Unraveling the Enzymatic Activity of Oxygenated Carbon Nanotubes and Their Application in the Treatment of Bacterial Infections

Sensitive surface plasmon resonance biosensor by optimized carboxylate functionalized carbon nanotubes/chitosan for amlodipine detecting

The adoption of biophotonic sensing technologies holds significant promise for application in health care and biomedical industries in all aspects of human life. Then, this piece of writing employs the powerful effective medium theory and FDTD simulation to anticipate the most favorable state and plasmonic attributes of a magnificent nanocomposite, comprising carboxylate functionalized carbon nanotubes and chitosan (CS). Furthermore, it thoroughly explores the exhibited surface plasmon resonance behaviors of this composite versus the quantity of CS variation. Subsequently, enlightening simulations are conducted on the nanocomposite with a delicate layer and a modified golden structure integrating as a composite. The intricate simulations eventually unveil an optimal combination to pave the way for crafting an exceptional specific biosensor that far surpasses its counterpart as a mere Au thin layer in terms of excellence. The proposed biosensor demonstrated linear behavior across a wide range from 0.01 μM to 150 μM and achieved a detection limit of 10 nM, with a sensitivity of 134◦RIU-1.

The potential use of nanozymes as an antibacterial agents in oral infection, periodontitis, and peri-implantitis

Several studies suggest that oral pathogenic biofilms cause persistent oral infections. Among these is periodontitis, a prevalent condition brought on by plaque biofilm. It can even result in tooth loss. Furthermore, the accumulation of germs around a dental implant may lead to peri-implantitis, which damages the surrounding bone and gum tissue. Furthermore, bacterial biofilm contamination on the implant causes soft tissue irritation and adjacent bone resorption, severely compromising dental health. On decontaminated implant surfaces, however, re-osseointegration cannot be induced by standard biofilm removal techniques such as mechanical cleaning and antiseptic treatment. A family of nanoparticles known as nanozymes (NZs) comprise highly catalytically active multivalent metal components. The most often employed NZs with antibacterial activity are those that have peroxidase (POD) activity, among other types of NZs. Since NZs are less expensive, more easily produced, and more stable than natural enzymes, they hold great promise for use in various applications, including treating microbial infections. NZs have significantly contributed to studying implant success rates and periodontal health maintenance in periodontics and implantology. An extensive analysis of the research on various NZs and their applications in managing oral health conditions, including dental caries, dental pulp disorders, oral ulcers, peri-implantitis, and bacterial infections of the mouth. To combat bacteria, this review concentrates on NZs that imitate the activity of enzymes in implantology and periodontology. With a view to the future, there are several ways that NZs might be used to treat dental disorders antibacterially.

Photo-Switchable Peroxidase/Catalase-Like Activity of Carbon Quantum Dots

Nanozymes possess multi-enzyme activities over the natural enzymes, which produce multi-pathway synergistic effects for varies of biomedical applications. Unfortunately, their multi-enzyme activities are in fighting, significantly reducing the synergistic effects. Dynamic regulation of their multi-enzyme activities is the bottleneck for intelligent therapies. Herein, we construct a novel oxygen-nitrogen functionalized carbon quantum dots (O/N-CQDs) with peroxidase-like (Reactive oxygen species (ROS) producer) activity. Interestingly, the peroxidase-like activity can be reversibly converted to catalase-like (ROS scavenger) activity under visible light irradiation. It is found that both the peroxidase/catalase-like activity of O/N-CQDs can be precisely manipulated by the light intensity. The mechanism of switchable enzyme activities is attributed to the polarization of quinoid nitrogen in polyaniline (PANI) precursor retained on O/N-CQDs under visible light, which consumes the ROS to produce O2 and H2O. As a proof-of-concept demonstration, we are able to non-intrusively up and down regulate the ROS level in cells successfully by simply switching off and on the light respectively, potentially facilitating the precise medicine based on the development of the disease. Indeed, the photo-switchable peroxidase/catalase-like activity of O/N-CQDs opens a non-invasive strategy for better manipulations of the multi-activity of nanozymes, promising their wider and more intelligent biomedical applications.

Oxygen-doped carbon nanotubes with dual active cites to enhance •OH formation through three electron oxygen reduction

The electro-Fenton (EF) process generates H2O2 through the 2e- oxygen reduction reaction (ORR), which is subsequently activated to •OH by iron-based catalysts. To alleviate the potential risk of external Fe-based catalysts, along with metal dissolution in acidic or neutral environments, in this study we employed oxygen-doped carbon nanotubes (OCNT) as a bifunctional, metal-free cathode to establish a metal-free EF process for organic pollutant degradation. The results demonstrate that the metal-free electrode has excellent H2O2 accumulation (12 mg L-1 cm-1) and degrades sulfathiazole (STZ) with 97.05 % efficiency in 180 min with an explanation kinetic of 0.0189 min-1. For the first time, this enhancement came from the dual active site centers in OCNT: Ⅰ) -COOH and defects active sites were responsible for H2O2 production, Ⅱ) then -CO triggered H2O2 into •OH, avoiding the introduction of metal-based catalysts. These findings suggest that the EF system with in situ oxygen-doped cathodes have great potential for treating antibiotic wastewater.

Multienzyme-Like Nanozymes: Regulation, Rational Design, and Application

Nanomaterials with more than one enzyme-like activity are termed multienzymic nanozymes, and they have received increasing attention in recent years and hold huge potential to be applied in diverse fields, especially for biosensing and therapeutics. Compared to single enzyme-like nanozymes, multienzymic nanozymes offer various unique advantages, including synergistic effects, cascaded reactions, and environmentally responsive selectivity. Nevertheless, along with these merits, the catalytic mechanism and rational design of multienzymic nanozymes are more complicated and elusive as compared to single-enzymic nanozymes. In this review, the multienzymic nanozymes classification scheme based on the numbers/types of activities, the internal and external factors regulating the multienzymatic activities, the rational design based on chemical, biomimetic, and computer-aided strategies, and recent progress in applications attributed to the advantages of multicatalytic activities are systematically discussed. Finally, current challenges and future perspectives regarding the development and application of multienzymatic nanozymes are suggested. This review aims to deepen the understanding and inspire the research in multienzymic nanozymes to a greater extent.

