Positional assembly of hemin and gold nanoparticles in graphene-mesoporous silica nanohybrids for tandem catalysis

Application of Nanozymes and its Progress in the Treatment of Ischemic Stroke

Nanozymes are a new kind of material which has been applied since the beginning of this century, and its birth has promoted the development of chemistry, materials science, and biology. Nanozymes can be used as a substitute for natural enzyme and has a wide range of applications; therefore, it has attracted extensive attention from all sectors of the community, and the number of studies has constantly increasing. In this paper, we introduced the outstanding achievements in the field of nanozymes in recent years from the main function, the construction of nanozyme-based biosensors, and the treatment of ischemic stroke, and we also illustrated the internal mechanism and the catalytic principle. In the end, the obstacles and challenges in the future development of nanozymes were proposed.

Coal waste-derived synthesis of yellow oxidized graphene quantum dots with highly specific superoxide dismutase activity: characterization, kinetics, and biological studies

The disintegration of coal-based precursors for the scalable production of nanozymes relies on the fate of solvothermal pyrolysis. Herein, we report a novel economic and scalable strategy to fabricate yellow luminescent graphene quantum dots (YGQDs) by remediating unburnt coal waste (CW). The YGQDs (size: 7-8 nm; M.W: 3157.9 Da) were produced using in situ "anion-radical" assisted bond cleavage in water (within 8 h; at 121 °C) with yields of ∼87%. The presence of exposed surface and edge groups, such as COOH, C-O-C, and O-H, as structural defects accounted for its high fluorescence with εmax ∼530 nm at pH 7. Besides, these defects also acted as radical stabilizers, demonstrating prominent anti-oxidative activity of ∼4.5-fold higher than standard ascorbic acid (AA). In addition, the YGQDs showed high biocompatibility towards mammalian cells, with 500 μM of treatment dose showing <15% cell death. The YGQDs demonstrated specific superoxide dismutase (SOD) activity wherein 15 μM YGQDs equalled the activity of 1-unit biological SOD (bSOD), measured using the pyrogallol assay. The Km for YGQDs was ∼10-fold higher than that for bSOD. However, the YGQDs retained their SOD activity in harsh conditions like high temperatures or denaturing reactions, where the activity of bSOD is completely lost. The binding affinity of YGQDs for superoxide ions, measured from isothermal calorimetry (ITC) studies, was only 10-fold lower than that of bSOD (Kd of 586 nM vs. 57.3 nM). Further, the pre-treatment of YGQDs (∼10-25 μM) increased the cell survivability to >75-90% in three cell lines during ROS-mediated cell death, with the highest survivability being shown for C6-cells. Next, the ROS-induced apoptosis in C6-cells (model for neurodegenerative diseases study), wherein YGQDs uptake was confirmed by confocal microscopy, showed ∼5-fold apoptosis alleviation with only 5 μM pretreatment. The YGQDs also restored the expression of pro-inflammatory Th1 cytokines (TNF-α, IFN-γ, IL-6) and anti-inflammatory Th2 cytokines (IL-10) to their basal levels, with a net >3-fold change observed. This further explains the molecular mechanism for the antioxidant property of YGQDs. The high specific SOD activity associated with YGQDs may provide the cheapest alternative source for producing large-scale SOD-based nanozymes that can treat various oxidative stress-linked disorders/diseases.

Nanomaterials with Glucose Oxidase-Mimicking Activity for Biomedical Applications

Glucose oxidase (GOD) is an oxidoreductase that catalyzes the aerobic oxidation of glucose into hydrogen peroxide (H₂O₂) and gluconic acid, which has been widely used in industrial raw materials production, biosensors and cancer treatment. However, natural GOD bears intrinsic disadvantages, such as poor stability and a complex purification process, which undoubtedly restricts its biomedical applications. Fortunately, several artificial nanomaterials have been recently discovered with a GOD-like activity and their catalytic efficiency toward glucose oxidation can be finely optimized for diverse biomedical applications in biosensing and disease treatments. In view of the notable progress of GOD-mimicking nanozymes, this review systematically summarizes the representative GOD-mimicking nanomaterials for the first time and depicts their proposed catalytic mechanisms. We then introduce the efficient modulation strategy to improve the catalytic activity of existing GOD-mimicking nanomaterials. Finally, the potential biomedical applications in glucose detection, DNA bioanalysis and cancer treatment are highlighted. We believe that the development of nanomaterials with a GOD-like activity will expand the application range of GOD-based systems and lead to new opportunities of GOD-mimicking nanomaterials for various biomedical applications.

