Recent advances in nanoparticulate biomimetic catalysts for combating bacteria and biofilms

Due to the abuse of antibiotics and the tendency of bacteria to form protective biofilms, the design and development of new efficient agents that can eliminate bacteria and biofilms are still highly desired but remain a great challenge; on the other hand, natural enzymes with unique catalytic characteristics can cause an irreversible damage to the bacteria without inducing drug-resistance in the bacteria. However, the intrinsic drawbacks, such as insufficient stability and high purification cost, of enzymes significantly limit their antimicrobial applications. Therefore, significant research efforts have been devoted towards the development of quality-equivalent or even superior enzyme substitutes with low cost and high stability. In this regard, nanomaterials with extraordinary enzyme-mimetic catalytic activities (termed as nanozymes) are considered as suitable candidates. To date, nanozymes have been proved to be promising materials for combating bacteria and biofilms under mild conditions. In this review, we have summarized the recent progress of nanozymes in this highly active field. The antibacterial mechanisms of nanozymes and the roles of their sizes, morphologies, compositions, surface modifications and microenvironment on their overall performance have been discussed. Moreover, the current challenges and prospects in this research area have been discussed. We believe that nanozymes with unique features and functions can provide a wealth of opportunities via their clinical and industrial applications.

Protein-protected metal nanoclusters: An emerging ultra-small nanozyme

Protein-protected metal nanoclusters (MNCs), typically consisting of several to a hundred metal atoms with a protein outer layer used for protecting clusters from aggregation, are excellent fluorescent labels for biomedical applications due to their extraordinary photoluminescence, facile synthesis and good biocompatibility. Interestingly, many protein-protected MNCs have also been reported to exhibit intrinsic enzyme-like activities, namely peroxidase, oxidase and catalase activities, and are consequently used for biological analysis and environmental treatment. These findings have extended the horizon of protein-protected MNCs' properties as well as their application in various fields. Furthermore, in the field of nanozymes, protein-protected MNCs have emerged as an outstanding new addition. Due to their ultra-small size (<2 nm), they usually have higher catalytic activity, more suitable size for in vivo application, better biocompatibility and photoluminescence in comparison with large size nanozymes. In this review, we will systematically introduce the significant advances in this field and critically discuss the challenges that lie ahead. Ultra-small nanozymes based on protein-protected MNCs are on the verge of attracting great interest across various disciplines and will stimulate research in the fields of nanotechnology and biology. This article is characterized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.

Recent Advances in Nanozyme Research

As a new generation of artificial enzymes, nanozymes have the advantages of high catalytic activity, good stability, low cost, and other unique properties of nanomaterials. Due to their wide range of potential applications, they have become an emerging field bridging nanotechnology and biology, attracting researchers in various fields to design and synthesize highly catalytically active nanozymes. However, the thorough understanding of experimental phenomena and the mechanisms beneath practical applications of nanozymes limits their rapid development. Herein, the progress of experimental and computational research of nanozymes on two issues over the past decade is briefly reviewed: (1) experimental development of new nanozymes mimicking different types of enzymes. This covers their structures and applications ranging from biosensing and bioimaging to therapeutics and environmental protection. (2) The catalytic mechanism proposed by experimental and theoretical study. The challenges and future directions of computational research in this field are also discussed.

Single-Atom Nanozyme Based on Nanoengineered Fe-N-C Catalyst with Superior Peroxidase-Like Activity for Ultrasensitive Bioassays

Single-atom catalysts are becoming a hot research topic owing to their unique characteristics of maximum specific activity and atomic utilization. Herein, a new single-atom nanozyme (SAN) based on single Fe atoms anchored on N-doped carbons supported on carbon nanotube (CNT/FeNC) is proposed. The CNT/FeNC with robust atomic Fe-N_x moieties is synthesised, showing superior peroxidase-like activity. Furthermore, the CNT/FeNC is used as the signal element in a series of paper-based bioassays for ultrasensitive detection of H₂ O₂ , glucose, and ascorbic acid. The SAN provides a new type of signal element for developing various biosensing techniques.