Biosystem-Inspired Engineering of Nanozymes for Biomedical Applications

Nanozymes with intrinsic enzyme-mimicking activities have shown great potential to become surrogates of natural enzymes in many fields by virtue of their advantages of high catalytic stability, ease of functionalization, and low cost. However, due to the lack of predictable descriptors, most of the nanozymes reported in the past have been obtained mainly through trial-and-error strategies, and the catalytic efficacy, substrate specificity, as well as practical application effect under physiological conditions, are far inferior to that of natural enzymes. To optimize the catalytic efficacies and functions of nanozymes in biomedical settings, recent studies have introduced biosystem-inspired strategies into nanozyme design. In this review, recent advances in the engineering of biosystem-inspired nanozymes by leveraging the refined catalytic structure of natural enzymes, simulating the behavior changes of natural enzymes in the catalytic process, and mimicking the specific biological processes or living organisms, are introduced. Furthermore, the currently involved biomedical applications of biosystem-inspired nanozymes are summarized. More importantly, the current opportunities and challenges of the design and application of biosystem-inspired nanozymes are discussed. It is hoped that the studies of nanozymes based on bioinspired strategies will be beneficial for constructing the new generation of nanozymes and broadening their biomedical applications.

Application of the Peroxidase‒like Activity of Nanomaterials for the Detection of Pathogenic Bacteria and Viruses

Infectious diseases caused by pathogenic bacteria and viruses pose a significant threat to human life and well-being. The prompt identification of these pathogens, characterized by speed, accuracy, and efficiency, not only aids in the timely screening of infected individuals and the prevention of further transmission, but also facilitates the precise diagnosis and treatment of patients. Direct smear microscopy, microbial culture, nucleic acid-based polymerase chain reaction (PCR), and enzyme-linked immunosorbent assay (ELISA) based on microbial surface antigens or human serum antibodies, have made substantial contributions to the prevention and management of infectious diseases. Due to its shorter processing time, simple equipment requirements, and no need for professional and technical personnel, ELISA has inherent advantages over other methods for detecting pathogenic bacteria and viruses. Horseradish peroxidase mediated catalysis of substrate coloration is the key for the detection of target substances in ELISA. However, the variability, high cost, and environmental susceptibility of natural peroxidase greatly limit the application of ELISA in pathogen detection. Compared with natural enzymes, nanomaterials with enzyme-mimicking activity are inexpensive, highly environmentally stable, easy to store and mass producing, etc. Based on their peroxidase-like activities and unique physicochemical properties, nanomaterials can greatly improve the efficiency and ease of use of ELISA-like detection methods for pathogenic bacteria and viruses. This review introduces recent advances in the application of nanomaterials with peroxidase-like activity for the detection of pathogenic bacteria (both gram-negative bacteria and gram-positive bacteria) and viruses (both RNA viruses and DNA viruses). The emphasis is on the detection principle and the evaluation of effectiveness. The limitations and prospects for future translations are also discussed.

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.

Artificial enzyme innovations in electrochemical devices: advancing wearable and portable sensing technologies

With the rapid evolution of sensing technologies, the integration of nanoscale catalysts, particularly those mimicking enzymatic functions, into electrochemical devices has surfaced as a pivotal advancement. These catalysts, dubbed artificial enzymes, embody a blend of heightened sensitivity, selectivity, and durability, laying the groundwork for innovative applications in real-time health monitoring and environmental detection. This minireview penetrates into the fundamental principles of electrochemical sensing, elucidating the unique attributes that establish artificial enzymes as foundational elements in this field. We spotlight a range of innovations where these catalysts have been proficiently incorporated into wearable and portable platforms. Navigating the pathway of amalgamating these nanoscale wonders into consumer-appealing devices presents a multitude of challenges; nevertheless, the progress made thus far signals a promising trajectory. As the intersection of materials science, biochemistry, and electronics progressively intensifies, a flourishing future seems imminent for artificial enzyme-infused electrochemical devices, with the potential to redefine the landscapes of wearable health diagnostics and portable sensing solutions.

Nanozymes with versatile redox capabilities inspired in metalloenzymes

Metalloenzymes represent exemplary systems in which an organic scaffold combines with a functional inorganic entity, resulting in excellent redox catalysts. Inspired by these natural hybrid biomolecules, biomolecular templates have garnered significant attention for the controlled synthesis of inorganic nanostructures. These nanostructures ultimately benefit from the protection and colloidal stabilization provided by the biomacromolecule. In this study, we have employed this strategy to prepare nanozymes with redox capabilities, utilizing the versatile catalytic profile of Pt-loaded nanomaterials. Thus, we have investigated protein-templated Pt-based nanoclusters of different sizes and compositions, which exhibit remarkable oxidase, catalase, and reductase-like activities. The interplay between the composition and catalytic activity highlighted the size of the nanocluster as the most prominent factor in determining the performance of the nanozymes. Additionally, we have demonstrated the use of protein-templated nanozymes as potential co-catalysts in combination with enzymes for coupled reactions, under both sequential and concurrent one-pot conditions. This study provides valuable insights into nanozyme design and its wide range of applications in the design of complex catalytic systems.

Metal-Free Peroxidase-Mimetic Nanocatalysts for Chemodynamic Vascular-Disrupting Cancer Therapy

Metal ion-facilitated chemodynamic therapy (CDT) is an emerging method for treating cancer. However, its potential is hindered by its low catalytic performance in weakly acidic tumor microenvironments (TMEs) and the severe toxicity of free metal ions. A new approach to tumor therapy, chemodynamic vascular disruption (CVD), is introduced using metal-free, peroxidase (POD)-mimetic multihydroxylated [70] fullerene (MHF) nanocatalysts. The research shows that MHF contains C···O active sites, as demonstrated by density functional theory (DFT) calculations, and converts H2 O2 into ∙OH across a pH range of 6.0-10.0. The generation of ∙OH and the dismantling of tumor blood vessels are observed in real-time using mouse dorsal skin-fold chamber (DSFC) models. Applying proteomics, it is discovered that the CVD mechanism involves the nanocatalytic MHF enhancing H2 O2 decomposition in the TME, producing ∙OH. This damages tumor vascular endothelial junction proteins, causing vascular leakage and subsequently cutting off the vascular supply to the tumor cells. This method deviates from the traditional CDT that targets tumor cells. Instead, the proficient MHF nanocatalysts aim to directly disrupt the tumor vasculature, enhancing anti-tumor efficiency without triggering harmful toxicity. The proposed CVD therapeutic strategy enhances the application of gentle carbon nanocatalysts in cancer therapy, offering new perspectives on nanocatalytic medicine.