Heme-Dependent Supramolecular Nanocatalysts: A Review

Enzymes fold into three-dimensional structures to distribute amino acid residues for catalysis, which inspired the supramolecular approach to construct enzyme-mimicking catalysts. A key concern in the development of supramolecular strategies is the ability to confine and orient functional groups to form enzyme-like active sites in artificial materials. This review introduces the design principles and construction of supramolecular nanomaterials exhibiting catalytic functions of heme-dependent enzymes, a large class of metalloproteins, which rely on a heme cofactor and spatially configured residues to catalyze diverse reactions via a complex multistep mechanism. We focus on the structure-activity relationship of the supramolecular catalysts and their applications in materials synthesis/degradation, biosensing, and therapeutics. The heme-free catalysts that catalyze reactions achieved by hemeproteins are also briefly discussed. Towards the end of the review, we discuss the outlook on the challenges related to catalyst design and future prospective, including the development of structure-resolving techniques and design concepts, with the aim of creating enzyme-mimicking materials that possess catalytic power rivaling that of natural enzymes..

COF-based artificial probiotic for modulation of gut microbiota and immune microenvironment in inflammatory bowel disease

Conventional strategies for treating inflammatory bowel disease merely relieve inflammation and excessive immune response, but fail to solve the underlying causes of IBD, such as disrupted gut microbiota and intestinal barrier. Recently, natural probiotics have shown tremendous potential for the treatment of IBD. However, probiotics are not recommended for IBD patients, as they may cause bacteremia or sepsis. Herein, for the first time, we constructed artificial probiotics (Aprobiotics) based on artificial enzyme-dispersed covalent organic frameworks (COFs) as the "organelle" and a yeast shell as the membrane of the Aprobiotics to manage IBD. The COF-based artificial probiotics, with the function of natural probiotics, could markedly relieve IBD by modulating the gut microbiota, suppressing intestinal inflammation, protecting the intestinal epithelial cells, and regulating immunity. This nature-inspired approach may aid in the design of more artificial systems for the treatment of various incurable diseases, such as multidrug-resistant bacterial infection, cancer, and others.

Advances in the One-Step Approach of Polymeric Materials Using Enzymatic Techniques

The formulation in which biochemical enzymes are administered in polymer science plays a key role in retaining their catalytic activity. The one-step synthesis of polymers with highly sequence-controlled enzymes is a strategy employed to provide enzymes with higher catalytic activity and thermostability in material sustainability. Enzyme-catalyzed chain growth polymerization reactions using activated monomers, protein-polymer complexation techniques, covalent and non-covalent interaction, and electrostatic interactions can provide means to develop formulations that maintain the stability of the enzyme during complex material processes. Multifarious applications of catalytic enzymes are usually attributed to their efficiency, pH, and temperature, thus, progressing with a critical structure-controlled synthesis of polymer materials. Due to the obvious economics of manufacturing and environmental sustainability, the green synthesis of enzyme-catalyzed materials has attracted significant interest. Several enzymes from microorganisms and plants via enzyme-mediated material synthesis have provided a viable alternative for the appropriate synthesis of polymers, effectively utilizing the one-step approach. This review analyzes more and deeper strategies and material technologies widely used in multi-enzyme cascade platforms for engineering polymer materials, as well as their potential industrial applications, to provide an update on current trends and gaps in the one-step synthesis of materials using catalytic enzymes.

Recent advances in biomedical applications of 2D nanomaterials with peroxidase-like properties

Significant progress has been made in developing two-dimensional (2D) nanomaterials owing to their ultra-thin structure, high specific surface area, and many other advantages. Recently, 2D nanomaterials with enzyme-like properties, especially peroxidase (POD)-like activity, are highly desirable for many biomedical applications. In this review, we first classify the types of 2D POD-like nanomaterials and then summarize various strategies for endowing 2D nanomaterials with POD-like properties. Representative examples of biomedical applications are reviewed, emphasizing in antibacterial, biosensing, and cancer therapy. Last, the future challenges and prospects of 2D POD-like nanomaterials are discussed. This review is expected to provide an in-depth understanding of 2D POD-like materials for biomedical applications.

