (PET) was utilized for the preparation of a hydrogel-based catalyst via a cross-linking reaction of PET-derived oligo(terephthalamide)s followed by the electroless metallization. The polymeric matrix of PET-derived hydrogel plays multiple roles of (i) an adsorption media for noble metal ions such as Au³⁺ and Ag⁺, (ii) a reducing agent of Au³⁺ and Ag⁺ ions to Au⁰ and Ag⁰, and (iii) a matrix for the controlled growth of Au and Ag nanoparticles (AuNPs and AgNPs). The obtained hybrid hydrogels after metallization contained well-dispersed AuNPs and AgNPs of 6.1 ± 3.7 nm or 6.1 ± 1.4 nm size, respectively. The catalytic activities of the hybrid hydrogels with metal nanoparticles were studied in a model system of p-nitrophenol reduction in an aqueous solution. The hybrid materials of both Au@hydrogel and Ag@hydrogel were catalytically active for the reduction of p-nitrophenol, obeying the first-order kinetics. Importantly, the AuNPs or AgNPs in the hydrogel matrix preserved the original catalytic activity after multiple p-nitrophenol reduction reactions, showing a promising reusability of the catalysts. The proposed here approach aims to broaden the scope of conversion routes of plastic waste to value-added materials as well as to develop new types of polymeric matrices for templating and growth of metal nanoparticles for catalytic applications.

Coacervate-Based Plexcitonic Assembly toward Peroxidase-like Activity and Ultrasensitive Glucose Sensing

Inbuilt catalytic centers anchored inside the confined architecture of artificial nanoreactors have gained tremendous attention owing to their vast applicability in various catalytic transformations. However, designing homogeneously distributed catalytic units with exposed surfaces in confined environment is a challenging task. Here, we have utilized quantum dot (QD)-embedded coacervate droplets (QD-Ds) as a confined compartment for the in situ synthesis of gold nanoparticles (Au NPs) without any additional reducing agent. High-resolution transmission electron microscopy images reveal homogeneous distribution of 5.6 ± 0.2 nm-sized Au NPs inside the QD-Ds (Au@QD-Ds). The in situ synthesized Au NPs are found to be stable over a period of 28 days without any agglomeration. Control experiments reveal that the free surface carboxylic acid groups of embedded QDs simultaneously act as reducing and stabilizing agents for Au NPs. Notably, these Au@QD-Ds exhibit superior peroxidase-like activity compared to bulk aqueous Au NPs and Au@QDs under similar experimental conditions. The observed peroxidase-like activity follows the classical Michaelis-Menten model inside the Au@QD-Ds via the fast electron-transfer pathway. The enhanced peroxidase-like activity has been explained by considering confinement, mass action, and the ligand-free surface of embedded Au NPs. The present plexcitonic nanocomposites exhibit excellent recyclability over several consecutive cycles without any compromise in their catalytic activity. Finally, a cascade reaction with glucose oxidase (GOx)-loaded Au@QD-Ds have been utilized for colorimetric detection of glucose with a limit of detection of 272 nM in solution as well as on filter paper. The present work highlights a facile and robust methodology for the fabrication of optically active functional hybrid plexcitonic assemblies and may find importance in various fields including bioanalytical chemistry and optoelectronics.

Green synthesis of reduced graphene oxide/chitosan/gold nanoparticles composites and their catalytic activity for reduction of 4-nitrophenol

Gold nanoparticles (AuNPs) have attracted extensive attention in the past few years due to their unique properties and great potential application in catalysis. However, the application of AuNPs remains a significant challenge due to the lack of high efficiency and stability caused by aggregation. Immobilization of AuNPs on appropriate support shows promising results in avoiding aggregation and improving catalytic activity. In this work, reduced graphene oxide/chitosan/gold nanoparticles (rGO/CHS/AuNPs) composites were prepared using chitosan with different molecular weights (MW) as a reducing agent and stabilizer, and characterized by FT-IR, XRD, XPS, SEM, FESEM, EDS, TEM, HRTEM, and TGA. The preparation conditions of rGO/CHS/AuNPs composites, including chitosan MW, CHS/GO mass ratio, reaction temperature and time, and HAuCl₄ concentration were investigated in detail. The results indicated that reduction activity of chitosan for GO increased with the decrease of chitosan MW. The C/O ratio of rGO reduced by low molecular weight chitosan (LMWC) with viscosity-average molecular weight (Mv) of 21 kDa was 6.34. Small spherical AuNPs were uniformly immobilized on the rGO surface. The particle size of AuNPs increased from 9.29 to 13.03 nm as chitosan MW decreased from 465 to 21 kDa. The rGO/CHS/AuNPs showed good catalytic activity for the reduction of 4-NP in the presence of NaBH₄. The catalytic activity of rGO/CHS/AuNPs was closely related to chitosan MW. rGO/CHS/AuNPs synthesized by LMWC with Mv of 21 kDa showed the highest kinetic rate constant of 0.2067 min^-1. The results of this experimental study could be useful in the development of effective catalysts for the reduction of aromatic nitro compounds.