Unprecedented peroxidase-mimicking activity of single-atom nanozyme with atomically dispersed Fe-Nx moieties hosted by MOF derived porous carbon

Due to robustness, easy large-scale preparation and low cost, nanomaterials with enzyme-like characteristics (defined as 'nanozymes') are attracting increasing interest for various applications. However, most of currently developed nanozymes show much lower activity in comparison with natural enzymes, and the deficiency greatly hinders their use in sensing and biomedicine. Single-atom catalysts (SACs) offer the unique feature of maximum atomic utilization, providing a potential pathway to improve the catalytic activity of nanozymes. Herein, we propose a Fe-N-C single-atom nanozyme (SAN) that exhibits unprecedented peroxidase-mimicking activity. The SAN consists of atomically dispersed Fe─Nx moieties hosted by metal-organic frameworks (MOF) derived porous carbon. Thanks to the 100% single-atom active Fe dispersion and the large surface area of the porous support, the Fe-N-C SAN provided a specific activity of 57.76 U mg-1, which was almost at the same level as natural horseradish peroxidase (HRP). Attractively, the SAN presented much better storage stability and robustness against harsh environments. As a proof-of-concept application, highly sensitive biosensing of butyrylcholinesterase (BChE) activity using the Fe-N-C SAN as a substitute for natural HRP was further verified.

Metal and metal-oxide nanozymes: bioenzymatic characteristics, catalytic mechanism, and eco-environmental applications

Phenolic contaminants (R-OH) are a category of highly toxic organic compounds that are widespread in aquatic ecosystems and can induce carcinogenic risk to wildlife and humans; natural enzymes as green catalysts are capable of step-polymerizing these compounds to produce diverse macromolecular self-coupling products via radical-mediated C-C and C-O-C bonding at either the ortho- or para-carbon position, thereby evading the bioavailability and ecotoxicity of these compounds. Intriguingly, certain artificial metal and metal-oxide nanomaterials are known as nanozymes. They not only possess the unique properties of nanomaterials but also display intrinsic enzyme-mimicking activities. These artificial nanozymes are expected to surmount the shortcomings, such as low stability, easy inactivation, difficult recycling, and high cost, of natural enzymes, thus contributing to eco-environmental restoration. This review highlights the available studies on the enzymatic characteristics and catalytic mechanisms of natural enzymes and artificial metal and metal-oxide nanozymes in the removal and transformation of R-OH. These advances will provide key research directions beneficial to the multifunctional applications of artificial nanozymes in aquatic ecosystems.

Development of Nanozymes for Food Quality and Safety Detection: Principles and Recent Applications

The public concerns about agrifood safety call for innovative and reformative analytical techniques to meet the inspection requirements of high sensitivity, specificity, and reproducibility. Enzyme-mimetic nanomaterials or nanozymes, which combine enzyme-like properties with nanoscale features, emerge as an excellent tool for quality and safety detection in the agrifood sector, due to not only their robust capacity in detection but also their attraction in future-oriented exploitations. However, in-depth understanding about the fundamental principles of nanozymes for food quality and safety detection remains limited, which makes their applications largely empirical. This review provides a comprehensive overview of the principles, designs, and applications of nanozyme-based detection technique in the agrifood industry. The discussion mainly involves three mimicking types, that is, peroxidase, oxidase, and catalase-like nanozymes, capable of detecting major agrifood analytes. The current principles and strategies are classified and then discussed in details through discriminating the roles of nanozymes in diverse detection platforms. Thereafter, recent applications of nanozymes in detecting various endogenous ingredients and exogenous contaminants in foods are reviewed, and the outlook of profound developments are explained. Evidenced by the increasing publications, nanozyme-based detection techniques are narrowing the gap to practical-oriented food analytical methods, while some challenges in optimization of nanozymes, diversification of recognition-to-signal manners, and sustainability of methodology need to conquer in the future.

