Progress and Perspective on Carbon-Based Nanozymes for Peroxidase-like Applications

Pre-ligand-induced porous MOF as a peroxidase mimic for electrochemical analysis of deoxynivalenol (DON)

Developing convenient and sensitive vomitoxin detection methods is crucial to prevent human health risks from excess deoxynivalenol (DON) in food products. This study synthesized porous electrochemical nanomaterial calcined PA-NH2-MIL-101 (CPNM) with abundant amino group modifications using a palmitic acid (PA) pre-ligand and amino functionalization scheme. PA-induced defect generation and which formed a high-stability porous structure that increased the peroxidase-like catalytic active site and thus improving electrochemical analytical performance. In addition, introducing amino groups in CPNM facilitated the covalent immobilization of DON antibodies. Therefore, an electrochemical immunosensing platform for detecting DON was developed by utilizing the electrocatalytic signals generated by Fe-MOF (MIL-101) nanozymes and thionine molecules. The proposed sensor showed a large linear range of 10-107 pg mL-1 with a detection limit of 9.6 pg mL-1 (S/N = 3) under optimized optimal conditions. Consequently, this innovative electrochemical immunosensing technique based on CPNM nanozymes paves the way for DON detection in food.

Proton Driving Mechanism Revealed in Sulfur-Doped Single-Atom FeN2O2 Carbon Dots for Superior Peroxidase Activity

Heteroatom-doped single-atom nanozymes (SAEs) hold great promise as enzyme mimics, yet their catalytic mechanisms remain unclear. This study reveals that the proton driving mechanism induced by sulfur doping in single-atom FeN2O2 carbon dots (S-FeCDs) significantly enhances peroxidase (POD)-like activity. Synthesized via low-temperature carbonization, S-FeCDs exhibit FeN2O2 coordination with sulfur in the second shell, as confirmed by XAFS and AC-STEM. The POD-specific activity of S-FeCDs reached 295 U mg-1, which is 11.2-fold higher than that of sulfur-free FeCDs, with natural enzyme-like kinetics. In situ experiments, kinetic and mechanistic studies revealed that sulfur doping promotes H2O dissociation, enhances H+ adsorption, reduces the ΔG for H2O2-to-·OH conversion. DFT revealed a lowered energy barrier for the rate-determining step (2*OH → *O + *H2O) from 2.50 to 1.62 eV. In vivo, S-FeCDs demonstrated broad pH efficacy in MRSA-infected wound models, achieving near-complete healing within 7 days. The proton driving mechanism was further validated through nitro compound reduction, demonstrating accelerated N─H bond activation. This work highlights the critical role of sulfur-induced proton dynamics in enhancing SAEs performance, providing a rational strategy for designing multifunctional nanozymes in biomedical and catalytic applications.

COF-Derived Carbon Materials: Synthesis Strategies and Emerging Applications

Covalent organic framework (COF)-derived carbon materials seamlessly inherit the periodic porous architecture and high specific surface area of their precursors, while simultaneously enabling the confinement of nanoparticles in designated regions. This unique feature mitigates agglomeration, enhances intrinsic properties, and imparts novel functionalities to the resulting materials. Consequently, COF-derived carbon materials have garnered significant attention across diverse fields, including energy, environmental remediation, and biomedical applications. Despite this burgeoning interest, a comprehensive review encompassing the synthesis, classification, and multifaceted applications of these materials remains scarce. In this context, the state-of-the-art advancements in COF-derived carbon materials are reviewed systematically here. It categorizes the materials, delineates their primary synthesis strategies, and highlights their versatile applications in catalysis, electrochemical energy storage, water treatment, sensing, and cancer therapy. Lastly, fresh insights into the challenges and future prospects of COF-derived carbon materials, paving the way for their expanded exploration and utilization are offered here.

Nanomineralzyme as a novel sustainable class of nanozyme: Chalcopyrite-based nanozyme for the visual detection of total antioxidant capacity in citrus fruit

Chemically-synthesized Nanozymes that are widely used as alternatives to enzymes face challenges such as high precursor costs, complex preparation processes, and limited catalytic efficiency. To overcome these drawbacks, we introduce naturally derived nanozymes, nanomineralzymes, as a promising alternative, offering benefits like affordability, cost-effectiveness, and scalability. Chalcopyrite (CP, CuFeS2) was sourced from a mineral deposit, and CP nanoparticles were produced by milling. These nanoparticles exhibited strong peroxidase-like activity, achieving a low Michaelis-Menten constant using 3,3',5,5'-tetramethylbenzidine as a substrate. Characterizations revealed the presence of cuprous, cupric, ferrous, and ferric ions in the CP mineral. The proposed mechanism involves an enhanced Fenton and Fenton-like process due to the metal ions' multi-valence states. CP nanozyme activity was inhibited to produce radicals due to hydrogen atom transfer and single electron transfer with ascorbic acid, glutathione and cysteine. The CP mineralzyme-based total antioxidant capacity probe was successfully used for detection of TAC in citrus fruits.

Atomic Pt-Layer-Coated Au Peroxidase Nanozymes with Enhanced Activity for Ultrasensitive Colorimetric Immunoassay of Interleukin-12

Interleukin-12 (IL-12), a crucial biomarker for immune and inflammatory responses, plays a pivotal role in diagnosing and managing diverse pathological conditions. Although colorimetric enzyme-linked immunosorbent assays (CELISAs) have been extensively employed to detect IL-12 in biological samples, their sensitivity is inherently limited by the catalytic efficiency of enzyme labels, presenting substantial challenges in achieving ultrasensitive detection and enabling pre-symptomatic diagnosis of diseases. In this study, we address this limitation by developing a novel peroxidase nanozyme, featuring ultrathin Pt skins consisting of only ~4 atomic layers, coated on Au nanoparticles (denoted as Au@Pt4LNPs). These Au@Pt4LNPs exhibit remarkable catalytic performance, achieving a ~1063-fold enhancement in peroxidase-like activity compared to horseradish peroxidase (HRP), while minimizing Pt consumption, thereby improving Pt utilization efficiency and reducing costs. This advancement facilitates the construction of an ultrasensitive CELISA capable of detecting IL-12 at femtomolar concentrations. Using Au@Pt4LNPs as the signal labels, the developed CELISA demonstrates a quantitative detection range from 0.1 to 100 pg mL-1, with a limit of detection (LOD) as low as 0.084 pg mL-1 (1.1 fM), offering ~10 times greater sensitivity than the HRP-based CELISA. This study highlights the potential of Au@Pt4LNP nanozymes as advanced signal labels, opening new avenues for next-generation ultrasensitive bioassays.

