An Enzyme‐Mimicking Single‐Atom Catalyst as an Efficient Multiple Reactive Oxygen and Nitrogen Species Scavenger for Sepsis Management

A Nanozyme-Based Electrode for High-Performance Neural Recording

Implanted neural electrodes have been widely used to treat brain diseases that require high sensitivity and biocompatibility at the tissue-electrode interface. However, currently used clinical electrodes cannot meet both these requirements simultaneously, which hinders the effective recording of electronic signals. Herein, nanozyme-based neural electrodes incorporating bioinspired atomically precise clusters are developed as a general strategy with a heterogeneous design for multiscale and ultrasensitive neural recording via quantum transport and biocatalytic processes. Owing to the dual high-speed electronic and ionic currents at the electrode-tissue interface, the impedance of nanozyme electrodes is 26 times lower than that of state-of-the-art metal electrodes, and the acquisition sensitivity for the local field potential is ≈10 times higher than that of clinical PtIr electrodes, enabling a signal-to-noise ratio (SNR) of up to 14.7 dB for single-neuron recordings in rats. The electrodes provide more than 100-fold higher antioxidant and multi-enzyme-like activities, which effectively decrease 67% of the neuronal injury area by inhibiting glial proliferation and allowing sensitive and stable neural recording. Moreover, nanozyme electrodes can considerably improve the SNR of seizures in acute epileptic rats and are expected to achieve precise localization of seizure foci in clinical settings.

Self-Cascade Redox Modulator Trilogically Renovates Intestinal Microenvironment for Mitigating Endotoxemia

Endotoxemia is a life-threatening multiple organ failure disease caused by bacterial endotoxin infection. Unfortunately, current single-target therapy strategies have failed to prevent the progression of endotoxemia. Here, we reported that alanine fullerene redox modulator (AFRM) remodeled the intestinal microenvironment for multiple targets endotoxemia mitigation by suppressing inflammatory macrophages, inhibiting macrophage pyroptosis, and repairing epithelial cell barrier integrity. Specifically, AFRM exhibited broad-spectrum and self-cascade redox regulation properties with superoxide dismutase (SOD)-like enzyme, peroxidase (POD)-like enzyme activity, and hydroxyl radical (•OH) scavenging ability. Guided by proteomics, we demonstrated that AFRM regulated macrophage redox homeostasis and down-regulated LPS/TLR4/NF-κB and MAPK/ERK signaling pathways to suppress inflammatory hyperactivation. Of note, AFRM could attenuate inflammation-induced macrophage pyroptosis via inhibiting the activation of gasdermin D (GSDMD). In addition, our results revealed that AFRM could restore extracellular matrix and cell-tight junction proteins and protect the epithelial cell barrier integrity by regulating extracellular redox homeostasis. Consequently, AFRM inhibited systemic inflammation and potentiated intestinal epithelial barrier damage repair during endotoxemia in mice. Together, our work suggested that fullerene based self-cascade redox modulator has the potential in the management of endotoxemia through synergistically remodeling the inflammation and epithelial barriers in the intestinal microenvironment.

Multi-Enzyme Co-Expressed Nanomedicine for Anti-Metastasis Tumor Therapy by Up-Regulating Cellular Oxidative Stress and Depleting Cholesterol

Tumor cells movement and migration are inseparable from the integrity of lipid rafts and the formation of lamellipodia, and lipid rafts are also a prerequisite for the formation of lamellipodia. Therefore, destroying the lipid rafts is an effective strategy to inhibit tumor metastasis. Herein, a multi-enzyme co-expressed nanomedicine: cholesterol oxidase (CHO) loaded Co─PN3 single-atom nanozyme (Co─PN3 SA/CHO) that can up-regulate cellular oxidative stress, disrupt the integrity of lipid rafts, and inhibit lamellipodia formation to induce anti-metastasis tumor therapy, is developed. In this process, Co─PN3 SA can catalyze oxygen (O2 ) and hydrogen peroxide (H2 O2 ) to generate reactive oxygen species (ROS) via oxidase-like and Fenton-like properties. The doping of P atoms optimizes the adsorption process of the intermediate at the active site and enhances the ROS generation properties of nanomedicine. Meantime, O2 produced by catalase-like catalysis can combine with excess cholesterol to generate more H2 O2 under CHO catalysis, achieving enhanced oxidative damage to tumor cells. Most importantly, cholesterol depletion in tumor cells also disrupts the integrity of lipid rafts and inhibits the formation of lamellipodia, greatly inhibiting the proliferation and metastasis of tumor cells. This strategy by up-regulating cellular oxidative stress and depleting cellular cholesterol constructs a new idea for anti-metastasis-oriented cancer therapy strategies.

Nanocellulose/Fe3O4/Ag Nanozyme with Robust Peroxidase Activity for Enhanced Antibacterial and Wound Healing Applications

Peroxidase memetic nanozymes with their free radical-mediated catalytic actions proved as efficacious antibacterial agents for combating bacterial resistance. Herein, nanocellulose (NC) extracted from Eragrostis teff straw was used to prepare NC/Fe3O4/Ag peroxidase nanozyme as an antibacterial and wound healing agent. Characterization of the nanozyme with XRD, FTIR, SEM-EDX, and XPS confirmed the presence of silver NPs and the magnetite phase of iron oxide dispersed on nanocellulose. The peroxidase activity of the prepared nanozyme was examined using TMB and H2O2 as substrates which turned blue in acidic pH (λmax = 652 nm). With a lower Km (0.387 mM), the nanozyme showed a comparable affinity for TMB with that reported for the HRP enzyme. Furthermore, the nanozyme remained efficient over a broader temperature range while maintaining 61.53% of its activity after the fourth cycle. In vitro, antibacterial tests against Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) bacterial strains showed that NC/Fe3O4/Ag exhibits concentration-dependent and enhanced antibacterial effect for Escherichia coli compared to NC and NC-Fe3O4 and negative control. Furthermore, the wound-healing performance of the NC-Fe3O4-Ag nanozyme was investigated in vivo using an animal model (mice). The nanozyme showed 30% higher wound healing performance compared to the control base ointment and is comparable with the commercial nitrofurazone ointment. The results show the potential of the prepared nanozyme for wound-healing purposes.

Nanomedicine-Enabled Chemical Regulation of Reactive X Species for Versatile Disease Treatments

Reactive X species (RXS), encompassing elements such as O, N, C, S, Se, Cl, Br, I, and H, play vital roles in cell biology and physiological function, impacting cellular signal transduction, metabolic regulation, and disease processes. The redox unbalance of RXS is firmly implicated in an assortment of physiological and pathological disorders, including cancer, diabetes, cardiovascular disease, and neurodegenerative diseases. However, the intricate nature and multifactorial dependence of RXS pose challenges in comprehending and precisely modulating their biological behavior. Nanomaterials with distinct characteristics and biofunctions offer promising avenues for generating or scavenging RXS to maintain redox homeostasis and advance disease therapy. This minireview provides a tutorial summary of the relevant chemistry and specific mechanisms governing different RXS, focusing on cellular metabolic regulation, stress responses, and the role of nanomedicine in RXS generation and elimination. The challenges associated with chemically regulating RXS for diverse disease treatments are further discussed along with the future prospects, aiming to facilitate the clinical translation of RXS-based nanomedicine and open new avenues for improved therapeutic interventions.