Nanozymes: From New Concepts, Mechanisms, and Standards to Applications

Nanozymes are nanomaterials with intrinsic enzyme-like characteristics that have been booming over the past decade because of their capability to address the limitations of natural enzymes such as low stability, high cost, and difficult storage. Along with the rapid development and ever-deepening understanding of nanoscience and nanotechnology, nanozymes hold promise to serve as direct surrogates of traditional enzymes by mimicking and further engineering the active centers of natural enzymes. In 2007, we reported the first evidence that Fe₃O₄ nanoparticles (NPs) have intrinsic peroxidase-mimicking activity, and since that time, hundreds of nanomaterials have been found to mimic the catalytic activity of peroxidase, oxidase, catalase, haloperoxidase, glutathione peroxidase, uricase, methane monooxygenase, hydrolase, and superoxide dismutase. Uniquely, a broad variety of nanomaterials have been reported to simultaneously exhibit dual- or multienzyme mimetic activity. For example, Fe₃O₄ NPs show pH-dependent peroxidase-like and catalase-like activities; Prussian blue NPs simultaneously possess peroxidase-, catalase-, and superoxide dismutase-like activity; and Mn₃O₄ NPs mimic all three cellular antioxidant enzymes including superoxide dismutase, catalase, and glutathione peroxidase. Taking advantage of the physiochemical properties of nanomaterials, nanozymes have shown a broad range of applications from in vitro detection to replacing specific enzymes in living systems. With the emergence of the new concept of "nanozymology", nanozymes have now become an emerging new field connecting nanotechnology and biology. Since the landmark paper on nanozymes was published in 2007, we have extensively explored their catalytic mechanism, established the corresponding standards to quantitatively determine their catalytic activities, and opened up a broad range of applications from biological detection and environmental monitoring to disease diagnosis and biomedicine development. Here we mainly focus on our progress in the systematic design and construction of functionally specific nanozymes, the standardization of nanozyme research, and the exploration of their applications for replacing natural enzymes in living systems. We also show that, by combining the unique physicochemical properties and enzyme-like catalytic activities, nanozymes can offer a variety of multifunctional platforms with a broad of applications from in vitro detection to in vivo monitoring and therapy. For instance, targeting antibody-conjugated ferromagnetic nanozymes simultaneously provide three functions: target capture, magnetic separation, and nanozyme color development for target detection. We finally will address the prospect of nanozyme research to become "nanozymology". We expect that nanozymes with unique physicochemical properties and intrinsic enzyme-mimicking catalytic properties will attract broad interest in both fundamental research and practical applications and offer new opportunities for traditional enzymology.

Carbogenic Nanozyme with Ultrahigh Reactive Nitrogen Species Selectivity for Traumatic Brain Injury

Reactive oxygen and nitrogen species (RONS), especially reactive nitrogen species (RNS) are intermediate products during incidence of nervous system diseases, showing continuous damage for traumatic brain injury (TBI). Here, we developed a carbogenic nanozyme, which shows an antioxidant activity 12 times higher than ascorbic acid (AA) and behaves as multienzyme mimetics. Importantly, the nanozyme exhibits an ultrahigh scavenging efficiency (∼16 times higher than AA) toward highly active RNS, such as ^•NO and ONOO^- as well as traditional reactive oxygen species (ROS) including O₂^•-, H₂O₂, and ^•OH. In vitro experiments show that neuron cells injured by H₂O₂ or lipopolysaccharide can be significantly recovered after carbogenic nanozyme treatment via scavenging all kinds of RONS. Moreover, the carbogenic nanozyme can serve as various enzyme mimetics and eliminate the harmful peroxide and glutathione disulfide from injured mice, demonstrating its potential as a therapeutic for acute TBI.

Catalytic Mechanisms of Nanozymes and Their Applications in Biomedicine

The research on nanozymes has increased dramatically in recent years and a new interdiscipline, nanozymology, has emerged. A variety of nanomaterials have been designed to mimic the characteristics of natural enzymes, which connects an important bridge between nanotechnology and biological science. Unlike natural enzymes, the nanoscale properties of nanozymes endow them with the potential to regulate their enzymatic-like activity from different perspectives. The mechanisms behind those methods are intriguing. In this Review, we introduce these mechanisms from the aspects of surface chemistry, surface modification, molecular imprinting, and hybridization and then focus attention on some specific catalytic mechanisms of several representative nanozymes. The applications of nanozymes ranging from bioassay, imaging, to disease therapy are also discussed in detail to prove the fact that the inherent physicochemical properties of nanomaterials not only make nanozymes the analogues of biological enzymes, but also endow them with incomparable advantages and broad prospects in biomedical fields. Finally, four characteristics and some challenges of nanozymes are summarized.