Carbon-Based Enzyme Mimetics for Electrochemical Biosensing

Natural enzymes are used as special reagents for the preparation of electrochemical (bio)sensors due to their ability to catalyze processes, improving the selectivity of detection. However, some drawbacks, such as denaturation in harsh experimental conditions and their rapid de- gradation, as well as the high cost and difficulties in recycling them, restrict their practical applications. Nowadays, the use of artificial enzymes, mostly based on nanomaterials, mimicking the functions of natural products, has been growing. These so-called nanozymes present several advantages over natural enzymes, such as enhanced stability, low cost, easy production, and rapid activity. These outstanding features are responsible for their widespread use in areas such as catalysis, energy, imaging, sensing, or biomedicine. These materials can be divided into two main groups: metal and carbon-based nanozymes. The latter provides additional advantages compared to metal nanozymes, i.e., stable and tuneable activity and good biocompatibility, mimicking enzyme activities such as those of peroxidase, catalase, oxidase, superoxide dismutase, nuclease, or phosphatase. In this review article, we have focused on the use of carbon-based nanozymes for the preparation of electrochemical (bio)sensors. The main features of the most recent applications have been revised and illustrated with examples selected from the literature over the last four years (since 2020).

Rescuing Nucleus Pulposus Cells From Senescence via Dual-Functional Greigite Nanozyme to Alleviate Intervertebral Disc Degeneration

High levels of reactive oxygen species (ROS) lead to progressive deterioration of mitochondrial function, resulting in tissue degeneration. In this study, ROS accumulation induced nucleus pulposus cells (NPCs) senescence is observed in degenerative human and rat intervertebral disc, suggesting senescence as a new therapeutic target to reverse intervertebral disc degeneration (IVDD). By targeting this, dual-functional greigite nanozyme is successfully constructed, which shows the ability to release abundant polysulfides and presents strong superoxide dismutase and catalase activities, both of which function to scavenge ROS and maintain the tissue at physical redox level. By significantly lowering the ROS level, greigite nanozyme rescues damaged mitochondrial function in IVDD models both in vitro and in vivo, rescues NPCs from senescence and alleviated the inflammatory response. Furthermore, RNA-sequencing reveals ROS-p53-p21 axis is responsible for cellular senescence-induced IVDD. Activation of the axis abolishes greigite nanozyme rescued NPCs senescence phenotype, as well as the alleviated inflammatory response to greigite nanozyme, which confirms the role of ROS-p53-p21 axis in greigite nanozyme's function to reverse IVDD. In conclusion, this study demonstrates that ROS-induced NPCs senescence leads to IVDD and the dual-functional greigite nanozyme holds strong potential to reverse this process, providing a novel strategy for IVDD management.

A Homing Missile-Like Nanotherapeutic with Single-Atom Catalytic Sites for In Situ Elimination of Intracellular Bacterial Pathogens

Intracellular bacterial pathogens hiding in host cells tolerate the innate immune system and high-dose antibiotics, resulting in recurrent infections that are difficult to treat. Herein, a homing missile-like nanotherapeutic (FeSAs@Sa.M) composed of a single-atom iron nanozyme (FeSAs) core coated with infected macrophage membrane (Sa.M) is developed for in situ elimination of intracellular methicillin-resistant S. aureus (MRSA). Mechanically, the FeSAs@Sa.M initially binds to the extracellular MRSA via the bacterial recognition ability of the Sa.M component. Subsequently, the FeSAs@Sa.M can be transported to the intracellular MRSA-located regions in the host cell like a homing missile under the guidance of the extracellular MRSA to which it is attached, generating highly toxic reactive oxygen species (ROS) for intracellular MRSA killing via the enzymatic activities of the FeSAs core. The FeSAs@Sa.M is far superior to FeSAs in killing intracellular MRSA, proposing a feasible strategy for treating intracellular infections by in situ generating ROS in bacterial residing regions.

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.

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.

Dimensionality Engineering of Single-Atom Nanozyme for Efficient Peroxidase-Mimicking

In nature, enzymatic reactions occur in well-functioning catalytic pockets, where substrates bind and react by properly arranging the catalytic sites and amino acids in a three-dimensional (3D) space. Single-atom nanozymes (SAzymes) are a new type of nanozymes with active sites similar to those of natural metalloenzymes. However, the catalytic centers in current SAzymes are two-dimensional (2D) architectures and the lack of collaborative substrate-binding features limits their catalytic activity. Herein, we report a dimensionality engineering strategy to convert conventional 2D Fe-N-4 centers into 3D structures by integrating oxidized sulfur functionalities onto the carbon plane. Our results suggest that oxidized sulfur functionalities could serve as binding sites for assisting substrate orientation and facilitating the desorption of H₂O, resulting in an outstanding specific activity of up to 119.77 U mg^-1, which is 6.8 times higher than that of conventional FeN₄C SAzymes. This study paves the way for the rational design of highly active single-atom nanozymes.

"Three-in-one" platform based on Fe-CDs nanozyme for dual-mode/dual-target detection and NIR-assisted bacterial killing

As nanozymes, carbon dots (CDs) have attracted increasing attention due to their remarkable properties. Besides general enzyme activity, their photoluminescence and photothermal properties have been explored rarely, whereas their synergistic effects might produce CDs-based nanozymes of high performance. Here, iron-doped CDs (Fe-CDs) with tunable fluorescence and enhanced peroxidase-like activity were designed to develop a novel "three-in-one" multifunctional platform to provide dual-mode/dual-target detection and near infrared (NIR)-assisted antibacterial ability. This proposed strategy for a H₂O₂ test exhibited a wide linear relationship with a low limit of detection (LOD) of 0.16 μM (colorimetric) and 0.14 μM (ratiometric fluorescent). Furthermore, due to the nature of cholesterol being oxidized to H₂O₂ by cholesterol oxidase, sensitive and selective detection of cholesterol was realized, and the LOD was 0.42 μM (colorimetric) and 0.27 μM (ratiometric fluorescent), surpassing that reported previously. This result suggested that Fe-CDs could be used for dual-mode quantification of large family of H₂O₂-producing metabolites, thereby paving the way for developing multi-mode sensing strategies based on nanozymes. Moreover, this platform showed synergistic effects for antibacterial application, indicating great prospects for bacterial killing as well as wound disinfection and healing. Hence, this platform could contribute to the construction of multifunctional CDs with high performance.