Fabrication of heterogeneous chemical patterns on stretchable hydrogels using single-photon lithography

Curved hydrogel surfaces bearing chemical patterns are highly desirable in various applications, including artificial blood vessels, wearable electronics, and soft robotics. However, previous studies on the fabrication of chemical patterns on hydrogels employed two-photon lithography, which is still not widely accessible to most laboratories. This work demonstrates a new patterning technique for fabricating curved hydrogels with chemical patterns on their surfaces without two-photon microscopy. In this work, we show that exposing hydrogels in fluorophore solutions to single photons via confocal microscopy enables the patterning of fluorophores on hydrogels. By applying this technique to highly stretchable hydrogels, we demonstrate three applications: (1) improving pattern resolution by fabricating patterns on stretched hydrogels and then returning the hydrogels to their initial, unstretched length; (2) modifying the local stretchability of hydrogels at a microscale resolution; and (3) fabricating perfusable microchannels with chemical patterns by winding chemically patterned hydrogels around a template, embedding the hydrogels in a second hydrogel, and then removing the template. The patterning method demonstrated in this work may facilitate a better mimicking of the physicochemical properties of organs in tissue engineering and may be used to make hydrogel robots with specific chemical functionalities.

Recent developments in hydrogels containing copper and palladium for the catalytic reduction/degradation of organic pollutants

The elimination of toxic and hazardous contaminants from different environmental media has become a global challenge, causing researchers to focus on the treatment of pollutants. Accordingly, the elimination of inorganic and organic pollutants using sustainable, effective, and low-cost heterogeneous catalysts is considered as one of the most essential routes for this aim. Thus, many efforts have been devoted to the synthesis of novel compounds and improving their catalytic performance. Recently, palladium- and copper-based hydrogels have been used as catalysts for reduction, degradation, and decomposition reactions because they have significant features such as high mechanical strength, thermal stability, and high surface area. Herein, we summarize the progress achieved in this field, including the various methods for the synthesis of copper- and palladium-based hydrogel catalysts and their applications for environmental remediation. Moreover, palladium- and copper-based hydrogel catalysts, which have certain advantages, including high catalytic ability, reusability, easy work-up, and simple synthesis, are proposed as a new group of effective catalysts.

The elimination of toxic and hazardous contaminants from different environmental media has become a global challenge, causing researchers to focus on the treatment of pollutants.

DNA Nanotechnology-Enabled Fabrication of Metal Nanomorphology

In recent decades, DNA nanotechnology has grown into a highly innovative and widely established field. DNA nanostructures have extraordinary structural programmability and can accurately organize nanoscale materials, especially in guiding the synthesis of metal nanomaterials, which have unique advantages in controlling the growth morphology of metal nanomaterials. This review started with the evolution in DNA nanotechnology and the types of DNA nanostructures. Next, a DNA-based nanofabrication technology, DNA metallization, was introduced. In this section, we systematically summarized the DNA-oriented synthesis of metal nanostructures with different morphologies and structures. Furthermore, the applications of metal nanostructures constructed from DNA templates in various fields including electronics, catalysis, sensing, and bioimaging were figured out. Finally, the development prospects and challenges of metal nanostructures formed under the morphology control by DNA nanotechnology were discussed.

Microbial cell factories a new dimension in bio-nanotechnology: exploring the robustness of nature

Bio-based nanotechnology has its existence in biological dimensions e.g. microbial cell factories (bacteria, fungi. algae, yeast, cyanobacteria) plants, and biopolymers. They provide multipurpose biological platforms to supply well-designed materials for diverse nano-biotechnological applications. The "green or bio-based synthesis of nanoparticles (NPs)" has witnessed a research outburst in the past decade. The bio-based synthesis of NPs using microbial cell factories is a benign process and requires mild conditions for the synthesis with end products being less/non-toxic. As a result, its application has extended in multitudinous industries including environment, cosmetics, and pharmaceutical. Thus, the present review summarizes all the significant aspects of nanotechnology and the reason to switch towards the bio-based synthesis of NPs using microbial cell factories. It consists of a detailed description of the bio-based methods employed for the synthesis and classification of NPs. Also, a comprehensive study on the application of bio-based NPs in the various industrial and biotechnological domains has been discussed. The limitation and its solution would help identify the applicability of NPs to "identified and unidentified" sectors.