Zn-Shik-PEG nanoparticles alleviate inflammation and multi-organ damage in sepsis

Sepsis is defined as a life-threatening organ dysfunction caused by excessive formation of reactive oxygen species (ROS) and dysregulated inflammatory response. Previous studies have reported that shikonin (Shik) possess prominent anti-inflammatory and antioxidant effects and holds promise as a potential therapeutic drug for sepsis. However, the poor water solubility and the relatively high toxicity of shikonin hamper its clinical application. To address this challenge, we constructed Zn2+-shikonin nanoparticles, hereafter Zn-Shik-PEG NPs, based on an organic-inorganic hybridization strategy of metal-polyphenol coordination to improve the aqueous solubility and biosafety of shikonin. Mechanistic studies suggest that Zn-Shik-PEG NPs could effectively clear intracellular ROS via regulating the Nrf2/HO-1 pathway, meanwhile Zn-Shik-PEG NPs could inhibit NLRP3 inflammasome-mediated activation of inflammation and apoptosis by regulating the AMPK/SIRT1 pathway. As a result, the Zn-Shik-PEG NPs demonstrated excellent therapeutic efficacies in lipopolysaccharide (LPS) as well as cecal ligation puncture (CLP) induced sepsis model. These findings suggest that Zn-Shik-PEG NPs may have therapeutic potential for the treatment of other ROS-associated and inflammatory diseases.

Diatomic iron nanozyme with lipoxidase-like activity for efficient inactivation of enveloped virus

Enveloped viruses encased within a lipid bilayer membrane are highly contagious and can cause many infectious diseases like influenza and COVID-19, thus calling for effective prevention and inactivation strategies. Here, we develop a diatomic iron nanozyme with lipoxidase-like (LOX-like) activity for the inactivation of enveloped virus. The diatomic iron sites can destruct the viral envelope via lipid peroxidation, thus displaying non-specific virucidal property. In contrast, natural LOX exhibits low antiviral performance, manifesting the advantage of nanozyme over the natural enzyme. Theoretical studies suggest that the Fe-O-Fe motif can match well the energy levels of Fe2 minority β-spin d orbitals and pentadiene moiety π* orbitals, and thus significantly lower the activation barrier of cis,cis-1,4-pentadiene moiety in the vesicle membrane. We showcase that the diatomic iron nanozyme can be incorporated into air purifier to disinfect airborne flu virus. The present strategy promises a future application in comprehensive biosecurity control.

Spatial Position Regulation of Cu Single Atom Site Realizes Efficient Nanozyme Photocatalytic Bactericidal Activity

Recently, single-atom nanozymes have made significant progress in the fields of sterilization and treatment, but their catalytic performance as substitutes for natural enzymes and drugs is far from satisfactory. Here, a method is reported to improve enzyme activity by adjusting the spatial position of a single-atom site on the nanoplatforms. Two types of Cu single-atom site nanozymes are synthesized in the interlayer (CuL /PHI) and in-plane (CuP /PHI) of poly (heptazine imide) (PHI) through different synthesis pathways. Experimental and theoretical analysis indicates that the interlayer position of PHI can effectively adjust the coordination number, coordination bond length, and electronic structure of Cu single atoms compared to the in-plane position, thereby promoting photoinduced electron migration and O2 activation, enabling effective generate reactive oxygen species (ROS). Under visible light irradiation, the photocatalytic bactericidal activity of CuL /PHI against aureus is ≈100%, achieving the same antibacterial effect as antibiotics, after 10 min of low-dose light exposure and 2 h of incubation.

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

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

Single-atom catalysts-based catalytic ROS clearance for efficient psoriasis treatment and relapse prevention via restoring ESR1

Psoriasis is a common inflammatory disease of especially high recurrence rate (90%) which is suffered by approximately 3% of the world population. The overexpression of reactive oxygen species (ROS) plays a critical role in psoriasis progress. Here we show that biomimetic iron single-atom catalysts (FeN4O2-SACs) with broad-spectrum ROS scavenging capability can be used for psoriasis treatment and relapse prevention via related gene restoration. FeN4O2-SACs demonstrate attractive multiple enzyme-mimicking activities based on atomically dispersed Fe active structures, which are analogous to those of natural antioxidant enzymes, iron superoxide dismutase, human erythrocyte catalase, and ascorbate peroxidase. Further, in vitro and in vivo experiments show that FeN4O2-SACs can effectively ameliorate psoriasis-like symptoms and prevent the relapse with augmented efficacy compared with the clinical drug calcipotriol. Mechanistically, estrogen receptor 1 (ESR1) is identified as the core protein upregulated in psoriasis treatment through RNA sequencing and bioinformatic analysis. Together, this study provides a proof of concept of psoriasis catalytic therapy (PCT) and multienzyme-inspired bionics (MIB).

Single-atom nanozymes: classification, regulation strategy, and safety concerns

Nanozymes, nanomaterials possessing enzymatic activity, have been studied extensively by researchers. However, their complex composition, low density of active sites, and inadequate substrate selectivity have hindered the maturation and widespread acceptance of nanozymes. Single-atom nanozymes (SAzymes) with atomically dispersed active sites are leading the field of catalysis due to their exceptional performance. The maximum utilization rate of atoms, low cost, well-defined coordination structure, and active sites are the most prominent advantages of SAzymes that researchers favor. This review systematically categorizes SAzymes based on their support type and describes their specific applications. Additionally, we discuss regulation strategies for SAzyme activity and provide a comprehensive summary of biosafety challenges associated with these enzymes.

Reactive X (where X = O, N, S, C, Cl, Br, and I) species nanomedicine

Reactive oxygen, nitrogen, sulfur, carbonyl, chlorine, bromine, and iodine species (RXS, where X = O, N, S, C, Cl, Br, and I) have important roles in various normal physiological processes and act as essential regulators of cell metabolism; their inherent biological activities govern cell signaling, immune balance, and tissue homeostasis. However, an imbalance between RXS production and consumption will induce the occurrence and development of various diseases. Due to the considerable progress of nanomedicine, a variety of nanosystems that can regulate RXS has been rationally designed and engineered for restoring RXS balance to halt the pathological processes of different diseases. The invention of radical-regulating nanomaterials creates the possibility of intriguing projects for disease treatment and promotes advances in nanomedicine. In this comprehensive review, we summarize, discuss, and highlight very-recent advances in RXS-based nanomedicine for versatile disease treatments. This review particularly focuses on the types and pathological effects of these reactive species and explores the biological effects of RXS-based nanomaterials, accompanied by a discussion and the outlook of the challenges faced and future clinical translations of RXS nanomedicines.

Artificial Peroxisome hNiPt@Co-NC with Tetra-enzyme Activities for Colorimetric Glutathione Sensing

Artificial peroxisome plays an important part in protocell system construction and disease therapy. However, it remains an enormous challenge to exploit a practicable artificial peroxisome with multiple and stable activities. Nanozymes with multienzyme mimetic activities stand out for artificial peroxisome preparation. Herein, a novel nanozyme─Co-nanoparticle-embedded N-enriched carbon nanocubes (Co,N-CNC) decorated by hollow NiPt nanospheres (hNiPt@Co-NC) with featured tetra-enzyme mimetic activities of natural peroxisome─was prepared. Due to the synergistic effect of hollow NiPt nanospheres (hNiPtNS) and cubic porous Co,N-CNC support, hNiPt@Co-NC exhibited oxidase (OXD), peroxidase (POD), catalase (CAT), and superoxide dismutase (SOD)-like activities with comparable catalytic efficiency, enabling it to be a competitive candidate for artificial peroxisome investigation. Based on the high OXD-mimetic activity of hNiPt@Co-NC, a facile colorimetric platform was proposed for reduced glutathione (GSH) detection with a wide linear range (0.1-5 μM, 5-100 μM) and a low detection limit (27 nM). Thus, the hNiPt@Co-NC with tetra-enzyme mimetic activities possessed bright prospects in diversified biotechnological applications, including artificial organelles, biosensing, and medical diagnostics.