Oxidative stress-augmented Cu-doped hollow mesoporous carbon nanozyme for photothermal/photodynamic synergistic therapy

Photodynamic therapy (PDT) has witnessed remarkable progress in recent years owing to its specific properties. Given that the antioxidation system of tumor microenvironment (TME) adversely affects treatment outcomes, powerful TME modulators can significantly resolve the limitation of PDT. Herein, we developed a PEG-modified Cu2+-doped hollow mesoporous carbon nanozyme (CHC-PEG) and loaded insoluble photosensitizer IR780 into its pores and cavities to construct the multifunctional nano-system IR780/CHCP. CHC-PEG nanozyme could perform photothermal therapy (PTT) effect and protect IR780 from aggregation-caused quenching (ACQ) effect, while exerting peroxidase (POD)-mimetic activity and the ability of consuming glutathione (GSH) to achieve oxidative stress-augmented PDT effect. When exposed to near-infrared (NIR) light, IR780 was stimulated to produce singlet oxygen (1O2) and CHC-PEG could increase the temperature of TME to exert stronger POD-mimetic activity for producing more hydroxyl radicals (OH), therefore the IR780/CHCP nano-system exhibited remarkable tumor growth inhibition. Benefited by the enhanced synergistic effect, IR780/CHCP exhibited remarkable in vivo tumor growth inhibition, with the tumor inhibition rate of 93 %, and had no significant effect on major organs. Above all, IR780/CHCP could resist the antioxidant system in TME to enhance the level of oxidative stress, thereby enabling effective anti-tumor therapy. This study introduced a novel strategy to effectively promote the synergistic PTT/PDT effect by the enhanced oxidative stress.

Optically tunable catalytic cancer therapy using enzyme-like chiral plasmonic nanoparticles

Cascade enzymatic reactions in living organisms are fundamental reaction mechanisms in coordinating various complex biochemical processes such as metabolism, signal transduction, and gene regulation. Many studies have attempted to mimic cascade reactions using nanoparticles with enzyme-like activity; however, precisely tuning each reaction within complex networks to enhance the catalytic activity remains challenging. Here, we present enzyme-like chiral plasmonic nanoparticles for optically tunable catalytic cancer therapy. We create chiral plasmonic nanoparticles with glucose oxidase (GOD) and peroxidase (POD) activities, followed by introducing circularly polarized light (CPL). By sequentially activating GOD and POD reactions with right-handed CPL (RC) followed by left-handed CPL (LC), we achieve 1.25- and 1.9-fold enhanced catalytic performance (overall 1.3 times enhancement) compared to non-controlled cascade reactions by creating an optimal acidic environment for the subsequent reaction. Moreover, the D-Au nanoparticle shows a 2-fold higher binding selectivity to D-glucose substrates, attributed to chirality matching. In both cell studies and male mouse models, sequentially irradiated groups (RC followed by LC) exhibit the highest radical generation and the most efficient treatment outcomes compared to the other systems under different irradiation conditions. We believe that our system holds strong potential for medical applications, suggesting a promising platform for catalytic therapy.

Carbon-based nanozymes for cancer therapy and diagnosis: A review

Carbon-based nanozymes (CNs) have emerged as a significant innovation in targeted cancer therapy, demonstrating great potential for advancing cancer diagnosis and treatment. With exceptional catalytic properties, remarkable biocompatibility, and the ability to precisely target cancer cells, CNs provide a promising avenue for the development of novel oncological therapies. By functionalizing their surfaces with targeting ligands, such as antibodies or peptides, CNs can specifically recognize and bind to cancer cells. This targeted approach ensures that therapeutic agents are delivered directly to the tumor site, minimizing off-target effects, and reducing systemic toxicity. Additionally, the enzyme-like activities of CNs, when combined with conventional therapies such as chemotherapeutics, photothermal therapy, and photodynamic therapy, or other modalities can enhance therapeutic outcomes. Integrating CNs into clinical practice could significantly improve therapeutic efficacy, reduce probable side effects, enhance patient outcomes, and drive a shift towards more personalized cancer care. Besides, CNs can also be employed in biosensors and diagnostic nanomaterials, enabling rapid, selective, and highly accurate detection of specific biomarkers. Their versatile functionalities open new avenues for refining imaging techniques, ultimately contributing to early diagnosis and better clinical decision-making. This review consolidates recent studies exploring CNs in cancer targeting, highlighting both their diagnostic and therapeutic potential in oncology.

Determination of deoxynivalenol (DON) by a label-free electrochemical immunosensor based on NiFe PBA nanozymes

Deoxynivalenol (DON) contamination in food products significantly threatens human health, necessitating a reliable and sensitive detection method. This study aims to develop a simple, low-cost, and effective electrochemical immunoassay method for detecting DON based on the nickel‑iron bimetallic Prussian blue analog (NiFe PBA). The NiFe PBA nanozymes with high peroxidase-like activity were synthesized using an environmentally friendly chemical precipitation method. In the presence of hydrogen peroxide (H2O2), the current change of thionine oxidation initiated by NiFe PBA nanozymes can be exploited to diagnose DON. Under optimal conditions, the proposed method achieved quantitative detection of DON in the range of 10-107 pg mL-1 with a detection limit of 4.5 pg mL-1 (S/N = 3), demonstrating excellent selectivity, reproducibility, and stability. In addition, the DON immunosensor provides satisfactory results for the detection in real samples, demonstrating the feasibility of the proposed sensor in detecting of DON in such products.