Fabrication of defective graphene oxide for efficient hydrogen production and enhanced 4-nitro-phenol reduction

Hydrogen has been considered as one of the most promising alternative energy source to solve the future energy demands due to its high energy capacity and emission-free character. The generation of hydrogen from non-fossil sources is necessary for the sustainable development of human life on this planet. The hydrolysis of sodium borohydride can quickly produce a large amount of hydrogenin situand on-demand in the presence of the catalyst, which can be used as an alternative energy source. So, it is crucial to fabricate the highly efficient, robust, and economical catalyst for the production of hydrogen via hydrolysis of sodium borohydride. Herein, a facile and efficient approach for the synthesis of metal-functionalized reduced graphene oxide for the production of hydrogen at room temperature was used. Moreover, the synthesized catalyst has also been tested in the field of environmental catalysis for the reduction of toxic 4-nitrophenol to valuable 4-aminophenol in the presence of sodium borohydride. The enhanced activity of prepared metal-functionalized reduced graphene oxide is ascribed to a strong affinity between Fe-N_Xand reduced graphene oxide which facilitates electron transfer as well as synergistic effect. Overall, this work presents a crucial procedure for green chemistry reactions when a carbonaceous material is selected as a catalyst.

Galactose Grafted Two-Dimensional Nanosheets as a Scaffold for the In Situ Synthesis of Silver Nanoparticles: A Potential Catalyst for the Reduction of Nitroaromatics

Two major hurdles in NP-based catalysis are the aggregation of the NPs and their recycling. Immobilization of NPs onto a 2D support is the most promising strategy to overcome these difficulties. Herein, amphiphilicity-driven self-assembly of galactose-hexaphenylbenzene-based amphiphiles into galactose-decorated 2D nanosheet is reported. The extremely dense decoration of reducing sugar on the surface of the sheets is used for the in situ synthesis and immobilization of ultrafine catalytically active AgNPs by using Tollens' reaction. The potential of the system as a catalyst for the reduction of various nitroaromatics is demonstrated. Enhanced catalytic activity is observed for the immobilized AgNPs when compared to the corresponding discrete AgNPs. Recovery of the catalytic system from the reaction mixture by ultrafiltration and its subsequent recycling for several cycles without dropping its activity is shown. This is the first report demonstrating the in situ synthesis and immobilization of ultrafine AgNPs onto a 2D nanosheet that exhibits excellent catalytic performance for the reduction of nitroaromatics.

Polymethylolacrylamide/AuNPs Nanocomposites: Electrochemical Synthesis and Functional Characteristics

In this study the advantages of the electrochemical approach to the formation of polymer/metal nanoparticle composites are demonstrated. The method enables one to simplify the multistage processes of traditional technologies for the production of such materials through combining all intermediate processes in one stage and reducing the total formation time to 3–10 min. The possibility of a single-stage formation of a polymethylolacrylamide/AuNPs composite through including AuNPs into an electrically non-conducting polymethylolacrylamide film (carrier) formed by electropolymerization through potentiostatic electrolysis is also demonstrated for the first time. It is established that the addition of tetrachloroauric acid (HAuCl₄·4H₂O) into a monomeric composition containing acrylamide, formaldehyde, N,N′-methylene-bis-acrylamide, zinc chloride, and H₂O results in simultaneous electrochemical initiation of polymerization with the formation of a polymer film on the cathode, electrolytic reduction of gold ions to Au⁰, and immobilization of AuNPs particles into the growing polymer matrix. It was found that the formation of the PMAA / AuNPs composite is energetically more favorable than the synthesis of the main PMAA film, since it proceeds at a lower cathodic potential. The inclusion of AuNPs into the polymethylolacrylamide film was confirmed visually, as well as by X-ray phase analysis, small-angle X-ray scattering, microscopy, and element analysis. The gold content in the composite increases along with the increase of the concentration of HAuCl₄ in the electrolyte. The radius of the AuNPs particles was found to range between 3 and 7 nm. The AuNPs particles are spherical in shape and can combine into larger clusters containing up to 10 or more particles. The dynamics of formation, structure, and morphology of the polymethylolacrylamide/AuNPs composite were investigated. It was revealed that gold nanoparticles are mainly concentrated in the near-electrode and near-solution layers of the composite. We found that the composite has electrocatalytic activity. The possibility of its use as a sensor for hydrogen peroxide is demonstrated.