Reactive oxygen nanobiocatalysts: activity-mechanism disclosures, catalytic center evolutions, and changing states

Benefiting from low costs, structural diversities, tunable catalytic activities, feasible modifications, and high stability compared to the natural enzymes, reactive oxygen nanobiocatalysts (RONBCs) have become dominant materials in catalyzing and mediating reactive oxygen species (ROS) for diverse biomedical and biological applications. Decoding the catalytic mechanism and structure-reactivity relationship of RONBCs is critical to guide their future developments. Here, this timely review comprehensively summarizes the recent breakthroughs and future trends in creating and decoding RONBCs. First, the fundamental classification, activity, detection method, and reaction mechanism for biocatalytic ROS generation and elimination have been systematically disclosed. Then, the merits, modulation strategies, structure evolutions, and state-of-art characterisation techniques for designing RONBCs have been briefly outlined. Thereafter, we thoroughly discuss different RONBCs based on the reported major material species, including metal compounds, carbon nanostructures, and organic networks. In particular, we offer particular insights into the coordination microenvironments, bond interactions, reaction pathways, and performance comparisons to disclose the structure-reactivity relationships and mechanisms. In the end, the future challenge and perspectives for RONBCs are also carefully summarised. We envision that this review will provide a comprehensive understanding and guidance for designing ROS-catalytic materials and stimulate the wide utilisation of RONBCs in diverse biomedical and biological applications.

Three-in-one covalent organic framework nanozyme: Self-reporting, self-correcting and light-responsive for fluorescence sensing 3-nitrotyrosine

Most current redox-type nanozyme-based colorimetric sensing platforms are susceptible to interference from the reductant when using chromogenic probe, and the unstable H2O2 used in the peroxidase-like nanozyme-based systems is prone to difficulty in sensing signal reproducibility, while peroxidase-like nanozyme with oxidase-mimicking activity is easy to bring background interference by O2. Since the strong structural designability of covalent organic frameworks (COFs) endows them great application value in the sensing fields, therefore, we envision the construction a COF oxidase-like nanozyme-based controllable sensing system that integrates self-reporting, self-correcting and light-responsive functions to avoid these affects. Herein, 3-nitrotyrosine (3-NT) biomarker was selected as model analyte. 1,3,5-triformylphloroglucinol (Tp) and 3,6-diaminoacridine (DA) were acted as building monomers of the multifunctional COF nanozyme (termed as TpDA). Owing to the excellent light-responsive oxidase-mimicking property of TpDA, 3-NT can be efficiently oxidized, the inner filter effect (IFE) between TpDA and the 3-NT oxidation product greatly quenches the intrinsic fluorescence of TpDA, making it a controllable self-reporting system for fluorescence turn-off sensing 3-NT. Additionally, the excessive reactive oxygen species (ROS) that generated continuously during photocatalysis can resist the interference of endogenous reductants. This study not only provides new insights to avoid the interference of H2O2, background and reductants from conventional redox-type nanozyme-based colorimetric systems but also opens avenues to rational construct versatile COF nanozyme-based sensor.

Multifunctional nanozyme-reinforced copper-coordination polymer nanoparticles for drug-resistance bacteria extinction and diabetic wound healing

BACKGROUND

Drug-resistant bacterial infections in chronic wounds are a persistent issue, as they are resistant to antibiotics and can cause excessive inflammation due to generation of reactive oxygen species (ROS). An effective solution would be to not only combat bacterial infections but also scavenge ROS to relieve inflammation at the wound site. Scaffolds with antioxidant properties are attractive for their ability to scavenge ROS, and there is medical demand in developing antioxidant enzyme-mimicking nanomaterials for wound healing.

METHODS

In this study, we fabricated copper-coordination polymer nanoparticles (Cu-CPNs) through a self-assembly process. Furthermore, ε-polylysine (EPL), an antibacterial and cationic polymer, was integrated into the Cu-CPNs structure through a simple one-pot self-assembly process without sacrificing the glutathione peroxidase (GPx) and superoxide dismutase (SOD)-mimicking activity of Cu-CPNs.

RESULTS

The resulting Cu-CPNs exhibit excellent antioxidant propertiesin mimicking the activity of glutathione peroxidase and superoxide dismutase and allowing them to effectively scavenge harmful ROS produced in wound sites. The in vitro experiments showed that the resulting Cu-CPNs@EPL complex have superior antioxidant properties and antibacterial effects. Bacterial metabolic analysis revealed that the complex mainly affects the cell membrane integrity and nucleic acid synthesis that leads to bacterial death.

CONCLUSIONS

The Cu-CPNs@EPL complex has impressive antioxidant properties and antibacterial effects, making it a promising solution for treating drug-resistant bacterial infections in chronic wounds. The complex's ability to neutralize multiple ROS and reduce ROS-induced inflammation can help relieve inflammation at the wound site. Schematic illustration of the ROS scavenging and bacteriostatic function induced by Cu-CPNs@EPL nanozyme in the treatment of MRSA-infected wounds.

Atomization-Induced High Intrinsic Activity of a Biocompatible MgAl-LDH Supported Ru Single-Atom Nanozyme for Efficient Radicals Scavenging

Developing efficient nanozymes to mimic natural enzymes for scavenging reactive radicals remains a significant challenge owing to the insufficient activity of conventional nanozymes. Herein, we report a novel Ru single-atom nanozyme (SAE), featuring atomically dispersed Ru atoms on a biocompatible MgAl-layered double hydroxide (Ru1 /LDH). The prepared Ru1 /LDH SAE shows high intrinsic peroxidase (POD)-like catalytic activity, which outperforms the Ru nanoclusters (NCs) nanozyme by a factor of 20 and surpasses most SAEs. The density functional theory calculations reveal that the high intrinsic POD-like activity of Ru1 /LDH can be attributed to a heterolytic path of H2 O2 dissociation on the single Ru sites, which requires lower free energy (0.43 eV) compared to the homolytic path dissociation on Ru NC (0.63 eV). In addition, the Ru1 /LDH SAE shows excellent multiple free radicals scavenging ability, including superoxide anion radical (O2 ⋅- ), hydroxyl radical (⋅OH), nitric oxide radical (NO⋅) and 2, 2-diphenyl-1-picrylhydrazyl radical (DPPH⋅). Given the advantages of Ru1 /LDH with high enzymatic activities, biosafety, and ease to scale up, it paves the way for exploring SAEs in the practical biological immunity system.

Copper-Single-Atom Coordinated Nanotherapeutics for Enhanced Sonothermal-Parallel Catalytic Synergistic Cancer Therapy

Phototherapy and sonotherapy are recognized by scientific medicine as effective strategies for treating certain cancers. However, these strategies have limitations such as an inability to penetrate deeper tissues and overcome the antioxidant tumor microenvironment. In this study, a novel "BH" interfacial-confined coordination strategy to synthesize hyaluronic acid-functionalized single copper atoms dispersed over boron imidazolate framework-derived nanocubes (HA-NC_Cu) to achieve sonothermal-catalytic synergistic therapy is reported. Notably, HA-NC_Cu demonstrates exceptional sonothermal conversion performance under low-intensity ultrasound irradiation, attained through intermolecular lattice vibrations. In addition, it shows promise as an efficient biocatalyst, able to generate high-toxicity hydroxyl radicals in response to tumor-endogenous hydrogen peroxide and glutathione. Density functional theory calculations reveal that the superior parallel catalytic performance of HA-NC_Cu originates from the CuN4 C/B active sites. Both in vitro and in vivo evaluations consistently demonstrate that the sonothermal-catalytic synergistic strategy significantly improves tumor inhibition rate (86.9%) and long-term survival rate (100%). In combination with low-intensity ultrasound irradiation, HA-NC_Cu triggers a dual death pathway of apoptosis and ferroptosis in MDA-MB-231 breast cancer cells, comprehensively limiting primary triple-negative breast cancer. This study highlights the applications of single-atom-coordinated nanotherapeutics in sonothermal-catalytic synergistic therapy, which may create new opportunities in biomedical research.

