A Remarkably Efficient MnFe2O4‐based Oxidase Nanozyme

Nanomaterials‐based enzyme mimetics (nanozymes) have attracted considerable interest due to their applications in imaging, diagnostics, and therapeutic treatments. Particularly, metal‐oxide nanozymes have been shown to mimic the interesting redox properties and biological activities of metalloenzymes. Here we describe an efficient synthesis of MnFe₂O₄ nanomaterials and show how the morphology can be controlled by using a simple co‐precipitation method. The nanomaterials prepared by this method exhibit a remarkable oxidase‐like activity. Interestingly, the activity is morphology‐dependent, with nanooctahedra (NOh) exhibiting a catalytic efficiency of 2.21×10⁹ m ^?1 s^?1, the highest activity ever reported for a nanozyme.     

A Redox Modulatory Mn3O4 Nanozyme with Multi‐Enzyme Activity Provides Efficient Cytoprotection to Human Cells in a Parkinson's Disease Model

Nanomaterials with enzyme‐like activities (nanozymes) attracts significant interest due to their therapeutic potential for the treatment of various diseases. Herein, we report that a Mn₃O₄ nanozyme functionally mimics three major antioxidant enzymes, that is, superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) and the multienzyme activity is size as well as morphology‐dependent. The redox modulatory effect of Mn₃O₄ plays a crucial role in protecting the cells from MPP+ induced cytotoxicity in a Parkinson disease (PD)‐like cellular model, indicating that manganese‐based nanomaterials having multi‐enzyme activity can robustly rescue the cells from oxidative damage and thereby possess therapeutic potential to prevent ROS‐mediated neurological disorders.     

A Nanozyme with Photo‐Enhanced Dual Enzyme‐Like Activities for Deep Pancreatic Cancer Therapy

Nanozymes have attracted extensive interest owing to their high stability, low cost and easy preparation, especially in the field of cancer therapy. However, the relatively low catalytic activity of nanozymes in the tumor microenvironment (TME) has limited their applications. Herein, we report a novel nanozyme (PtFe@Fe₃O₄) with dual enzyme‐like activities for highly efficient tumor catalytic therapy. PtFe@Fe₃O₄ shows the intrinsic photothermal effect as well as photo‐enhanced peroxidase‐like and catalase‐like activities in the acidic TME, thereby effectively killing tumor cells and overcoming the tumor hypoxia. Importantly, a possible photo‐enhanced synergistic catalytic mechanism of PtFe@Fe₃O₄ was first disclosed. We believe that this work will advance the development of nanozymes in tumor catalytic therapy.     

Self‐Assembly of Multi‐nanozymes to Mimic an Intracellular Antioxidant Defense System

In this work, for the first time, we constructed a novel multi‐nanozymes cooperative platform to mimic intracellular antioxidant enzyme‐based defense system. V₂O₅ nanowire served as a glutathione peroxidase (GPx) mimic while MnO₂ nanoparticle was used to mimic superoxide dismutase (SOD) and catalase (CAT). Dopamine was used as a linker to achieve the assembling of the nanomaterials. The obtained V₂O₅@pDA@MnO₂ nanocomposite could serve as one multi‐nanozyme model to mimic intracellular antioxidant enzyme‐based defense procedure in which, for example SOD, CAT, and GPx co‐participate. In addition, through assembling with dopamine, the hybrid nanocomposites provided synergistic antioxidative effect. Importantly, both in vitro and in vivo experiments demonstrated that our biocompatible system exhibited excellent intracellular reactive oxygen species (ROS) removal ability to protect cell components against oxidative stress, showing its potential application in inflammation therapy.     

Defect‐Rich Adhesive Nanozymes as Efficient Antibiotics for Enhanced Bacterial Inhibition

Nanozymes have emerged as a new generation of antibiotics with exciting broad‐spectrum antimicrobial properties and negligible biotoxicities. However, their antibacterial efficacies are unsatisfactory due to their inability to trap bacteria and their low catalytic activity. Herein, we report nanozymes with rough surfaces and defect‐rich active edges. The rough surface increases bacterial adhesion and the defect‐rich edges exhibit higher intrinsic peroxidase‐like activity compared to pristine nanozymes due to their lower adsorption energies of H₂O₂ and desorption energy of OH*, as well as the larger exothermic process for the whole reaction. This was demonstrated using drug‐resistant Gram‐negative Escherichia coli and Gram‐positive Staphylococcus aureus in vitro and in vivo. This strategy can be used to engineer nanozymes with enhanced antibacterial function and will pave a new way for the development of alternative antibiotics.     