Peroxidase-Like Activity of Smart Nanomaterials and Their Advanced Application in Colorimetric Glucose Biosensors

Diabetes is a dominating health issue with 425 million people suffering from the disease worldwide and 4 million deaths each year. To avoid further complications, the diabetic patient blood glucose level should be strictly monitored despite there being no cure for diabetes. Colorimetric biosensing has attracted significant attention because of its low cost, simplicity, and practicality. Recently, some nanomaterials have been found that possess unexpected peroxidase-like activity, and great advances have been made in fabricating colorimetric glucose biosensors based on the peroxidase-like activity of these nanomaterials using glucose oxidase. Compared with natural horseradish peroxidase, the nanomaterials exhibit flexibility in structure design and composition, and have easy separation and storage, high stability, simple preparation, and tunable catalytic activity. To highlight the significant progress in the field of nanomaterial-based peroxidase-like activity, this work discusses the various smart nanomaterials that mimic horseradish peroxidase and its mechanism and development history, and the applications in colorimetric glucose biosensors. Different approaches for tunable peroxidase-like activity of nanomaterials are summarized, such as size, morphology, and shape; surface modification and coating; and metal doping and alloy. Finally, the conclusion and challenges facing peroxidase-like activity of nanomaterials and future directions are discussed.

Molecularly imprinted nanozymes with faster catalytic activity and better specificity

Nanozymes are nanomaterials mimicking the activity of natural enzymes, while most nanozymes lack substrate specificity. Molecular imprinting on nanozymes provides a simple solution to this problem, and the catalytic activity is also enhanced. To understand enhanced activity, a surface science approach is taken by dissecting the nanozyme reaction into adsorption of substrates, reaction, and product release. Each step is individually studied using reaction kinetics measurement, dynamic light scattering, UV-vis spectrometry. Enrichment of local substrate concentration due to imprinting is around 8-fold, and increased substrate concentration could contribute to increased activity. Diffusion of the substrate across the imprinted gel layer is studied by a pre-incubation experiment, also highlighting the difference between imprinted and non-imprinted gel layers. The activation energy is measured and a substrate-imprinted sample had the lowest activation energy of 13.8 kJ mol-1. Product release is also improved after imprinting as indicated by isothermal titration calorimetry using samples respectively imprinted with the substrate and the product. This study has rationalized improved activity and specificity of molecularly imprinted nanozymes and may guide further rational design of such materials.

Nanozymes: Classification, Catalytic Mechanisms, Activity Regulation, and Applications

Because of the high catalytic activities and substrate specificity, natural enzymes have been widely used in industrial, medical, and biological fields, etc. Although promising, they often suffer from intrinsic shortcomings such as high cost, low operational stability, and difficulties of recycling. To overcome these shortcomings, researchers have been devoted to the exploration of artificial enzyme mimics for a long time. Since the discovery of ferromagnetic nanoparticles with intrinsic horseradish peroxidase-like activity in 2007, a large amount of studies on nanozymes have been constantly emerging in the next decade. Nanozymes are one kind of nanomaterials with enzymatic catalytic properties. Compared with natural enzymes, nanozymes have the advantages such as low cost, high stability and durability, which have been widely used in industrial, medical, and biological fields. A thorough understanding of the possible catalytic mechanisms will contribute to the development of novel and high-efficient nanozymes, and the rational regulations of the activities of nanozymes are of great significance. In this review, we systematically introduce the classification, catalytic mechanism, activity regulation as well as recent research progress of nanozymes in the field of biosensing, environmental protection, and disease treatments, etc. in the past years. We also propose the current challenges of nanozymes as well as their future research focus. We anticipate this review may be of significance for the field to understand the properties of nanozymes and the development of novel nanomaterials with enzyme mimicking activities.