Scientific Insights into the Quantum Dots (QDs)-Based Electrochemical Sensors for State-of-the-Art Applications

Size-dependent optical and electronic properties are unique characteristics of quantum dots (QDs). A significant advantage is the quantum confinement effect that allows their precise tuning to achieve required characteristics and behavior for the targeted applications. Regarding the aforementioned factors, QDs-based sensors have exhibited dramatic potential for the diverse and advanced applications. For example, QDs-based devices have been potentially utilized for bioimaging, drug delivery, cancer therapy, and environmental remediation. In recent years, use of QDs-based electrochemical sensors have been further extended in other areas like gas sensing, metal ion detection, monitoring of organic pollutants, and detection of radioactive isotopes. Objective of this study is to rationalize the QDs-based electrochemical sensors for state-of-the-art applications. This review article comprehensively illustrates the importance of aforementioned devices along with sources from which QDs devices have been formulated and fabricated. Other distinct features of QDs devices are associated with their extremely high active surfaces, inherent ability of reproducibility, sensitivity, and selectivity for the targeted analyte detection. In this review, major categories of QD materials along with justification of their key roles in electrochemical devices have been demonstrated and discussed. All categories have been evaluated with special emphasis on the advantages and drawbacks/challenges associated with QD materials. However, in the interests of readers and researchers, recent improvements also have been included and discussed. On the evaluation, it has been concluded that despite significant challenges, QDs-based electrochemical sensors exhibit excellent performances for state-of-the-art and targeted applications.

Onion-Like Carbon Nanozyme: Controlling Peroxidase-Like Activity by Carbon Hybridization Patterns for Antibacterial Therapy

Since the inception of the concept of nanozymes, there has been a growing interest in the rational design and controllable synthesis of nanozymes with adjustable activities. In this study, onion-liked carbon (OLC) with remarkable peroxidase-like (POD) activity are developed through delicately controlling the sp2/sp3 configuration. The investigation reveals that enzymatic activity of OLC increases first and then decreases with the increased graphitic degree, with the highest activity observed at a moderate sp2/sp3 ratio of 17.17%. A series of experiments and theoretical calculations are conducted to elucidate the catalytic mechanism, and the structure-dependent activity is attributed to a synergistic effect of surface adsorption and electron transfer processes. The POD activity enables the OLC to catalyze the decomposition of H2O2, producing reactive oxygen species for eradicating Gram-positive and Gram-negative bacteria. Additionally, toxicity tests based on nematode and mouse models confirmed the excellent biocompatibility of OLC. Furthermore, the OLC exhibited antibacterial ability and promoted bacterial-infected wound healing in a mouse model. This work not only gives a deeper understanding of the structure-activity relationship and catalytic mechanism of carbon-based nanozymes, but also unveils a novel avenue for antibacterial therapy and wound healing applications.

Establishment of a visual assessment platform for total antioxidant capacity of Ganoderma sichuanense based on Arg-CeO2 hydrogel nanozyme utilizing a self-programmed smartphone app and a self-designed 3D-printed device

A multienzyme-like L-argininemodified CeO2 (Arg-CeO2) nanozyme was prepared for accurate total antioxidant capacity (TAC) determination of Ganoderma sichuanense (G. sichuanense). It exhibits oxidase-like and peroxidase-like activities catalyzing the generation of superoxide anion free radicals and hydroxyl radicals, accelerating 3, 3', 5, 5'-tetramethylbenzidine (TMB) chromogenic reaction. Antioxidants can effectively eliminate the generated free radicals, inhibiting the TMB chromogenic reaction. Hence, TAC can be assessed by Arg-CeO2 catalyzed TMB chromogenic reaction using ascorbic acid (AA) as a reference substance. TAC of G. sichuanense extracted using different solvents was determined, indicating the highest TAC observed in the G. sichuanense extracted by the mixture solvent (deionized water/ethanol/ethyl acetate = 1 : 1 : 1). A visual assessment platform based on Arg-CeO2 hydrogel nanozyme utilizing a self-programmed smartphone app and a self-designed 3D printed device is established. TAC using AA as a reference substance (3.33 ~ 83.33 µM) can be detected with a detection limit as low as 0.58 µM. The platform can realize one-step quantitative determination of TAC in G. sichuanense within 40 min. The proposed visual assessment platform presented exhibits promising application prospects in the field of TAC assessment in food.

Fe-codoped carbon dots serving as a peroxidase mimic to generate in situ hydrogen peroxide for the visual detection of glucose

Nanozyme technology has gained significant regard and been successfully implemented in various applications including chemical sensing, bio-medicine, and environmental monitoring. Fe-CDs were synthesized and characterized well in this study. As compared to HRP (3.7 mM), the Fe-CDs exhibited a higher affinity towards H2O2 (0.2 mM) using the steady-state kinetic assay and stronger catalytic capability by changing the color of TMB to the blue color of the oxidized state, oxTMB. Additionally, an efficient peroxidase mimic, Fe-CDs/GOx, based on the hybrid cascade system to produce in situ H2O2 for the visual detection of glucose (color change: colorless to blue, and then to green), has been developed in detail, with limits of detection (LODs) for H2O2 and glucose of 0.33 μM and 1.17 μM, respectively. The changes further demonstrate a linear relationship between absorbance and H2O2 concentration, ranging from 10 to 60 μM, and for glucose (1 to 60 μM). To assess the accuracy and detection capability of the Fe-CDs/GOx system, we evaluated a real human serum sample obtained from adult males in a local hospital. In conclusion, Fe-CDs serving as a peroxidase mimic have the potential for various applications in the fields of biomedicine and nanozymes.

Nanozymes: Classification and Analytical Applications - A Review

The recent discovery of a new class of nanomaterials called nanozymes, which have the action of enzymes and are thus of tremendous significance, has altered our understanding of these previously believed to be biologically inert nanomaterials. As a significant and exciting class of synthetic enzymes, nanozymes have distinct advantages over natural enzymes. They are less expensive, more stable, and easier to work with and store, making them a viable substitute. This practical advantage of nanozymes over natural enzymes reassures us about the potential of this new technology. Peroxidase-like nanozymes have been investigated for the purpose of creating adaptable biosensors via the use of molecularly imprinted polymers (MIPs) or particular bio recognition ligands, including enzymes, antibodies, and aptamers. This review delves into the distinctions between synthetic and natural enzymes, explaining their structures and analytical applications. It primarily focuses on carbon-based nanozymes, particularly those that contain both carbon and hydrogen, as well as metal-based nanozymes like Fe, Cu, and Au, along with their metal oxide (FeO, CuO), which have applications in many fields today. Analytical chemistry finds great use for nanozymes for sensing and other applications, particularly in comparison with other classical methods in terms of selectivity and sensitivity. Nanozymes, with their unique catalytic capabilities, have emerged as a crucial tool in the early diagnosis of COVID-19. Their application in nanozyme-based sensing and detection, particularly through colorimetric and fluorometric methods, has significantly advanced our ability to detect the virus at an early stage.

