Nanocatalytic medicine enabled next-generation therapeutics for bacterial infections

The rapid rise of antibiotic-resistant strains and the persistence of biofilm-associated infections have significantly challenged global public health. Unfortunately, current clinical high-dose antibiotic regimens and combination therapies often fail to completely eradicate these infections, which can lead to adverse side effects and further drug resistance. Amidst this challenge, however, the burgeoning development in nanotechnology and nanomaterials brings hopes. This review provides a comprehensive summary of recent advancements in nanomaterials for treating bacterial infections. Firstly, the research progress of catalytic therapies in the field of antimicrobials is comprehensively discussed. Thereafter, we systematically discuss the strategies of nanomaterials for anti-bacterial infection therapies, including endogenous response catalytic therapy, exogenous stimulation catalytic therapy, and catalytic immunotherapy, in order to elucidate the mechanism of nanocatalytic anti-infections. Based on the current state of the art, we conclude with insights on the remaining challenges and future prospects in this rapidly emerging field.

Characterisation of a colourimetric biosensor SapYZUM13@Mn3O4-NH2 reveals the mechanisms underlying its rapid and sensitive detection of viable Staphylococcus aureus in food

In this study, a colourimetric biosensor based on bacteriophage SapYZUM13 and an aminated Mn3O4 (Mn3O4-NH2) nanozyme was constructed and evaluated for its ability to detect Staphylococcus aureus in food. The biosensor had a detection time of 20 min, with a detection limit of 2 × 101 CFU/mL and recovery rate of 92.42-106.96%, indicating its high reliability and accuracy in detecting the food pathogen. Mechanistically, SapYZUM13@Mn3O4-NH2 exhibited oxidase-mimicking capability, producing O2•- free radicals which oxidise 3,3',5,5'-tetramethylbenzidine (TMB) to yield blue-coloured oxTMB. In the presence of S. aureus, the oxidase activity decreased remarkably owing to shielding of the nanozyme active sites. Moreover, SapYZUM13@Mn3O4-NH2 could detect viable S. aureus from various sources, likely because of the special receptor-binding proteins of SapYZUM13 adsorbing to the wall teichoic acids on the S. aureus cell surface. Thus, SapYZUM13@Mn3O4-NH2 has broad application prospects for the detection of viable S. aureus in various foods.

Colorimetric sensor array for identifying antioxidants based on pyrolysis-free synthesis of Fe-N/C single-atom nanozymes

Iron-anchored nitrogen/doped carbon single-atom nanozymes (Fe-N/C), which possess homogeneous active sites and adjustable catalytic environment, represent an exemplary model for investigating the structure-function relationship and catalytic activity. However, the development of pyrolysis-free synthesis technique for Fe-N/C with adjustable enzyme-mimicking activity still presents a significant challenge. Herein, Fe-N/C anchored three carrier morphologies were created via a pyrolysis-free approach by covalent organic polymers. The peroxidase-like activity of these Fe-N/C nanozymes was regulated via the pores of the anchored carrier, resulting in varying electron transfer efficiency due to disparities in contact efficacy between substrates and catalytic sites within diverse microenvironments. Additionally, a colorimetric sensor array for identifying antioxidants was developed: (1) the Fe-N/C catalytically oxidized two substrates TMB and ABTS, respectively; (2) the development of a colorimetric sensor array utilizing oxTMB and oxABTS as sensing channels enabled accurate discrimination of antioxidants such as ascorbic acid (AsA), glutathione (GSH), cysteine (Cys), gallic acid (GA), and caffeic acid (CA). Subsequently, the sensor array underwent rigorous testing to validate its performance, including assessment of antioxidant mixtures and individual antioxidants at varying concentrations, as well as target antioxidants and interfering substances. In general, the present study offered valuable insights into the active origin and rational design of nanozyme materials, and highlighting their potential applications in food analysis.