Fe₃O₄Nanoparticles Loaded on Lignin Nanoparticles Applied as a Peroxidase Mimic for the Sensitively Colorimetric Detection of H₂O₂

Lignin is the second largest naturally renewable resource and is primarily a by-product of the pulp and paper industry; however, its inefficient use presents a challenge. In this work, Fe₃O₄ nanoparticles loaded on lignin nanoparticles (Fe₃O₄@LNPs) were prepared by the self-assembly method and it possessed an enhanced peroxidase-like activity. Fe₃O₄@LNPs catalyzed the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H₂O₂ to generate a blue color, was observable by the naked eye. Under the optimal conditions, Fe₃O₄@LNPs showed the ability of sensitive colorimetric detection of H₂O₂within a range of 5⁻100 μM and the limit of detection was 2 μM. The high catalytic activity of Fe₃O₄@LNPs allows its prospective use in a wide variety of applications, including clinical diagnosis, food safety, and environmental monitoring.

Sensitive colorimetric sensor for point-of-care detection of acetylcholinesterase using cobalt oxyhydroxide nanoflakes

Point-of-care monitoring of acetylcholinesterase (AChE) is of significant importance for pesticide poisoning and disease diagnosis because it plays a pivotal role in biological nerve conduction systems. Herein, we designed a colorimetric strategy for the facile and accurate detection of AChE based on tandem catalysis with a multi-enzyme system, which is constituted by cobalt oxyhydroxide nanoflakes (CoOOH NFs) and choline oxidase (CHO). In this sensor, AChE catalytically hydrolyzed acetylcholine (ACh) to produce choline, which was further efficiently oxidized by CHO to yield H₂O₂. CoOOH NFs, as a nanozyme, efficiently catalyzed 3,3',5,5'-tetramethylbenzidine (TMB) into blue oxTMB with the help of H₂O₂, accompanied by an enhancement of absorbance intensity. The resulting intensity could be employed as the signal output of the CHO/CoOOH/ACh system in monitoring AChE. Under optimal conditions, the developed sensor possessed a sensitive response to AChE with a detection limit of 33 μU mL^-1. Interestingly, the proposed platform was applied to fabricate a paper-based sensor for rapidly recognizing AChE by direct observation with the naked eyes. Combined with a smartphone and ImageJ software, we further developed an image-processing algorithm for the quantitative detection of AChE with highly promising results, which validated the outstanding potential of on-site application in clinical diagnostics and pesticide poisoning.

Exosome-like Nanozyme Vesicles for H2O2-Responsive Catalytic Photoacoustic Imaging of Xenograft Nasopharyngeal Carcinoma

Photoacoustic imaging (PAI) is an attractive imaging modality, which is promising for clinical cancer diagnosis due to its advantages on deep tissue penetration and fine spatial resolution. However, few tumor catalytic/responsive PAI strategies are developed. Here, we design an exosome-like nanozyme vesicle for in vivo H₂O₂-responsive PAI of nasopharyngeal carcinoma (NPC). The intrinsic peroxidase-like activity of graphene quantum dot nanozyme (GQDzyme) effectively converts the 2,2'-azino- bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) into its oxidized form in the presence of H₂O₂. The oxidized ABTS exhibits strong near-infrared (NIR) absorbance, rendering it to be an ideal contrast agent for PAI. Thus, GQDzyme/ABTS nanoparticle is a novel type of catalytic PAI contrast agent, which is sensitive to H₂O₂ produced from NPC cells. Furthermore, we develop an approach to construct exosome-like nanozyme vesicle via biomimetic functionalization of GQDzyme/ABTS nanoparticle with natural erythrocyte membrane modified with folate acid. In vivo animal experiments demonstrated that this exosome-like nanozyme vesicle effectively accumulated in NPC and selectively triggered catalytic PAI for NPC. In addition, our nanozyme vesicle exhibits excellent biocompatibility and stealth ability for long blood circulation. Together, we demonstrate that GQDzyme/ABTS based exosome-like nanozyme vesicle is an ideal nanoplatform for developing deep-tissue tumor-targeted catalytic PAI in vivo.