Microenvironment-sensitive nanozymes for tissue regeneration

Tissue defect is one of the significant challenges encountered in clinical practice. Nanomaterials, including nanoparticles, nanofibers, and metal-organic frameworks, have demonstrated an extensive potential in tissue regeneration, offering a promising avenue for future clinical applications. Nonetheless, the intricate landscape of the inflammatory tissue microenvironment has engendered challenges to the efficacy of nanomaterial-based therapies. This quandary has spurred researchers to pivot towards advanced nanotechnological remedies for overcoming these therapeutic constraints. Among these solutions, microenvironment-sensitive nanozymes have emerged as a compelling instrument with the capacity to reshape the tissue microenvironment and enhance the intricate process of tissue regeneration. In this review, we summarize the microenvironmental characteristics of damaged tissues, offer insights into the rationale guiding the design and engineering of microenvironment-sensitive nanozymes, and explore the underlying mechanisms that underpin these nanozymes' responsiveness. This analysis includes their roles in orchestrating cellular signaling, modulating immune responses, and promoting the delicate process of tissue remodeling. Furthermore, we discuss the diverse applications of microenvironment-sensitive nanozymes in tissue regeneration, including bone, soft tissue, and cartilage regeneration. Finally, we shed our sights on envisioning the forthcoming milestones in this field, prospecting a future where microenvironment-sensitive nanozymes contribute significantly to the development of tissue regeneration and improved clinical outcomes.

Copper-doped cherry blossom carbon dots with peroxidase-like activity for antibacterial applications

Safety concerns arising from bacteria present a significant threat to human health, underscoring the pressing need for the exploration of novel antimicrobial materials. Nanozymes, as a new type of nanoscale material, have attracted widespread attention for antibacterial applications owing to their ability to mimic the catalytic activity of natural enzymes. In this work, we have constructed copper-doped cherry blossom carbon dots (Cu-CDs) with excellent peroxidase-like (POD) activity using a one-pot hydrothermal method. The utilization of cherry blossom as a natural material precursor significantly enhances its biocompatibility. Furthermore, the incorporation of copper ions initiates Fenton-like reaction-triggered POD-like catalytic activity, effectively eradicating bacteria by converting hydrogen peroxide (H2O2) into hydroxyl radicals (·OH). The antibacterial test results demonstrate that Cu-CDs exhibit a bactericidal efficacy of over 90% against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). This study presents a novel environmentally friendly nanozyme material derived from natural sources, exhibiting significant antimicrobial properties and offering innovative insights for the advancement of antimicrobial materials.

Prunella vulgaris-phytosynthesized platinum nanoparticles: Insights into nanozymatic activity for H2O2 and glutamate detection and antioxidant capacity

Artificial nanozymes (enzyme-mimics), specifically metallic nanomaterials, have garnered significant attention recently due to their reduced preparation cost and enhanced stability in a wide range of environments. The present investigation highlights, for the first time, a straightforward green synthesis of biogenic platinum nanoparticles (PtNPs) from a natural resource, namely Prunella vulgaris (Pr). To demonstrate the effectiveness of the phytochemical extract as an effective reducing agent, the PtNPs were characterized by various techniques such as UV-vis spectroscopy, High-resolution Transmission electron microscopy (HR-TEM), zeta-potential analysis, Fourier-transform infrared spectroscopy (FTIR), and Energy dispersive spectroscopy (EDS). The formation of PtNPs with narrow size distribution was verified. Surface decoration of PtNPs was demonstrated with multitudinous functional groups springing from the herbal extract. To demonstrate their use as viable nanozymes, the peroxidase-like activity of Pr/PtNPs was evaluated through a colorimetric assay. Highly sensitive visual detection of H2O2 with discrete linear ranges and a low detection limit of 3.43 μM was demonstrated. Additionally, peroxidase-like catalytic activity was leveraged to develop a colorimetric platform to quantify glutamate biomarker levels with a high degree of selectivity, the limit of detection (LOD) being 7.00 μM. The 2,2-Diphenyl-1-picrylhydrazyl (DPPH) test was used to explore the scavenging nature of the PtNPs via the degradation of DPPH. Overall, the colorimetric assay developed using the Pr/PtNP nanozymes in this work could be used in a broad spectrum of applications, ranging from biomedicine and food science to environmental monitoring.

Cascade Co8FeS8@Co1-xS nano-enzymes trigger efficiently apoptosis-ferroptosis combination tumor therapy

This study involved the preparation of Metal Organic Frameworks (MOF)-derived Co8FeS8@Co1-xS nanoenzymes with strong interfacial interactions. The nanoenzymes presented the peroxidase (POD)-like activity and the oxidation activity of reduced glutathione (GSH). Accordingly, the dual activities of Co8FeS8@Co1-xS provided a self-cascading platform for producing significant amounts of hydroxyl radical (•OH) and depleting reduced glutathione, thereby inducing tumor cell apoptosis and ferroptosis. More importantly, the Co8FeS8@Co1-xS inhibited the anti-apoptosis protein B-cell lymphoma-2 (Bcl-2) and activated caspase family proteins, which caused tumor cell apoptosis. Simultaneously, Co8FeS8@Co1-xS affected the iron metabolism-related genes such as Heme oxygenase-1 (Hmox-1), amplifying the Fenton response and promoting apoptosis and ferroptosis. Therefore, the nanoenzyme synergistically killed anti-apoptotic tumor cells carrying Kirsten rat sarcoma viral oncogene homolog (KRAS) mutations. Furthermore, Co8FeS8@Co1-xS demonstrated good biocompatibility, which paved the way for constructing a synergistic catalytic nanoplatform for an efficient tumor treatment.