Perspectives on Usage of Functional Nanomaterials in Antimicrobial Therapy for Antibiotic-Resistant Bacterial Infections

The clinical applications of nanotechnology are emerging as widely popular, particularly as a potential treatment approach for infectious diseases. Diseases associated with multiple drug-resistant organisms (MDROs) are a global concern of morbidity and mortality. The prevalence of infections caused by antibiotic-resistant bacterial strains has increased the urgency associated with researching and developing novel bactericidal medicines or unorthodox methods capable of combating antimicrobial resistance. Nanomaterial-based treatments are promising for treating severe bacterial infections because they bypass antibiotic resistance mechanisms. Nanomaterial-based approaches, especially those that do not rely on small-molecule antimicrobials, display potential since they can bypass drug-resistant bacteria systems. Nanoparticles (NPs) are small enough to pass through the cell membranes of pathogenic bacteria and interfere with essential molecular pathways. They can also target biofilms and eliminate infections that have proven difficult to treat. In this review, we described the antibacterial mechanisms of NPs against bacteria and the parameters involved in targeting established antibiotic resistance and biofilms. Finally, yet importantly, we talked about NPs and the various ways they can be utilized, including as delivery methods, intrinsic antimicrobials, or a mixture.

Chemically functionalized manufactured sand as the novel additive for enhancing the properties of cement-based composites

The extensive applications of manufactured sand (AS) in cement-based composites were restricted because of its coarse surface texture, poor gradation and inevitable agglomeration. In this paper, a specifically designed polycarboxylate superplasticizer (PCE) decorated manufactured sand (AS-PCE) composite was synthesized via radical polymerization. The AS-PCE composite was characterized by FTIR, TGA, XPS and SEM. The load of PCE on the surface of AS was ∼12 wt%. Our results show that AS-PCE can promote cement hydration reaction and refine the microstructure of a cement-based material, thus, reinforcing its mechanical strength. Meanwhile, the fluidity of cement mortar with 1 wt% AS-PCE particles was increased by 35% after 1 h hydration, due to the steric hindrance effect provided by polycarboxylate superplasticizer affiliated with AS-PCE. The AS-PCE can also significantly enhance the mechanical strength (especially, the flexural strength was about 25% increased after curing for 28 days) of mortar. The excellent improvements result from the synergistic effects of AS-PCE including superb dispersibility, promotion of cement hydration reaction and the repair of interfacial defects between AS particles and the cementitious material. The research provides a promising method for the AS application in cement-based materials.

Nanozymes and nanoflower: Physiochemical properties, mechanism and biomedical applications

Natural enzymes possess several drawbacks which limits their application in industries, wastewater remediation and biomedical field. Therefore, in recent years researchers have developed enzyme mimicking nanomaterials and enzymatic hybrid nanoflower which are alternatives of enzyme. Nanozymes and organic inorganic hybrid nanoflower have been developed which mimics natural enzymes functionalities such as diverse enzyme mimicking activities, enhanced catalytic activities, low cost, ease of preparation, stability and biocompatibility. Nanozymes include metal and metal oxide nanoparticles mimicking oxidases, peroxidases, superoxide dismutase and catalases while enzymatic and non-enzymatic biomolecules were used for preparing hybrid nanoflower. In this review nanozymes and hybrid nanoflower have been compared in terms of physiochemical properties, common synthetic routes, mechanism of action, modification, green synthesis and application in the field of disease diagnosis, imaging, environmental remediation and disease treatment. We also address the current challenges facing nanozyme and hybrid nanoflower research and the possible way to fulfil their potential in future.

Activity Regulating Strategies of Nanozymes for Biomedical Applications

On accounts of the advantages of inherent high stability, ease of preparation and superior catalytic activities, nanozymes have attracted tremendous potential in diverse biomedical applications as alternatives to natural enzymes. Optimizing the activity of nanozymes is significant for widening and boosting the applications into practical level. As the research of the catalytic activity regulation strategies of nanozymes is boosting, it is essential to timely review, summarize, and analyze the advances in structure-activity relationships for further inspiring ingenious research into this prosperous area. Herein, the activity regulation methods of nanozymes in the recent 5 years are systematically summarized, including size and morphology, doping, vacancy, surface modification, and hybridization, followed by a discussion of the latest biomedical applications consisting of biosensing, antibacterial, and tumor therapy. Finally, the challenges and opportunities in this rapidly developing field is presented for inspiring more and more research into this infant yet promising area.

Investigating the electrochemical advanced oxidation mechanism of N-doped graphene aerogel: Molecular dynamics simulation combined with DFT method

Nitrogen-doped graphene as a perfectly-efficient and environmentally compatible electrocatalyst won widespread attention in electrochemical advanced oxidation processes (EAOP). However, the relationship between surface structure regulation and activity of catalysts is still lacking in systematic scientific guidance. Herein, nitrogen-doped graphene aerogel (NGA) was conveniently prepared through hydrothermal treatment, and then utilized to fabricate the gas diffusion electrode (GDE) as the cathode for tetracycline (TC) removal. High free radical yield (81.2 μM) and fast reaction rate (0.1469 min^-1) were found in NGA system. The molecular dynamics simulation (MD) results showed that the interaction energy of NGA was greater than the raw graphene aerogel (GA). The adsorption activation of H₂O₂ and the degradation of TC occurred in the first adsorption layer of catalysts, and both processes turned more orderly after nitrogen doping. Moreover, the van der Waals interaction was stronger than the electrostatic interaction. Density function theory (DFT) revealed that the adsorption energy of H₂O₂ at graphitic N, pyridinic N, and pyrrolic N sites was -0.03 eV, -0.39 eV, and -0.30 eV, respectively. Pyridinic N sites were inferred as the main functional regions of in-situ activation •OH, there were more likely to occur ectopic reaction in pyrrolic N, and graphitic N were responsible for improving H₂O₂ production. By revealing the microstructure and activation characteristics of NGA, an experiment-simulation complementary strategy is provided in the EAOP to discover or to optimize new catalysts.

A multi-enzyme-like activity exhibiting mussel-inspired nanozyme hydrogel for bacteria-infected wound healing

Bacterial infection, tissue hypoxia, and inflammatory and oxidative stress are several key problems in wound healing of chronic infections. Herein, a multi-enzyme-like activity exhibiting multifunctional hydrogel made up of mussel-inspired carbon dot reduced-Ag (CDs/AgNPs) and Cu/Fe-nitrogen-doped carbon (Cu,Fe-NC) was designed. Due to the loss of glutathione (GSH) and oxidase (OXD)-like activity of the nanozyme (decomposes O₂ to generate a superoxide anion radical (O₂˙^-) and hydroxyl radical production (˙OH)), the multifunctional hydrogel exhibited excellent antibacterial performance. More importantly, during the bacterial elimination within the inflammatory phase of wound healing, the hydrogel could act as a catalase (CAT)-like agent to supply adequate O₂ by catalyzing intracellular H₂O₂ for hypoxia abatement. The catechol groups on the CDs/AgNPs endowed them with the dynamic redox equilibrium properties of phenol-quinones, thus providing the hydrogel with mussel-like adhesion properties. The multifunctional hydrogel was shown to excellently promote bacterial infection wound healing and maximize the efficiency of nanozymes.