Bifunctional Pdots-Based Novel ECL Nanoprobe with Qualitative and Quantitative Dual Signal Amplification Characteristics for Trace Cytokine Analysis

In this work, a novel methodology to design bifunctional ECL-luminophores with self-enhanced and TSA-amplified characteristics was proposed for improving the sensing performance of ECL-immunosensor toward trace cytokine analysis. Thanks to the qualitative- and quantitative- dual signal amplification technique, the as-prepared ECL biosensor demonstrated excellent detection performance. By analyzing the prospective cytokine biomarkers (IL-6), the ECL immunosensor exhibited a broad examination range with quite low detection limit and quite high selectivity, which was far superior to commercial ELISA kits and ever reported works. In particular, the novel ECL nanoprobe developed here could also be applied to monitor other immune toxicities or disease-related cytokines by using the respective antibodies corresponding to these targets. Moreover, the concept and construction strategy of self-amplified ECL-luminophores presented here could be further extended to design a series of Pdots-derived multicolored ECL probes to meet the needs of multipathway detection applications.

Recent progress in the design of analytical methods based on nanozymes

Nanomaterials with intrinsic enzyme-like properties (nanozymes) have attracted growing interest owing to their striking merits over the traditional enzymes, such as low cost, easy surface modification, high stability and robustness, and tunable activity. These features enable them to be considered as a potent substitute for natural enzymes to construct novel analytical platforms to detect various analytes from small molecules to proteins and cells. In this review, we focus on recent advances in the design strategies using nanozyme catalytic mediated signal amplification for sensing applications. The progress of nanozyme-based analytical systems in the detection of different types of analytes, including ions, small biomolecules, biomacromolecules and others, is summarized. Furthermore, the future challenges and opportunities of nanozyme-based analytical methods are discussed.

Photocatalytic Fuel Cell-Assisted Molecularly Imprinted Self-Powered Sensor: A Flexible and Sensitive Tool for Detecting Aflatoxin B1

The self-powered electrochemical sensor has gained big achievements in energy and devices, but it is challenging in analytical application owing to its low energy conversion efficiency and limited selectivity caused by the plentiful interference in actual samples. Herein, a new self-powered biosensor was constructed by the integration of a photocatalytic fuel cell (PFC) with a molecular imprinting polymer (MIP) to achieve sensitive and specific detection of aflatoxin B1 (AFB₁). Compared with other fuel cells, the PFC owns the advantages of low cost, high energy, good stability, and friendly environment by using light as the excitation source. MoS₂-Ti₃C₂T_x MXene (MoS₂-MX) served as the photoanode material for the first time by forming a heterojunction structure, which can enhance the photocurrent by about 3-fold and greatly improve the photoelectric conversion efficiency. Aiming at the poor selectivity of the self-powered sensor, the MIP was introduced to achieve the specific capture and separation of targets without sample pretreatment. Using the MIP and PFC as recognition and signal conversion elements, respectively, the proposed self-powered biosensor showed a wide dynamic range of 0.01-1000 ng/mL with a detection limit of 0.73 pg/mL, which opened opportunities to design more novel self-powered biosensors and promoted its application in food safety and environmental monitoring.

Luminescence approaches for the rapid detection of disease-related receptor proteins using transition metal-based probes

Protein biomarkers, particularly abnormally expressed receptor proteins, have been proved to be one of the crucial biomarkers for the rapid assessment, diagnosis, prognosis and prediction of specific human diseases. Transition metal based strategies in particular possess delightful strengths in the in-field and real-time visualization of receptor proteins owing to their unique photophysical properties. In this review, we highlight recent advances in the development of detection methods for receptor protein biomarkers using transition metal based approaches, particularly those employing transition metal complexes. We first discuss the strengths and weaknesses of various strategies used for protein biomarker monitoring in live cells. We then describe the principles of the various sensing platforms and their application for receptor protein detection. Finally, we discuss the challenges and future inspirations in this specific field.

