Filling in the Gaps between Nanozymes and Enzymes: Challenges and Opportunities

Self-synergy-powered Ni/Fe nanocube-based cholesterol detection with dual modes

Nanoenzyme-leveraged multimode detection would benefit enhancing sensitivity and mitigating detection error. Moreover, multienzyme-like nanozymes hold tremendous potential in sensing by offering synergistic effects and cascaded catalysis. Herein, cost-effective multienzymic Ni/Fe nanocubes (Ni/FeNCs) were synthesized via a facile co-precipitation, and verified to catalyze H2O2 decomposition as peroxidase (POD) and catalase (CAT) mimics. Thereby, a dual-mode sensing platform based on Ni/FeNC and cholesterol oxidase (ChOx) was developed for cholesterol detection. Utilizing the H2O2 produced via the oxidation of cholesterol catalyzed by ChOx, OH•/O2•- radicals and O2 were formed efficiently via Ni/FeNCs-based H2O2 decomposition, facilitating the generation of chemiluminescence (CL) and fluorescence signals. For CL assay, an Ni/FeNC-luminol-H2O2 CL system was fabricated, where both POD-mimic-mediated radical decomposition of H2O2 and ferricyanide ions in Ni/FeNCs could induce CL reaction with respective mechanism. Notably, these two CL processes were both deduced to be enhanced by in-situ generated O2. This dual-catalyzed luminol CL system, involving self-cascade catalysis of ferricyanogen and CAT mimic as well as the self-synergy between POD-like and CAT-like activities of Ni/FeNCs, was proposed for the first time, and able to boost CL signal. To generate fluorescent signal, o-phenylenediamine was introduced, and oxidized by both OH•/O2•- and O2 produced via POD/CAT-mimic-mediated H2O2 decomposition to 2,3-diaminophenazinc, which could quench the fluorescence of WS2 quantum dots via internal filtration effect. The Ni/FeNC-based dual-mode assay is applicable and flexible for cholesterol detection. Particularly, the low-cost Ni/FeNC is a promising candidate of luminol-H2O2 CL system due to its dual-CL-mechanism involving self-cascade and synergistic catalysis.

Achievements and challenges in glucose oxidase-instructed multimodal synergistic antibacterial applications

Glucose oxidase (GOx) with unique catalytic properties and inherent biocompatibility can effectively oxidize both endogenous and exogenous glucose with oxygen (O2) into gluconic acid and hydrogen peroxide (H2O2). Accordingly, the GOx-based catalytic chemistry offers new possibilities for designing and constructing multimodal synergistic antibacterial systems. The consumption of glucose permanently downregulates bacterial cell metabolism by blocking essential energy supplies, inhibiting their growth and survival. Additionally, the production of gluconic acid could downregulates the pH within the bacterial infection microenvironment, enhancing the production of hydroxyl radicals (∙OH) from H2O2 via enhanced Fenton or Fendon-like reactions and triggering the pH-responsive release of drugs. Furthermore, the generated H2O2 in situ avoids the addition of exogenous hydrogen peroxide. Therefore, it is possible to design GOx-based multimodal antibacterial synergistic therapies by combining GOx-instructed cascade reactions with other therapeutic approaches such as chemodynamic therapies (CDT), hypoxia-activated prodrugs, photosensitizers, and stimuli-responsive drug release. Such multimodal strategies are expected to exhibit better therapeutic effects than single therapeutic modes. This tutorial review highlights recent advancements in GOx-instructed multimodal synergistic antibacterial systems, focusing on design philosophy and construction strategies. Current challenges and future prospects for advancing GOx-based multimodal antibacterial synergistic therapies are discussed.

Bimetallic oxide (CoNi2O4) nanozyme as ROS independent for ascorbic acid detection with computational study

Herein, spinel CoNi2O4 nanoflowers (NFs) were successfully synthesized by a two-step hydrothermal annealing process and testified to have intrinsic enzyme mimic activities. The CoNi2O4 NFs can effectively oxidize the chromogenic substrate 3, 3', 5, 5'-tetramethylbenzidine (TMB) to ox-TMB showing catalytic behavior that follows enzyme kinetics of Michaelis-Menten equation with a low constant (Km = 0.0143 mM). Innovatively, experimental data and Density Functional Theory (DFT) calculations disclosed the stable structure and mechanism of spinal CoNi2O4NFs, which demonstrated oxidase-like activity and reactive oxygen species independence across a wide temperature range. Accordingly, a colorimetric biosensor for rapid and sensitive detection of ascorbic acid (AA) was successfully developed, displaying excellent stability, selectivity, sensitivity and low limit of detection (0.44 μM). This biosensor was applied to vitamin C capsules and fresh lemon fruit, showing favorable reproducibility and feasibility. DFT and molecular modeling (MD) calculations indicate a cobalt atom as the optimal site for catalytic conversion, while the amine group in the TMB molecule is the optimal nucleophilic attack site.

Dual Activities of Flower-Like Gold-Iron Oxide Nanozyme for Peroxidase-Mimicking and Glucose Detection

Nanozymes, constituting of inorganic nanomaterials, are the sustainable and cost-effective alternatives of the naturally abundant enzymes. For more than a decade, nanozymes have shown astonishingly enhanced enzymatic activity as compared to its naturally occurring counterpart and emerged as a potential platform in biomedical science. The current study reports a novel flower shaped gold-iron oxide nanocomposite prepared via a facile and green solution phase redox mediated synthesis. The precursor gold salt conversion to nanometallic Au(0) is mediated by iron metal powder, which acts both as reductant and metal source in the resultant gold nanoparticle decorated iron oxide nanocomposite. Calcination of the synthesized nanocomposites leads to morphological evolution into unique flower shape with improved homogeneity between gold and iron components along with metal surface exposure. The gold-iron oxide nanocomposites have been utilized first time for peroxidase mimicking study and exhibit enhanced catalytic activity at 25 °C with low Michaelis-Menten constant (Km) and higher maximum reaction velocity (Vmax) as compared to the natural enzyme Horseradish peroxidase (HRP). In addition, combined assembly of this nanozyme with natural enzyme glucose oxidase also serves a potential platform for the visible colorimetric detection and quantification of glucose with limit of detection (LOD) of 15 μM.

In Situ Assembled Metal-Phenolic Nanozyme Biointerfaces Revitalize Stem Cells and Optimize Diabetic Implant Osseointegration

The hyperglycemic microenvironment of diabetes inevitably leads to the accumulated reactive oxygen species (ROS) and impairs the function of stem cells, thereby impeding the process of osseointegration after implant placement. In this study, a self-assembled metal-phenolic nanozyme coating is presented for alleviating diabetic oxidative stress and improving osseointegration at implant interfaces. The antioxidant-like enzyme activity is induced by phenolic ligand-metal charge transfer (LMCT) during the coordination of epigallocatechin-3-gallate (EGCG) with copper phosphate nanosheets (Cu NS). The metal-phenolic nanozyme biointerfaces exhibits scavenging activity against a range of free radicals and facilitated the adhesion, migration, and osteogenic differentiation of stem cells, thereby enhancing the osseointegration of implants in diabetic rats. Additionally, the nanozyme coating strategy inhibits bacterial invasion and supports the adhesion of soft tissue cells. This study provides a prospective approach for surface modification to safeguard and enhance the osseointegration of implants in diabetic subjects.

Nanozyme-based visual diagnosis and therapeutics for myocardial infarction: The application and strategy

BACKGROUND

Myocardial infarction (MI) is a heart injury caused by ischemia and low oxygen conditions. The occurrence of MI lead to the activation of a large number of neutrophils and macrophages, inducing severe inflammatory injury. Meanwhile, the inflammatory response produces much more free radicals, further exacerbating the inflammatory response and tissue damage. Efforts are being dedicated to developing antioxidants and enzymes, as well as small molecule drugs, for treating myocardial ischemia. However, poor pharmacokinetics and potential side effects limit the clinical application of these drugs. Recent advances in nanotechnology have paved new pathways in biomedical and healthcare environments. Nanozymes exhibit the advantages of biological enzymes and nanomaterials, including with higher catalytic activity and stability than natural enzymes. Thus, nanozymes provide new possibilities for the diagnosis and treatment of oxidative stress and inflammation-related diseases.