Nanozyme-Based Supramolecular Self-Assembly As an Artificial Host Defense System For Treatment of Bacterial Infections

The proper functioning of host defense system (HDS) is the key to combating bacterial infection in biological organisms. However, the delicate HDS may be dysfunctional or dysregulated, resulting in persistent infection, tissue damage, or delayed wound healing. Herein, a powerful artificial "host defense system" (aHDS) is designed and constructed for treatment of bacterial infections. First, the aHDS can quickly trap the bacteria by electrostatic interactions. Next, the system can be stimulated to produce large amounts of cytotoxic reactive oxygen species (ROS) and exert strong antibacterial effects, which can further regulate the immune microenvironment, leading to macrophage polarization from M0 to pro-inflammatory phenotype (M1) for synergistic bacteria killing. At the later stages, the system can exhibit excellent antioxidant enzyme-like activities to reprogram the M1 macrophage to anti-inflammatory phenotype (M2) for accelerating wound healing. This powerful aHDS can effectively combat the bacteria and avoid excessive inflammatory responses for the treatment of bacteria-infected wounds.

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.

Cascade nanozymatic network mimicking cells with selective and linear perception of H2O2

A single stimulus leading to multiple responses is an essential function of many biological networks, which enable complex life activities. However, it is challenging to duplicate a similar chemical reaction network (CRN) using non-living chemicals, aiming at the disclosure of the origin of life. Herein, we report a nanozyme-based CRN with feedback and feedforward functions for the first time. It demonstrates multiple responses at different modes and intensities upon a single H₂O₂ stimulus. In the two-electron cascade oxidation of 3,3',5,5'-tetramethylbenzidine (TMB), the endogenous product H₂O₂ competitively inhibited substrates in the first one-electron oxidation reaction on a single-atom nanozyme (Co-N-CNTs) and strikingly accelerated the second one-electron oxidation reaction under a micellar nanozyme. As a proof-of-concept, we further confined the nanozymatic network to a microfluidic chip as a simplified artificial cell. It exhibited remarkable selectivity and linearity in the perception of H₂O₂ stimulus against more than 20 interferences in a wide range of concentrations (0.01-100 mM) and offered an instructive platform for studying primordial life-like processes.

Copper-Zinc Bimetallic Single-Atom Catalysts with Localized Surface Plasmon Resonance-Enhanced Photothermal Effect and Catalytic Activity for Melanoma Treatment and Wound-Healing

Nanomaterials with photothermal combined chemodynamic therapy (PTT-CDT) have attracted the attention of researchers owing to their excellent synergistic therapeutic effects on tumors. Thus, the preparation of multifunctional materials with higher photothermal conversion efficiency and catalytic activity can achieve better synergistic therapeutic effects for melanoma. In this study, a Cu-Zn bimetallic single-atom (Cu/PMCS) is constructed with augmented photothermal effect and catalytic activity due to the localized surface plasmon resonance (LSPR) effect. Density functional theory calculations confirmed that the enhanced photothermal effect of Cu/PMCS is due to the appearance of a new d-orbital transition with strong spin-orbit coupling and the induced LSPR. Additionally, Cu/PMCS exhibited increased catalytic activity in the Fenton-like reaction and glutathione depletion capacity, further enhanced by increased temperature and LSPR. Consequently, Cu/PMCS induced better synergistic anti-melanoma effects via PTT-CDT than PMCS in vitro and in vivo. Furthermore, compared with PMCS, Cu/PMCS killed bacteria more quickly and effectively, thus facilitating wound healing owing to the enhanced photothermal effect and slow release of Cu2+ . Cu/PMCS promoted cell migration and angiogenesis and upregulated the expression of related genes to accelerate wound healing. Cu/PMCS has potential applications in treating melanoma and repairing wounds with its antitumor, antibacterial, and wound-healing properties.

Artificial-enzymes-armed Bifidobacterium longum probiotics for alleviating intestinal inflammation and microbiota dysbiosis

Inflammatory bowel disease can be caused by the dysfunction of the intestinal mucosal barrier and dysregulation of gut microbiota. Traditional treatments use drugs to manage inflammation with possible probiotic therapy as an adjuvant. However, current standard practices often suffer from metabolic instability, limited targeting and result in unsatisfactory therapeutic outcomes. Here we report on artificial-enzyme-modified Bifidobacterium longum probiotics for reshaping a healthy immune system in inflammatory bowel disease. Probiotics can promote the targeting and retention of the biocompatible artificial enzymes to persistently scavenge elevated reactive oxygen species and alleviate inflammatory factors. The reduced inflammation caused by artificial enzymes improves bacterial viability to rapidly reshape the intestinal barrier functions and restore the gut microbiota. The therapeutic effects are demonstrated in murine and canine models and show superior outcomes to traditional clinical drugs.

Engineering Cell Membrane-Cloaked Catalysts as Multifaceted Artificial Peroxisomes for Biomedical Applications

Artificial peroxisomes (APEXs) or peroxisome mimics have caught a lot of attention in nanomedicine and biomaterial science in the last decade, which have great potential in clinically diagnosing and treating diseases. APEXs are typically constructed from a semipermeable membrane that encloses natural enzymes or enzyme-mimetic catalysts to perform peroxisome-/enzyme-mimetic activities. The recent rapid progress regarding their biocatalytic stability, adjustable activity, and surface functionality has significantly promoted APEXs systems in real-life applications. In addition, developing a facile and versatile system that can simulate multiple biocatalytic tasks is advantageous. Here, the recent advances in engineering cell membrane-cloaked catalysts as multifaceted APEXs for diverse biomedical applications are highlighted and commented. First, various catalysts with single or multiple enzyme activities have been introduced as cores of APEXs. Subsequently, the extraction and function of cell membranes that are used as the shell are summarized. After that, the applications of these APEXs are discussed in detail, such as cancer therapy, antioxidant, anti-inflammation, and neuron protection. Finally, the future perspectives and challenges of APEXs are proposed and outlined. This progress review is anticipated to provide new and unique insights into cell membrane-cloaked catalysts and to offer significant new inspiration for designing future artificial organelles.

Manganese-Based Antioxidase-Inspired Biocatalysts with Axial Mn-N5 Sites and 2D d-π-Conjugated Networks for Rescuing Stem Cell Fate

Constructing highly effective biocatalysts with controllable coordination geometry for eliminating reactive oxygen species (ROS) to address the current bottlenecks in stem-cell-based therapeutics remains challenging. Herein, inspired by the coordination structure of manganese-based antioxidase, we report a manganese-coordinated polyphthalocyanine-based biocatalyst (Mn-PcBC) with axial Mn-N5 sites and 2D d-π-conjugated networks that serves as an artificial antioxidase to rescue stem cell fate. Owing to the unique chemical and electronic structures, Mn-PcBC displays efficient, multifaceted, and robust ROS-scavenging activities, including elimination of H2 O2 and O2 ⋅- . Consequently, Mn-PcBC efficiently rescues the bioactivity and functionality of stem cells in high-ROS-level microenvironments by protecting the transcription of osteogenesis-related genes. This study offers essential insight into the crucial functions of axially coordinated Mn-N5 sites in ROS scavenging and suggests new strategies to create efficient artificial antioxidases for stem-cell therapies.