Enhanced Peroxidase-Like and Antibacterial Activity of Ir-CoatedPd-Pt Nanodendrites as Nanozyme

To inhibit the growth of bacteria, the DA-PPI nanozyme with enhanced peroxidase-like activity was synthesized. The DA-PPI nanozyme was obtained by depositing high-affinity element iridium (Ir) on the surface of Pd-Pt dendritic structures. The morphology and composition of DA-PPI nanozyme were characterized using SEM, TEM, and XPS. The kinetic results showed that the DA-PPI nanozyme possessed a higher peroxidase-like activity than that of Pd-Pt dendritic structures. The PL, ESR, and DFT were employed to explain the high peroxidase activity. As a proof of concept, the DA-PPI nanozyme could effectively inhibit E. coli (G^-) and S. aureus (G⁺) due to its high peroxidase-like activity. The study provides a new idea for the design of high active nanozymes and their application in the field of antibacterial.

Unraveling the Structure Transition and Peroxidase Mimic Activity of Copper Sites over Atomically Dispersed Copper-Doped Carbonized Polymer Dots

The lack of systematic structural resolution makes it difficult to build specific transition-metal-atom-doped carbonized polymer dots (TMA-doped CPDs). Herein, the structure-activity relationship between Cu atoms and CPDs was evaluated by studying the peroxidase-like properties of Glu-Cu-CPDs prepared by using copper glutamate (Glu) with a Cu-N₂ O₂ initial structure. The results showed that the Cu atoms bound to Glu-Cu-CPDs in the form of Cu-N₂ C₂ , indicating that Cu-O bonds changed into Cu-C bonds under hydrothermal conditions. This phenomenon was also observed in other copper-doped CPDs. Moreover, the carboxyl and amino groups content decreased after copper-atom doping. Theoretical calculations revealed a dual-site catalytic mechanism for catalyzing H₂ O₂ . The detection of intracellular H₂ O₂ suggested their application prospects. Our study provides an in-depth understanding of the formation and catalytic mechanism of TMA-doped-CPDs, allowing for the generation specific TMA-doped-CPDs.

Biomimetic Prussian blue nanozymes with enhanced bone marrow-targeting for treatment of radiation-induced hematopoietic injury

There is an urgent medical need to develop effective therapies that can ameliorate damage to the radiation-exposed hematopoietic system. Nanozymes with robust antioxidant properties have a therapeutic potential for mitigating radiation-induced hematopoietic injury. However, enhancing nanozyme recruitment to injured tissues in vivo while maintaining their catalytic activity remains a great challenge. Herein, we present the design and preparation of a biomimetic nanoparticle, a mesenchymal stem cell membrane camouflaged Prussian blue nanozyme (PB@MSCM), which exhibits biocompatible surface properties and demonstrates enhanced injury site-targeting towards the irradiated murine bone marrow niche. Notably, the constructed PB@MSCM possessed redox enzyme-mimic catalytic activity and could scavenge overproduced reactive oxygen species in the irradiated bone marrow cells, both in vitro and ex vivo. More importantly, the administration of PB@MSCM significantly mitigated hematopoietic cell apoptosis and accelerated the regeneration of hematopoietic stem and progenitor cells. Our findings provide a new targeted strategy to improve nanozyme therapy in vivo and mitigate radiation-induced hematopoietic injury.

In Situ Structure Transformation of a Sprayed Gel for pH-Ultrasensitive Nano-Catalytic Antibacterial Therapy

Nano-catalytic bacterial killing provides new opportunities to address ever-increasing antibiotic resistance. However, the intrinsic catalytic activity usually depends on a much lower pH conditions (pH = 2-5) than that in the weakly acidic bacterial microenvironments (pH = 6-7) for reactive oxygen species production by Fenton reactions. Herein, a MnSiO₃ -based pH-ultrasensitive "in situ structure transformation" is first reported to significantly promote the adhesion between material and bacteria, and shorten the diffusion distance (<20 nm) to compensate ultra-short life (<200 ns) of ·OH generated by Mn²⁺ -mediated Fenton-like reaction, finally enhancing its nano-catalytic antibacterial performance in weakly acidic conditions. A separated spray bottle is further designed to achieve in situ gelation at the wound site, which demonstrates excellent shape adaptability to complicated and rough surfaces of wounds, allowing for long-term nano-catalyst release. As a result, bacterial-infected wound healing is efficiently promoted. Herein, the in situ sprayed nano-catalytic antibacterial gel presents a promising paradigm for bacterial infection treatment.

Highly Sensitive Colorimetric Detection of Glutathione in Human Serum Based on Iron-Copper Metal-Organic Frameworks

Emerging metal-organic framework (MOF)-based mimic enzymes have been exploited to design a colorimetric sensor for the detection of biomolecules. However, it is challenging to figure out the glutathione (GSH) detection method and the corresponding sensing mechanism using an MOF-based colorimetric sensor. In this work, a novel iron-copper MOF with high activity is synthesized by a wet-chemical method. A GSH colorimetric sensor based on the peroxidase-like properties of the iron-copper MOF is developed. Hydrogen peroxide is converted to hydroxyl radicals by the peroxidase-like properties of the iron-copper MOF mimic enzyme, which can catalyze the colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxidized TMB (ox-TMB). The kinetic constant of the MOF mimic enzyme (0.02 mM for H₂O₂) is superior to horseradish peroxidase (HRP). The GSH content can be quantified by proposing a sensor based on the colorimetric method and color turn-off mechanism. The turn-off mechanism of GSH analysis includes two aspects. On the one hand, the blue ox-TMB can be deoxidized to colorless TMB by GSH. On the other hand, hydroxyl radicals (^•OH) can be consumed by GSH. The linear range and limit of detection are 2-20 and 0.439 μM, respectively. At the same time, GSH detection also shows good specificity and anti-interference characteristics. Therefore, MOF-based colorimetric sensors have been used to qualitatively and quantitatively measure GSH contents in human serum. The mechanism and application of the iron-copper MOF pave a way for the development of mimic enzymes with polymetallic active sites in the field of colorimetric sensing.