AIM OF REVIEW

We describe the application of nanozymes in the diagnosis and therapy of MI, aiming to bridge the gap between the diagnostic and therapeutic needs of MI.

KEY SCIENTIFIC CONCEPTS OF REVIEW

We describe the application of nanozymes in the diagnosis and therapy of MI, and discuss the new strategies for improving the diagnosis and treatment of MI. We review in detail the applications of nanozymes to achieve highly sensitive detection of biomarkers of MI. Due to their unique enzyme catalytic capabilities, nanozymes have the ability to sensitively detect biomolecules through colorimetric, fluorescent, and electrochemical assays. In addition, nanozymes exhibit excellent antioxidase-mimicking activity to treat MI by modulating reduction/oxidation (REDOX) homeostasis. Nanozymes can also passively or actively target MI tissue sites, thereby protecting ischemic myocardial tissue and reducing the infarct area. These innovative applications of nanozymes in the field of biomedicine have shown promising results in the diagnosis and treatment of MI, offering a novel therapeutic strategy.

Nanozymes in Biomedical Applications: Innovations Originated From Metal-Organic Frameworks

Nanozymes exhibit significant potential in medical theranostics, environmental protection, energy development, and biopharmaceuticals due to their exceptional catalytic performance. Compared with natural enzymes, nanozymes have the advantages of simple preparation and purification, convenient production and low cost. Therefore, it is very important to prepare nanozymes quickly and efficiently, which not only helps to expand their application scope, but also can further exert their great potential in various fields. Metal-organic frameworks (MOF) materials serve as versatile substrates for constructing nanozymes, offering unique advantages like adjustable structure, high specific surface area, and porous channels. MOF coordination nodes constructed from metal ions or metal clusters have unique properties that can be leveraged to tailor nanozyme characteristics for different applications. This review describes and analyzes recent methods for constructing nanozymes using MOF materials, and explores their application prospects in biomedicine. By expounding the preparation techniques and biomedical applications of nanozymes, this review aims to inspire researchers to develop innovative nanozyme materials and explore new application directions.

A review towards sustainable analyte detection: Biomimetic inspiration in biosensor technology

The branch of biomimetics has witnessed a profound impact on the field of biosensor technology, reflected in sustainable analyte detection. A vast array of biosensor platforms with improved/upgraded performance have been developed and reported. No wonder the motivation from the field of biomimetics has a huge impact on generating detection systems with escalated degrees of manipulation and tunability at different levels. More recently, biomimetic biosensor technology has found potential in constructing bio-inspired materials such as aptamers, MIPs, nanozymes, DNAzymes, Synzymes, etc. to be integrated with biosensor fabrication. The establishment of a sensing setup is not limited to the bioreceptor fabrication; the construction of transducing element using biomimetic material have been reported too. Moreover, to serve a biosensing of target analyte from a fatal diseased sample different biomimetic architectures can be designed that mimic in-vivo microenvironmental surroundings to get an exact microenvironment equivalent to natural conditions leading towards designing of a precise treatment strategy. This research area is ever-evolving as there is a scope for upgradation and refinement due to advancing technologies including nanotechnology, biomimetic nanomaterials, microfluidics, optical sensors, etc. This review is an attempt to comprehend and juxtapose the very primary innovations in the field of biomimetic biosensor technology to realize its comprehensive and wide-range scope and possibilities.

Enzyme cascade nanozyme based colorimetric sensor for detection of uric acid as a biomarker of hyperuricemia

A Cr-doped VO2 nanobelt (Cr/VO2) with remarkable peroxidase-like activity was synthesized and coupled with uricase to catalyze the cascade reaction for  detection of uric acid. Notably, the affinity of Cr/VO2 for 3,3',5,5'-tetramethylbenzidine dihydrochloride hydrate (TMB) and hydrogen peroxide (H2O2) is tenfold and 20-fold higher, respectively, than that of horseradish peroxidase (HRP). The Cr/VO2 exhibits highly reactive and stable peroxidase activity at temperatures of 20-60 ℃. Thus, the reaction catalyzed by Cr/VO2 can be carried out at room temperature, greatly simplifying the testing process. This enzyme cascade nanozyme based colorimetric assay enables the selective and simple detection of uric acid within 30 min with a detection limit of only 0.34 μM, and has an observable potential in clinical applications.

Applications of Nanotechnology for Spatial Omics: Biological Structures and Functions at Nanoscale Resolution

Spatial omics methods are extensions of traditional histological methods that can illuminate important biomedical mechanisms of physiology and disease by examining the distribution of biomolecules, including nucleic acids, proteins, lipids, and metabolites, at microscale resolution within tissues or individual cells. Since, for some applications, the desired resolution for spatial omics approaches the nanometer scale, classical tools have inherent limitations when applied to spatial omics analyses, and they can measure only a limited number of targets. Nanotechnology applications have been instrumental in overcoming these bottlenecks. When nanometer-level resolution is needed for spatial omics, super resolution microscopy or detection imaging techniques, such as mass spectrometer imaging, are required to generate precise spatial images of target expression. DNA nanostructures are widely used in spatial omics for purposes such as nucleic acid detection, signal amplification, and DNA barcoding for target molecule labeling, underscoring advances in spatial omics. Other properties of nanotechnologies include advanced spatial omics methods, such as microfluidic chips and DNA barcodes. In this review, we describe how nanotechnologies have been applied to the development of spatial transcriptomics, proteomics, metabolomics, epigenomics, and multiomics approaches. We focus on how nanotechnology supports improved resolution and throughput of spatial omics, surpassing traditional techniques. We also summarize future challenges and opportunities for the application of nanotechnology to spatial omics methods.

Kinetic Profiling of Oxidoreductase-Mimicking Nanozymes: Impact of Multiple Activities, Chemical Transformations, and Colloidal Stability

In contrast to homogeneous enzyme catalysis, nanozymes are nanosized heterogeneous catalysts that perform reactions on a rigid surface. This fundamental difference between enzymes and nanozymes is often overlooked in kinetic studies and practical applications. In this article, using 14 nanozymes of various compositions (core@shell, metal-organic frameworks, metal, and metal oxide nanoparticles), we systematically demonstrate that nontypical features of nanozymes, such as multiple catalytic activities, chemical transformations, and aggregation, need to be considered in nanozyme catalysis. Ignoring these features results in the inaccurate quantification of catalytic activity. Neglecting the multiple activities led to a six-time underestimation of Mn2O3 oxidation activity and mischaracterization of this material as a low-active peroxidase-mimicking nanozyme. Additionally, overlooking chemical stability during catalytic reactions led to the reporting of high peroxidase-mimicking activity for Au@Ag nanoparticles, which, in reality, exhibited no intrinsic activity and oxidized the substrate through the leakage of Ag+ ions. Ignoring the chemical stability of Au@Prussian Blue nanoparticles may lead to more than four times overestimation of peroxidase-mimicking activity after just 24 h of storage. Finally, disregarding the colloidal stability of nanozymes led to a five-time inaccuracy in catalytic activity. These findings underscore the necessity of optimizing procedures to account for these factors in nanozyme kinetic measurements, which will in turn ensure more reliable biosensors and the success of other practical applications.