Carbon-mediated synthesis of shape-controllable manganese phosphate as nanozymes for modulation of superoxide anions in HeLa cells

Here we present a facile method to fabricate shape-controllable transition metal phosphates by using hollow carbon structures as substrates for superoxide sensing.

Ultrafine and monodispersed iridium nanoparticles supported on nitrogen-functionalized carbon: an efficient oxidase mimic for glutathione colorimetric detection

Ultrafine and monodispersed Ir NPs supported on nitrogen-functionalized carbon served as an efficient oxidase mimic for glutathione colorimetric detection.

Intentional hydrolysis to overcome the hydrolysis problem: detection of Ce(iv) by producing oxidase-like nanozymes with F−

Fluoride boosts the oxidase-like activity of hydrolyzed Ce(iv) but inhibits the activity of Ce(iv), allowing intentional hydrolysis to be performed for consistent analysis of Ce(iv).

Nanomaterials with enzyme-like characteristics (nanozymes): next-generation artificial enzymes (II)

An updated comprehensive review to help researchers understand nanozymes better and in turn to advance the field.

Unraveling the enzyme-like activity of heterogeneous single atom catalyst

Herein, we report a heterogeneous single iron atom catalyst exhibiting excellent peroxidase, oxidase and catalase enzyme-like activities (defined as single atom enzymes, SAEs), exceeding those of Fe₃O₄ nanozymes by a factor of 40.

A cobalt-doped iron oxide nanozyme as a highly active peroxidase for renal tumor catalytic therapy

The Fe₃O₄ nanozyme, the first reported nanozyme with intrinsic peroxidase-like activity, has been successfully employed for various diagnostic applications. However, only a few studies have been reported on the therapeutic applications of the Fe₃O₄ nanozyme partly due to its low affinity to the substrate H₂O₂. Herein, we report a new strategy for improving the peroxidase-like activity and affinity of the Fe₃O₄ nanozyme to H₂O₂ to generate reactive oxygen species (ROS) for kidney tumor catalytic therapy. We showed that cobalt-doped Fe₃O₄ (Co@Fe₃O₄) nanozymes possessed stronger peroxidase activity and a 100-fold higher affinity to H₂O₂ than the Fe₃O₄ nanozymes. The lysosome localization properties of Co@Fe₃O₄ enable Co@Fe₃O₄ to catalyze the decomposition of H₂O₂ at ultralow doses for the generation of ROS bursts to effectively kill human renal tumor cells both in vitro and in vivo. Moreover, our study provides the first evidence that the Co@Fe₃O₄ nanozyme is a powerful nanozyme for the generation of ROS bursts upon the addition of H₂O₂ at ultralow doses, presenting a potential novel avenue for tumor nanozyme catalytic therapy.

Cobalt dopant in Fe₃O₄ nanozymes improved their binding affinity to H₂O₂ and enhanced the tumor catalytic therapy efficacy.

Constructing peptide-based artificial hydrolases with customized selectivity

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

Mesoporous Encapsulated Chiral Nanogold for Use in Enantioselective Reactions

Although various nanomaterials have been designed for biocatalysis, few of them can accelerate chemical reactions with high selectivity and stereocontrol, which remains them from being perfect alternatives to nature enzymes. Herein, inspired by the natural enzymes, an enantioselective nanomaterial has been constructed, with gold nanoparticles (AuNPs) as active centers, chiral cysteine (Cys) as selectors for chiral recognition, and expanded mesoporous silica (EMSN) as a skeleton of the artificial enzyme. In the oxidation of chiral 3,4-dihydroxy-phenylalanine (DOPA), the nanozyme with d-Cys shows preference to l-DOPA while the artificial enzyme with l-Cys shows preference to d-DOPA. Subsequent calculation of apparent steady-state kinetic parameters and activation energies together with molecular dynamics (MD) simulations showed that the different affinity precipitated by hydrogen bonding formation between chiral Cys and DOPA is the origin of chiral selectivity.