Metal-Organic Framework Functionalized Bioceramic Scaffolds with Antioxidative Activity for Enhanced Osteochondral Regeneration

Osteoarthritis (OA) is a degenerative disease that often causes cartilage lesions and even osteochondral damage. Osteochondral defects induced by OA are accompanied by an inflammatory arthrosis microenvironment with overproduced reactive oxygen species (ROS), resulting in the exacerbation of defects and difficulty regenerating osteochondral tissues. Therefore, it is urgently needed to develop osteochondral scaffolds that can not only promote the integrated regeneration of cartilage and subchondral bone, but also possess ROS-scavenging ability to protect tissues from oxidative stress. Herein, zinc-cobalt bimetallic organic framework (Zn/Co-MOF) functionalized bioceramic scaffolds are designed for repairing osteochondral defects under OA environment. By functionalizing Zn/Co-MOF on the 3D-printed beta-tricalcium phosphate (β-TCP) scaffolds, the Zn/Co-MOF functionalized β-TCP (MOF-TCP) scaffolds with broad-spectrum ROS-scavenging ability are successfully developed. Benefiting from its catalytic active sites and degradation products, Zn/Co-MOF endows the scaffolds with excellent antioxidative and anti-inflammatory properties to protect cells from ROS invasion, as well as dual-bioactivities of simultaneously inducing osteogenic and chondrogenic differentiation in vitro. Furthermore, in vivo results confirm that MOF-TCP scaffolds accelerate the integrated regeneration of cartilage and subchondral bone in severe osteochondral defects. This study offers a promising strategy for treating defects induced by OA as well as other inflammatory diseases.

Single-Atom Nanocatalytic Therapy for Suppression of Neuroinflammation by Inducing Autophagy of Abnormal Mitochondria

Catalysts have achieved efficacy in scavenging reactive oxygen species (ROS) to eliminate neuroinflammation, but it ignores the essential fact of blocking the source of ROS regeneration. Here, we report the single-atom catalysts (SACs) Pt/CeO₂, which can effectively catalyze the breakdown of existing ROS and induce mitochondrial membrane potential (Δψm) depolarization by interfering with the α-glycerophosphate shuttle pathway and malate-aspartate shuttle pathway, indirectly triggering the self-clearance of dysfunctional mitochondria and thus eradicating the source of ROS generation. In a therapeutic model of Parkinson's disease (PD), Pt/CeO₂ wrapped by neutrophil-like (HL-60) cell membranes and modified by rabies virus glycoprotein (RVG29) effectively crosses the blood-brain barrier (BBB), enters dopaminergic neurons entering the neuroinflammatory region breaking down existing ROS and inducing mitophagy by electrostatic adsorption targeting mitochondria to prevent ROS regeneration after catalyst discharge. This strategy of efficiently eliminating ROS at the lesion and fundamentally blocking the source of ROS production can address both symptoms and root causes and provides a mechanism of explanation and action target for the treatment of inflammation-related diseases.

Cerium End-Deposited Gold Nanorods-Based Photoimmunotherapy for Boosting Tumor Immunogenicity

BACKGROUND

Triple-negative breast cancer (TNBC) was closely related to high metastatic risk and mortality and has not yet found a targeted receptor for targeted therapy. Cancer immunotherapy, especially photoimmunotherapy, shows promising potential in TNBC treatment because of great spatiotemporal controllability and non-trauma. However, the therapeutic effectiveness was limited by insufficient tumor antigen generation and the immunosuppressive microenvironment.

METHODS

We report on the design of cerium oxide (CeO₂) end-deposited gold nanorods (CEG) to achieve excellent near-infrared photoimmunotherapy. CEG was synthesized through hydrolyzing of ceria precursor (cerium acetate, Ce(AC)₃) on the surface of Au nanorods (NRs) for cancer therapy. The therapeutic response was first verified in murine mammary carcinoma (4T1) cells and then monitored by analysis of the anti-tumor effect in xenograft mouse models.

RESULTS

Under near-infrared (NIR) light irradiation, CEG can efficiently generate hot electrons and avoid hot-electron recombination to release heat and form reactive oxygen species (ROS), triggering immunogenic cell death (ICD) and activating part of the immune response. Simultaneously, combining with PD-1 antibody could further enhance cytotoxic T lymphocyte infiltration.

CONCLUSIONS

Compared with CBG NRs, CEG NRs showed strong photothermal and photodynamic effects to destroy tumors and activate a part of the immune response. Combining with PD-1 antibody could reverse the immunosuppressive microenvironment and thoroughly activate the immune response. This platform demonstrates the superiority of combination therapy of photoimmunotherapy and PD-1 blockade in TNBC therapy.

Oxygen doping of cobalt-single-atom coordination enhances peroxymonosulfate activation and high-valent cobalt-oxo species formation

The high-valent cobalt-oxo species (Co(IV)=O) is being increasingly investigated for water purification because of its high redox potential, long half-life, and antiinterference properties. However, generation of Co(IV)=O is inefficient and unsustainable. Here, a cobalt-single-atom catalyst with N/O dual coordination was synthesized by O-doping engineering. The O-doped catalyst (Co-OCN) greatly activated peroxymonosulfate (PMS) and achieved a pollutant degradation kinetic constant of 73.12 min-1 g-2, which was 4.9 times higher than that of Co-CN (catalyst without O-doping) and higher than those of most reported single-atom catalytic PMS systems. Co-OCN/PMS realized Co(IV)=O dominant oxidation of pollutants by increasing the steady-state concentration of Co(IV)=O (1.03 × 10-10 M) by 5.9 times compared with Co-CN/PMS. A competitive kinetics calculation showed that the oxidation contribution of Co(IV)=O to micropollutant degradation was 97.5% during the Co-OCN/PMS process. Density functional theory calculations showed that O-doping influenced the charge density (increased the Bader charge transfer from 0.68 to 0.85 e), optimized the electron distribution of the Co center (increased the d-band center from -1.14 to -1.06 eV), enhanced the PMS adsorption energy from -2.46 to -3.03 eV, and lowered the energy barrier for generation of the key reaction intermediate (*O*H2O) during Co(IV)=O formation from 1.12 to 0.98 eV. The Co-OCN catalyst was fabricated on carbon felt for a flow-through device, which achieved continuous and efficient removal of micropollutants (degradation efficiency of >85% after 36 h operation). This study provides a new protocol for PMS activation and pollutant elimination through single-atom catalyst heteroatom-doping and high-valent metal-oxo formation during water purification.

Engineering Single-Atom Nanozymes for Catalytic Biomedical Applications

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

Amplification of Lipid Peroxidation by Regulating Cell Membrane Unsaturation To Enhance Chemodynamic Therapy

Lipid peroxidation (LPO) is one of the most damaging processes in chemodynamic therapy (CDT). Although it is well known that polyunsaturated fatty acids (PUFAs) are much more susceptible than saturated or monounsaturated ones to LPO, there is no study exploring the effect of cell membrane unsaturation degree on CDT. Here, we report a self-reinforcing CDT agent (denoted as OA@Fe-SAC@EM NPs), consisting of oleanolic acid (OA)-loaded iron single-atom catalyst (Fe-SAC)-embedded hollow carbon nanospheres encapsulated by an erythrocyte membrane (EM), which promotes LPO to improve chemodynamic efficacy via modulating the degree of membrane unsaturation. Upon uptake of OA@Fe-SAC@EM NPs by cancer cells, Fe-SAC-catalyzed conversion of endogenous hydrogen peroxide into hydroxyl radicals, in addition to initiating the chemodynamic therapeutic process, causes the dissociation of the EM shell and the ensuing release of OA that can enrich cellular membranes with PUFAs, enabling LPO amplification-enhanced CDT.