Holistic insights into carbon nanotubes and MXenes as a promising route to bio-sensing applications

Essential biosensor use has become increasingly important in drug discovery and recognition, biomedicine, food safety, security, and environmental research. It directly contributed to the development of specialized, reliable diagnostic instruments known as biosensors, which use biological sensing components. Traditional biosensors have poor performance, so scientists need to develop advanced biosensors with promising selectivity, sensitivity, stability, and reusability. These are all parameter modifications associated with the characteristics of the sensing material. Carbon nanotubes (CNTs) and MXenes are promising as targeted sensing agents in advanced functional materials because of their promising chemical and physical properties and limited toxic effects. Based on available data and sensing performance, MXene is better for biosensing applications than CNTs. Because of their large specific surface area (SSA), superior electrical conductivity, and adaptable surface chemistry that facilitates simple functionalization and robust interactions with biomolecules, MXenes are typically regarded as the superior option for biosensors. Additionally, because of their hydrophilic nature, they are more suited to biological settings, which increases their sensitivity and efficacy in identifying biological targets. MXenes are more suitable for biosensing applications due to their versatility and compatibility with aquatic environments, even if CNTs have demonstrated stability and muscular mechanical strength. However, MXenes offer better thermal stability, which is crucial for applications in diverse temperature environments. This study reviews and compares the biosensing capabilities, synthesis methods, unique properties, and toxicity of CNTs and MXenes. Both nanomaterials effectively detect various pollutants in food, biological substances, and human bodies, making them invaluable in environmental monitoring and medical diagnostics. In conclusion, CNTs work better for biosensors that must be strong, flexible, and long-lasting under different conditions. MXenes, on the other hand, work better when chemical flexibility and compatibility with wet environments are essential.

Breaking Barriers in Photothermal Tumor Therapy: A Cascade of Strain-Engineered Nanozyme in Action

Cancer, a deadly and constantly evolving disease, has always been difficult to treat due to the complexity of the tumor microenvironment (TME). Cancer nanomedicines are proving to be a much better alternative for treatment due to their stability and ability to provide an efficient targeted therapy. An amorphous alloy bimetallene with an introduction of 2 % tensile strain with photothermal multiple enzyme-like catalytic activity is being presented here that functions as a TME-responsive nanozyme. Labeled as RhRu, this bimetallene, under acidic conditions, functions as oxidase (OXD) - like, peroxidase (POD) - like and catalase (CAT) - like enzymes, by producing radicals and disrupting the tumor cells. This effect is enhanced especially upon irradiation of laser and introduction of tensile strain in its heterophase boundaries. This current highlight discusses the strain engineering tactic of la-RhRu bimetallene and its potency as an anti-tumor therapeutic.

Iron Single-Atom Nanozyme with Inflammation-Suppressing for Inhibiting Multidrug-Resistant Bacterial Infection and Facilitating Wound Healing

Infection with drug-resistant bacteria and the formation of biofilms are the main factors contributing to wound healing insufficiency. Antibacterial agents with enzyme-like properties have exhibited considerable potential for efficient eradication of drug-resistant microorganisms due to their superior sensitivities and minimal side effects. In this work, we prepared a kind of Fe-centered single-atom nanozyme (Fe-SAzyme) with high biocompatibility and stability via a facile one-pot hydrothermal method, which was suitable for the treatment of wounds infected with drug-resistant bacteria. The Fe-SAzyme exhibited remarkable peroxidase-like catalytic activities, catalyzing the conversion of hydrogen peroxide (H2O2) to highly toxic hydroxyl radicals (•OH), which could not only damage bacterial cells but also inhibit, disrupt, and eradicate the formation of bacterial biofilms. Thus, Fe-SAzyme demonstrated a broad-spectrum antibacterial performance capable of effectively eliminating multidrug-resistant bacteria. The coexistence of ferrous (Fe2+) and ferric (Fe3+) ions in Fe-SAzyme conferred the nanozyme with anti-inflammatory activity, effectively suppressing excessive inflammation. Meanwhile, Fe-SAzyme could significantly downregulate inflammatory cytokines tumor necrosis factor-α and interleukin-1β and upregulate growth factors VEGF and epidermal growth factor, which can prevent bacterial infection, mitigate inflammation, promote fibroblast proliferation, and improve wound closure. Thus, Fe-SAzyme had shown favorable therapeutic efficiency in promoting bacteria-infected wound healing. This study provides Fe-SAzyme as a promising candidate for the development of new strategies to treat multidrug-resistant bacterial infections.

Integrating enzyme-nanoparticles bring new prospects for the diagnosis and treatment of immune dysregulation in periodontitis

Enzymes play a significant role in mediating inflammatory and immune responses in periodontitis. Effective diagnosis, timely treatment, and continuous management of periodontal enzymes are essential to prevent undesirable consequences; however, this remains a significant challenge. Nanoparticles (NPs) have attracted significant attention in biomedicine because of their advantageous nanosized effects. NPs are conjugated with specific enzyme substrates at responsive sites that are triggered by periodontitis enzyme biomarkers, leading to functional or characteristic changes. In contrast, NPs with enzyme-mimetic activities exhibit catalytic activity, effectively destroying pathogenic biofilms and modulating the immune response in periodontitis. The unique properties of enzyme-targeting NPs have enabled the development of biosensors and fluorescent probes capable of identifying enzyme biomarkers associated with periodontitis. Enzyme-responsive and enzyme-mimetic NPs both exert therapeutic applications in the treatment of periodontitis. In this review, we provide a comprehensive overview of the enzymes associated with periodontitis, the mechanisms of enzyme-responsive and enzyme-mimetic NPs, recent advancements in the use of NPs for detecting these enzymes, and the therapeutic applications of NPs in targeting or mimicking enzyme functions. We also discuss the challenges and prospects of using NPs in the diagnosis and treatment of periodontitis.

Optical detection of uric acid based on a citric acid functionalized copper-doped biochar nanozyme

Uric acid is the end product of purine metabolism and is a key biomarker for various diseases. Under normal conditions, there is a balance between its production and excretion. Its higher concentration can cause inflammation and severe pain, which makes it necessary to monitor its level for the diagnosis, management, and treatment of various pathological conditions. The current work reports on the synthesis of a copper-doped biochar (Cu@BC) nanocomposite and its functionalization with citric acid. The synthesis of the mimic enzyme was confirmed through various spectroscopic techniques. The nanozyme catalyzes hydrogen peroxide to oxidize tetramethylbenzidine (TMB) with an optical change from colorless to blue-green. This optical transformation was confirmed through a UV-vis spectrophotometer, which gave an expected λ max of 652 nm characteristic of TMBoxi. The incorporation of uric acid into this reaction mixture resulted in the reduction of TMBoxi to TMBred, accompanied by an optical change from blue-green to colorless, which was again confirmed with a UV-vis spectrophotometer. The fabricated sensor's performance was finely-tuned to report on its various key components. The best response was achieved at 2 mg of the nanozyme, pH 6, time 150 seconds, TMB, and hydrogen peroxide 0.9 and 1.5 mM, respectively. Under the above-mentioned optimized conditions, the fabricated sensor detected uric acid in the range of 1-90 μM with limits of detection and quantification of 0.17 and 0.58 μM, respectively, with an R 2 of 0.997. The proposed sensor was highly selective and successfully detected uric acid in real sample solutions.

Nanotechnology Approaches for Prevention and Treatment of Chemotherapy-Induced Neurotoxicity, Neuropathy, and Cardiomyopathy in Breast and Ovarian Cancer Survivors

Nanotechnology has emerged as a promising approach for the targeted delivery of therapeutic agents while improving their efficacy and safety. As a result, nanomaterial development for the selective targeting of cancers, with the possibility of treating off-target, detrimental sequelae caused by chemotherapy, is an important area of research. Breast and ovarian cancer are among the most common cancer types in women, and chemotherapy is an essential treatment modality for these diseases. However, chemotherapy-induced neurotoxicity, neuropathy, and cardiomyopathy are common side effects that can affect breast and ovarian cancer survivors quality of life. Therefore, there is an urgent need to develop effective prevention and treatment strategies for these adverse effects. Nanoparticles (NPs) have extreme potential for enhancing therapeutic efficacy but require continued research to elucidate beneficial interventions for women cancer survivors. In short, nanotechnology-based approaches have emerged as promising strategies for preventing and treating chemotherapy-induced neurotoxicity, neuropathy, and cardiomyopathy. NP-based drug delivery systems and therapeutics have shown potential for reducing the side effects of chemotherapeutics while improving drug efficacy. In this article, the latest nanotechnology approaches and their potential for the prevention and treatment of chemotherapy-induced neurotoxicity, neuropathy, and cardiomyopathy in breast and ovarian cancer survivors are discussed.