Regulating Local Coordination Sphere of Ir Single Atoms at the Atomic Interface for Efficient Oxygen Evolution Reaction

Single-atom catalysts dispersed on an oxide support are essential for overcoming the sluggishness of the oxygen evolution reaction (OER). However, the durability of most metal single-atoms is compromised under harsh OER conditions due to their low coordination (weak metal-support interactions) and excessive disruption of metal-Olattice bonds to enable lattice oxygen participation, leading to metal dissolution and hindering their practical applicability. Herein, we systematically regulate the local coordination of Irsingle-atoms at the atomic level to enhance the performance of the OER by precisely modulating their steric localization on the NiO surface. Compared to conventional Irsingle-atoms adsorbed on NiO surface, the atomic Ir atoms partially embedded within the NiO surface (Iremb-NiO) exhibit a 2-fold increase in Ir-Ni second-shell interaction revealed by X-ray absorption spectroscopy (XAS), suggesting stronger metal-support interactions. Remarkably, Iremb-NiO with tailored coordination sphere exhibits excellent alkaline OER mass activity and long-term durability (degradation rate: ∼1 mV/h), outperforming commercial IrO2 (∼26 mV/h) and conventional Irsingle-atoms on NiO (∼7 mV/h). Comprehensive operando X-ray absorption and Raman spectroscopies, along with pH-dependence activity tests, identified high-valence atomic Ir sites embedded on the NiOOH surface during the OER followed the lattice oxygen mechanism, thereby circumventing the traditional linear scaling relationships. Moreover, the enhanced Ir-Ni second-shell interaction in Iremb-NiO plays a crucial role in imparting structural rigidity to Ir single-atoms, thereby mitigating Ir-dissolution and ensuring superior OER kinetics alongside sustained durability.

Antioxidant activities of metal single-atom nanozymes in biomedicine

Nanozymes are a class of nanomaterials with enzyme-like activity that can mimic the catalytic properties of natural enzymes. The small size, high catalytic activity, and strong stability of nanozymes compared to those of natural enzymes allow them to not only exist in a wide temperature and pH range but also maintain stability in complex environments. Recently developed single-atom nanozymes have metal active sites composed of a single metal atom fixed to a carrier. These metal atoms can act as independent catalytically active centers. Metal single-atom nanozymes have a homogeneous single-atom structure and a suitable coordination environment for stronger catalytic activity and specificity than traditional nanozymes. The antioxidant metal single-atom nanozymes with the ability of removing reactive oxygen species (ROS) can simulate superoxidase dismutase, catalase, and glutathione peroxidase to show different effects in vivo. Furthermore, due to the similar structure of antioxidant enzymes, a metal single-atom nanozyme often has multiple antioxidant activities, and this synergistic effect can more efficiently remove ROS related to oxidative stress. The versatility of single-atom nanozymes encompasses a broad spectrum of biomedical applications such as anti-oxidation, anti-infection, immunomodulatory, biosensing, bioimaging, and tumor therapy applications. Herein, the nervous, circulatory, digestive, motor, immune, and sensory systems are considered in order to demonstrate the role of metal single-atom nanozymes in biomedical antioxidants.

Spatiotemporally Guided Single-Atom Bionanozyme for Targeted Antibiofilm Treatment

The heterogeneous and dynamic microenvironment of biofilms complicates bacterial infection treatment. Nanozyme catalytic therapy has recently been promising in treating biofilm infections. However, active nanozymes designed with the required precision targeting the biofilm microenvironment are lacking. This work proposes a spatiotemporally guided single-atom bionanozyme (BioSAzyme) for targeted antibiofilm therapy based on protein engineering of copper single-atom nanozyme (Cu SAzyme). The Cu SAzyme, synthesized via a novel mechanochemistry-assisted method, features highly accessible Cu-N4 active sites exposed on 2D N-doped carbon, exhibiting excellent triple enzyme-like activities according to experimental results and density functional theory calculations. Inheriting biofunctionality from both glucose oxidase and concanavalin A, BioSAzyme can localize the biofilm glycocalyx and catalyze endogenous glucose into H₂O₂ and gluconic acid, thus triggering multiplex cascade reactions with pH self-adaption to consume glucose and glutathione and generate •OH radicals. This spatiotemporally guided bionanocatalytic agent effectively inhibits E. coli O157: H7 and methicillin-resistant S. aureus biofilms in vitro and in vivo. Taking together, this work opens up new avenues for the rational design of single-atom nanozymes for precise antibiofilm therapy.