Smart and Functionalized Development of Nucleic Acid-Based Hydrogels: Assembly Strategies, Recent Advances, and Challenges

Nucleic acid-based hydrogels that integrate intrinsic biological properties of nucleic acids and mechanical behavior of their advanced assemblies are appealing bioanalysis and biomedical studies for the development of new-generation smart biomaterials. It is inseparable from development and incorporation of novel structural and functional units. This review highlights different functional units of nucleic acids, polymers, and novel nanomaterials in the order of structures, properties, and functions, and their assembly strategies for the fabrication of nucleic acid-based hydrogels. Also, recent advances in the design of multifunctional and stimuli-responsive nucleic acid-based hydrogels in bioanalysis and biomedical science are discussed, focusing on the applications of customized hydrogels for emerging directions, including 3D cell cultivation and 3D bioprinting. Finally, the key challenge and future perspectives are outlined.

Ultraviolet-induced in situ gold nanoparticles for point-of-care testing of infectious diseases in loop-mediated isothermal amplification

The present study investigated ultraviolet-induced in situ gold nanoparticles (AuNPs) coupled with loop-mediated isothermal amplification (LAMP) for the point-of-care testing (POCT) of two major infectious pathogens, namely, Coronavirus (COVID-19) and Enterococcus faecium (E. faecium spp.). In the process, gold ions in a gold chloride (HAuCl4) solution were reduced using trisodium citrate (Na3Ct), a reducing agent, and upon UV illumination, red-colored AuNPs were produced in the presence of LAMP amplicons. The nitrogenous bases of the target deoxyribonucleic acid (DNA) acted as a physical support for capturing gold ions dissolved in the sample. The high affinity of gold with the nitrogenous bases enabled facile detection within 10 min, and the detection limit of COVID-19 plasmid DNA was as low as 42 fg μL-1. To ensure POCT, we designed a portable device that contained arrays of reagent chambers and detection chambers. In the portable device, colorimetric reagents such as HAuCl4 and Na3Ct were contained in the reagent chambers; these reagents were subsequently transferred to the detection chambers where LAMP amplicons were present and thus allowed convenient sample delivery and multiplex detection. Owing to the high sensitivity of the in situ AuNPs, simplicity of portable device fabrication, and rapid colorimetric detection, we strongly believe that the fabricated portable device could serve as a kit for rapid POCT for instantaneous detection of infectious diseases, and could be readily usable at the bedside.

Preparation of Cu–Cu2O–CuO by solid combustion ignited by dielectric barrier discharge and its activity towards p-nitrophenol reduction

Dielectric barrier discharge induces solid powder combustion at room temperature and atmosphere to prepare a high-activity catalyst for p-nitrophenol reduction.

Rosin-based chiral wormlike Micelles: Rheological behavior and its application in preparing ultrasmall gold nanoparticles

Innovations in surfactant structures are a feasible way to prepare unique molecular aggregates with interesting properties. Herein, taking dehydroabietic acid as the starting material, a new amine oxide surfactant, abbreviated as R-8-AO, was synthesized. Cryogenic transmission electron microscopy (cryo-TEM) images and circular dichroism (CD) spectra reveal that at suitable concentrations, R-8-AO molecules form rarely discovered right-handed chiral wormlike micelles, which have a cross-sectional diameter of 5-6 nm. The overlap concentration of R-8-AO is approximately 8 mM, above which the wormlike micelles began to entangle in solutions. Due to the strong van der Waals forces between R-8-AO molecules, the scaling law gives an exponent of 7.88, which is higher than the theory predicted value. Gold nanoparticles were synthesized in-situ by irradiating mixed solutions of HAuCl₄ and wormlike micelles formed by R-8-AO with UV light. These ultrasmall spherical gold nanoparticles, which are located at the surface of wormlike micelles, have a uniform particle size of 3 ± 1 nm, as observed by TEM. In addition, the gold nanoparticles form a worm-like morphology induced by the wormlike micelles, showing soft-aggregate-directed nanoparticle assembly. This work is first to reveal the effectiveness of preparing ultrasmall gold nanoparticles with new morphological wormlike micelles as soft templates. The resulting organic-inorganic hybrid aggregates are also expected to find applications in catalysis and electronic fields.