Covalent organic frameworks-derived carbon nanospheres based nanoplatform for tumor specific synergistic therapy via oxidative stress amplification and calcium overload

Combinational therapy in cancer treatment that integrates the merits of different therapies is an effective approach to improve therapeutic outcomes. Herein, a simple nanoplatform (N-CNS-CaO2-HA/Ce6 NCs) that synergized chemodynamic therapy (CDT), photodynamic therapy (PDT), photothermal therapy (PTT), and Ca2+ interference therapy (CIT) has been developed to combat hypoxic tumors. With high photothermal effect, excellent peroxidase-like activity, and inherent mesoporous structure, N-doped carbon nanospheres (N-CNSs) were prepared via in situ pyrolysis of an established nanoscale covalent organic frameworks (COFs) precursor. These N-CNSs acted as PTT/CDT agents and carriers for the photosensitizer chlorin e6 (Ce6), thereby yielding a minimally invasive PDT/PTT/CDT synergistic therapy. Hyaluronic acid (HA)-modified CaO2 nanoparticles (CaO2-HA NPs) coated on the surface of the nanoplatform endowed the nanoplatform with O2/H2O2 self-supply capability to respond to and modulate the tumor microenvironment (TME), which greatly facilitated the tumor-specific performance of CDT and PDT. Moreover, the reactive oxygen species (ROS) produced during PDT and CDT enhanced the Ca2+ overloading due to CaO2 decomposition, amplifying the intracellular oxidative stress and leading to mitochondrial dysfunction. Notably, the HA molecules not only increased the cancer-targeting efficiency but also prevented CaO2 degradation during blood circulation, providing double insurance of tumor-selective CIT. Such a nanotherapeutic system possessed boosted antitumor efficacy with minimized systemic toxicity and showed great potential for treating hypoxic tumors.

Preparation and Application of Carbon Dots Nanozymes

Carbon dot (CD) nanozymes have enzyme-like activity. Compared with natural enzymes, CD nanozymes offer several advantages, including simple preparation, easy preservation, good stability and recycling, which has made them a popular research topic in various fields. In recent years, researchers have prepared a variety of CD nanozymes for biosensing detection, medicine and tumor therapy, and many of them are based on oxidative stress regulation and reactive oxygen species clearance. Particularly to expand their potential applications, elemental doping has been utilized to enhance the catalytic capabilities and other properties of CD nanozymes. This review discusses the prevalent techniques utilized in the synthesis of CD nanozymes and presents the diverse applications of CD nanozymes based on their doping characteristics. Finally, the challenges encountered in the current utilization of CD nanozymes are presented. The latest research progress of synthesis, application and the challenges outlined in the review can help and encourage the researchers for the future research on preparation, application and other related researches of CD nanozymes.

Antioxidant nanozymes as next-generation therapeutics to free radical-mediated inflammatory diseases: A comprehensive review

Recent developments in exploring the biological enzyme mimicking properties in nanozymes have opened a separate avenue, which provides a suitable alternative to the natural antioxidants and enzymes. Due to high and tunable catalytic activity, low cost of synthesis, easy surface modification, and good biocompatibility, nanozymes have garnered significant research interest globally. Several inorganic nanomaterials have been investigated to exhibit catalytic activities of some of the key natural enzymes, including superoxide dismutase (SOD), catalase, glutathione peroxidase, peroxidase, and oxidase, etc. These nanozymes are used for diverse biomedical applications including therapeutics, imaging, and biosensing in various cells/tissues and animal models. In particular, inflammation-related diseases are closely associated with reactive oxygen and reactive nitrogen species, and therefore effective antioxidants could be excellent therapeutics due to their free radical scavenging ability. Although biological enzymes and other artificial antioxidants could perform well in scavenging the reactive oxygen and nitrogen species, however, suffer from several drawbacks such as the requirement of strict physiological conditions for enzymatic activity, limited stability in the environment beyond their optimum pH and temperature, and high cost of synthesis, purification, and storage make then unattractive for broad-spectrum applications. Therefore, this review systematically and comprehensively presents the free radical-mediated evolution of various inflammatory diseases (inflammatory bowel disease, mammary gland fibrosis, and inflammation, acute injury of the liver and kidney, mammary fibrosis, and cerebral ischemic stroke reperfusion) and their mitigation by various antioxidant nanozymes in the biological system. The mechanism of free radical scavenging by antioxidant nanozymes under in vitro and in vivo experimental models and catalytic efficiency comparison with corresponding natural enzymes has also been presented.

Nanozyme-Engineered Hydrogels for Anti-Inflammation and Skin Regeneration

Inflammatory skin disorders can cause chronic scarring and functional impairments, posing a significant burden on patients and the healthcare system. Conventional therapies, such as corticosteroids and nonsteroidal anti-inflammatory drugs, are limited in efficacy and associated with adverse effects. Recently, nanozyme (NZ)-based hydrogels have shown great promise in addressing these challenges. NZ-based hydrogels possess unique therapeutic abilities by combining the therapeutic benefits of redox nanomaterials with enzymatic activity and the water-retaining capacity of hydrogels. The multifaceted therapeutic effects of these hydrogels include scavenging reactive oxygen species and other inflammatory mediators modulating immune responses toward a pro-regenerative environment and enhancing regenerative potential by triggering cell migration and differentiation. This review highlights the current state of the art in NZ-engineered hydrogels (NZ@hydrogels) for anti-inflammatory and skin regeneration applications. It also discusses the underlying chemo-mechano-biological mechanisms behind their effectiveness. Additionally, the challenges and future directions in this ground, particularly their clinical translation, are addressed. The insights provided in this review can aid in the design and engineering of novel NZ-based hydrogels, offering new possibilities for targeted and personalized skin-care therapies.

Nanozymes With Osteochondral Regenerative Effects: An Overview of Mechanisms and Recent Applications

With the discovery of the intrinsic enzyme-like activity of metal oxides, nanozymes garner significant attention due to their superior characteristics, such as low cost, high stability, multi-enzyme activity, and facile preparation. Notably, in the field of biomedicine, nanozymes primarily focus on disease detection, antibacterial properties, antitumor effects, and treatment of inflammatory conditions. However, the potential for application in regenerative medicine, which primarily addresses wound healing, nerve defect repair, bone regeneration, and cardiovascular disease treatment, is garnering interest as well. This review introduces nanozymes as an innovative strategy within the realm of bone regenerative medicine. The primary focus of this approach lies in the facilitation of osteochondral regeneration through the modulation of the pathological microenvironment. The catalytic mechanisms of four types of representative nanozymes are first discussed. The pathological microenvironment inhibiting osteochondral regeneration, followed by summarizing the therapy mechanism of nanozymes to osteochondral regeneration barriers is introduced. Further, the therapeutic potential of nanozymes for bone diseases is included. To improve the therapeutic efficiency of nanozymes and facilitate their clinical translation, future potential applications in osteochondral diseases are also discussed and some significant challenges addressed.