Multi-mechanism antitumor/antibacterial effects of Cu-EGCG self-assembling nanocomposite in tumor nanotherapy and drug-resistant bacterial wound infections

Chemotherapy and surgery stand as primary cancer treatments, yet the unique traits of the tumor microenvironment hinder their effectiveness. The natural compound epigallocatechin gallate (EGCG) possesses potent anti-tumor and antibacterial traits. However, the tumor's adaptability to chemotherapy due to its acidic pH and elevated glutathione (GSH) levels, coupled with the challenges posed by drug-resistant bacterial infections post-surgery, impede treatment outcomes. To address these challenges, researchers strive to explore innovative treatment strategies, such as multimodal combination therapy. This study successfully synthesized Cu-EGCG, a metal-polyphenol network, and detailly characterized it by using synchrotron radiation and high-resolution mass spectrometry (HRMS). Through chemodynamic therapy (CDT), photothermal therapy (PTT), and photodynamic therapy (PDT), Cu-EGCG showed robust antitumor and antibacterial effects. Cu+ in Cu-EGCG actively participates in a Fenton-like reaction, generating hydroxyl radicals (·OH) upon exposure to hydrogen peroxide (H2O2) and converting to Cu2+. This Cu2+ interacts with GSH, weakening the oxidative stress response of bacteria and tumor cells. Density functional theory (DFT) calculations verified Cu-EGCG's efficient GSH consumption during its reaction with GSH. Additionally, Cu-EGCG exhibited outstanding photothermal conversion when exposed to 808 nm near-infrared (NIR) radiation and produced singlet oxygen (1O2) upon laser irradiation. In both mouse tumor and wound models, Cu-EGCG showcased remarkable antitumor and antibacterial properties.

Single-atom nanozymes: Emerging talent for sensitive detection of heavy metals

In recent years, the increasingly severe pollution of heavy metals has posed a significant threat to the environment and human safety. Heavy metal ions are highly non-biodegradable, with a tendency to accumulate through biomagnification. Consequently, accurate detection of heavy metal ions is of paramount importance. As a new type of synthetic nanomaterials, single-atom nanozymes (SANs) boast exceptional enzyme-like properties, setting them apart from natural enzymes. This unique feature affords SANs with a multitude of advantages such as dispersed active sites, low cost and variety of synthetic methods over natural enzymes, making them an enticing prospect for various applications in industrial, medical and biological fields. In this paper, we systematically summarize the synthetic methods and catalytic mechanisms of SANs. We also briefly review the analytical methods for heavy metal ions and present an overall overview of the research progress in recent years on the application of SANs in the detection of environmental heavy metal ions. Eventually, we propose the existing challenges and provide a vision for the future.

Single-Atom Iridium Nanozyme-Based Persistent Luminescence Nanoparticles for Multimodal Imaging-Guided Combination Tumor Therapy

Persistent luminescence nanoparticles (PLNPs) can achieve autofluorescence-free afterglow imaging, while near-infrared (NIR) emission realizes deep tissue imaging. Nanozymes integrate the merits of nanomaterials and enzyme-mimicking activities with simple preparation. Here PLNPs are prepared of Zn1.2Ga1.6Ge0.2O4:Cr0.0075 with NIR emission at 700 nm. The PLNPs are then incubated with IrCl3 solution, and the nanoparticles are collected and annealed at 750 °C to obtain iridium@PLNPs. Iridium is observed on the PLNPs at the atomic level as a single-atom nanozyme with peroxidase-like catalytic activity, photothermal conversion, and computed tomography (CT) contrast capability. After coating with exosome membrane (EM), the Ir@PLNPs@EM composite exhibits long-lasting NIR luminescence, peroxidase-like catalytic activity, photothermal conversion, and CT contrast capability, with the targeting capability and biocompatibility from EM. Thus, NIR afterglow/photothermal/CT trimodal imaging-guided photothermal-chemodynamic combination therapy is realized as validated with the in vitro and in vivo inhibition of tumor growth, while toxicity and side effects are avoided as drug-free treatment. This work offers a promising avenue for advanced single-atom nanozyme@PLNPs to promote the development of nanozymes and PLNPs for clinical applications.