The Fe‐N‐C Nanozyme with Both Accelerated and Inhibited Biocatalytic Activities Capable of Accessing Drug–Drug Interactions

Emerging as a cost‐effective and robust enzyme mimic, nanozymes have drawn increasing attention with broad applications ranging from cancer therapy to biosensing. Developing nanozymes with both accelerated and inhibited biocatalytic properties in a biological context is intriguing to peruse more advanced functions of natural enzymes, but remains challenging, because most nanozymes are lack of enzyme‐like molecular structures. By re‐visiting and engineering the well‐known Fe‐N‐C electrocatalyst that has a heme‐like Fe‐N_x active sites, herein, it is reported that Fe‐N‐C could not only catalyze drug metabolization but also had inhibition behaviors similar to cytochrome P450 (CYP), endowing it a potential replacement of CYP for preliminary evaluation of massive potential chemicals, drug dosing guide, and outcome prediction. In addition, in contrast to electrocatalysts, the highly graphitic framework of Fe‐N‐C may not be obligatory for a competitive CYP‐like activity.     

Synthesis,characterization, and functionalization of zirconium tungstate (ZrW2O8) nano‐rods for advanced polymer nanocomposites

Nanomaterials based on zirconium tungstate (ZrW₂O₈) exhibit numerous outstanding properties that make them ideal candidates for the development of high‐performance composites. Low coefficient of thermal expansion for advanced materials is a promising direction in the field of insulating nanocomposites. However, the agglomeration of zirconium tungstate (ZrW₂O₈)‐based nanomaterials in the polymer matrix is a limiting factor in their successful applications, and studies on surface functionalization ZrW₂O₈ for advanced nanocomposites are very limited. In this work, ZrW₂O₈ nano‐rods were synthesized using a hydrothermal method and subsequently functionalized in a solvent‐free aqueous medium using dopamine. Both pristine and functionalized nano‐rods were thoroughly characterized using Fourier transform infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, X‐ray diffraction, Scanning Electron Microscopy (SEM), and transmission electron microscopy techniques, which confirmed the successful functionalization of the nanomaterials. Polymer nanocomposites were also prepared using epoxy resin as a model matrix. Polymer nanocomposites with functionalized ZrW₂O₈ nano‐rods exhibited low coefficient of thermal expansion and enhanced tensile properties. The improved properties of the nanocomposites render them suitable for electronic applications. Copyright © 2017 John Wiley & Sons, Ltd.     

2D/2D h‐BN/N‐doped MoS2 Heterostructure Catalyst with Enhanced Peroxidase‐like Performance for Visual Colorimetric Determination of H2O2

Recently, nanozymes have attracted extensive attention because of their advantages of combining nanomaterials with enzymes. Herein, hexagonal boron nitride (h‐BN) and nitride‐doped molybdenum disulfide (N?MoS₂) nano‐composites (h‐BN/N?MoS₂) were synthesized by facile and cost‐effective liquid exfoliation with a solvothermal method in nontoxic ethanol solution. The results show that h‐BN, as a co‐catalyst, can not only dope into the lattice of MoS₂ but also form a heterogeneous structure with MoS₂NSs. It expanded the layer spacing and specific surface area of MoS₂NSs, which was beneficial to the contact between the catalyst and the substrate, and resulted in a synergistic enhancement of the catalytic activity of hydrogen peroxide (H₂O₂) with MoS₂. A colorimetric determination platform of h‐BN/N?MoS₂‐TMB‐H₂O₂ was constructed. It exhibited a wide linear range of 1–1000 μM with a low limit of detection (LOD) of 0.4 μM under optimal conditions, high sensitivity and stability, as well as good reliability (99.4–110.0%) in practice, making the measurement system more widely applicable.1. Introduction     

Surface Modifications and Optoelectronic Characterization of TiO2‐Nanoparticles: Design of New Photo‐Electronic Materials