Recent advances in hydrogels for preventing tumor recurrence

Malignant tumors remain a high-risk disease with high mortality all over the world. Among all the cancer treatments, surgery is the primary approach in the clinical treatment of tumors. However, tumor invasion and metastasis pose challenges for complete tumor resection, accompanied by high recurrence rates and reduced quality of life. Hence, there is an urgent need to explore effective adjuvant therapies to prevent postoperative tumor recurrence and relieve the pain of the patients. Nowadays, the booming local drug delivery systems which can be applied as postoperative adjuvant therapies have aroused people's attention, along with the rapid development in the pharmaceutical and biological materials fields. Hydrogels are a kind of unique carrier with prominent biocompatibility among a variety of biomaterials. Due to their high similarity to human tissues, hydrogels which load drugs/growth factors can prevent rejection reactions and promote wound healing. In addition, hydrogels are able to cover the postoperative site and maintain sustained drug release for the prevention of tumor recurrence. In this review, we survey controlled drug delivery hydrogels such as implantable, injectable and sprayable formulations and summarize the properties required for hydrogels used as postoperative adjuvant therapies. The opportunities and challenges in the design and clinical application of these hydrogels are also elaborated.

Modulation of the biocatalytic activity and selectivity of CeO2 nanozymes via atomic doping engineering

Artificial enzymes show prospects in biomedical applications due to their stable enzymatic catalytic activity and ease of preparation. CeO₂ nanozymes represent a versatile platform showing multiple enzyme-mimicking activities, although their biocatalytic activities and selectivity are relatively poor for biomedical use. Herein, we developed Mn- and Co-doped CeO₂ nanozymes (M/CeO₂, M = Mn or Co) via atomic engineering to achieve a significant increase in enzyme-like activity. The M/CeO₂ nanozymes exhibited outstanding peroxidase-like activity with a reaction rate about 8-10 times higher than that of CeO₂. Importantly, the Co/CeO₂ nanozyme preferred for catalase-like activity with a 4-6-fold higher catalytic rate than CeO₂, while the Mn/CeO₂ nanozyme had a predilection for improving the superoxide dismutase-like capacity. This indicated the selective modulation of enzyme-mimicking activities via atomic doping engineering. Cellular level experiments revealed the in vitro therapeutic effects of the nanozymes. Mn/CeO₂ and Co/CeO₂ selectively modulated the intracellular redox imbalance in lipopolysaccharide (LPS)- or H₂O₂-stimulated nerve cells and improved cell survival. This work provides a feasible strategy for the design of catalytically selective artificial enzymes and facilitates the widespread application of CeO₂ nanozymes in redox-related diseases.

Nanozyme-like single-atom catalyst combined with artesunate achieves photothermal-enhanced nanocatalytic therapy in the near-infrared biowindow

Selectively generating active free radical (AFR) in tumor microenvironment (TME) can promote irreversible oxidation of biomolecules and damage tumor cells, resulting in effective tumor inhibition. However, therapeutic efficacy of AFR-based tumor suppression approaches is often limited by insufficient amount of H₂O₂ or O₂ within TME. To overcome this obstacle, we design a pH/photothermal dual responsive nanosystem (PFeSA@AS) for combined photothermal and nanocatalytic therapy in the near-infrared biowindow. Here the Fe single-atom dispersed N, S-doped carbon nanosheets (FeSA) nanozyme is dispersed by phospholipid-polyethylene glycol-amine (DSPE-PEG-NH₂), and further loads artesunate (AS) via an amide reaction. Upon 808-nm laser irradiation in TME, the AS is released and further be catalyzed by the FeSA nanozyme to produce cytotoxic C-centered AFRs, and further be accelerated due to the photothermal conversion performance of FeSA (23.35%). The nanocatalytic process of FeSA nanozyme is realized by density functional theory (DFT). The tumor inhibition rates of a CT26 xenograft model is 92% through a photothermal-enhanced nanocatalytic synergistic therapy, and negligible systematic toxicity is observed. This work offers a potential paradigm of multifunctional single atomic catalysts (SACs) for enhancing tumor nanocatalytic therapy. STATEMENT OF SIGNIFICANCE: We designed a pH/photothermal dual responsive nanosystem (PFeSA@AS) for nanocatalytic therapy: (1) the nanosystem responsively releases AS under 808-nm laser irradiation in TME; (2) FeSA in the nanosystem can act as heme mimetic to convert AS into high cytotoxic C-centered free radicals for nanocatalytic therapy; (3) the photothermal conversion performance of FeSA further enhances the catalytic process to yield abundant AFR. Both in vitro and in vivo results demonstrate that this nanosystem can efficiently inhibit tumor growth through a photothermal-enhanced nanocatalytic synergistic therapy.

Electron transfer-based antioxidant nanozymes: Emerging therapeutics for inflammatory diseases

Inflammatory diseases are usually featured with relatively high level of reactive oxygen species (ROS). The excess ROS facilitate the polarization of microphages into proinflammatory M1 phenotype, and cause DNA damage, protein carbonylation, and lipid peroxidation, resulting in further deterioration of inflammatory diseases. Therefore, alleviating oxidative stress by ROS scavenging has been an effective strategy for reversing inflammation. Inspired by the natural antioxidant enzymes, electron transfer-based artificial antioxidant nanozymes have been emerging therapeutics for the treatment of inflammatory diseases. The present review starts with the basic knowledge of ROS and diseases, followed by summarizing the possible active centers for the preparation of antioxidant nanozymes. The strategies for the design of antioxidant nanozymes on the purpose of higher catalytic activity are provided, and the applications of the developed antioxidant nanozymes on the therapy of inflammatory diseases are discussed. A perspective is included for the design and applications of artificial antioxidant nanozymes in biomedicine as well.

Passively-targeted mitochondrial tungsten-based nanodots for efficient acute kidney injury treatment

Acute kidney injury (AKI) can lead to loss of kidney function and a substantial increase in mortality. The burst of reactive oxygen species (ROS) plays a key role in the pathological progression of AKI. Mitochondrial-targeted antioxidant therapy is very promising because mitochondria are the main source of ROS in AKI. Antioxidant nanodrugs with actively targeted mitochondria have achieved encouraging success in many oxidative stress-induced diseases. However, most strategies to actively target mitochondria make the size of nanodrugs too large to pass through the glomerular system to reach the renal tubules, the main damage site of AKI. Here, an ultra-small Tungsten-based nanodots (TWNDs) with strong ROS scavenging can be very effective for treatment of AKI. TWNDs can reach the tubular site after crossing the glomerular barrier, and enter the mitochondria of the renal tubule without resorting to complex active targeting strategies. To our knowledge, this is the first time that ultra-small negatively charged nanodots can be used to passively target mitochondrial therapy for AKI. Through in-depth study of the therapeutic mechanism, such passive mitochondria-targeted TWNDs are highly effective in protecting mitochondria by reducing mitochondrial ROS and increasing mitophagy. In addition, TWNDs can also reduce the infiltration of inflammatory cells. This work provides a new way to passively target mitochondria for AKI, and give inspiration for the treatment of many major diseases closely related to mitochondria, such as myocardial infarction and cerebral infarction.