A comprehensive review on the applications of carbon-based nanostructures in wound healing: from antibacterial aspects to cell growth stimulation

A wound is defined as damage to the integrity of biological tissue, including skin, mucous membranes, and organ tissues. The treatment of these injuries is an important challenge for medical researchers. Various materials have been used for wound healing and dressing applications among which carbon nanomaterials have attracted significant attention due to their remarkable properties. In the present review, the latest studies on the application of carbon nanomaterials including graphene oxide (GO), reduced graphene oxide (rGO), carbon dots (CDs), carbon quantum dots (CQDs), carbon nanotubes (CNTs), carbon nanofibers (CNFs), and nanodiamonds (NDs) in wound dressing applications are evaluated. Also, a variety of carbon-based nanocomposites with advantages such as biocompatibility, hemocompatibility, reduced wound healing time, antibacterial properties, cell-adhesion, enhanced mechanical properties, and enhanced permeability to oxygen has been reported for the treatment of various wounds.

ROS generation strategy based on biomimetic nanosheets by self-assembly of nanozymes

Reactive oxygen species (ROS) play an important role in physiology and have been applied in tumor therapy. However, insufficient endogenous H₂O₂ and hypoxia in cancer cells can lead to limited ROS production and poor therapeutic efficacy. Herein, we develop a biomimetic nanosheet material based on the self-assembly of nanozymes that could supply H₂O₂ under acidic conditions and catalyze a cascade of intracellular biochemical reactions to produce ROS under both normoxic and hypoxic conditions without any external stimuli. In this system, the copper peroxide nanosheets (CPNS), which are pH-responsive, were prepared through coordination of H₂O₂ to Cu²⁺ and then modified using ultrafine Pt NPs to form CPNS@Pt. The CPNS could decompose under acidic conditions, allowing the simultaneous release of Fenton catalytic Cu²⁺ and H₂O₂ accompanied by a Fenton-type reaction between them. On the other hand, Pt NPs were also released. The released Pt NPs behave as an oxidase mimic and catalase mimic. In this way, the well-defined CPNS@Pt can not only relieve hypoxic conditions but also generate ROS to induce cell apoptosis, thereby paving the way for the development of a nanozyme with multienzyme activity as a therapeutic strategy.

Mo@ZIF-8 nanozyme preparation and its antibacterial property evaluation

Types of nanozymes can produce free radicals and/or reactive oxygen species (ROS) to serve as broad spectrum antibacterial materials. Developing nanozyme-based antibacterial materials with good biocompatibility exhibits promising application prospects. In this study, we doped Mo to ZIF-8 (both components have good biocompatibility) to prepare a new nanozyme, Mo@ZIF-8, which can produce hydroxyl radicals (•OH) triggered by a low dosage of hydrogen peroxide (H₂O₂), exhibiting effective antibacterial capability against both Gram-negative bacteria (Escherichia coli) and Gram-positive bacteria (Staphylococcus aureus). This work provides a reference for the design of antibacterial nanozymes with good biocompatibility.

Protein-Mimicking Nanoparticles in Biosystems

Proteins are essential elements for almost all life activities. The emergence of nanotechnology offers innovative strategies to create a diversity of nanoparticles (NPs) with intrinsic capacities of mimicking the functions of proteins. These artificial mimics are produced in a cost-efficient and controllable manner, with their protein-mimicking performances comparable or superior to those of natural proteins. Moreover, they can be endowed with additional functionalities that are absent in natural proteins, such as cargo loading, active targeting, membrane penetrating, and multistimuli responding. Therefore, protein-mimicking NPs have been utilized more and more often in biosystems for a wide range of applications including detection, imaging, diagnosis, and therapy. To highlight recent progress in this broad field, herein, representative protein-mimicking NPs that fall into one of the four distinct categories are summarized: mimics of enzymes (nanozymes), mimics of fluorescent proteins, NPs with high affinity binding to specific proteins or DNA sequences, and mimics of protein scaffolds. This review covers their subclassifications, characteristic features, functioning mechanisms, as well as the extensive exploitation of their great potential for biological and biomedical purposes. Finally, the challenges and prospects in future development of protein-mimicking NPs are discussed.

Bacteria Wear ICG Clothes for Rapid Detection of Intracranial Infection in Patients After Neurosurgery and Photothermal Antibacterial Therapy Against Streptococcus Mutans

Bacterial infection is one of the most serious physiological conditions threatening human health. There is an increasing demand for more effective bacterial diagnosis and treatment through non-invasive approaches. Among current antibacterial strategies of non-invasive approaches, photothermal antibacterial therapy (PTAT) has pronounced advantages with properties of minor damage to normal tissue and little chance to trigger antimicrobial resistance. Therefore, we developed a fast and simple strategy that integrated the sensitive detection and photothermal therapy of bacteria by measuring adenosine triphosphate (ATP) bioluminescence following targeted photothermal lysis. First, 3-azido-d-alanine (d-AzAla) is selectively integrated into the cell walls of bacteria, photosensitizer dibenzocyclooctyne, and double sulfonic acid-modified indocyanine green (sulfo-DBCO-ICG) are subsequently designed to react with the modified bacteria through in vivo click chemistry. Next, the sulfo-DBCO-ICG modified bacteria under irradiation of 808 nm near-infrared laser was immediately detected by ATP bioluminescence following targeted photothermal lysis and even the number of bacteria on the infected tissue can be significantly reduced through PTAT. This method has demonstrated the ability to detect the presence of the bacteria for ATP value in 32 clinical samples. As a result, the ATP value over of 100 confirmed the presence of bacteria in clinical samples for 22 patients undergoing craniotomy and ten otitis media patients. Overall, this study paves a brand new avenue to facile diagnosis and a treatment platform for clinical bacterial infections.