Nanozymes: A comprehensive review on emerging applications in cancer diagnosis and therapeutics

Nanozymes, a new class of nanomaterials-based artificial enzymes, have gained huge attraction due to their high operational stability, working efficiency in extreme conditions, and resistance towards protease digestion. Nowadays, they are effectively substituted for natural enzymes for catalysis by closely resembling the active sites found in natural enzymes. Nanozymes can compensate for natural enzymes' drawbacks, such as high cost, poor stability, low yield, and storage challenges. Due to their transforming nature, nanozymes are of utmost importance in the detection and treatment of cancer. They enable precise cancer detection, tailored drug delivery, and catalytic therapy. Through enhanced diagnosis, personalized therapies, and reduced side effects, their adaptability and biocompatibility can transform the management of cancer. The review focuses on metal and metal oxide-based nanozymes, highlighting their catalytic processes, and their applications in the prevention and treatment of cancer. It emphasizes their potential to alter diagnosis and therapy, particularly when it comes to controlling reactive oxygen species (ROS). The article reveals the game-changing importance of nanozymes in the future of cancer care and describes future research objectives, making it a useful resource for researchers, and scientists. Lastly, outlooks for future perspective areas in this rapidly emerging field have been provided in detail.

Camouflaged Nanoreactors Mediated Radiotherapy-Adjuvant Chemodynamic Synergistic Therapy

Chemodynamic therapy based on the Fenton-like catalysis ability of Fe3O4 has the advantages of no involvement of chemical drugs and minimal adverse effects as well as the limitation of depletable efficacy. Radiotherapy based on high-energy radiation offers the convenience of treatment and cost-effectiveness but lacks precision and cellular adaptation of tumor cells. Approaching such dilemmas from a nanoscale materials perspective, we aim to bridge the weaknesses of both treatment methods by combining the principles of two therapeutics reciprocally. We have designed a camouflaged Fe3O4@HfO2 composite nanoreactor (FHCM), which combines a chemodynamic therapeutic agent Fe3O4 and a radiosensitizer HfO2 that both has passed clinical trials and was inspired by a cell membrane biomimetic technique. FHCM is employed as conceived radiotherapy-adjuvant chemodynamic synergistic therapy of malignant tumors, which has undergone dual scrutiny from both the physical and biological aspects. Experimental results obtained at different levels, including theory, material characterizations, and in vitro and in vivo verifications, suggest that FHCM effectively impaired tumor cells through physical and molecular biological mechanisms involving a HfO2-Fe3O4 photoelectron-electron transfer chain and DNA damage-ferroptosis-immunity chain. It is worth noting that compared to single therapies such as only chemodynamic therapy or radiotherapy, FHCM-mediated radiotherapy-adjuvant chemodynamic synergistic therapy exhibits stronger tumor inhibition efficacy. It significantly addresses the inherent limitations of chemodynamic therapy and radiotherapy and underscores the feasibility and importance of using existing clinical weapons, such as radiotherapy, as auxiliary strategies to overcome certain flaws of emerging antitumor therapeutics like chemodynamic therapy.

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

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

Colorimetric sensor array for discriminating and determinating phenolic pollutants basing on different ratio of ligands in Cu/MOFs

The high toxicity and low biodegradability of the phenolic pollutants destroyed the balance of the environment and influenced human health seriously. Here, we developed a three-dimensional coloremetric sensor array for discriminating and determinating phenolic pollutants basing on the distinct Cu/nucleotides MOFs. Firstly, three laccase-mimic Cu/MOFs (Cu/AMP, Cu/CMP, and Cu/GMP) were obtained by regulating the molar ratio of Cu2+ and nucleotides. Then the Cu/MOFs as the recognition elements of the sensor array catalyzed the pollutants-4-AAP-H2O2 system, obtaining the colored benzoquinone products. Subsequently, the data array obtaining from the combined training matrix (3 Cu/MOFs × 6 pollutants × 5 replicates) was projected into a new dimensional space to obtain the 3D canonical scores, and classified into individual clusters by introducing LDA method. No overlap in their respective LDA plots for the six phenolic pollutants with different concentrations suggested the prominent discriminating performance of the sensor array. Furthermore, the sensor array exhibited high selectivity compared to the "lock-and-key" sensors even other active matrices coexisting in water samples. Importantly, the most influential discrimination factor was used to monitor the levels of the six targets, evidencing the potential application in assessing water pollution and maintaining human health.

Cu-MOF derived CuO@g-C3N4 nanozyme for cascade catalytic colorimetric sensing

The use of peroxidase mimics has great potential for various real applications due to their strong catalytic activity. Herein, a facile strategy was proposed to directly prepare CuO@g-C3N4 by Cu-MOF derivatization and demonstrated its efficacy in constructing a multiple enzymatic cascade system by loading protein enzymes onto it. The resulting CuO@g-C3N4 possessed high peroxidase-like activity, with a Michaelis constant (Km) of 0.25 and 0.16 mM for H2O2 and 3,3',5,5'-tetramethylbenzidine (TMB), respectively. Additionally, the high surface area of CuO@g-C3N4 facilitated the loading of protein enzymes and maintained their activity over an extended period, expanding the potential applications of CuO@g-C3N4. To test its feasibility, CuO@g-C3N4/protein oxidase complex was prepared and used to sense the ripeness and freshness of fruits and meat, respectively. The mechanism relied on the fact that the ripeness of fruits increased and freshness of food decreased with the release of marked targets, such as glucose and xanthine, which could produce H2O2 when digested by the corresponding oxidase. The peroxidase mimics of CuO@g-C3N4 could then sensitively colorimetric detect H2O2 in present of TMB. The obtained CuO@g-C3N4/oxidase complex exhibited an excellent linear response to glucose or xanthine in the range of 1.0-120 μmol/L or 8.0-350 μmol/L, respectively. Furthermore, accurate quantification of glucose and xanthine in real samples is achieved with spiked recoveries ranging from 80.2% to 120.0% and from 94.2% to 112.0%, respectively. Overall, this work demonstrates the potential of CuO@g-C3N4 in various practical applications, such as food freshness detection.