One-Pot, In-Situ Synthesis of 8-Armed Poly(Ethylene Glycol)-Coated Ag Nanoclusters as a Fluorescent Sensor for Selective Detection of Cu2

Fluorescent nanomaterials, such as quantum dots, have developed rapidly in recent years and have been significantly developed. Herein, we demonstrate a facile, one-pot, and in-situ synthesis strategy to obtain fluorescent silver nanoclusters (AgNCs) coated with eight-armed poly (ethylene glycol) polymers (8PEG-AgNCs) via a direct gel-mediated process. During the synthesis, ammonium (NH₃) served as the crosslinker for the gel formation via a amine-type Michael addition reaction. This hydrogel can be used as a template to synthesize AgNCs using its volume-limiting effect. The in-situ generation of AgNCs takes place inside the nanocages of the formed gels, which guarantees the homogenous distribution of AgNCs in the gel matrix, as well as the efficient coating of PEG on the nanoclusters. After the degradation of gels, the released 8PEG-AgNCs nanohybrids showed strong blue fluorescence and exhibited long-term stability in aqueous solution for nearly one year. Results showed that the fabricated sensor revealed excellent fluorescent sensitivity for the selective detection of Cu²⁺ with a detection limit of 50 nM and a wide linear detection range of 5–100 μM. It is proposed that the greater cross-linking density leads to smaller gel pores and allows the synthesis of AgNCs with fluorescent properties. These results indicate that this novel hydrogel with certain biodegradation has the potential to be applied as a fluorescent sensor for catalytic synthesis, fluorescence tracing in cells, and fluorescence detection fields. Meanwhile, the novel design principle has a certain versatility to accelerate the development and application of other kinds of metal nanoclusters and quantum dots.

In-situ stabilization of silver nanoparticles in polymer hydrogels for enhanced catalytic reduction of macro and micro pollutants

The in-situ stabilization of Ag nanoparticles is carried out by the use of reducing agent and synthesized three different types of hydrogen (anionic, cationic, and neutral) template. The morphology, constitution and thermal stability of the synthesized pure and Ag-entrapped hybrid hydrogels were efficiently confirmed using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and thermo gravimetric analysis (TGA). The prepared hybrid hydrogels were used in the decolorization of methylene blue (MB) and azo dyes congo red (CR), methyl Orange (MO), and reduction of 4-nitrophenol (4-NP) and nitrobenzene (NB) by an electron donor NaBH4. The kinetics of the reduction reaction was also assessed to determine the activation parameters. The hybrid hydrogen catalysts were recovered by filtration and used continuously up to six times with 98% conversion of pollutants without substantial loss in catalytic activity. It was observed that these types of hydrogel systems can be used for the conversion of pollutants from waste water into useful products.

Novel g-C3N4/Fe-ZnO/RGO nanocomposites with boosting visible light photocatalytic activity for MB, Cr (VI), and outstanding catalytic activity toward para-nitrophenol reduction

A novel g-C₃N₄/Fe-ZnO/RGO nanocomposite has been synthesized using the facile solvothermal method to boost the catalytic efficiency of ZnO. The structure and morphology of nanocomposites were examined by a wide range of characterization methods. The obtained g-C₃N₄/Fe-ZnO/RGO nanocomposite (Z-scheme heterostructure) exhibits improved photocatalytic activity toward the photodegradation of MB, Cr (VI) under visible-light irradiation and 4-nitrophenol reduction. The enhancement in activity of nanocomposite is ascribed to a unique heterostructure system, which facilitates excellent transport and separation of the photogenerated charge carrier, resulting in prolonged lifetime leading to continuous generation of reactive species. Moreover, the synergistic effect on the interface of ZnO and g-C₃N₄ and the introduction of reduced graphene oxide (RGO) serve as a booster for charge separation at the Z-scheme, which ultimately speeds up the degradation of pollutants. The present study provides a novel and facile approach for establishing an efficient nanocomposite for environmental remediation.

A Reductive Supramolecular Hydrogel: A Platform for Facile Fabrication of Diverse Metal-Nanoparticle-Decorated Conductive Networks with Spatiotemporal Control

Nanoparticle-hydrogel hybrid composites have a great potential for a broad range of applications, such as antibacterial materials, stimuli-responsive materials and catalysis. A novel supramolecular hydrogel system was developed using an amino acid based amphiphile containing a terminal pyrrole moiety as a gelator. The pyrrole moiety could serve as both reducing agent and monomer, and a variety of metal precursors penetrating into the hydrogel could be reduced in situ into metal nanoparticles while the pyrrole moieties preorganized in hydrogel were oxidized into polyprroles, affording metal-nanoparticle-decorated covalent conductive networks. This strategy allows the facile fabrication of diverse mono- or multimetallic nanoparticle-polymer networks from one hydrogel by a simple reaction-diffusion approach. More importantly, besides homogeneous composites, unique multisegment heterogeneous systems with spatiotemporal control were also easily accessible. Furthermore, based on the same multifunctional molecule, the fabrication of hierarchically pore-structured metal-nanoparticles-polymers as well as metal-nanoparticles-carbon structures was also realized.