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Mitochondrial-targeted antioxidant therapy is a very promising treatment for AKI.

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TWNDs have a strong ability to scavenge ROS, and their small size allows them to cross the glomerular filtration barrier.

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TWNDs passively target the mitochondria of renal tubular cells and are highly effective in restoring renal function.

Regulating the N Coordination Environment of Co Single-Atom Nanozymes for Highly Efficient Oxidase Mimics

Single-atom catalysts with well-defined atomic structures and precisely regulated coordination environments have been recognized as potential substitutes for natural metalloenzymes. Inspired by the metal coordination structure of natural enzymes, we show here that the oxidase-like activity of single-atom Co catalysts greatly depends on their local N coordination around the Co catalytic sites. We synthesized a series of Co single-atom catalysts with different nitrogen coordination numbers (Co-N_x(C), x = 2, 3, and 4) and demonstrated that the oxidase-like activity of single-atom Co catalysts could be effectively tailored by fine-tuning the N coordination. Among the studied single-atom Co catalysts, the Co-N₃(C) with three-coordinate N atoms shows the optimum oxygen adsorption structure and robust reactive oxygen species (ROS) generation, thus presenting the preferable oxidase-like catalytic activity. This work facilitates the future development of rational nanozyme designs for targeting reactions at the atomic level.

Glutathione peroxidase-like nanozymes: mechanism, classification, and bioapplication

The field of nanozymes is developing rapidly. In particular, glutathione peroxidase (GPx)-like nanozymes, which catalytically reduce H₂O₂/organic hydroperoxides to H₂O/alcohols, have attracted considerable attention. GPx-like nanozymes are powerful antioxidant enzymes known to combat oxidative stress. They have broad applications, including cytoprotection, anti-inflammation, neuroprotection, tumor therapy, and anti-aging. Although much progress has been made, GPx-like nanozymes have not been well discussed or fully reviewed as other nanozymes. This review aims to summarize recent advances on GPx-like nanozymes from the vantage point of mechanism, classification, and bioapplication. Future prospects for advancing their design and application are also discussed.

Tuning Local Coordination Environments of Manganese Single-Atom Nanozymes with Multi-Enzyme Properties for Selective Colorimetric Biosensing

Single-atom nanozymes (SAzymes) are promising in next-generation nanozymes, nevertheless, how to rationally modulate the microenvironment of SAzymes with controllable multi-enzyme properties is still challenging. Herein, we systematically investigate the relationship between atomic configuration and multi-enzymatic performances. The constructed Mn_SA -N₃ -coordinated SAzymes (Mn_SA -N₃ -C) exhibits much more remarkable oxidase-, peroxidase-, and glutathione oxidase-like activities than that of Mn_SA -N₄ -C. Based on experimental and theoretical results, these multi-enzyme-like behaviors are highly dependent on the coordination number of single atomic Mn sites by local charge polarization. As a consequence, a series of colorimetric biosensing platforms based on Mn_SA -N₃ -C SAzymes is successfully built for specific recognition of biological molecules. These findings provide atomic-level insight into the microenvironment of nanozymes, promoting rational design of other demanding biocatalysts.

Nitrogen-Neighbored Single-Cobalt Sites Enable Heterogeneous Oxidase-Type Catalysis

The development of biomimetic catalytic systems that can imitate or even surpass natural enzymes remains an ongoing challenge, especially for bioinspired syntheses that can access non-natural reactions. Here, we show how an all-inorganic biomimetic system bearing robust nitrogen-neighbored single-cobalt site/pyridinic-N site (Co-N4/Py-N) pairs can act cooperatively as an oxidase mimic, which renders an engaged coupling of oxygen (O2) reduction with synthetically beneficial chemical transformations. By developing this broadly applicable platform, the scalable synthesis of greater than 100 industrially and pharmaceutically appealing O-silylated compounds including silanols, borasiloxanes, and silyl ethers via the unprecedented aerobic oxidation of hydrosilane under ambient conditions is demonstrated. Moreover, this heterogeneous oxidase mimic also offers the potential for expanding the catalytic scope of enzymatic synthesis. We anticipate that the strategy demonstrated here will pave a new avenue for understanding the underlying nature of redox enzymes and open up a new class of material systems for artificial biomimetics.

Coordination-Driven Self-Assembly Strategy-Activated Cu Single-Atom Nanozymes for Catalytic Tumor-Specific Therapy

How to optimize the enzyme-like catalytic activity of nanozymes to improve their applicability has become a great challenge. Herein, we present an l-cysteine (l-Cys) coordination-driven self-assembly strategy to activate polyvinylpyrrolidone (PVP)-modified Cu single-atom nanozymes MoOx-Cu-Cys (denoted as MCCP SAzymes) aiming at catalytic tumor-specific therapy. The Cu single atom content of MCCP can be rationally modulated to 10.10 wt %, which activates the catalase (CAT)-like activity of MoOx nanoparticles to catalyze the decomposition of H2O2 in acidic microenvironments to increase O2 production. Excitingly, the maximized CAT-like catalytic efficiency of MCCP is 138-fold higher than that of typical MnO2 nanozymes and exhibits 14.3-fold higher affinity than natural catalase, as demonstrated by steady-state kinetics. We verify that the well-defined l-Cys-Cu···O active sites optimize CAT-like activity to match the active sites of natural catalase through an l-Cys bridge-accelerated electron transfer from Cys-Cu to MoOx disclosed by density functional theory calculations. Simultaneously, the high loading Cu single atoms in MCCP also enable generation of •OH via a Fenton-like reaction. Moreover, under X-ray irradiation, MCCP converts O2 to 1O2 for cascading radiodynamic therapy, thereby facilitating the multiple reactive oxygen species (ROS) for radiosensitization to achieve substantial antitumor.

Metal-Based Nanozymes with Multienzyme-Like Activities as Therapeutic Candidates: Applications, Mechanisms, and Optimization Strategy

Most nanozymes in development for medical applications only exhibit single-enzyme-like activity, and are thus limited by insufficient catalytic activity and dysfunctionality in complex pathological microenvironments. To overcome the impediments of limited substrate availabilities and concentrations, some metal-based nanozymes may mimic two or more activities of natural enzymes to catalyze cascade reactions or to catalyze multiple substrates simultaneously, thereby amplifying catalysis. Metal-based nanozymes with multienzyme-like activities (MNMs) may adapt to dissimilar catalytic conditions to exert different enzyme-like effects. These multienzyme-like activities can synergize to realize "self-provision of the substrate," in which upstream catalysts produce substrates for downstream catalytic reactions to overcome the limitation of insufficient substrates in the microenvironment. Consequently, MNMs exert more potent antitumor, antibacterial, and anti-inflammatory effects in preclinical models. This review summarizes the cellular effects and underlying mechanisms of MNMs. Their potential medical utility and optimization strategy from the perspective of clinical requirements are also discussed, with the aim to provide a theoretical reference for the design, development, and therapeutic application of their catalytic effects.