Single-Atom Ce-N-C Nanozyme Ameliorates Type 2 Diabetes Mellitus by Improving Glucose Metabolism Disorders and Reducing Oxidative Stress

Type 2 diabetes mellitus (T2DM) as a chronic metabolic disease has become a global public health problem. Insulin resistance (IR) is the main pathogenesis of T2DM. Oxidative stress refers to an imbalance between free radical production and the antioxidant system, causing insulin resistance and contributing to the development of T2DM via several molecular mechanisms. Besides, the reduction in hepatic glycogen synthesis also leads to a decrease in peripheral insulin sensitivity. Thus, reducing oxidative stress and promoting glycogen synthesis are both targets for improving insulin resistance and treating T2DM. The current study aims to investigate the pharmacological effects of single-atom Ce-N-C nanozyme (SACe-N-C) on the improvement of insulin resistance and to elucidate its underlying mechanisms using HFD/STZ-induced C57BL/6J mice and insulin-resistant HepG2 cells. The results indicate that SACe-N-C significantly improves hepatic glycogen synthesis and reduces oxidative stress, as well as pancreatic and liver injury. Specifically, compared to the T2DM model group, fasting blood glucose decreased by 29%, hepatic glycogen synthesis increased by 17.13%, and insulin secretion increased by 18.87%. The sod and GPx in the liver increased by 17.80% and 25.28%, respectively. In terms of mechanism, SACe-N-C modulated glycogen synthesis through the PI3K/AKT/GSK3β signaling pathway and activated the Keap1/Nrf2 pathway to alleviate oxidative stress. Collectively, this study suggests that SACe-N-C has the potential to treat T2DM.

Atomically dispersed single-atom catalysts (SACs) and enzymes (SAzymes): synthesis and application in Alzheimer's disease detection

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by cognitive decline and memory loss. Conventional diagnostic methods, such as neuroimaging and cerebrospinal fluid analysis, typically detect AD at advanced stages, limiting the efficacy of therapeutic interventions. Early detection is crucial for improving patient condition by enabling timely administration of treatments that may decelerate disease progression. In this context, single-atom catalysts (SACs) and single-atom nanozymes (SAzymes) have emerged as promising tools offering highly sensitive and selective detection of Alzheimer's biomarkers. SACs, consisting of isolated metal atoms on a support surface, deliver unparalleled atomic efficiency, increased reactivity, and reduced operational costs, although certain challenges in terms of stability, aggregation, and other factors persist. The advent of SAzymes, which integrate SACs with natural metalloprotease catalysts, has further advanced this field by enabling controlled electronic exchange, synergistic productivity, and enhanced biosafety. Particularly, M-N-C SACs with M-Nx active sites mimic the selectivity and sensitivity of natural metalloenzymes, providing a robust platform for early detection of AD. This review encompasses the advancements in SACs and SAzymes, highlighting their pivotal role in bridging the gap between conventional enzymes and nanozyme and offering enhanced catalytic efficiency, controlled electron transfer, and improved biosafety for Alzheimer's detection.

Oxygen-Binding Sites of Enriched Gold Nanoclusters for Capturing Mitochondrial Reverse Electrons

Reverse electron transfer (RET), an abnormal backward flow of electrons from complexes III/IV to II/I of mitochondria, causes the overproduction of a reduced-type CoQ to boost downstream production of mitochondrial superoxide anions that leads to ischemia-reperfusion injury (IRI) to organs. Herein, we studied low-coordinated gold nanoclusters (AuNCs) with abundant oxygen-binding sites to form an electron-demanding trapper that allowed rapid capture of electrons to compensate for the CoQ/CoQH2 imbalance during RET. The AuNCs were composed of only eight gold atoms that formed a Cs-symmetrical configuration with all gold atoms exposed on the edge site. The geometry and atomic configuration enhance oxygen intercalation to attain a d-band electron deficiency in frontier orbitals, forming an unusually high oxidation state for rapid mitochondrial reverse electron capture under a transient imbalance of CoQ/CoQH2 redox cycles. Using hepatic IRI cells/animals, we corroborated that the CoQ-like AuNCs prevent inflammation and liver damage from IRI via recovery of the mitochondrial function.

Hollow CeO2-Based Nanozyme with Self-Accelerated Cascade Reactions for Combined Tumor Therapy

Nanozymes have obvious advantages in improving the efficiency of cancer treatment. However, due to the lack of tissue specificity, low catalytic efficiency, and so on, their clinical applications are limited. Herein, the nanoplatform CeO2@ICG@GOx@HA (CIGH) with self-accelerated cascade reactions is constructed. The as-prepared nanozyme shows the superior oxidase (OXD)-like, superoxide dismutase (SOD)-like, catalase (CAT)-like and peroxidase (POD)-like activities. At the same time, under 808 nm near-infrared (NIR) irradiation, the photodynamic and photothermal capabilities are also significantly enhanced due to the presence of indocyanine green (ICG). We demonstrate that the nanozyme CIGH can efficiently accumulate in the tumor and exhibit amplified cascade antitumor effects with negligible systemic toxicity through the combination of photodynamic therapy (PDT), photothermal therapy (PTT), chemodynamic therapy (CDT) and starvation therapy. The nanozyme prepared in this study provides a promising candidate for catalytic nanomedicines for efficient tumor therapy.