The Role of Nanomaterials in Modulating the Structure and Function of Biomimetic Catalysts

Nanomaterial-incorporated enzyme mimics have so far been examined in various cases, and their properties are governed by the properties of both catalysts and materials. This review summarizes recent efforts in understanding the role of inorganic nanomaterials for modulating biomimetic catalytic performance. Firstly, the importance of enzyme mimics, and the necessity for tuning their catalysis will be outlined. Based on structural characteristics, these catalysts are divided into two types: traditional artificial enzymes, and novel nanomaterial-based enzyme mimics. Secondly, the mechanisms on how nano-sized materials interact with these catalysts will be examined. Intriguingly, incorporating various nanomaterials into biomimetic catalysts may provide a convenient and highly efficient method for the modulation of activities as well as stabilities or introduce new and attractive features. Finally, the perspectives of the main challenges and future opportunities in the areas of nanomaterial-incorporated biomimetic catalysis will be discussed. In this regard, nanomaterials as a kind of promising scaffold for tuning catalysis will attract more and more attention and be practically applied in numerous fields.

Hollow zeolite microspheres as a nest for enzymes: a new route to hybrid heterogeneous catalysts

In the field of heterogeneous catalysis, the successful integration of enzymes and inorganic catalysts could pave the way to multifunctional materials which are able to perform advanced cascade reactions. However, such combination is not straightforward, for example in the case of zeolite catalysts for which enzyme immobilization is restricted to the external surface. Herein, this challenge is overcome by developing a new kind of hybrid catalyst based on hollow zeolite microspheres obtained by the aerosol-assisted assembly of zeolite nanocrystals. The latter spheres possess open entry-ways for enzymes, which are then loaded and cross-linked to form cross-linked enzyme aggregates (CLEAs), securing their entrapment. This controlled design allows the combination of all the decisive features of the zeolite with a high enzyme loading. A chemo-enzymatic reaction is demonstrated, where the structured zeolite material is used both as a nest for the enzyme and as an efficient inorganic catalyst. Glucose oxidase (GOx) ensures the in situ production of H2O2 subsequently utilized by the TS-1 zeolite to catalyze the epoxidation of allylic alcohol toward glycidol. The strategy can also be used to entrap other enzymes or combination of enzymes, as demonstrated here with combi-CLEAs of horseradish peroxidase (HRP) and glucose oxidase. We anticipate that this strategy will open up new perspectives, leveraging on the spray-drying (aerosol) technique to shape microparticles from various nano-building blocks and on the entrapment of biological macromolecules to obtain new multifunctional hybrid microstructures.

Electrostatic Interaction-Induced Formation of Enzyme-on-MOF as Chemo-Biocatalyst for Cascade Reaction with Unexpectedly Acid-Stable Catalytic Performance

Combining biocatalytic and chemocatalytic reactions in a one-pot reaction not only avoids the tedious isolation of intermediates during the reactions but also provides a desirable alternative to extend the range of catalytic reactions. Here, we report a facile strategy to immobilize an enzyme, glucose oxidase (GOx), on PCN-222(Fe) induced by electrostatic interaction in which PCN-222(Fe) serves as both a support and chemocatalyst. The immobilization was confirmed through ζ potential measurement, confocal laser scanning microscopy, Fourier transform infrared spectrometry, and UV-vis spectroscopy. This chemo-biocatalyst was applied to a cascade reaction to catalyze glucose oxidation and ABTS (ABTS = 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (or pyrogallol) oxidation. The catalytic kinetics studies show that these chemo-biocatalytic cascade reactions obey the Michaelis-Menten equation, which indicates that the cascade reactions follow the typical enzymatic dynamic regulation process. Interestingly, GOx/PCN-222(Fe) exhibits an exceptional acid-stable catalytic performance as evidenced by circular dichroism spectroscopy where no significant structure change was observed toward acidic solutions with different pH values. GOx/PCN-222(Fe) also displays desirable recyclability since no significant loss of conversion rates was found after six repeated reactions. This work presents a convenient strategy to construct metal-organic framework based chemo-biocatalysts, which may find potential applications in sensing and nanomachines.