The Exploration of Nanozymes for Biosensing of Pathological States Tailored to Clinical Theranostics

The nanozymes (NZs) are the artificial catalyst deployed for biosensing with their uniqueness (high robustness, surface tenability, inexpensive, and stability) for obtaining a better response/miniaturization of the varied sensors than their traditional ancestors. Nowadays, nanomaterials with their broadened scale such as metal-organic frameworks (MOFs), and metals/metal oxides are widely engaged in generating NZ-based biosensors (BS). Diverse strategies like fluorescent, colorimetric, surface-enhanced Raman scattering (SERS), and electrochemical sensing principles were implemented for signal transduction of NZs. Despite broad advantages, numerous encounters (like specificity, feasibility, stability, and issues in scale-up) are affecting the potentialities of NZs-based BS, and thus need prior attention for a promising exploration for a revolutionary outcome in advanced theranostics. This review includes different types of NZs, and the progress of numerous NZs tailored bio-sensing techniques in detecting abundant bio analytes for theranostic purposes. Further, the discussion highlighted some recent challenges along with their progressive way of possibly overcoming followed by commercial outbreaks.

Photoactive nanocatalysts as DTT-assisted BSA-AuNCs with enhanced oxidase-mimicking ability for sensitive fluorometric detection of antioxidants

Redox imbalance and oxidative stress are increasingly recognized as significant factors in health disorders such as neurodegenerative disorders, premature aging and cancer. However, detecting antioxidant levels that is crucial for managing oxidative stress, can be challenging due to existing assays' limitations, such as insensitivity to thiol-containing antioxidants. This study presents a simple fluorescence-based assay for antioxidant detection employing the enhanced photocatalytic oxidase-like activity of dithiothreitol (DTT)-assisted bovine serum albumin (BSA)-stabilized gold nanoclusters (DTT@BSA-AuNCs). The reported nanozyme exhibits remarkable stability, versatility, and catalytic activity. Under LED irradiation, DTT@BSA-AuNCs generate singlet oxygen, which converts non-fluorescent thiamine to fluorescent thiochrome, utilizing dissolved oxygen for catalysis. Antioxidants inhibit thiochrome formation, leading to fluorescence quenching. This method enables sensitive detection of antioxidants such as ascorbic acid and glutathione with limits of detection of 0.08 µM and 0.32 µM, respectively, under neutral pH, outperforming previous studies. The assay successfully detects antioxidants in human saliva and cancer cell models. The DTT@BSA-AuNCs-based assay offers a cost-effective, sensitive, and straightforward approach for detecting antioxidants in biological samples, facilitating improved monitoring of oxidative stress in various diseases.

Emerging Nanomaterials as Versatile Nanozymes: A New Dimension in Biomedical Research

The enzyme-mimicking nature of versatile nanomaterials proposes a new class of materials categorized as nano-enzymes, ornanozymes. They are artificial enzymes fabricated by functionalizing nanomaterials to generate active sites that can mimic enzyme-like functions. Materials extend from metals and oxides to inorganic nanoparticles possessing intrinsic enzyme-like properties. High cost, low stability, difficulty in separation, reusability, and storage issues of natural enzymes can be well addressed by nanozymes. Since 2007, more than 100 nanozymes have been reported that mimic enzymes like peroxidase, oxidase, catalase, protease, nuclease, hydrolase, superoxide dismutase, etc. In addition, several nanozymes can also exhibit multi-enzyme properties. Vast applications have been reported by exploiting the chemical, optical, and physiochemical properties offered by nanozymes. This review focuses on the reported nanozymes fabricated from a variety of materials along with their enzyme-mimicking activity involving tuning of materials such as metal nanoparticles (NPs), metal-oxide NPs, metal-organic framework (MOF), covalent organic framework (COF), and carbon-based NPs. Furthermore, diverse applications of nanozymes in biomedical research are discussed in detail.

The impact of hollow core-shell nanozymes in biosensing: A case study of p-Fe3O4@PDA@ZIF-67

BACKGROUND

Nanozymes, a new class of nanomaterials, have emerged as promising substitutes for enzymes in biosensor design due to their exceptional stability, affordability, and ready availability. While nanozymes address many limitations of natural enzymes, they still face challenges, particularly in achieving the catalytic activity levels of their natural counterparts. This indicates the need for enhancing the sensitivity of biosensors based on nanozymes. The catalytic activity of nanozyme can be significantly improved by regulating its size, morphology, and surface composition of nanomaterial.

RESULTS

In this work, a kind of hollow core-shell structure was designed to enhance the catalytic activity of nanozymes. The hollow core-shell structure material consists of a nanozymes core layer, a hollow layer, and a MOF shell layer. Taking the classic peroxidase like Fe3O4 as an example, the development of a novel nanozyme@MOF, specifically p-Fe3O4@PDA@ZIF-67, is detailed, showcasing its application in enhancing the sensitivity of sensors based on Fe3O4 nanozymes. This innovative nanocomposite, featuring that MOF layer was designed to adsorb the signal molecules of the sensor to improve the utilization rate of reactive oxygen species generated by the nanozymes catalyzed reactions and the hollow layer was designed to prevent the active sites of nanozymes from being cover by the MOF layer. The manuscript emphasizes the nanocomposite's remarkable sensitivity in detecting hydrogen peroxide (H2O2), coupled with high specificity and reproducibility, even in complex environments like milk samples.

SIGNIFICANCE AND NOVELTY

This work firstly proposed and proved that Fe3O4 nanozyme@MOF with hollow layer structure was designed to improve the catalytic activity of the Fe3O4 nanozyme and the sensitivity of the sensors based on Fe3O4 nanozyme. This research marks a significant advancement in nanozyme technology, demonstrating the potential of structural innovation in creating high-performance, sensitive, and stable biosensors for various applications.

When nanozymes meet enzyme: Unlocking the dual-activity potential of integrated biocomposites

Integrating enzymes and nanozymes in various applications is a topic of significant interest. The researchers have explored the encapsulation of enzymes using diverse nanostructures to create nanomaterial-enzyme hybrids. These nanomaterials introduce unique properties that contribute to the additional activity along with the stabilization of enzymes in immobilized form, enabling a cascade of second-order reactions. This review centers on dual-activity nanozymes, providing insights into their applications in biosensors and biocatalysis. These applications leverage the enhanced catalytic activity and stability offered by dual-activity nanozymes. These nanozymes find promising applications in fields like bioremediation, offering eco-friendly solutions for mitigating environmental pollution while showing potential in medical diagnostics. The review delves into various techniques for creating enzyme-nanozyme hybrid catalysts, including adsorption, encapsulation, and incorporation methods. The review also addresses the challenges that must be overcome, such as overlapping catalytic surfaces and disparities in reaction rates in multi-enzyme cascade reactions. It concludes by presenting strategies to tackle these issues and offers insights into the field's promising future, suggesting that machine learning may drive further advancements in enzyme-nanozyme integration. This comprehensive exploration illuminates the present and charts a promising course for future innovations in the seamless integration of enzymes and nanozymes, heralding a new era of catalytic possibilities.

Application of Multifunctional Nanozymes in Tumor Therapy

Tumors are one of the main diseases threatening human life and health. The emergence of nanotechnology in recent years has introduced a novel therapeutic avenue for addressing tumors. Through the amalgamation of nanotechnology's inherent attributes with those of natural enzymes, nanozymes have demonstrated the ability to initiate catalytic reactions, modulate the biological microenvironment, and facilitate the adoption of multifaceted therapeutic approaches, thereby exhibiting considerable promise in the realm of cancer treatment. In this Review, the application of nanozymes in chemodynamic therapy, radiotherapy, photodynamic therapy, photothermal therapy, and starvation therapy are summarized. Moreover, a detailed discussion regarding the mechanism of conferring physiotherapeutic functionality upon catalytic nanosystems is provided. It is posited that this innovative catalytic treatment holds significant potential to play a crucial role within the domain of nanomedicine.