Atomically Engineered Chlorine Coordination of Iron in Active Centers for Selectively Catalytic H2O2 Decomposition Toward Efficient Antitumor-Specific Therapy

The intervention of endogenous H2O2 via nanozymes provides a potential antitumor-specific therapy; however, the role of the nanozyme structure in relation to the selective decomposition of H2O2 to hydroxyl radicals (•OH) is yet to be fully understood, which limits the development of this therapeutic approaches. Herein, an iron single-atom nanozyme (Fe─N2Cl2─C SAzyme) is reported, which is prepared through precise Fe─Cl coordination based on the construction of a characteristic Fe-containing molecule. Fe─N2Cl2─C exhibits efficient catalytic H2O2 decomposition (2.19 × 106 mm-1 s-1), which is the highest among reported SAzymes. More importantly, it is found that H2O2 selectively decomposed into •OH on the Fe─N2Cl2─C surface, which is attributable to the d orbitals of the Fe active center matching the O-2p electrons of the adsorbed hydroxide (*OH) intermediate. Fe─N2Cl2─C is strongly cytotoxic toward a variety of cancer-cell lines in vitro but not to normal cells. Furthermore, Fe─N2Cl2─C shows an outstanding specific therapeutic effect in vivo; it efficiently destroys solid malignant tumors without injuring normal tissue. Altogether, these findings highlight the selective catalytic decomposition of H2O2 to •OH, which is achieved by engineering the active center on the atomic level, thereby providing an avenue for the development of specific nanomedicines with efficient antitumor activities.

A Bioinspired Single-Atom Fe Nanozyme with Excellent Laccase-Like Activity for Efficient Aflatoxin B1 Removal

The applications of natural laccases are greatly restricted because of their drawbacks like poor biostability, high costs, and low recovery efficiency. M/NC single atom nanozymes (M/NC SAzymes) are presenting as great substitutes due to their superior enzyme-like activity, excellent selectivity and high stability. In this work, inspired by the catalytic active center of natural enzyme, a biomimetic Fe/NC SAzyme (Fe-SAzyme) with O2-Fe-N4 coordination is successfully developed, exhibiting excellent laccase-like activity. Compared with their natural counterpart, Fe-SAzyme has shown superior catalytic efficiency and excellent stability under a wide range of pH (3.0-9.0), temperature (4-80 °C) and NaCl strength (0-300 mm). Interestingly, density functional theory (DFT) calculations reveal that the high catalytic performance is attributed to the activation of O2 by O2-Fe-N4 sites, which weakened the O─O bonds in the oxygen-to-water oxidation pathway. Furthermore, Fe-SAzyme is successfully applied for efficient aflatoxin B1 removal based on its robust laccase-like catalytic activity. This work provides a strategy for the rational design of laccase-like SAzymes, and the proposed catalytic mechanism will help to understand the coordination environment effect of SAzymes on laccase-like catalytic processes.

Vanadium Single Atoms Embedded in MoS2 Enabled Gut-Brain Axis Neurotransmitter Detection at pM Levels

The detection of monoamine neurotransmitters is of paramount importance as the neurotransmitters are the chemical messengers regulating the gut-brain axis (GBA). It requires real-time, ultrasensitive, and selective sensing of the neurotransmitters in the gastric/intestinal fluid. However, multi-components present in the gastric/intestinal fluid make sensing challenging to achieve in terms of ultra-high sensitivity and selectivity. Herein, an approach is introduced to utilize vanadium single atom catalytic (SAC) centers in van der Waals MoS2 (V-MoS2) to selectively detect real-time serotonin (5-HT) in artificial gastric/intestinal fluid. The synergetic effect of V-SACs and the surface S-bonds on the MoS2 surface, enables an extremely wide range of 5-HT detection (from 1 pM to 100 µM), with optimum selectivity and interference resistance. By combining density functional theory calculations and scanning transmission electron microscopy, it is concluded that the V-SACs embedded in the MoS2 network create active sites that greatly facilitate the charge exchange between the material and the 5-HT molecules. This result allows the 5-HT detection in GBA studies to be more reliable, and the material tunability provides a general platform to achieve real-time and multi-component detection of other monoamine neurotransmitters in GBA such as dopamine and norepinephrine.