TiO₂ nanoparticles are of great current interest for applications in photo‐electronic materials including light‐energy conversion, artificial photosynthetic systems as well as photocatalysis. The success of these applications relies on the exciton recombination dynamics and visible‐light sensitivity of the TiO₂ nanomaterials. Thus, in order to develop the highly efficient photo‐electronic materials absorbing visible light, different low dimensional TiO₂ nanostructures such as nanodiscs, nanofibers and nanochains were synthesized, and thereafter their surfaces were modified by incorporating with Sn‐porphyrins and heteropoly acid. The optoelectronic properties of the surface‐modified nanomaterials were investigated with regard to the optical properties and the surface exciton dynamics by using both steady‐state and ultrafast time‐resolved laser spectroscopic techniques including single nanoparticle photoluminescence technique. These results were correlated with the photo‐electronic properties including photocatalytic activities and solar cell efficiencies, indicating that the electron transfer mechanism in the modified nanostructures may be similar to the “Z‐scheme” of the plant photosynthetic system so that both photocatalytic activity and solar cell efficiencies were synergistically enhanced by using two color illumination.     

Constructing magnetic Fe3O4‐Au@CeO2 hybrid nanofibers for selective catalytic degradation of organic dyes

Au nanoparticles (Au NPs) play a vital role in heterogeneous catalytic reactions. However, pristine Au NPs usually suffer from poor selectivity and difficult recyclability. In this work, Fe₃O₄‐Au@CeO₂ hybrid nanofibers were prepared via a simple one‐pot redox reaction between HAuCl₄ and Ce (NO₃)₃ in the presence of Fe₃O₄ nanofibers. CeO₂ shell was uniformly coated on the surface of Fe₃O₄ nanofibers to form a unique core‐shell structure, while Au NPs were encapsulated inside the CeO₂ shell. The as‐prepared Fe₃O₄‐Au@CeO₂ hybrid nanofibers have been proved to be positively surface charged due to the formation of CeO₂ shell, enabling them to be good candidates for predominant selective catalytic activity towards the degradation of negatively charged organic dyes. In addition, the Fe₃O₄‐Au@CeO₂ hybrid nanofibers showed magnetic properties, offering them excellent recyclable usability. This work presents a facile and effective solution to prepare magnetic noble metal/metal oxide hybrid nanomaterials with unique chemical structure and surface characteristic for promising applications in heterogeneous catalysis.     

An Enzyme‐Mimicking Single‐Atom Catalyst as an Efficient Multiple Reactive Oxygen and Nitrogen Species Scavenger for Sepsis Management

Sepsis, characterized by immoderate production of multiple reactive oxygen and nitrogen species (RONS), causes high morbidity and mortality. Despite progress made with nanozymes, efficient antioxidant therapy to eliminate these RONS remains challenging, owing largely to the specificity and low activity of exploited nanozymes. Herein, an enzyme‐mimicking single‐atom catalyst, Co/PMCS, features atomically dispersed coordinatively unsaturated active Co‐porphyrin centers, which can rapidly obliterate multiple RONS to alleviate sepsis. Co/PMCS can eliminate O₂^.? and H₂O₂ by mimicking superoxide dismutase, catalase, and glutathione peroxidase, while removing ^.OH via the oxidative‐reduction cycle, with markedly higher activity than nanozymes. It can also scavenge ^.NO through formation of a nitrosyl–metal complex. Eventually, it can reduce proinflammatory cytokine levels, protect organs from damage, and confer a distinct survival advantage to the infected sepsis mice.     

Structure‐Dependent Electrocatalysis of Ni(OH)2 Hourglass‐like Nanostructures Towards L‐Histidine

As the properties of nanomaterials are strongly dependent on their size, shape and nanostructures, probing the relations between macro‐properties and nanostructures is challenging for nanoscientists. Herein, we deliberately chose three types of Ni(OH)₂ with hexagonal, truncated trigonal, and trigonal hourglass‐like nanostructures, respectively, as the electrode modifier to demonstrate the correlation between the nanostructures and their electrocatalytic performance towards L ‐histidine. It was found that the hexagonal hourglass‐like Ni(OH)₂ sample had the best electrocatalytic activity, which can be understood by a cooperative mechanism: on one hand, the hexagonal sample possesses the largest specific surface area and the tidiest nanostructure, resulting in the most orderly packing on the electrode surface; on the other hand, its internal structure with the most stacking faults would generate a lot of unstable protons, leading to an enhanced electronic conductivity. The findings are important because they provide a clue for materials design and engineering to meet a specific requirement for electrocatalysis of L ‐histidine, possibly even for other biomolecules. In addition, the hexagonal Ni(OH)₂‐based biosensor shows excellent sensitivity and selectivity in the determination of L ‐histidine and offers a promising feature for the analytical application in real biological samples.     