Self-intensified synergy of a versatile biomimetic nanozyme and doxorubicin on electrospun fibers to inhibit postsurgical tumor recurrence and metastasis

Tumor-positive resection margins after surgery can result in tumor recurrence and metastasis. Although adjuvant postoperative radiotherapy and chemotherapy have been adopted in clinical practice, they lack efficacy and result in unavoidable side effects. Herein, a self-intensified in-situ therapy approach using electrospun fibers loaded with a biomimetic nanozyme and doxorubicin (DOX) is developed. The fabricated PEG-coated zeolite imidazole framework-67 (PZIF67) is demonstrated as a versatile nanozyme triggering reactions in cancer cells based on endogenous H₂O₂ and •O₂^-. The PZIF67-generated •OH induces reactive oxygen species (ROS) overload, implementing chemodynamic therapy (CDT). The O₂ produced by PZIF67 inhibits the expression of hypoxia-up-regulated proteins, thereby suppressing tumor progression. PZIF67 also catalyzes the degradation of glutathione, further disturbing the intracellular redox homeostasis and enhancing CDT. Furthermore, the introduced DOX not only kills cancer cells individually, but also replenishes the continuously consumed substrates for PZIF67-catalyzed reactions. The PZIF67-weakened drug resistance strengthens the cytotoxicity of DOX. The combined application of PZIF67 and DOX also suppresses metastasis-associated genes. Both in vitro and in vivo results demonstrate that the self-intensified synergy of PZIF67 and DOX on electrospun fibers efficiently prevents postsurgical tumor recurrence and metastasis, offering a feasible therapeutic regimen for operable malignant tumors.

In situ synthesized nanozyme for photoacoustic-imaging-guided photothermal therapy and tumor hypoxia relief

Nanozymes have attracted extensive research interest due to their ideal enzymatic catalytic performance; however, uncontrollable activities and nonspecific accumulation limit their further clinical application. To overcome these obstacles, we proposed in situ synthesized nanozyme, and realized the concept through an intelligent nanosystem (ISSzyme) based on Prussian blue (PB) precursor. PB nanozyme was synthesized at the tumor sites through the interaction of ISSzyme with glutathione, which was demonstrated by comparing with conventional PB nanozyme. ISSzyme is capable of tumor-specific photoacoustic imaging (PAI) and photothermal therapy (PTT), reducing the false-positive signals of PAI and the treatment side effects of PTT. ISSzyme has catalase-like activities, resulting in tumor hypoxia relief and metastasis inhibition. More importantly, the in situ synthesized PB nanozyme has the favorable property of minimal liver accumulation. Considering the above advantages, ISSzyme is expected to shed light on the design of the next-generation artificial enzymes, with many new biomedical applications.

Work function mediated interface charge kinetics for boosting photocatalytic water sterilization

Photocatalytic sterilization is an eco-friendly strategy to utilize solar energy for treating water contaminated with resistant bacteria. Here, we propose interface engineering to induce an internal electric field (IEF) in leaf-like Ti₃C₂Tx/TiO₂ based on the work function (Φ) theory, which enhances photocatalytic sterilization performance by steering interface charge kinetics. Density functional theory (DFT) calculations and in situ irradiation X-ray photoelectron spectroscopy (ISI-XPS) results show that photogenerated charge carriers can be directionally separated by the IEF. The efficient charge kinetics benefits the reactive oxygen species (ROS) generation and hence a superior broad-spectrum sterilization performance. We employ the intrinsic physical characteristics of MXene to steer interface charge kinetics for photocatalysis, which exhibits great potential in water disinfection.

Multienzyme-Mimicking Au@Cu2O with Complete Antioxidant Capacity for Reactive Oxygen Species Scavenging

Most enzyme catalysts are unable to achieve effective oxidation resistance because of the monotonous mimicking function or production of secondary reactive oxygen species (ROS). Herein, the Au@Cu₂O heterostructure with multienzyme-like activities is deigned, which has significantly improved antioxidant capacity compared with pure Cu₂O for the scavenging of highly cell-damaging secondary ROS, i.e.,·OH. Experiments and theoretical calculations show that the heterostructure exhibits a built-in electric field and lattice mismatch at the metal-semiconductor interface, which facilitate to generate abundant oxygen vacancies, redox couples, and surface electron deficiency. On the one hand, the presence of rich oxygen vacancies and redox couple can enhance the adsorption and activation of oxygen-containing ROS (including O₂^·- and H₂O₂). On the other hand, the electron transfer between the electron-deficient Au@Cu₂O surface and electron donor would promote peroxide-like activity and avoid producing ·OH. Importantly, endogenous ·OH could be eliminated in both acidic and neutral conditions, which is no longer limited by the volatile physiological environment. Therefore, Au@Cu₂O can simulate superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and glutathione peroxidase (GPx) to form a complete antioxidant system. The deigned nanoenzyme is explored in the real sample world such as A549 cells and zebrafish. This work provides theoretical and practical strategies for the construction of a complete antioxidant enzyme system.

Solid Migration to Assemble a Flower-like Nanozyme with Highly Dense Single Copper Sites for Specific Phenol Oxidation

Nanozymes with high catalytic stability and sustainability have emerged as powerful competitors to natural enzymes for diverse biocatalytic applications. However, constructing a nanozyme with high specificity is one of their biggest challenges. Herein, we develop a facile solid migration strategy to access a flower-like single copper site nanozyme (Cu SSN) via direct transformation of copper foam activated by 2-methylimidazole. With highly clustered CuN₃ sites whose local structure is similar to that of natural polyphenol oxidase, the Cu SSN exhibits excellent activity and specificity to oxidize phenols without peroxidase-like activity. Furthermore, the Cu SSN shows high sensitivity in the colorimetric detection of epinephrine with a low detection limit of 0.10 μg mL^-1, exceeding that of most previously reported enzyme-mimicking catalysts. This work not only provides a simple method for the large-scale preparation of high-performance nanozymes but also offers an inspiration for the design of highly specific nanozymes by mimicking the synergy among sites in natural enzymes.

Single-atom nanozymes: From bench to bedside

Single-atom nanozymes (SANs) are the new emerging catalytic nanomaterials with enzyme-mimetic activities, which have many extraordinary merits, such as low-cost preparation, maximum atom utilization, ideal catalytic activity, and optimized selectivity. With these advantages, SANs have received extensive research attention in the fields of chemistry, energy conversion, and environmental purification. Recently, a growing number of studies have shown the great promise of SANs in biological applications. In this article, we present the most recent developments of SANs in anti-infective treatment, cancer diagnosis and therapy, biosensing, and antioxidative therapy. This text is expected to better guide the readers to understand the current state and future clinical possibilities of SANs in medical applications.

Engineering Antioxidative Cascade Metal-Phenolic Nanozymes for Alleviating Oxidative Stress during Extracorporeal Blood Purification

Oxidative stress is a compelling risk factor in chronic kidney diseases and is further aggravated for individuals during extracorporeal blood purification, ultimately leading to multiple complications. Herein, antioxidative cascade metal-phenolic nanozymes (metal-tannic acid nanozymes, M-TA NMs) are synthesized via metal ions-mediated oxidative coupling of polyphenols; then M-TA NMs engineered hemoperfusion microspheres (Cu-TAn@PMS) are constructed for alleviating oxidative stress. M-TA NMs show adjustable broad-spectrum antioxidative activities toward multiple reactive nitrogen and oxygen species (RNOS) due to the adjustable catalytic active centers. Importantly, M-TA NMs could mimic the cascade processes of superoxide dismutase and catalase to maintain intracellular redox balance. Detailed structural and spectral analyses reveal that the existence of a transition metal could decrease the electronic energy band gaps of M-TA NMs to offer better electron transfers for RNOS scavenging. Notably, dynamic blood experiments demonstrate that Cu-TAn@PMS could serve as an antioxidant defense system for blood in hemoperfusion to scavenge intracellular reactive oxygen species (ROS) effectively even in the complex blood environment and further protect endogenous antioxidative enzymes and molecules. In general, this work developed antioxidative cascade nanozymes engineered microspheres with excellent therapeutic efficacy for the treatment of oxidative stress-related diseases, which exhibited potential for clinical blood purification and extended the biomedical applications of nanozymes.