Mechanism and Application of Surface-Charged Ferrite Nanozyme-Based Biosensor toward Colorimetric Detection of l-Cysteine

Peroxidase-like nanozymes with robust catalytic capacity and detection specificity have been proposed as substitutes to natural peroxidases in biochemical sensing. However, the catalytic activity enhancement, detection mechanism, and application of nanozyme-based biosensors toward l-cysteine (l-Cys) detection still remain significant challenges. In this work, a doped ferrite nanozyme with well-defined structure and surface charges is fabricated by a two-step method of continuous flow coprecipitation and high-temperature annealing. The resulted ferrite nanozyme possesses an average size of 54.5 nm and a zeta-potential of 6.45 mV. A high-performance biosensor is manufactured based on the peroxidase-like catalytic feature of the doped ferrite. The ferrite nanozyme can oxidize the 3,3',5,5'-tetramethylbenzidine (TMB) with the assistance of H₂O₂ because of the instinctive capacity to decompose H₂O₂ into ·OH. The Michaelis-Menten constants (0.0911 mM for TMB, 0.140 mM for H₂O₂) of the ferrite nanozyme are significantly smaller than those of horseradish peroxidase. A reliable colorimetric method is established to selectively analyze l-Cys via a facile mixing-and-detecting methodology. The detection limit and linear range are 0.119 μM and 0.2-20 μM, respectively. Taking the merits of the ferrite nanozyme-based biosensors, the l-Cys level in the human serum can be qualitatively detected. It can be anticipated that the surface-charged ferrite nanozyme shows great application prospects in the fields of bioanalytical chemistry and point-of-care testing.

Emerging Prospects of Nanozymes for Antibacterial and Anticancer Applications

The ability of some nanoparticles to mimic the activity of certain enzymes paves the way for several attractive biomedical applications which bolster the already impressive arsenal of nanomaterials to combat deadly diseases. A key feature of such 'nanozymes' is the duplication of activities of enzymes or classes of enzymes, such as catalase, superoxide dismutase, oxidase, and peroxidase which are known to modulate the oxidative balance of treated cells for facilitating a particular biological process such as cellular apoptosis. Several nanoparticles that include those of metals, metal oxides/sulfides, metal-organic frameworks, carbon-based materials, etc., have shown the ability to behave as one or more of such enzymes. As compared to natural enzymes, these artificial nanozymes are safer, less expensive, and more stable. Moreover, their catalytic activity can be tuned by changing their size, shape, surface properties, etc. In addition, they can also be engineered to demonstrate additional features, such as photoactivated hyperthermia, or be loaded with active agents for multimodal action. Several researchers have explored the nanozyme-mediated oxidative modulation for therapeutic purposes, often in combination with other diagnostic and/or therapeutic modalities, using a single probe. It has been observed that such synergistic action can effectively by-pass the various defense mechanisms adapted by rogue cells such as hypoxia, evasion of immuno-recognition, drug-rejection, etc. The emerging prospects of using several such nanoparticle platforms for the treatment of bacterial infections/diseases and cancer, along with various related challenges and opportunities, are discussed in this review.

Ultrasmall Fe-doped carbon dots nanozymes for photoenhanced antibacterial therapy and wound healing

Pathogenic bacteria pose a devastating threat to public health. However, because of the growing bacterial antibiotic resistance, there is an urgent need to develop alternative antibacterial strategies to the established antibiotics. Herein, iron-doped carbon dots (Fe-CDs, ∼3 nm) nanozymes with excellent photothermal conversion and photoenhanced enzyme-like properties are developed through a facile one-pot pyrolysis approach for synergistic efficient antibacterial therapy and wound healing. In particular, Fe doping endows CDs with photoenhanced peroxidase (POD)-like activity, which lead to the generation of heat and reactive oxygen species (ROS) for Gram-positive and Gram-negative bacteria killing. This study demonstrates Fe-CDs have significant wound healing efficiency of Fe-CDs by preventing infection, promoting fibroblast proliferation, angiogenesis, and collagen deposition. Furthermore, the ultrasmall size of Fe-CDs possesses good biocompatibility favoring clinical translation. We believe that the nanozyme-mediated therapeutic platform presented here is expected to show promising applications in antibacterial.

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Iron doped carbon dots (Fe-CDs, ~3 nm) exhibited excellent photothermal conversion and photoenhanced enzyme-like properties.

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Fe-CDs as nanozyme and photothermal agent possess outstanding antibacterial ratio against both S. aureus and E. coli.

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The photoresponsive nanozyme-mediated therapeutic platform exhibited great promise for bacterial-infected wound healing.

Preparation of Two-Dimensional Pd@Ir Nanosheets and Application in Bacterial Infection Treatment by the Generation of Reactive Oxygen Species

Noble metal nanozymes have shown great promise in biomedicine; however, developing novel and high-performance noble metal nanozymes is still highly pressing and challenging. Herein, we, for the first time, prepared two-dimensional (2D) Pd@Ir bimetal nanosheets (NSs) with well-defined size and composition by a facile seed-mediated growth strategy. Enzyme-mimicked investigations find that the Pd@Ir NSs possess oxidase (OXD)-, peroxidase (POD)-, and catalase (CAT)-like multienzyme-mimetic activities. Especially, they exhibited much higher OXD- and POD-like activities than individual Pd NSs and Ir nanoparticles (NPs). The density functional theory (DFT) calculations reveal that the adsorption energy of O2 on Pd@Ir NSs is lower than that on the pure Pd NSs, which is more favorable for the conversion of O2 molecules from the triplet state (3O2) into the singlet state (1O2). Finally, based on the outstanding nanozyme activities to yield highly active singlet oxygen (1O2) and hydroxyl radicals (•OH) as well as excellent biosafety, the as-prepared Pd@Ir NSs were applied to treat bacteria-infected wounds, and satisfactory therapeutic outcomes were achieved. We believe that the highly efficient 2D Pd@Ir nanozyme will be an effective therapeutic reagent for various biomedical applications.

A Self-Assembled Fmoc-Diphenylalanine Hydrogel-Encapsulated Pt Nanozyme as Oxidase- and Peroxidase-Like Breaking pH Limitation for Potential Antimicrobial Application

Nanomaterials with oxidase- and peroxidase-like activities have potential in antibacterial therapy. The optimal activity of most nanozymes occurred in acidic pH (3.0-5.0), while the pH in biological systems is mostly near neutral. Herein, a general system using 9-fluorenylmethoxycarbonyl-modified diphenylalanine (Fmoc-FF) hydrogel for enhancing oxidase- and peroxidase-like activities of Pt NPs and other typical enzyme-like nanomaterials at neutral or even alkaline pH is proposed. In this system, Fmoc-FF hydrogel provides an acidic microenvironment for Pt NPs due to hydrogen protons (H⁺ ) produced by the dissociation of F at neutral pH. As a result, Pt NPs exhibits 6-fold enhanced oxidase-like and 26-fold peroxidase-like activity after being encapsulated into Fmoc-FF hydrogel at pH 7.0. Based on outstanding enzymatic activities and the antibacterial activity of Fmoc-FF hydrogel itself, Pt-Fmoc-FF hydrogel realizes excellent antibacterial effect. This design provides a universal strategy to break pH limitation of nanozymes and promotes the biological applications of nanozymes.