Synthesis of Spherical Mn2O3 Nanozymes from Different Green Precursors for their Innovative Applications in Catalytic Properties and Bioactivity

Here, spherical Mn2O3 nanozymes were synthesized via a one-step green method using different green precursors, and their physicochemical properties and biological activities were monitored with various green precursors. Powder X-ray diffraction (PXRD) was performed to determine the crystalline properties and phases involved in the formation of cubic Mn2O3 nanozymes. The synthesized nanozymes were spherical and examined by SEM and FESEM studies. All of the samples synthesized using different green precursors exhibited different sizes but similar spherical shapes. Moreover, all green-synthesized nanozymes catalyzed the oxidation reaction of the chromogenic substrate 3,3'5,5' tetramethylbenzidine (TMB) in the absence of H2O2, and A2 (lemon-mediated Mn2O3 nanozymes), which the followed Michaelis-Menten kinetics, showed the best activity. Therefore, A2 (lemon-mediated nanozyme) showed oxidase-mimicking activity with distinct Km and Vmax values calculated by the Lineweaver-Burk plot. Furthermore, the current nanozymes demonstrated a significant ability to kill both Gram-negative and Gram-positive bacteria as well as effectively destroy biofilms under physiological conditions. Moreover, the green-mediated nanozymes also displayed ROS-scavenging activity. Our nanozymes exhibited scavenging activity toward OH and O2-• radicals and metal chelation activity, which were investigated colorimetrically. Therefore, these nanozymes might be used as effective antibacterial agents and also for the consumption of reactive oxygen species.

Carbon dot enhanced peroxidase-like activity of platinum nanozymes

As one of the most intriguing nanozymes, the platinum (Pt) nanozyme has attracted tremendous research interest due to its various catalytic activities but its application is still limited by its poor colloidal stability and low affinity to substrates. Here, we design a highly stable Pt@carbon dot (Pt@CD) hybrid nanozyme with enhanced peroxidase (POD)-like activity (specific activity of 1877 U mg-1). The Pt@CDs catalyze the decomposition of hydrogen peroxide (H2O2) to produce singlet oxygen and hydroxyl radicals and exhibit high affinity to H2O2 and high specificity to 3,3',5,5'-tetramethyl-benzidine. We reveal that both the hydroxyl and carbonyl groups of CDs could coordinate with Pt2+ and then regulate the charge state of the Pt nanozyme, facilitating the formation of Pt@CDs and improving the POD-like activity of Pt@CDs. Colorimetric detection assays based on Pt@CDs for H2O2, dopamine, and glucose with a satisfactory detection performance are achieved. Moreover, the Pt@CDs show a H2O2-involving antibacterial effect by destroying the cell membrane. Our findings provide new opportunities for designing hybrid nanozymes with desirable stability and catalytic performance by using CDs as nucleating templates and stabilizers.

A platinum glutamate acid complex as a peroxidase mimic: high activity, controllable chemical modification, and application in biosensors

Recent strides in nanotechnology have given rise to nanozymes, nanomaterials designed to emulate enzymatic functions. Despite their promise, challenges such as batch-to-batch variability and limited atomic utilization persist. This study introduces Pt(Glu)2, a platinum glutamic acid complex, as a versatile small-molecule peroxidase mimic. Synthesized through a straightforward method, Pt(Glu)2 exhibits robust catalytic activity and stability. Steady-state kinetics reveal a lower Km value compared to that of natural enzymes, signifying strong substrate affinity. Pt(Glu)2 was explored for controllable chemical modification and integration into cascade reactions with natural enzymes, surpassing other nanomaterials. Its facile synthesis and seamless integration enhance cascade reactions beyond the capabilities of nanozymes. In biosensing applications, Pt(Glu)2 enabled simultaneous detection of cholesterol and alkaline phosphatase in human serum with high selectivity and sensitivity. These findings illustrate the potential of small molecule mimetics in catalysis and biosensing, paving the way for their broader applications.

Co-based Nanozymatic Profiling: Advances Spanning Chemistry, Biomedical, and Environmental Sciences

Nanozymes, next-generation enzyme-mimicking nanomaterials, have entered an era of rational design; among them, Co-based nanozymes have emerged as captivating players over times. Co-based nanozymes have been developed and have garnered significant attention over the past five years. Their extraordinary properties, including regulatable enzymatic activity, stability, and multifunctionality stemming from magnetic properties, photothermal conversion effects, cavitation effects, and relaxation efficiency, have made Co-based nanozymes a rising star. This review presents the first comprehensive profiling of the Co-based nanozymes in the chemistry, biology, and environmental sciences. The review begins by scrutinizing the various synthetic methods employed for Co-based nanozyme fabrication, such as template and sol-gel methods, highlighting their distinctive merits from a chemical standpoint. Furthermore, a detailed exploration of their wide-ranging applications in biosensing and biomedical therapeutics, as well as their contributions to environmental monitoring and remediation is provided. Notably, drawing inspiration from state-of-the-art techniques such as omics, a comprehensive analysis of Co-based nanozymes is undertaken, employing analogous statistical methodologies to provide valuable guidance. To conclude, a comprehensive outlook on the challenges and prospects for Co-based nanozymes is presented, spanning from microscopic physicochemical mechanisms to macroscopic clinical translational applications.

Multifunctional molecularly imprinted nanozymes with improved enrichment and specificity for organic and inorganic trace compounds

Although nanozymes exhibit properties superior to those of natural enzymes and conventional engineered enzymes, the development of highly specific nanozymes remains a challenge. New yolk-shell Fe3O4 molecularly imprinted (MIP@void@Fe3O4) nanozymes with peroxidase-like activity were developed by modelling the substrate channels of natural enzymes through molecular imprinting techniques and interfacial affinity modifications in this study. To establish a platform technology for the adsorption and determination of inorganic and organic contaminants, lead ion (Pb2+) and diazinon (DIZ), respectively, were selected as imprinting templates, and a hollow mesoporous shell was synthesized. The as-prepared MIP@void@Fe3O4 nanozymes, characterized using TEM, HRTEM, SEM, FT-IR, TGA, VSM and XPS, not only affirmed the successful fabrication of a magnetic nanoparticle with a unique hollow core-shell structure but also facilitated an exploration of the interfacial bonding mechanisms between Fe3O4 and other shell layers. The enrichment of the MIP@void@Fe3O4 nanozymes due to imprinting was approximately 5 times higher than the local substrate concentration and contributed to the increased activity. Based on selective and competitive recognition experiments, the synthesized nanozymes could selectively recognize organic and inorganic targets with the lowest detection limits (LOD) of 6.6 × 10-9 ppm for Pb2+ and 5.13 × 10-11 M for DIZ. Therefore, the proposed biosensor is expected to be a potent tool for trace pollutant detection, which provides a rational design for more advanced and subtle methods to bridge the activity gap between natural enzymes and nanozymes.

A colorimetric sensor array based on peroxidase activity nanozyme for the highly efficient differential sensing of tea polyphenols and Tieguanyin adulteration

Tieguanyin (TGY) is one of top ten famous teas in China, but in the process of brand building there is the phenomenon of falsehood, thus harming the interests of consumers. To solve theadulterate problem of TGY, a colorimetric sensor array (CSA) based onperoxidase activity of nanozyme was constructed. Nanozymes can catalyze 3,3',5,5'-tetramethylbenzidine (TMB) to 3,3',5,5'-tetramethyl -[1,1'-bis(cyclohexyl)]-2,2',5,5'-tetraene-4,4'-diimine (oxTMB), while the tea polyphenols (TPs) can inhibit this process, and the degree of inhibition varies significantly with the reaction time. We selected two nanozymesand three reaction time points to construct CSA. It can successfully distinguish TPsin TGY. The discriminative analysiscan achieve: (1)distinction between TGY and adulterated tea, (2)discrimination of TGY in various seasons and seasonal adulteration in different degrees. The method constructed in this work is promising for both the class and quality differentiation of TGY and other teas with TPs as the main activity.