Catalytically Synthesized Prussian Blue Nanoparticles Defeating Natural Enzyme Peroxidase

We synthesized Prussian Blue (PB) nanoparticles through catalytic reaction involving hydrogen peroxide (H₂O₂) activation. The resulting nanoparticles display the size-dependent catalytic rate constants in H₂O₂ reduction, which are significantly improved compared to natural enzyme peroxidase: for PB nanoparticles 200 nm in diameter, the turnover number is 300 times higher; for 570 nm diameter nanoparticles, it is 4 orders of magnitude higher. Comparing to the known peroxidase-like nanozymes, the advantages of the reported PB nanoparticles are their true enzymatic properties: (1) enzymatic specificity (an absence of oxidase-like activity) and (2) an ability to operate in physiological solutions. The ultrahigh activity and enzymatic specificity of the catalytically synthesized PB nanoparticles together with high stability and low cost, obviously peculiar to noble metal free inorganic materials, would allow the substitution of natural and recombinant peroxidases in biotechnology and analytical sciences.

Catalytic degradation of organophosphorous nerve agent simulants by polymer beads@graphene oxide with organophosphorus hydrolase-like activity based on rational design of functional bimetallic nuclear ligand

The degradation of organophosphorous nerve agents is of primary concern due to the severe toxicity of these agents. Based on the active center of organophosphorus hydrolase (OPH), a bimetallic nuclear ligand, (5-vinyl-1,3-phenylene)bis(di(1H-imidazol-2-yl) methanol) (VPIM), was designed and synthesized, which contains four imidazole groups to mimic the four histidines at OPH active center. By grafting VPIM on graphene oxide (GO) surface via polymerization, the VPIM-polymer beads@GO was produced. The obtained OPH mimics has an impressive activity in dephosphorylation reactions (turnover frequency (TOF) towards paraoxon: 2.3 s^-1). The synergistic catalytic effect of the bimetallic Zn²⁺ nuclear center and carboxyl groups on surface of GO possibly contributes to the high hydrolysis on organophosphate substrate. Thus, a biomimetic catalyst for efficient degradation of some organophosphorous nerve agent simulants, such as paraoxon and chlorpyrifos, was prepared by constructing catalytic active sites. The proposed mechanism and general synthetic strategy open new avenues for the engineering of functional GOs for biomimetic catalysts.

Integrated nanozymes: facile preparation and biomedical applications

Nanozymes have been viewed as the next generation of artificial enzymes due to their low cost, large specific surface area, and good robustness under extreme conditions. However, the moderate activity and limited selectivity of nanozymes have impeded their usage. To overcome these shortcomings, integrated nanozymes (INAzymes) have been developed by encapsulating two or more different biocatalysts (e.g., natural oxidases and peroxidase mimics) together within confined frameworks. On the one hand, with the assistance of natural enzymes, INAzymes are capable of specifically recognizing targets. On the other hand, nanoscale confinement brought about by integration significantly enhances the cascade reaction efficiency. In this Feature Article, we highlight the newly developed INAzymes, covering from synthetic strategies to versatile applications in biodetection and therapeutics. Moreover, it is predicted that INAzymes with superior activities, specificity, and stability will enrich the research of nanozymes and pave new ways in designing multifunctional nanozymes.

Recyclable ferromagnetic chitosan nanozyme for decomposing phenol

Decomposing phenol and phenolic compounds to purify the environment is a focus of social attention. The use of ferromagnetic nanoparticles (MNP) to degrade phenol and phenolic compounds possesses many advantages and has received extensive attention. However, the unsatisfied catalyst activity and stability of MNP hamper its industrial applications. To improve MNP's properties, a ferromagnetic chitosan nanozyme (MNP@CTS) was synthesized via an improved hydrothermal method and molecular self-assembly technology. Its particle size was 11.76 nm, polydispersity index (PDI) was 0.073, surface zeta potential was 40.34 mV, saturation magnetization value was 35.28 emu g^-1 and coercivity value was 17.56 Oe. The catalytic condition was extensively optimized among a range of pH and temperature, as well as initial concentrations of the substrate and H₂O₂, and MNP@CTS removed over 95% phenol from an aqueous solution within 5 h under the optimum conditions. Moreover, MNP@CTS was stable and could be regenerated for reuse for at least ten rounds. Thus, our findings open up a wide spectrum and lay a foundation of environmental friendly applications of MNP@CTS, showing several attractive features, such as easy preparation, low cost, excellent catalytic activity, good stability and reusability.