A Covalent Organic Framework Derived N-doped Carbon Nanozyme as the All-rounder for Targeted Catalytic Therapy and NIR-II Photothermal Therapy of Cancer

Nanomaterials with intrinsic enzyme-like activities (nanozymes) have gained significant attention in cancer catalytic therapy; however, developing metal-free nanozymes with multivariant enzyme-like activity as the "all-rounder" for cancer therapy remains challenging. Herein, a covalent organic framework (COF) derived carbon-based nanozyme is rationally devised to achieve synergistic catalytic therapy and second near-infrared (NIR-II) photothermal therapy of cancer. The developed nanozyme possesses multivariant enzyme-like activities, including oxidase (OXD)-like, catalase (CAT)-like, and peroxidase (POD)-like catalytic activities, which enables the nanozyme to produce adequate reactive oxygen species (ROS) for cancer cell killing. Furthermore, the nanozyme showed excellent photothermal converting activity that could kill cancer cells upon NIR-II laser irradiation, owing to the strong NIR-II absorption capacity of carbon-based materials. It is also worth noting that the nanozyme exhibited cytotoxicity specifically in tumor tissue profiting from the discrepant H2O2 level between tumor and normal tissue and the spatiotemporal controllability of laser irradiation. This work may inspire further development of intelligent nanozymes in biological applications across broad therapeutic and biomedical fields.

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).

Colorimetric mercury detection with enhanced sensitivity using magnetic-Au hybrid nanoparticles

Due to the neural toxicity of mercury, there is a need for the development of on-site detection systems for Hg²⁺ monitoring. To this end, a new colorimetric mercury detection probe, Fe₃O₄@SiO₂@Au (magnetic-Au; Mag-Au) hybrid nanoparticles, has been developed. The Au on the surface of Mag-Au is an indicator of Hg²⁺, which forms an AuHg alloy (amalgam) on their surface (Mag-Au@Hg), with excellent peroxidase-like activity. The oxidation of 3,3',5,5'-tetramethylbenzidine by Mag-Au@Hg resulted in a color change of the indicator solution, which was enhanced with increasing Hg²⁺ concentration. Mag-Au can be used to detect Hg²⁺ at nanomolar concentrations. Additionally, magnetic separation can be used to easily purify and concentrate the Mag-Au@Hg from samples, and thus avoid interference from unwanted residues or colored samples. The feasibility of Mag-Au for Hg²⁺ detection was tested with an artificial urine solution and it can be used to detect Hg²⁺ in various real samples, such as river water, seawater, food, and biological samples.

DNA controllable peroxidase-like activity of Ti3C2 nanosheets for colorimetric detection of microcystin-LR

The peroxidase-like activity of Ti₃C₂ nanosheets (Ti₃C₂ NSs) was evaluated by catalytic oxidation of colorless o-phenylenediamine (OPD) into orange-yellow 2,3-diaminophenazine (DAP) with the aid of H₂O₂. The catalytic behavior followed the typical Michaelis-Menten kinetics. Systematic studies about the catalytic activity of Ti₃C₂ NSs including cytochrome C (Cyt C) electron transfer experiments, radical capture experiments, and fluorescence analysis were conducted, revealing that the catalytic mechanism of Ti₃C₂ NSs was attributed to nanozyme-accelerated electron transfer between substrates and nanozyme-promoted generation of active species (superoxide anion free radical (·O₂^-) and holes (h⁺)). Single-stranded DNA (ssDNA) inhibited the peroxidase-like activity of Ti₃C₂ NSs, and the reduced catalytic activity was ascribed to DNA-hindered substrate accessibility to nanozyme surface. Based on the DNA controllable peroxidase-mimicking activity of Ti₃C₂ NSs, taking microcystin-LR (MC-LR) aptamer as an example, a label-free colorimetric aptasensor was proposed for the sensitive detection of MC-LR. The colorimetric aptasensor showed a wide linear range (0.01-60 ng mL^-1), low limit of detection (6.5 pg mL^-1), and high selectivity. The practicality of the colorimetric aptasensor was demonstrated by detecting different levels of MC-LR in spiked real water samples; satisfactory recoveries (97.2-102.1%) and low relative standard deviations (1.16-3.72%) were obtained.

Switchable enzyme mimics based on self-assembled peptides for polyethylene terephthalate degradation

Polyethylene terephthalate (PET), the most abundant polyester plastic, has become a global concern due to its refractoriness and accumulation in the environment. In this study, inspired by the structure and catalytic mechanism of the native enzyme, peptides, based on supramolecular self-assembly, were developed to construct enzyme mimics for PET degradation, which were achieved by combining the enzymatic active sites of serine, histidine and aspartate with the self-assembling polypeptide MAX. The two designed peptides with differences in hydrophobic residues at two positions exhibited a conformational transition from random coil to β-sheet by changing the pH and temperature, and the catalytic activity followed the self-assembly "switch" with the fibrils formed β-sheet, which could catalyze PET efficiently. Although the two peptides possessed same catalytic site, they showed different catalytic activities. Analysis of the structure - activity relationship of the enzyme mimics suggested that the high catalytic activity of the enzyme mimics for PET could be attributed to the formation of stable fibers of peptides and ordered arrangement of molecular conformation; in addition, hydrogen bonding and hydrophobic interactions, as the major forces, promoted effects of enzyme mimics on PET degradation. Enzyme mimics with PET-hydrolytic activity are a promising material for degrading PET and reducing environmental pollution.

Enhancing catalytic efficiency of carbon dots by modulating their Mn doping and chemical structure with metal salts

Nanozymes are emerging materials in various fields owing to their advantages over natural enzymes, such as controllable and facile synthesis, tunability in catalytic activities, cost-effectiveness, and high stability under stringent conditions. In this study, the effect of metal salts on the formation and catalytic activity of carbon dots (CDs), a promising nanozyme, is demonstrated. By introducing Mn sources that possess different counter anions, the chemical structure and composition of the CDs produced are affected, thereby influencing their enzymatic activities. The synergistic catalytic effect of the Mn and N-doped CDs (Mn&N-CDs) is induced by effective metal doping in the carbogenic domain and a high proportion of graphitic and pyridinic N. This highly enhanced catalytic effect of Mn&N-CDs allows them to respond sensitively to the interference factors of enzymatic reactions. Consequently, ascorbic acid, which is an essential nutrient for maintaining our health and is a reactive oxygen scavenger, can be successfully monitored using color change by forming oxidized 3,3',5,5'-tetramethylbenzidine with H₂O₂ and Mn&N-CDs. This study provides a basic understanding of the formation of CDs and how their catalytic properties can be controlled by the addition of different metal sources, thereby providing guidelines for the development of CDs for industrial applications.