Copper Nanoclusters as Multienzymes Mimic Activities of Oxidase and Ascorbic Acid Oxidase in the Presence of Imidazole

Artificial nanoenzymes based on metal nanoclusters have received great attention for multienzyme activities nowadays. In this work, pepsin-capped copper NCs (Cu-Pep NCs) are used as oxidase, ascorbic acid oxidase (AAO), and peroxidase mimics, and their activities are enhanced by the introduction of imidazole. The oxidase activity increased almost 7.5-fold, while 5-fold and 2-fold increases were observed for the peroxidase and AAO-like activity, respectively. The enhanced radical formation in the presence of imidazole moieties facilitates the enzymatic activity of the Cu-Pep-NCs/Imid system. This work describes the different enzymatic activities of the NCs, paving a new way for artificial nanoenzymes having enhanced activities.

A robust and facile label-free method for highly sensitive colorimetric detection of ascorbic acid in fresh fruits based on peroxidase-like activity of modified FeCo-LDH@WO3 nanocomposite

Many compounds such as amino acids and oligonucleotides have been shown to effectively change peroxidase-like activity of nanoparticles. While a few studies have focused on mimicking the active site of natural enzymes on nanozymes and thus increasing their substrate affinity. Therefore, in this work, the surface of FeCo@WO3 nanocomposite was modified using guanosine triphosphate (GTP) to mimic the histidine of peroxidase enzyme's active site and its modification was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier-transform infrared spectroscopy (FT-IR). Then, the peroxidase-mimicking activity of the modified nanocomposite was tested using a colorimetric method, based on the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2). It was found that GTP improves the activity of FeCo@WO3 as a natural peroxidase active site's distal histidine residue. Ascorbic acid (AA) is a powerful antioxidant that induces the reduction of blue color (oxidized TMB) ox-TMB to colorless TMB. The colorimetric method was applied for the sensitive detection of AA in common fruits. The linear range of AA was 10-100 μM with a limit of detection (LOD) of 0.27 μM, which provides a rapid and sensitive method for testing AA in the field of food analysis.

Confined synthesis of ternary FeCoMn single-atom nanozyme in N-doped hollow mesoporous carbon nanospheres for synergistic chemotherapy and chemodynamic cancer therapy

Recently, nanozymes show increasing biological applications and promising possibilities for therapeutic intervention, while their mediated therapeutic outcomes are severely compromised due to their insufficient catalytic activity and specificity. Herein, ternary FeCoMn single atoms were incorporated into N-doped hollow mesoporous carbon nanospheres by in situ confinement pyrolysis at 800 °C as high-efficiency nanozyme. The confinement strategy endows the as-prepared nanozyme with the enhanced catalase- and oxidase-like activities. Specifically, the FeCoMn TSAs/N-HCSs nanozyme can decompose intracellular H2O2 to generate O2 and subsequently convert O2 to cytotoxic superoxide radicals (O2∙-), which can initiate cascade enzymatic reactions in tumor microenvironment (TME) for chemodynamic therapy (CDT). Moreover, the cancer therapy was largely enhanced by loading with doxorubicin (DOX). Impressively, the FeCoMn TSAs/N-HCSs nanozyme-mediated CDT and the DOX-induced chemotherapy endow the DOX@FeCoMn TSAs/N-HCSs with effective tumor inhibition, showing the superior therapeutic efficacy.

Adenine phosphate-Cu nanozyme with multienzyme mimicking activity for efficient degrading phenolic compounds and detection of hydrogen peroxide, epinephrine and glutathione

BACKGROUND

With the development of nanotechnology, various nanomaterials with enzyme-like activity (nanozymes) have been reported. Due to their superior properties, nanozymes have shown important application potential in the fields of bioanalysis, disease detection, and environmental remediation. However, only a few nanomaterials with multi-enzyme mimicry activity have been reported. In this study, a novel multienzyme mimic was synthesized through a simple and rapid preparation protocol by coordinating copper ions with N3, N6 (amino), N7, and N9 on adenine phosphate.

RESULTS

The prepared adenine phosphate-Cu complex exhibits significant peroxidase, laccase, and oxidase mimicking activities. The Michaelis-Menten constant (Km) and the maximal velocity (Vmax) values of the peroxidase, laccase, and oxidase mimicking activities of AP-Cu nanozyme are 0.052 mM, 0.14 mM, and 2.49 mM; and 0.552 μM min-1, 6.70 μM min-1, and 2.24 μM min-1, respectively. Then, based on its laccase mimicking activity, the nanozyme was applied in the degradation of phenolic compounds. The calculated kinetic constant for the degradation of 2,4-dichlorophenol is 0.468 min-1 and the degradation efficiency of 2,4-dichlorophenol (0.1 mM) reaches 96.14% at 7 min. Finally, based on the multienzyme mimicking activity of adenine phosphate-Cu nanozyme, simple colorimetric sensing methods with high sensitivity and good selectivity were developed for the detection of hydrogen peroxide, epinephrine, and glutathione in the ranges of 20.0-200.0 μM (R2 = 0.9951), 5.0-100.0 μM (R2 = 0.9970), and 5.0-200.0 μM (R2 = 0.9924) with the limits of quantitation of 20.0 μM, 5.0 μM, and 5.0 μM, respectively.

SIGNIFICANCE

In short, the synthesis of nanozymes with multi-enzyme mimicry activity through coordination between copper ions and small molecule mimicry enzymes provides new ideas for the design and research of multi-enzyme mimics.

Bacteria-derived topologies of Cu2O nanozymes exert a variable antibacterial effect

The ability of bacteria to facilitate fabrication of nanomaterials has been adapted towards bacterial sensing applications. In this work, we fabricate spherical, cubic and truncated octahedron topologies of Cu2O nanoparticles via E. coli-facilitated redox reaction in an electrochemical setup. The Cu2O nanoparticles exhibit cytochrome c oxidase-like activity with the spherical topology displaying higher catalytic rate compared to the other geometries. The topology-dependent catalytic behavior of Cu2O nanoparticles has not been reported previously. The Cu2O nanozymes also display E. coli killing activity in a topology-correlated manner. The E. coli mediated redox reaction in an electrochemical setup is being reported for the first time for synthesis of different topologies of Cu2O which also exert a variable antibacterial effect.

Engineering hetero-structural iron nanozyme decorated liposome with a self-cascade catalysis performance

Metal-based enzyme mimics are considered as acceptable agents in fabricating heterogeneous biocomposites through valency integrations because of their biomedical or biological properties. As the basic substitute, it delights us to utilize Fe3O4 nanoparticles (NPs) as metallic enzymes and overcome the limitation of peroxide-like enzymatic activity in physiological conditions. In this work, we present the fabrication of a soy phosphatidylcholine/Fe3O4@Ag/GOx (SFAG) biocomposite as a cascade enzyme, which exhibits a peroxidase-like property in kinetic processes, as shown from an analysis of the glucose detection processes. We also explored the mechanism of an ultrasound & microfluidic approach for the synthesis of SFAG. The resultant SFAG implies a characteristic absorption peak (652 nm), size (55 μm), and surface charge (-32.93 ± 2.58 mV). This is utilized to confirm the peroxidase-like activity by catalyzing 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2 under physiological conditions. But also, SFAG conveys a positive effect on the peroxidase-like activity at pH = 5.8, 7.4, and 8.0. The Michaelis-Menten parameters (Km) and the Vmax values of H2O2 are 1.914 mM and 1.429 × 10-7 M s-1, which further confirms the catalytic performances of the SFAG structure. The established platform was also used successfully for the determination of glucose in PBS and diluted synthetic blood with excellent sensitivity and stability. The relative selection and sensitivity show that the SFAG structure has a great possibility as a cascade metallic enzyme in chemokinetic works.