CeO2 -Encapsulated Hollow Ag-Au Nanocage Hybrid Nanostructures as High-Performance Catalysts for Cascade Reactions

Inspired by bio-enzymes, multistep cascade reactions are highly attractive in catalysis. Despite extensive research in recent years, it remains a challenge to promote the stability and activity of catalysts. Here, well-defined core-shell structured Ag-Au nanocage@CeO₂ (Ag-Au NC@CeO₂ ) are designed by a simple and facile self-assembly method. The results indicate that the Ag-Au NC@CeO₂ has glucose oxidase-like activity and intrinsic peroxidase-like activity at the same time. As expected, Ag-Au NC@CeO₂ hybrid nanomaterials exhibit cascade reactions activity. Moreover, the hybrid materials are promising to detect glucose without bio-enzymes. This research has potential applications in biomedicine and biomimetic catalysis.

Enzyme-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization: Precision polymer synthesis via enzymatic catalysis

Enzyme-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization provides a sustainable strategy for efficient production of well-defined polymers under mild conditions. Horseradish peroxidase (HRP), a heme-containing metalloenzyme, catalyzes oxidation of acetylacetone (ACAC) by hydrogen peroxide (H₂O₂) to generate ACAC radicals, initiating polymerization of vinyl monomers. This HRP/H₂O₂/ACAC ternary initiating system is applied to RAFT polymerization of different types of vinyl monomers. Furthermore, to overcome the inherent limitation of necessity for oxygen-free conditions, another enzyme, glucose oxidase (GOx) or pyranose 2-oxidase (P2Ox), with excellent deoxygenation capability, is introduced to consume oxygen by catalyzing oxidation of glucose to generate H₂O₂. The generated H₂O₂ is directly supplied to HRP catalysis for radical generation. Both GOx-HRP and P2Ox-HRP cascade catalysis afford RAFT polymerization with oxygen tolerance. In this chapter, we mainly focus on detailed synthetic protocols of RAFT polymerizations initiated by HRP/H₂O₂/ACAC ternary initiating system and P2Ox-HRP cascade catalysis. The general characterization and analytical methods used in these enzyme-initiated RAFT polymerizations are also included.

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.

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.

Solution-Phase Synthesis of Platinum Nanoparticle-Decorated Metal-Organic Framework Hybrid Nanomaterials as Biomimetic Nanoenzymes for Biosensing Applications

The synthesis of nanomaterials with specific properties and functions as biomimetic nanoenzymes has attracted extensive attention in the past decades due to their great potential to substitute natural enzymes. Herein, a facile and simple method for the preparation of platinum nanoparticle (PtNP)-decorated two-dimensional metal-organic framework (MOF) nanocomposites was developed. A ligand with heme-like structure, Fe(III) tetra(4-carboxyphenyl)porphine chloride (TCPP(Fe)), was applied to synthesize MOF nanosheets (denoted as Cu-TCPP(Fe) nanosheets) in high yield. Ultrathin Cu-TCPP(Fe) nanosheets with thickness less than 10 nm were used as a novel template for the growth of ultrasmall and uniform PtNPs. Significantly, the obtained hybrid nanomaterials (PtNPs/Cu-TCPP(Fe) hybrid nanosheets) exhibit enhanced peroxidase-like activity compared to PtNPs, Cu-TCPP(Fe) nanosheets, and the physical mixture of both due to the synergistic effect. On account of the excellent peroxidase-like activity of PtNPs/Cu-TCPP(Fe) hybrid nanosheets, we established a colorimetric method for sensitive and rapid detection of hydrogen peroxide. Furthermore, by combining with glucose oxidase, a cascade colorimetric method was established to further detect glucose with excellent sensitivity and selectivity.

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.

Growth of Au Nanoparticles on 2D Metalloporphyrinic Metal-Organic Framework Nanosheets Used as Biomimetic Catalysts for Cascade Reactions

Inspired by the multiple functions of natural multienzyme systems, a new kind of hybrid nanosheet is designed and synthesized, i.e., ultrasmall Au nanoparticles (NPs) grown on 2D metalloporphyrinic metal-organic framework (MOF) nanosheets. Since 2D metalloporphyrinic MOF nanosheets can act as the peroxidase mimics and Au NPs can serve as artificial glucose oxidase, the hybrid nanosheets are used to mimic the natural enzymes and catalyze the cascade reactions. Furthermore, the synthesized hybrid nanosheets are used to detect biomolecules, such as glucose. This study paves a new avenue to design nanomaterial-based biomimetic catalysts with multiple complex functions.