Smart Biomimetic Nanozymes for Precise Molecular Imaging: Application and Challenges

New nanotechnologies for imaging molecules are widely being applied to visualize the expression of specific molecules (e.g., ions, biomarkers) for disease diagnosis. Among various nanoplatforms, nanozymes, which exhibit enzyme-like catalytic activities in vivo, have gained tremendously increasing attention in molecular imaging due to their unique properties such as diverse enzyme-mimicking activities, excellent biocompatibility, ease of surface tenability, and low cost. In addition, by integrating different nanoparticles with superparamagnetic, photoacoustic, fluorescence, and photothermal properties, the nanoenzymes are able to increase the imaging sensitivity and accuracy for better understanding the complexity and the biological process of disease. Moreover, these functions encourage the utilization of nanozymes as therapeutic agents to assist in treatment. In this review, we focus on the applications of nanozymes in molecular imaging and discuss the use of peroxidase (POD), oxidase (OXD), catalase (CAT), and superoxide dismutase (SOD) with different imaging modalities. Further, the applications of nanozymes for cancer treatment, bacterial infection, and inflammation image-guided therapy are discussed. Overall, this review aims to provide a complete reference for research in the interdisciplinary fields of nanotechnology and molecular imaging to promote the advancement and clinical translation of novel biomimetic nanozymes.

A High Catalytic Activity Nanozyme Based on Cobalt-Doped Carbon Dots for Biosensor and Anticancer Cell Effect

Nanozyme technology as an emerging field has been successfully applied to chemical sensing, biomedicine, and environmental monitoring. It is very significant for the advance of this field to construct nanozymes with high catalytic activity by a simple method and to develop their multifunctional applications. Here, a new type of cobalt-doped carbon dots (Co-CDs) nanozymes was designed using vitamin B₁₂ and citric acid as the precursors. The homogeneous cobalt doping at carbon nuclear led the Co-CDs to show significant peroxidase-like activity resembling natural metalloenzymes. Based on the high affinity of Co-CDs to H₂O₂ (K_m = 0.0598 mM), a colorimetric sensor for glucose detection was constructed by combining Co-CDs with glucose oxidase. On account of the high catalytic activity of nanozymes and the cascade strategy, a good linear relationship was obtained from 0.500 to 200 μM, with a detection limit of 0.145 μM. The biosensor has realized the accurate detection of glucose in human serum samples. Moreover, Co-CDs could specifically catalyze H₂O₂ in cancer cells to generate a variety of reactive oxygen species, leading to the death of cancer cells, which has useful application potential in tumor catalytic therapy. In this work, the catalytic activity of Co-CDs has been adequately exploited, which extends the application of carbon dots in multiple biotechnologies, including biosensing, disease diagnosis, and treatment.

Manganese-Based Nanozymes: Preparation, Catalytic Mechanisms, and Biomedical Applications

Manganese (Mn) has attracted widespread attention due to its low-cost, nontoxicity, and valence-rich transition. Various Mn-based nanomaterials have sprung up and are employed in diverse fields, particularly Mn-based nanozymes, which combine the physicochemical properties of Mn-based nanomaterials with the catalytic activity of natural enzymes, and are attracting a surge of research, especially in the field of biomedical research. In this review, the typical preparation strategies, catalytic mechanisms, advances and perspectives of Mn-based nanozymes for biomedical applications are systematically summarized. The application of Mn-based nanozymes in tumor therapy and sensing detection, together with an overview of their mechanism of action is highlighted. Finally, the prospective directions of Mn-based nanozymes from five perspectives: innovation, activity enhancement, selectivity, biocompatibility, and application broadening are discussed.

π-Conjugated Copper Phthalocyanine Nanoparticles as Highly Sensitive Sensor for Colorimetric Detection of Biomarkers

Though numerous nanomaterials with enzyme-like activities have been utilized as probes and sensors for detecting biological molecules, it is still challenging to construct highly sensitive detectors for biomarkers using polymeric materials. Benefiting from the π-d delocalization effect of electrons, excellent metal-chelating property, high electron transferability, and good chemical stability of π-conjugated phthalocyanine, the design of the copper phthalocyanine-based conjugated polymer nanoparticles (Cu-PcCP NPs) as a colorimetric sensor for a variety of biomarkers is reported. The Cu-PcCP NPs are synthesized through a simple microwave-assisted polymerization, and their chemical structures are thoroughly characterized. The colorimetric results of Cu-PcCP NPs demonstrate excellent peroxidase-like detecting activity and also great substrate selectivity than most of the reported Cu-based nanomaterials. The Cu-PcCP NPs can achieve a detection limit of 4.88 μM for the H₂ O₂ , 4.27 μM for the L-cysteine, and 21.10 μM for the glucose via a cascade catalytic system, which shows comparable detecting sensitivity as that of many earlier reported enzyme-like nanomaterials. Moreover, Cu-PcCP NPs present remarkable resistance to harsh conditions, including high temperature, low pH, and excessive salts. These highly specific π-conjugated copper-phthalocyanine nanoparticles not only overcome the current limitation of polymeric material-based sensors but also provide a new direction for designing next-generation enzyme-like nanomaterial-based colorimetric biosensors.

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.

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

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

In situ generated Fe3C embedded Fe-N-doped carbon nanozymes with enhanced oxidase mimic activity for total antioxidant capacity assessment

In this work, we reported new Fe₃C embedded Fe-N-doped carbon nanomaterials (Fe₃C@Fe-N-CMs) generated in situ by the facile pyrolysis of Fe-Zn ZIF precursors. The resulting Fe₃C@Fe-N-CMs were equipped with several desirable nanozyme features, including multiple efficient intrinsic active sites (i.e. Fe-N_x, Fe₃C@C, and C-N moieties), large specific surface area and abundant mesoporous structures. As a result, these Fe₃C@Fe-N-CMs displayed exceptional ability to mimic three enzymes: peroxidase, catalase and oxidase, while the Fe₃C@Fe-N-CMs pyrolyzed at 800 °C, named CMs-800, showed the best enzyme-like properties. After systematically investigating the catalytic mechanism, we further explored the application of the oxidase-like properties of CMs-800 in the detection of the total antioxidant capacity (TAC) in beverages and tablets. This study not only provided a new approach to construct multifunctional carbon-based nanozymes, but also expanded the application of carbon nanozymes in the field of food quality and safety.

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.