Post-Assay Chemical Enhancement for Highly Sensitive Lateral Flow Immunoassays: A Critical Review

Lateral flow immunoassay (LFIA) has found a broad application for testing in point-of-care (POC) settings. LFIA is performed using test strips-fully integrated multimembrane assemblies containing all reagents for assay performance. Migration of liquid sample along the test strip initiates the formation of labeled immunocomplexes, which are detected visually or instrumentally. The tradeoff of LFIA's rapidity and user-friendliness is its relatively low sensitivity (high limit of detection), which restricts its applicability for detecting low-abundant targets. An increase in LFIA's sensitivity has attracted many efforts and is often considered one of the primary directions in developing immunochemical POC assays. Post-assay enhancements based on chemical reactions facilitate high sensitivity. In this critical review, we explain the performance of post-assay chemical enhancements, discuss their advantages, limitations, compared limit of detection (LOD) improvements, and required time for the enhancement procedures. We raise concerns about the performance of enhanced LFIA and discuss the bottlenecks in the existing experiments. Finally, we suggest the experimental workflow for step-by-step development and validation of enhanced LFIA. This review summarizes the state-of-art of LFIA with chemical enhancement, offers ways to overcome existing limitations, and discusses future outlooks for highly sensitive testing in POC conditions.

Antioxidant and Prooxidant Nanozymes: From Cellular Redox Regulation to Next-Generation Therapeutics

Nanozymes, nanomaterials with enzyme-mimicking activity, have attracted tremendous interest in recent years owing to their ability to replace natural enzymes in various biomedical applications, such as biosensing, therapeutics, drug delivery, and bioimaging. In particular, the nanozymes capable of regulating the cellular redox status by mimicking the antioxidant enzymes in mammalian cells are of great therapeutic significance in oxidative-stress-mediated disorders. As the distinction of physiological oxidative stress (oxidative eustress) and pathological oxidative stress (oxidative distress) occurs at a fine borderline, it is a great challenge to design nanozymes that can differentially sense the two extremes in cells, tissues and organs and mediate appropriate redox chemical reactions. In this Review, we summarize the advances in the development of redox-active nanozymes and their biomedical applications. We primarily highlight the therapeutic significance of the antioxidant and prooxidant nanozymes in various disease model systems, such as cancer, neurodegeneration, and cardiovascular diseases. The future perspectives of this emerging area of research and the challenges associated with the biomedical applications of nanozymes are described.

Nanozyme: a rising star for cancer therapy

In recent years, nanozymes have attracted enormous attention due to their effectiveness in promoting various catalytic reactions. To date, thousands of nanozymes have been discovered, including oxidase-like nanozymes, peroxidase-like nanozymes, and catalase-like nanozymes, covering noble metal, transition metal, and carbon nanomaterials. These nanozymes have been widely applied in various fields, including environmental protection, biosensing and nanomedicine. There are many reviews about this rising star being used in analytical chemistry. However, few works about nanozymes were related to cancer therapy. In this study, we comprehensively summarize the latest research advances on the strategies for cancer therapy based on different nanozymes. With traditional cancer treatment (including chemotherapy, radiotherapy, phototherapy), nanozyme catalytic therapy exhibited a synergistic effect for limiting the growth of tumors. Opportunities and trends for nanozymes in future cancer therapy are also discussed.

Variations in Intracellular Organometallic Reaction Frequency Captured by Single-Molecule Fluorescence Microscopy

Studies of organometallic reactions in living cells commonly rely on ensemble-averaged measurements, which can obscure the detection of reaction dynamics or location-specific behavior. This information is necessary to guide the design of bioorthogonal catalysts with improved biocompatibility, activity, and selectivity. By leveraging the high spatial and temporal resolution of single-molecule fluorescence microscopy, we have successfully captured single-molecule events promoted by Ru complexes inside live A549 human lung cells. By observing individual allylcarbamate cleavage reactions in real-time, our results revealed that they occur with greater frequency inside the mitochondria than in the non-mitochondria regions. The estimated turnover frequency of the Ru complexes was at least 3-fold higher in the former than the latter. These results suggest that organelle specificity is a critical factor to consider in intracellular catalyst design, such as in developing metallodrugs for therapeutic applications.

DNA tetrahedron-mediated triplex molecular switch for extracellular pH monitoring

This study aimed to construct a novel DNA triplex molecular switch modified with DNA tetrahedron (DTMS-DT) with sensitive response to extracellular pH using a DNA tetrahedron as the anchoring unit and DNA triplex as the response unit. The results showed that the DTMS-DT had desirable pH sensitivity, excellent reversibility, outstanding anti-interference ability, and good biocompatibility. Confocal laser scanning microscopy suggested that the DTMS-DT could not only be stably anchored on the cell membrane but also be employed to dynamically monitor the change in extracellular pH. Compared with the reported probes for extracellular pH monitoring, the designed DNA tetrahedron-mediated triplex molecular switch exhibited higher cell surface stability and brought the pH-responsive unit closer to the cell membrane surface, making the results more reliable. In general, developing the DNA tetrahedron-based DNA triplex molecular switch is helpful for understanding and illustrating the pH dependent cell behaviors and disease diagnostics.

Copper Immobilized over 2D Hexagonal SBA-15 for Electrochemical and Colorimetric Sulfite Sensing

Sulfite (SO₃^2-) is considered a highly toxic anion for living organisms. Herein, we report the synthesis of copper immobilized over a 2D hexagonally ordered mesoporous silica material CuMS as an electrochemical and colorimetric dual-technique-based sensing platform for sulfite detection. The immobilization of copper on silica was achieved through the bis[3-(triethoxysilyl)propyl]tetrasulfide (TEPTS) ligand. Morphological and physical properties of the material were confirmed by several characterization techniques, including scanning electron microscopy, transmission electron microscopy, X-ray diffraction, N₂ sorption, and X-ray photoelectron spectroscopy. The CuMS material retained mesoporosity with a narrow pore size distribution (D ≈ 5.4 nm) and a high Brunauer-Emmett-Teller surface area of 682 m² g^-1 after the immobilization of copper. The prepared catalyst shows promising electrocatalytic activity toward sulfite oxidation. A linear variation in the peak current was obtained for SO₃^2- oxidation in the 0.2-15 mM range with a high sensitivity of 62.08 μA cm^-2, under optimum experimental conditions. The limit of detection (LOD) was found to be 1.14 nM. CuMS also shows excellent activity toward colorimetric detection of sulfite anions with an LOD of 0.4 nM. The proposed sensor shows high selectivity toward the sulfite anion, even in the presence of common interferents. The detection of sulfite in white wine with excellent recovery demonstrates the practical applicability of this sensor.

Rational design of polymeric nanozymes with robust catalytic performance via copper-ligand coordination

Incorporating copper (Cu) ions into polymeric particles can be a straightforward strategy for mimicking copper enzymes, but it is challenging to simultaneously control the structure of the nanozyme and of the active sites. In this report, we present a novel bis-ligand (L₂) containing bipyridine groups connected by a tetra-ethylene oxide (4EO) spacer. In phosphate buffer the Cu-L₂ mixture forms coordination complexes that (at proper composition) can bind polyacrylic acid (PAA) to produce catalytically active polymeric nanoparticles with well-defined structure and size, which we refer to as 'nanozymes'. Manipulating the L₂/Cu mixing ratio and using phosphate as a co-binding motif, cooperative copper centres are realized that exhibit promoted oxidation activity. The structure and activity of the so-designed nanozymes remain stable upon increasing temperature and over multiple cycles of application. Increasing ionic strength causes enhanced activity, a response also seen for natural tyrosinase. By means of our rational design we obtain nanozymes with optimized structure and active sites that in several respects outperform natural enzymes. This approach therefore demonstrates a novel strategy for developing functional nanozymes, which may well stimulate the application of this class of catalysts.