Self-Assembled DNA/Peptide-Based Nanoparticle Exhibiting Synergistic Enzymatic Activity

Designing enzyme-mimicking active sites in artificial systems is key to achieving catalytic efficiencies rivaling those of natural enzymes and can provide valuable insight in the understanding of the natural evolution of enzymes. Here, we report the design of a catalytic hemin-containing nanoparticle with self-assembled guanine-rich nucleic acid/histidine-rich peptide components that mimics the active site and peroxidative activity of hemoproteins. The chemical complementarities between the folded nucleic acid and peptide enable the spatial arrangement of essential elements in the active site and effective activation of hemin. As a result, remarkable synergistic effects of nucleic acid and peptide on the catalytic performances were observed. The turnover number of peroxide reached the order of that of natural peroxidase, and the catalytic efficiency is comparable to that of myoglobin. These results have implications in the precise design of supramolecular enzyme mimetics, particularly those with hierarchical active sites. The assemblies we describe here may also resemble an intermediate in the evolution of contemporary enzymes from the catalytic RNA of primitive cells.

Target-triggered cascade assembly of a catalytic network as an artificial enzyme for highly efficient sensing

Determining the catalytic activity of artificial enzymes is an ongoing challenge. In this work, we design a porphyrin-based enzymatic network through the target-triggered cascade assembly of catalytic nanoparticles. The nanoparticles are synthesized via the covalent binding of hemin to amino-coated gold nanoparticles and then the axial coordination of the Fe center with a dual-functional imidazole or pyridine derivative. The network, which is specifically formed by coordination polymerization triggered by Hg2+ as the target, shows high catalytic activity due to the triple amplification of enzymatic activity during the cascade assembly. The catalytic dynamics are comparable to those of natural horseradish peroxidase. The catalytic characteristics can be ultrasensitively regulated by the target, leading to a selective methodology for the analysis of sub-attomolar Hg2+. It has also been used for "signal-on" imaging of reactive oxygen species in living cells. This work provides a new avenue for the design of enzyme mimics, and a powerful biocatalyst with signal switching for the development of biosensing protocols.

Graphene Oxide Quantum Dots as Novel Nanozymes for Alcohol Intoxication

Alcohol overconsumption as a worldwide issue results in alcoholic liver disease (ALD), such as steatosis, alcoholic hepatitis, and cirrhosis. The treatment of ALD has been widely investigated but remains challenging. In this work, the protective effects of graphene oxide quantum dots (GOQDs) as novel nanozymes against alcohol overconsumption are discovered, and the specific mechanisms underlying these effects are elucidated via omics analysis. GOQDs dramatically alleviate the reduction of cell viability induced by ethanol and can act as nanozymes to accelerate ethanol metabolism and avoid the accumulation of toxic intermediates in cells. Mitochondrial damage and the excessive generation of free radicals were mitigated by GOQDs. The mechanisms underlying the cellular protective effects were also related to alterations in metabolic and protein signals, especially those involved in lipid metabolism. The moderately increased autophagy induced by GOQDs explained the removal of accumulated lipids and the subsequent elimination of excessive GOQDs. These findings suggest that GOQDs have an antagonistic capacity against the adverse effects caused by ethanol and provide new insights into the direct applications of GOQDs. In addition to traditional antioxidation, this work also establishes metabolomics and proteomics techniques as effective tools to discover the multiple functions of nanozymes.