Nanozymes: Versatile Platforms for Cancer Diagnosis and Therapy

Natural enzymes usually suffer from high production cost, ease of denaturation and inactivation, and low yield, making them difficult to be broadly applicable. As an emerging type of artificial enzyme, nanozymes that combine the characteristics of nanomaterials and enzymes are promising alternatives. On the one hand, nanozymes have high enzyme-like catalytic activities to regulate biochemical reactions. On the other hand, nanozymes also inherit the properties of nanomaterials, which can ameliorate the shortcomings of natural enzymes and serve as versatile platforms for diverse applications. In this review, various nanozymes that mimic the catalytic activity of different enzymes are introduced. The achievements of nanozymes in different cancer diagnosis and treatment technologies are summarized by highlighting the advantages of nanozymes in these applications. Finally, future research directions in this rapidly developing field are outlooked.

Incorporating Boron into Niobic Acid Nanosheets Enables Generation of Multiple Reactive Oxygen Species for Superior Antibacterial Action

Photocatalytic therapy is an alternative antibacterial pathway but most photocatalysts are limited by light absorption, charge transfer and insufficient production of reactive oxygen species (ROS). Herein, the authors utilize boron doped niobic acid nanosheets (B-HNbO₃ NSs) as a superior photocatalytic antibacterial platform. The experimental results and density functional theory (DFT) confirm that superior photocatalytic therapy activity is mainly due to boron doping, which not only promotes the generation and separation of electrons and holes, but also enhances the adsorption of water and oxygen molecules on B-HNbO₃ NSs. Consequently, multiple ROS including hydroxyl radicals (•OH), superoxide radicals (•O₂^- ), and singlet oxygen (¹ O₂ ) are generated under light irradiation, resulting in outstanding bacterial killing ability of B-HNbO₃ NSs. Besides, oxygen is produced during the therapy process, thus alleviating the inflammatory response caused by hypoxia. Furthermore, molecular dynamics (MD) simulations verify that the nanosheet structure makes it possess strong electrostatic attraction for bacterial cell membranes, leading to physical insertion and damage to bacterial cells. Therefore, bactericidal rates for four types of bacteria are all more than 99%, proving its excellent and broad-spectrum antibacterial capacity. Moreover, B-HNbO₃ NSs could be applied to treat biofilm-coated medical devices in vivo, suggesting its possibility in practical application.

Antibacterial Effect of Chitosan-Modified Fe3O4 Nanozymes on Acinetobacter baumannii

The aim of this study was to determine whether the antibacterial activity of chitosan-modified Fe₃O₄ (CS@Fe₃O₄) nanomaterials against Acinetobacter baumannii (A. baumannii) is mediated through changes in biofilm formation and reactive oxygen species (ROS) production. For this purpose, the broth dilution method was used to examine the effect of CS@Fe₃O₄ nanoparticles on bacterial growth. The effects of CS@Fe₃O₄ nanoparticles on biofilm formation were measured using a semi-quantitative crystal violet staining assay. In addition, a bacterial ROS detection kit was used to detect the production of ROS in bacteria. The results showed that CS@Fe₃O₄ nanoparticles had a significant inhibitory effect on the colony growth and biofilm formation of drug-resistant A. baumannii (p < 0.05). The ROS stress assay revealed significantly higher ROS levels in A. baumannii subjected to CS@Fe₃O₄ nanoparticle treatment than the control group (p < 0.05). Thus, we demonstrated for the first time that CS@Fe₃O₄ nanoparticles had an inhibitory effect on A. baumannii in vitro, and that the antibacterial effect of CS@Fe₃O₄ nanoparticles on drug-resistant A. baumannii was more significant than on drug-sensitive bacteria. Our findings suggest that the antibacterial mechanism of CS@Fe₃O₄ nanoparticles is mediated through inhibition of biofilm formation in drug-resistant bacteria, as well as stimulation of A. baumannii to produce ROS. In summary, our data indicate that CS@Fe₃O₄ nanoparticles could be used to treat infections caused by drug-resistant A. baumannii.

Enhancing the peroxidase-like activity of MIL-88B by ligand exchange with polydopamine

Metal-organic frameworks (MOFs) as nanozymes have been widely used in biosensing. However, MOFs have inherent defects of easy agglomeration, leading to the stacking of active surfaces. In addition, the low conductivity of MOFs is not conducive to the electron migration in the Fenton-like reaction, which leads to a further decrease in catalytic activity and severely restricts their application. In response to the above problems, it makes sense to develop a method to improve both the dispersion and conductivity of MOFs. Here, a simple ligand exchange method with polydopamine (PDA) was used to synthesize MOF PDA-MIL-88B. PDA-MIL-88B shows stronger peroxidase-like activity than MIL-88B. One reason is the good dispersibility of PDA-MIL-88B, which is conducive to exposing the active surface. In addition, the reduced electrochemical impedance of PDA-MIL-88B increases its electrical conductivity, which is favorable for electron migration in the Fenton-like reaction. As a result, PDA-MIL-88B can better catalyze 3,3',5,5'-tetramethylbenzidine to achieve redoximorphic color changes. PDA-MIL-88B can be used to detect glucose in human serum with good sensitivity and selectivity. This work can provide a strategy for MOFs to enhance the enzyme-like activity.

Carbon Nanomaterials (CNMs) and Enzymes: From Nanozymes to CNM-Enzyme Conjugates and Biodegradation

Carbon nanomaterials (CNMs) and enzymes differ significantly in terms of their physico-chemical properties—their handling and characterization require very different specialized skills. Therefore, their combination is not trivial. Numerous studies exist at the interface between these two components—especially in the area of sensing—but also involving biofuel cells, biocatalysis, and even biomedical applications including innovative therapeutic approaches and theranostics. Finally, enzymes that are capable of biodegrading CNMs have been identified, and they may play an important role in controlling the environmental fate of these structures after their use. CNMs’ widespread use has created more and more opportunities for their entry into the environment, and thus it becomes increasingly important to understand how to biodegrade them. In this concise review, we will cover the progress made in the last five years on this exciting topic, focusing on the applications, and concluding with future perspectives on research combining carbon nanomaterials and enzymes.