3,4,9,10‐Perylenetetracarboxylic Acid/Hemin Nanocomposites Act as Redox Probes and Electrocatalysts for Constructing a Pseudobienzyme‐Channeling Amplified Electrochemical Aptasensor

A simple wet‐chemical strategy for the synthesis of 3,4,9,10‐perylenetetracarboxylic acid (PTCA)/hemin nanocomposites through π–π interactions is demonstrated. Significantly, the hemin successfully conciliates PTCA redox activity with a pair of well‐defined redox peaks and intrinsic peroxidase‐like activity, which provides potential application of the PTCA self‐derived redox activity as redox probes. Additionally, PTCA/hemin nanocomposites exhibit a good membrane‐forming property, which not only avoids the conventional fussy process for redox probe immobilization, but also reduces the participation of the membrane materials that act as a barrier of electron transfer. On the basis of these unique properties, a pseudobienzyme‐channeling amplified electrochemical aptasensor is developed that is coupled with glucose oxidase (GOx) for thrombin detection by using PTCA/hemin nanocomposites as redox probes and electrocatalysts. With the addition of glucose to the electrolytic cell, the GOx on the aptasensor surface bioelectrocatalyzed the reduction of glucose to produce H₂O₂, which in turn was electrocatalyzed by the PTCA/hemin nanocomposites. Cascade schemes, in which an enzyme is catalytically linked to another enzyme, can produce signal amplification and therefore increase the biosensor sensitivity. As a result, a linear relationship for thrombin from 0.005 to 20 nM and a detection limit of 0.001 nM were obtained.     

Solution‐Processed Two‐Dimensional MoS2 Nanosheets: Preparation,Hybridization, and Applications

As one member of the emerging class of ultrathin two‐dimensional (2D) transition‐metal dichalcogenide (TMD) nanomaterials, the ultra‐thin MoS₂ nanosheet has attracted increasing research interest as a result of its unique structure and fascinating properties. Solution‐phase methods are promising for the scalable production, functionalization, hybridization of MoS₂ nanosheets, thus enabling the widespread exploration of MoS₂‐based nanomaterials for various promising applications. In this Review, an overview of the recent progress of solution‐processed MoS₂ nanosheets is presented, with the emphasis on their synthetic strategies, functionalization, hybridization, properties, and applications. Finally, the challenges and opportunities in this research area will be proposed.     

When Nanozymes Meet Single‐Atom Catalysis

Nanomaterials with enzyme‐like activities, coined nanozymes, have been researched widely as they offer unparalleled advantages in terms of low cost, superior activity, and high stability. The complex structure and composition of nanozymes has led to extensive investigation of their catalytic sites at an atomic scale, and to an in‐depth understanding of the biocatalysis occurring. Single‐atom catalysts (SACs), characterized by atomically dispersed active sites, have provided opportunities for mimicking metalloprotease and for bridging the gap between natural enzymes and nanozymes. In this Minireview, we illustrate the unique properties of nanozymes and we discuss recent advances in the synthesis, characterization, and applications of SACs. Subsequently, we outline the impressive progress made in single‐atom nanozymes and we discuss their applications in sensing, degradation of organic pollutants, and in therapeutic roles. Finally, we present the major challenges and opportunities remaining for a successful marriage of nanozymes and SACs.     

Enhanced Peroxidase-mimicking Activity of Plasmonic Gold-modified Mn3O4 Nanocomposites through Photoexcited Hot Electron Transfer

Enzyme-mimicking artificial nanomaterials often termed nanozymes have broad applications in many fields, including biosensing, pollutant degradation and cancer diagnosis. Herein, we introduce a plasmonic gold nanoparticle-modified Mn₃O₄ nanozyme (Mn₃O₄-Au). Visible or near infrared light excitation into the plasmonic absorption band of the surface-bound gold nanoparticles enhances the catalytic oxidation of tetramethylbenzidine (TMB). The mechanism of light-enhanced peroxidase activity is proposed based on the Mn₃O₄ conduction band mediated hot electron transfer from photoexcited gold nanoparticles to H₂O₂ which undergoes further oxygen-oxygen bond cleavage to yield hydroxyl radical. The surface decoration of plasmonic gold nanoparticles endows Mn₃O₄-Au to be a light-regulated nanozyme.     