Rational Design of Au@Pt Multibranched Nanostructures as Bifunctional Nanozymes

One of the current challenges in nanozyme-based nanotechnology is the utilization of multifunctionalities in one material. In this regard, Au@Pt nanoparticles (NPs) with excellent enzyme-mimicking activities due to the Pt shell and unique surface plasmon resonance features from the Au core have attracted enormous research interest. However, the unique surface plasmon resonance features from the Au core have not been widely utilized. The practical problem of the optical-damping nature of Pt hinders the research into the combination of Au@Pt NPs' enzyme-mimicking properties with their surface-enhanced Raman scattering (SERS) activities. Herein, we rationally tuned the Pt amount to achieve Au@Pt NPs with simultaneous plasmonic and enzyme-mimicking activities. The results showed that Au@Pt NPs with 2.5% Pt produced the highest Raman signal in 2 min, which benefited from the remarkably accelerated catalytic oxidation of 3,3',5,5'-tetramethylbenzidine with the decorated Pt and strong electric field retained from the Au core for SERS. This study not only demonstrates the great promise of combining bimetallic nanomaterials' multiple functionalities but also provides rational guidelines to design high-performance nanozymes for potential biomedical applications.

A label-free fluorescence assay for hydrogen peroxide and glucose based on the bifunctional MIL-53(Fe) nanozyme

A label-free nanozyme MIL-53(Fe) with the dual-function of catalyzing and emitting fluorescence was utilized for turn-on fluorescence detection of hydrogen peroxide and glucose. The proposed strategy provides a cost-effective, safe and sensitive method for the design and development of multiple enzyme cascade assays for various biomolecules.

Hydrolysis of Phosphate Esters Catalyzed by Inorganic Iron Oxide Nanoparticles Acting as Biocatalysts

Phosphorus ester hydrolysis is one of the key chemical processes in biological systems, including signaling, free-energy transaction, protein synthesis, and maintaining the integrity of genetic material. Hydrolysis of this otherwise kinetically stable phosphoester and/or phosphoanhydride bond is induced by enzymes such as purple acid phosphatase. Here, I report that, as in previously reported aged inorganic iron ion solutions, the iron oxide nanoparticles in the solution, which are trapped in a dialysis membrane tube filled with the various iron oxides, significantly promote the hydrolysis of the various phosphate esters, including the inorganic polyphosphates, with enzyme-like kinetics. This observation, along with those of recent studies of iron oxide, vanadium pentoxide, and molybdenum trioxide nanoparticles that behave as mimics of peroxidase, bromoperoxidase, and sulfite oxidase, respectively, indicates that the oxo-metal bond in the oxide nanoparticles is critical for the function of these corresponding natural metalloproteins. These inorganic biocatalysts challenge the traditional concept of replicator-first scenarios and support the metabolism-first hypothesis. As biocatalysts, these inorganic nanoparticles with enzyme-like activity may work in natural terrestrial environments and likely were at work in early Earth environments as well. They may have played an important role in the C, H, O, S, and P metabolic pathway with regard to the emergence and early evolution of life. Key Words: Enzyme-Hydrolysis-Iron oxide-Nanoparticles-Origin of life-Phosphate ester. Astrobiology 18, 294-310.

Iron nanostructured catalysts: design and applications

This review is focused on the recent advances in the design of iron nanostructures and their catalytic applications.

Highly active fluorogenic oxidase-mimicking NiO nanozymes

NiO nanoparticles can quickly catalyze oxidation of Amplex red to produce fluorescent products for intracellular imaging, much more efficiently than other types of tested nanozymes.

A dual-cell device designed as an oxidase mimic and its use for the study of oxidase-like nanozymes

A dual-cell device has been designed as an oxidase-like mimic with the oxidation of 3,3′,5,5′-tetramethylbenzidine as a model reaction.