Nanofabrication of Au nanoparticles over conductive metallohydrogel nanofibers for nanocatalysis application

A conductive and fluorescent metallohydrogel (1% w/v, CPH) has been synthesized and utilized for nanofabrication of AuNps and nanocatalysis applications.

Mussel-inspired immobilization of Au on bare and graphene-wrapped Ni nanoparticles toward highly efficient and easily recyclable catalysts

Bimetallic nanocatalysts have been gaining huge research attention in the heterogeneous catalysis community recently owing to their tunable properties and multifunctional characteristics. In this work, we fabricated a bimetallic core-shell nanocomposite catalyst by employing a mussel-inspired strategy for immobilizing gold nanoparticles (AuNP) on the surface of nickel nanoparticles (NiNP). NiNPs obtained from the reduction of Ni(ii) were first coated with polydopamine to provide the anchoring sites towards the robust immobilization of AuNPs. The as-synthesized nanocomposite (Ni-PD-Au) exhibited outstanding catalytic activity while reducing methylene blue (MB) and 4-nitrophenol (4-NP) yielding rate constants 13.11 min-1 and 4.21 min-1, respectively, outperforming the catalytic efficiency of its monometallic counterparts and other similar reported catalysts by large margins. The superior catalytic efficiency of the Ni-PD-Au was attributed to the well-known synergistic effect, which was experimentally investigated and compared with prior reports. Similar bio-inspired immobilization of AuNPs was also applied on graphene-wrapped NiNPs (Ni-G) instead of bare NiNPs to synthesize another composite catalyst (Ni-G-PD-Au), which yet again exhibited synergistic catalytic activity. A comparative study between the two nanocomposites suggested that Ni-PD-Au excelled in catalytic activity but Ni-G-PD-Au provided noteworthy stability showing ∼100% efficiency over 17 repeated cycles. However, along with excellent synergistic performance, both nanocomposites demonstrated high magnetization and thermal stability up to 350 °C ascertaining their easy separation and sustainability for high-temperature applications, respectively.

Functionalized DNA Hydrogels Produced by Polymerase-Catalyzed Incorporation of Non-Natural Nucleotides as a Surface Coating for Cell Culture Applications

Cells from most mammalian tissues require an extracellular matrix (ECM) for attachment and proper functioning. In vitro cell cultures therefore must be supplied with an ECM that satisfies both the biological needs of cells used and the technical demands of the experimental setup. The latter include matrix functionalization for cell attachment, favorable microscopic properties, and affordable production costs. Here, modified DNA materials are therefore developed as an ECM mimic. The material is prepared by chemical cross-linking of commonly available salmon sperm DNA. To render the material cell-compatible, it is enzymatically modified by DNA polymerase I to provide versatile attachment points for peptides, proteins, or antibodies via a modular strategy. Different cells specifically attach to the material, even from mixed populations. They can be mildly released for further cell studies by DNase I-mediated digestion of the DNA material. Additionally, neural stem cells not only attach and survive on the material but also differentiate to a neural lineage when prompted. Furthermore, the DNA material can be employed to capture and retain cells under flow conditions. The simple preparation of the DNA material and its wide scope of applications open new perspectives for various cell study challenges and medical applications.

Monolithic cellulose supported metal nanoparticles as green flow reactor with high catalytic efficiency

A highly effective, stable and reusable flow microreactor was developed by utilizing the environmentally sustainable porous monolithic cellulose based on a facile temperature induced phase separation (TIPS) method. The obtained microreator could be applied to efficiently and continuously catalysing the reduction reaction of 4-nitrophenol (an important reaction in water treatment) without any post-treatment or regeneration of catalysts. Moreover, the monolith overcame the brittleness of the crystalline cellulose and showed a good mechanical resilience, suggesting a great potential for the practical application in severe environment. Compared with previous reported Pd supported catalytic systems, this microreactor exhibited extremely high catalytic efficiency (turnover frequency, TOF = 4660 h^-1, almost 4 times higher than that of cellulose nanocrystals supported catalyst) and long-term stability. This work provided a new strategy to construct highly effective and reusable metal NPs involved catalytic system by utilizing biodegradable cellulose materials.