Protein-Directed Synthesis of Bifunctional Adsorbent-Catalytic Hemin-Graphene Nanosheets for Highly Efficient Removal of Dye Pollutants via Synergistic Adsorption and Degradation

Herein, for the first time, we report a "green", one-pot reduction/decoration method for the synthesis of bifunctional adsorbent-catalytic hemin-graphene nanosheets by using a common available protein (bovine serum albumin, BSA) as both a reductant and a stabilizer. Our prepared nanosheets are highly stable and possess intrinsic peroxidase-like catalytic activity due to the decoration of BSA and hemin. Furthermore, benefiting from the combined advantages of graphene and BSA, these nanosheets are able to efficiently adsorb dye pollutants from aqueous solution. More importantly, due to their adsorption and catalytic ability, these adsorbent-catalytic nanosheets can be applied to highly efficient dye removal via synergistic adsorption and degradation. Specifically, our catalysts can easily bring organic dyes to their surface by adsorption, and then activate H₂O₂ to generate hydroxyl radicals, leading to the degradation of the dyes. Such catalytic mechanism of our as-prepared nanosheets was analogous to that of natural enzymes, in which the extremely high catalytic efficiency is largely dependent upon their ability to bring substrates in close proximity to the active sites of enzymes. Our finding may open new potential applications of hemin-graphene hybrid nanosheets in environmental chemistry, biotechnology, and medicine.

A redox-responsive strategy using mesoporous silica nanoparticles for co-delivery of siRNA and doxorubicin

Co-delivery of gene and drug therapies for cancer treatment remains a major goal of nanocarrier research.

A biomimetic enzyme modified electrode for H2O2 highly sensitive detection

An efficient catalyst based on artificial bionic peroxidase was synthesized for electrocatalysis. A poly(ethyleneimine)/Au nanoparticle composite (PEI-AuNP) was prepared and it was then linked to hemin via a coupling reaction between carboxyl groups in hemin and amino groups in PEI without the activation of a carboxyl group by carbodiimide. Fourier transform infrared (FTIR) spectroscopy verified the formation of amido bonds within the structure. The presence of AuNPs contributed greatly in establishing the amido bonds within the composite. Transmission electron microscopy (TEM) and UV-visible spectroscopy were also used to characterize the PEI-AuNP-hemin catalyst. PEI-AuNP-hemin exhibited intrinsic peroxidase-like catalytic activities. The PEI-AuNP-hemin deposited on a glass carbon electrode had strong sensing for H2O2 with a well-defined linear relationship between the amperometric response and H2O2 concentration in the range from 1 μM to 0.25 mM. The detection limit was 0.247 nM with a high sensitivity of 0.347 mA mM(-1) cm(-2). The peroxidase-like catalytic activity of PEI-AuNP-hemin is discussed in relation to its microstructure. The study suggests that PEI-AuNP-hemin may have promising application prospects in biocatalysis and bioelectronics.

Integrated Nanozymes with Nanoscale Proximity for in Vivo Neurochemical Monitoring in Living Brains

Nanozymes, the nanostructures with enzymatic activities, have attracted considerable attention because, in comparison with natural enzymes, they offer the possibility of lowered cost, improved stability, and excellent recyclability. However, the specificity and catalytic activity of current nanozymes are still far lower than that of their natural counterparts, which in turn has limited their use such as in bioanalysis. To address these challenges, herein we report the design and development of integrated nanozymes (INAzymes) by simultaneously embedding two cascade catalysts (i.e., a molecular catalyst hemin and a natural enzyme glucose oxidase, GOx) inside zeolitic imidazolate framework (ZIF-8) nanostructures. Such integrated design endowed the INAzymes with major advantage in improved catalytic efficiency as the first enzymatic reaction occurred in close (nanoscale) proximity to the second enzyme, so products of the first reaction can be used immediately as substrates for the second reaction, thus overcoming the problems of diffusion-limited kinetics and product instability. The considerable high catalytic activity and stability enabled the INAzymes to efficiently draw a colorimetric detection of glucose with good sensitivity and selectivity. When facilitated with in vivo microdialysis, the INAzyme was successfully used for facile colorimetric visualization of cerebral glucose in the brain of living rats. Moreover, when further combined with microfluidic technology, an integrative INAzyme-based online in vivo analytical platform was constructed. The promising application of the platform was successfully illustrated by continuously monitoring the dynamic changes of striatum glucose in living rats' brain following ischemia/reperfusion. This study developed a useful approach to not only functional nanomaterial design but also advanced platforms developments for diverse targets monitoring.

Nanozymes in bionanotechnology: from sensing to therapeutics and beyond

Nanozymes are nanomaterials with enzyme-like characteristics, which have found broad applications in various areas including bionanotechnology and beyond.