Tumor‐Microenvironment‐Induced Degradation of Ultrathin Gadolinium Oxide Nanoscrolls for Magnetic‐Resonance‐Imaging‐Monitored,Activatable Cancer Chemotherapy

The development of biodegradable inorganic nanoparticles with a tumor microenvironment‐activated therapeutic mode of action is urgently needed for precision cancer medicine. Herein, the synthesis of ultrathin lanthanide nanoscrolls (Gd₂O₃ NSs) is reported, which biodegrade upon encountering the tumor microenvironment. The Gd₂O₃ NSs showed highly controlled magnetic properties, which enabled their high‐resolution magnetic resonance imaging (MRI). Importantly, Gd₂O₃ NSs degrade in a pH‐responsive manner and selectively penetrate tumor tissue, enabling the targeted release of anti‐cancer drugs. Gd₂O₃ NSs can be efficiently loaded with an anti‐cancer drug (DOX, 80 %) and significantly inhibit tumor growth with negligible cellular and tissue toxicity both in vitro and in vivo. This study may provide a novel strategy to design tumor microenvironment‐responsive inorganic nanomaterials for biocompatible bioimaging and biodegradation‐enhanced cancer therapy.     

Simultaneous Fenton‐like Ion Delivery and Glutathione Depletion by MnO2‐Based Nanoagent to Enhance Chemodynamic Therapy

Chemodynamic therapy (CDT) utilizes iron‐initiated Fenton chemistry to destroy tumor cells by converting endogenous H₂O₂ into the highly toxic hydroxyl radical (^.OH). There is a paucity of Fenton‐like metal‐based CDT agents. Intracellular glutathione (GSH) with ^.OH scavenging ability greatly reduces CDT efficacy. A self‐reinforcing CDT nanoagent based on MnO₂ is reported that has both Fenton‐like Mn²⁺ delivery and GSH depletion properties. In the presence of HCO₃^?, which is abundant in the physiological medium, Mn²⁺ exerts Fenton‐like activity to generate ^.OH from H₂O₂. Upon uptake of MnO₂‐coated mesoporous silica nanoparticles (MS@MnO₂ NPs) by cancer cells, the MnO₂ shell undergoes a redox reaction with GSH to form glutathione disulfide and Mn²⁺, resulting in GSH depletion‐enhanced CDT. This, together with the GSH‐activated MRI contrast effect and dissociation of MnO₂, allows MS@MnO₂ NPs to achieve MRI‐monitored chemo–chemodynamic combination therapy.     

Advances in Single‐Atom Nanozymes Research†

Nanozymes with intrinsic enzyme‐like properties have attracted significant interest owing to their capability to address the limitations of traditional enzymes such as fragility, high cost and difficult mass production. However, the currently reported nanozymes are generally less active than natural enzymes. In recent years, with the rapid development of nanoscience and nanotechnology, single‐atom nanozymes (SAzymes) with well‐defined electronic and geometric structures have shown a promise to serve as direct surrogates of traditional enzymes by mimicking the highly evolved catalytic center of natural enzymes. In this review, we will introduce the enzymatic characteristics and recent advances of SAzymes, and summarize their significant applications from in vitro detection to in vivo monitoring and therapy.     

Tumor‐Microenvironment‐Induced Degradation of Ultrathin Gadolinium Oxide Nanoscrolls for Magnetic‐Resonance‐Imaging‐Monitored,Activatable Cancer Chemotherapy

The development of biodegradable inorganic nanoparticles with a tumor microenvironment‐activated therapeutic mode of action is urgently needed for precision cancer medicine. Herein, the synthesis of ultrathin lanthanide nanoscrolls (Gd₂O₃ NSs) is reported, which biodegrade upon encountering the tumor microenvironment. The Gd₂O₃ NSs showed highly controlled magnetic properties, which enabled their high‐resolution magnetic resonance imaging (MRI). Importantly, Gd₂O₃ NSs degrade in a pH‐responsive manner and selectively penetrate tumor tissue, enabling the targeted release of anti‐cancer drugs. Gd₂O₃ NSs can be efficiently loaded with an anti‐cancer drug (DOX, 80 %) and significantly inhibit tumor growth with negligible cellular and tissue toxicity both in vitro and in vivo. This study may provide a novel strategy to design tumor microenvironment‐responsive inorganic nanomaterials for biocompatible bioimaging and biodegradation‐enhanced cancer therapy.