Yolk-shell structured nanoreactor Au@Co3O4/CeO2@mSiO2 with superior peroxidase-like activity as nanozyme for ultra-sensitive colorimetric biosensing

For yolk-shell structured nanoreactors, multiple active components can be precisely positioned on core and/or shell that can afford more exposed accessible active sites, and the internal voids can guarantee sufficient contact of reactants and catalysts. In this work, a unique yolk-shell structured nanoreactor Au@Co₃O₄/CeO₂@mSiO₂ was fabricated and applied as nanozyme for biosensing. The Au@Co₃O₄/CeO₂@mSiO₂ exhibited superior peroxidase-like activity with a lower Michaelis constant (K_m) and a higher affinity to H₂O₂. The enhanced peroxidase-like activity was attributed to the unique structure and the synergistic effects between the multiple active components. Colorimetric essays were developed based on Au@Co₃O₄/CeO₂@mSiO₂ for the ultra-sensitive sensing of glucose in the range of 3.9 nM-1.03 mM with the limit of detection as low as 3.2 nM. In the detection of glucose-6-phosphate dehydrogenase (G6PD), the cooperation between G6PD and Au@Co₃O₄/CeO₂@mSiO₂ triggered the redox cycling between NAD⁺ and NADH, thereby achieving the amplification of the signal and enhancing the sensitivity of the assay. The assay showed superior performance as compared to other methods with linear response of 5.0 × 10^-3-15 mU mL^-1 and lower detection limit of 3.6 × 10^-3 mU mL^-1. The fabricated novel multi-enzyme catalytical cascade reaction system allowed rapid and sensitive biodetection, demonstrating its potential in biosensors and biomedical applications.

Synergistic effect of silver nanoclusters and graphene oxide on visible light-driven oxidase-like activity: Construction of a sustainable nanozyme for total antioxidant capacity detection

The high cost and low reusability of natural enzymes greatly limit their application in biosensing. In this work, a sustainable nanozyme with light-driven oxidase-like activity was fabricated by integrating protein-capped silver nanoclusters (AgNCs) with graphene oxide (GO) through multiple non-covalent interactions. The prepared AgNCs/GO nanozyme could effectively catalyze the oxidation of various chromogenic substrates by activating dissolved O₂ to reactive oxygen species under visible light irradiation. Moreover, the oxidase-like activity of AgNCs/GO could be well controlled by switching on and off the visible light source. Compared with natural peroxidase and most of other oxidase-mimicking nanozymes, AgNCs/GO possessed improved catalytic activity owing to the synergistic effect between AgNCs and GO. More importantly, AgNCs/GO showed outstanding stability against precipitation, pH (2.0-8.0), temperature (10-80 °C), and storage and could be reused at least 6 cycles without obvious loss in catalytic activity. On this basis, AgNCs/GO nanozyme was used to develop a colorimetric assay for the determination of total antioxidant capacity in human serum, which had the merits of high sensitivity, low cost, and good safety. This work holds a promising prospect in developing sustainable nanozymes for biosensing and clinical diagnosis.

Engineering Single-Atom Nanozymes for Catalytic Biomedical Applications

Nanomaterials with enzyme-mimicking properties, coined as nanozymes, are a promising alternative to natural enzymes owing to their remarkable advantages, such as high stability, easy preparation, and favorable catalytic performance. Recently, with the rapid development of nanotechnology and characterization techniques, single atom nanozymes (SAzymes) with atomically dispersed active sites, well-defined electronic and geometric structures, tunable coordination environment, and maximum metal atom utilization are developed and exploited. With superior catalytic performance and selectivity, SAzymes have made impressive progress in biomedical applications and are expected to bridge the gap between artificial nanozymes and natural enzymes. Herein, the recent advances in SAzyme preparation methods, catalytic mechanisms, and biomedical applications are systematically summarized. Their biomedical applications in cancer therapy, oxidative stress cytoprotection, antibacterial therapy, and biosensing are discussed in depth. Furthermore, to appreciate these advances, the main challenges, and prospects for the future development of SAzymes are also outlined and highlighted in this review.

Nanozymes towards Personalized Diagnostics: A Recent Progress in Biosensing

This review highlights the recent advancements in the field of nanozymes and their applications in the development of point-of-care biosensors. The use of nanozymes as enzyme-mimicking components in biosensing systems has led to improved performance and miniaturization of these sensors. The unique properties of nanozymes, such as high stability, robustness, and surface tunability, make them an attractive alternative to traditional enzymes in biosensing applications. Researchers have explored a wide range of nanomaterials, including metals, metal oxides, and metal-organic frameworks, for the development of nanozyme-based biosensors. Different sensing strategies, such as colorimetric, fluorescent, electrochemical and SERS, have been implemented using nanozymes as signal-producing components. Despite the numerous advantages, there are also challenges associated with nanozyme-based biosensors, including stability and specificity, which need to be addressed for their wider applications. The future of nanozyme-based biosensors looks promising, with the potential to bring a paradigm shift in biomolecular sensing. The development of highly specific, multi-enzyme mimicking nanozymes could lead to the creation of highly sensitive and low-biofouling biosensors. Integration of nanozymes into point-of-care diagnostics promises to revolutionize healthcare by improving patient outcomes and reducing costs while enhancing the accuracy and sensitivity of diagnostic tools.

Iron oxides based nanozyme sensor arrays for the detection of active substances in licorice

With the increasing applications of traditional Chinese medicines worldwide, authenticity identification and quality control are significant for them to go global. Licorice is a kind of medicinal material with various functions and wide applications. In this work, colorimetric sensor arrays based on iron oxide nanozymes were constructed to discriminate active indicators in licorice. Fe₂O₃, Fe₃O₄, and His-Fe₃O₄ nanoparticles were synthesized by a hydrothermal method, possessing excellent peroxidase-like activity that can catalyze the oxidation of 3,3',5,5' -tetramethylbenzidine (TMB) in the presence of H₂O₂ to produce a blue product. When licorice active substances were introduced in the reaction system, they showed competitive effect on peroxidase-mimicking activity of nanozymes, resulting in inhibitory effect on the oxidation of TMB. Based on this principle, four licorice active substances including glycyrrhizic acid, liquiritin, licochalcone A, and isolicoflavonol with the concentration ranging from 1 μM to 200 μM were successfully discriminated by the proposed sensor arrays. This work supplies a low cost, rapid and accurate method for multiplex discrimination of active substances to guarantee the authenticity and quality of licorice, which is also expected to be applied to distinguish other substances.

Intrinsic Light-Activated Oxidase Mimicking Activity of Conductive Polyaniline Nanofibers: A Class of Metal-Free Nanozyme

In recent decades, studies have focused on inorganic nanozymes to overcome the intrinsic drawbacks of bioenzymes due to the demands of improving the reaction conditions and lack of robustness to harsh environmental factors. Many biochemical reactions catalyzed by enzymes require light activation. Light-activated nanozymes have distinct advantages, including being regulated by light stimuli, activating the molecular oxygen to produce reactive oxygen species (ROS) without interfering supplementary oxidants, and often showing a synergistic effect to catalyze some challenging reactions. Only a few studies have been done on this connection. Therefore, it is still a big challenge to develop a nanozyme regulated by light activation. Herein, we uncovered the light-activated oxidase mimicking activity of a conducting polymer polyaniline nanofibers (PANI-NFs). PANI-NFs exhibit intrinsic light-activated brilliant oxidase-like activity, can catalyze the colorless tetramethyl benzidine (TMB) to produce a blue product TMBox, and have a distinct K_m = 0.087 mM and a high V_max = 2.32 μM min^-1 value, measured by using Hanes-Woolf kinetics. We also report the light-activated oxidase activity of some other renowned carbocatalysts graphene oxide and graphitic carbon nitride and compare them with PANI-NFs. This type of property shown by the conductive polymer is amazing. The density functional theory is used to verify the stability and the mode of adsorption of the PANI NFs-TMB composite, which corroborates the experimental results. Furthermore, the current nanozyme demonstrated a significant ability to kill both Gram-negative and Gram-positive bacteria as well as effectively destroy biofilms under physiological conditions. We believe that this work provides the motivation to create a link between optoelectronics and biological activity in the near future.