Synthetic strategies and application of gold-based nanocatalysts for nitroaromatics reduction

With the increasing requirement of efficient organic transformations on the basic concept of Green Sustainable Chemistry, the development of highly efficient catalytic reaction system is greatly desired. In this case, gold (Au)-based nanocatalysts are promising candidates for catalytic reaction, especially for the reduction of nitroaromatics. They have attracted wide attention and well developed in the application of nitroaromatics reduction because of the unique properties compared with that of other conventional metal-based catalysts. With this respect, this review proposes recent trends in the application of Au nanocatalysts for efficient reduction process of nitroaromatics. Some typical approaches are compared and discussed to guide the synthesis of highly efficient Au nanocatalysts. The mechanism on the use of H₂ and NaBH₄ solution as the source of hydrogen is compared, and that proposed under light irradiation is discussed. The high and unique catalytic activity of some carriers, such as oxides and carbons-based materials, based on different sizes, structures, and shapes of supported Au nanocatalysts for nitroaromatics reduction are described. The catalytic performance of Au combining with other metal nanoparticles by alloy or doping, like multi-metal nanoparticles system, is further discussed. Finally, a short discussion is introduced to compare the catalysis with other metallic nanocatalysts.

In situ reduction of chloroauric acid (HAuCl4) for generation of catalytic Au nanoparticle embedded triazine based covalent organic polymer networks

A facile synthetic route was applied to generate Au@COPN-1 hybrids via in situ reduction of Au³⁺ with no additional reducing agent. Au@COPN-1 is a promising catalyst platform and good biocompatibility confirmed by dynamic real-time cell analysis.

Nucleic acids and analogs for bone regeneration

With the incidence of different bone diseases increasing, effective therapies are needed that coordinate a combination of various technologies and biological materials. Bone tissue engineering has also been considered as a promising strategy to repair various bone defects. Therefore, different biological materials that can promote stem cell proliferation, migration, and osteoblastic differentiation to accelerate bone tissue regeneration and repair have also become the focus of research in multiple fields. Stem cell therapy, biomaterial scaffolds, and biological growth factors have shown potential for bone tissue engineering; however, off-target effects and cytotoxicity have limited their clinical use. The application of nucleic acids (deoxyribonucleic acid or ribonucleic acid) and nucleic acid analogs (peptide nucleic acids or locked nucleic acids), which are designed based on foreign genes or with special structures, can be taken up by target cells to exert different effects such as modulating protein expression, replacing a missing gene, or targeting specific gens or proteins. Due to some drawbacks, nucleic acids and nucleic acid analogs are combined with various delivery systems to exert enhanced effects, but current studies of these molecules have not yet satisfied clinical requirements. In-depth studies of nucleic acid or nucleic acid analog delivery systems have been performed, with a particular focus on bone tissue regeneration and repair. In this review, we mainly introduce delivery systems for nucleic acids and nucleic acid analogs and their applications in bone repair and regeneration. At the same time, the application of conventional scaffold materials for the delivery of nucleic acids and nucleic acid analogs is also discussed.

Used with an appropriate delivery system, nucleic acids and nucleic acid analogs have excellent potential for bone repair and regeneration. Owing to various challenges with bone tissue regeneration, current research is largely focused on gene therapy, which employs genes to treat or prevent disease, and such new materials as nucleic acids (DNA and RNA) and nucleic acid analogs (compounds structurally similar to naturally occurring nucleic acids). A team headed by Yunfeng Lin at Sichuan University, China conducted a review of delivery systems for nucleic acids and nucleic acid analogs and their application in bone repair and regeneration. The authors identified the use of biomaterial scaffolds (which mimic living tissue) as one of the most important research areas for gene therapy, and that strategy has proven effective with all types of bone regeneration and repair.

Mild Synthesis of Copper Nanoparticles with Enhanced Oxidative Stability and Their Application in Antibacterial Films

Copper nanoparticles possess unique physical and chemical properties; however, their application is often restricted, owing to their tendency to oxidize. In this work, we prepared copper nanoparticles with enhanced oxidative stability via a simple and low-cost method, where a modified starch was used as an environmentally friendly reducing agent and biocompatible polyethylenimine was used as a stabilizer. The prepared copper nanoparticles could be stored in air for at least 6 months without any oxidation in a dried state. Interestingly, our synthesis could even be performed at room temperature with a longer reaction time. We used various characterization methods to study the reaction mechanism. The prepared copper nanoparticles were further uniformly doped into an agar film, and this composite showed excellent bacterial killing efficiency, owing to the antibacterial properties of the copper nanoparticles. Our composite film shows potential for various clinical applications, such as wound dressing materials.

Self-assembly of DNA-tetraphenylethylene amphiphiles into DNA-grafted nanosheets as a support for the immobilization of gold nanoparticles: a recyclable catalyst with enhanced activity

Preventing the aggregation of NPs and their recovery are the two major hurdles in NP based catalysis. Immobilization of NPs on a support has proven to be a promising strategy to overcome these difficulties. Herein we report the design of high aspect ratio two-dimensional (2D) crystalline DNA nanosheets formed from the amphiphilicity-driven self-assembly of DNA-tetraphenylethylene amphiphiles and also demonstrate the potential of DNA nanosheets for the immobilization of catalytically active NPs. The most remarkable feature of this approach is the high loading of NPs in a non-aggregated manner, and hence exhibiting enhanced catalytic activity. Recycling of NP loaded nanosheets for several cycles without reduction in catalytic efficiency by simple ultrafiltration is also demonstrated.

Highly Stable and Multiemissive Silver Nanoclusters Synthesized in Situ in a DNA Hydrogel and Their Application for Hydroxyl Radical Sensing

Oligonucleotide-stabilized silver nanoclusters (AgNCs) show promising applications in bioimaging and bio-/chemo-sensing. However, their unsatisfactory photostability limits their practical applications. In this work, fluorescent AgNCs were synthesized in situ in a DNA hydrogel, consisting of cross-linked enzymatically amplified polymeric DNAs with cytosine-rich sequences in the presence of Ag⁺. The fluorescence property of the resultant AgNCs was optimized by a rational design of the DNA sequences to cover a broad spectrum with comparable green and red emissions. Under the protection of the DNA hydrogel, the AgNCs showed significantly improved photostability in an ambient oxygen environment, as well as low cytotoxicity even at a high concentration. Therefore, these properties show the rolling-circle-amplification-stabilized AgNCs to be a promising possible fluorescent probe for the detection of reactive oxygen/nitrogen species (ROS/RNS) in live cells because red-emitting species are susceptible to oxidation and consequently convert to green-emitting species. Finally, the as-prepared AgNCs were demonstrated to be a sensitive and specific probe for cellular imaging and the monitoring of ROS/RNS levels, which broadens the applications of AgNCs and provides a new tool for related biological investigations.

Tailored Macroporous Hydrogels with Nanoparticles Display Enhanced and Tunable Catalytic Activity

This work demonstrates that a model system of poly( N-isopropylacrylamide) (PNIPAam) macroporous hydrogels, with tailored microstructures and comprising gold (Au) or silver (Ag) nanoparticles, display enhanced and tunable catalytic activity. These nanocomposites are prepared using polymer templates obtained from melt-processed cocontinuous polymer blends. The reaction rate, controlled by both hydrogel porosity and the PNIPAam lower critical solution temperature, increases by more than an order of magnitude as compared to nonporous gels, and is comparable to micro- or nanocarrier-based systems, with easier catalyst recovery. The fabrication process is scalable, and is compatible with broad choices of polymer blend, gel, and nanoparticle chemistries.

Programmable and Multifunctional DNA-Based Materials for Biomedical Applications

DNA encodes the genetic information; recently, it has also become a key player in material science. Given the specific Watson-Crick base-pairing interactions between only four types of nucleotides, well-designed DNA self-assembly can be programmable and predictable. Stem-loops, sticky ends, Holliday junctions, DNA tiles, and lattices are typical motifs for forming DNA-based structures. The oligonucleotides experience thermal annealing in a near-neutral buffer containing a divalent cation (usually Mg²⁺ ) to produce a variety of DNA nanostructures. These structures not only show beautiful landscape, but can also be endowed with multifaceted functionalities. This Review begins with the fundamental characterization and evolutionary trajectory of DNA-based artificial structures, but concentrates on their biomedical applications. The coverage spans from controlled drug delivery to high therapeutic profile and accurate diagnosis. A variety of DNA-based materials, including aptamers, hydrogels, origamis, and tetrahedrons, are widely utilized in different biomedical fields. In addition, to achieve better performance and functionality, material hybridization is widely witnessed, and DNA nanostructure modification is also discussed. Although there are impressive advances and high expectations, the development of DNA-based structures/technologies is still hindered by several commonly recognized challenges, such as nuclease instability, lack of pharmacokinetics data, and relatively high synthesis cost.