Fast Reaction of the Prussian Blue Based Nanozyme "Artificial Peroxidase" with the Substrates: Pre-Steady-State Kinetic Approach

This letter introduces the pre-steady-state kinetic approach, which is traditional for evaluation of elementary constants in molecular (enzyme) catalysis, for nanozymes. Apparently, the most active peroxidase-mimicking nanozyme based on catalytically synthesized Prussian Blue nanoparticles has been chosen. The elementary constants (k1) for the nanozymes' reduction by an electron-donor substrate (being the fastest stage according to steady-state kinetic data) have been determined by means of stopped-flow spectroscopy. These constants have been found to be dependent on both the size of the nanozyme and the reducing substrate redox potential. For the smallest nanozymes (32 nm in diameter), log(k1) linearly decays with an increase of the substrate redox potential (cotangent value ≈125 mV). On the contrary, for the largest nanozymes with a diameter above 150 nm, k1 is almost independent of it. Moreover, for the substrate with the lowest redox potential (K4[Fe(CN)6]), the rate constant under discussion (k1) is almost independent of the nanozymes' size. Perhaps, the rate of the intrananozyme electron transfer causing bleaching becomes comparative or even lower than that of the nanoparticle interaction with the fastest substrate. Anyway, the elementary constant of nanozyme reduction with potassium ferrocyanide (k1) reaches the value of 1 × 1010 M-1 s-1, which is 3-4 orders of magnitude faster than for enzymes peroxidases. The obtained results obviously demonstrate that the pre-steady-state kinetic approach is able to discover novel advantages of nanozymes from both fundamental and practical points of view.

Oxygen-bridged W-Pd atomic pairs enable H2O2 activation for sensitive immunoassays

Regulating the performance of peroxidase (POD)-like nanozymes is a prerequisite for achieving highly sensitive and accurate immunoassays. Inspired by natural enzyme catalysis, we design a highly active and selective nanozyme by loading atomically dispersed tungsten (W) sites on Pd metallene (W-O-Pdene) to construct an artificial three-dimensional (3D) catalytic center. The 3D asymmetric W-O-Pd atomic pairs can effectively stretch the O-O bonds in H2O2 and further promote the desorption of H2O to enhance POD-like activity. Moreover, the W-O-Pd sites with unique spatial structures demonstrate satisfactory specificity for H2O2 activation, effectively preventing the interference of dissolved oxygen. Accordingly, the highly active and specific W-O-Pdene nanozymes are utilized for sensitive and accurate prostate-specific antigen (PSA) immunoassay with a low detection limit of 1.92 pg mL-1, superior to commercial enzyme-linked immunosorbent assay.

Theory-guided design of S-doped Fe/Co dual-atom nanozymes for highly efficient oxidase mimics

The advent of dual-atom nanozymes (DAzymes) featuring distinctive bimetallic active sites garnered significant attention, representing enhanced iterations of conventional single-atom nanozymes. The quest for an effective and universal strategy to modulate the catalytic activity of DAzymes posed a formidable challenge, yet few published reports addressed this. Herein, we designed and synthesized S-doped Fe/Co DAzymes (S-FeCo-NC) under theoretical guidance and revealed their excellent oxidase-like activity. Experimental and theoretical calculations indicated that the superior oxidase-like activity exhibited by S-FeCo-NC was attributed to the S-doping, which modulated the local electronic structure of the dual-atom active site. This modulation of the local electronic structure significantly optimizes oxygen adsorption energy, thereby accelerating the rate of enzyme-catalyzed reactions. As a proof-of-concept, this study integrated S-FeCo-NC with the cascade inhibition reaction of acetylcholinesterase (AChE) to devise a sensitive analytical platform for detecting organophosphorus pesticides. This study paved the way for elucidating the correlation between the local electronic structure of the active site and enzyme activity, offering novel methodologies and insights for the rational design of DAzymes.

Nanozyme-Enabled Biomedical Diagnosis: Advances, Trends, and Challenges

As nanoscale materials with the function of catalyzing substrates through enzymatic kinetics, nanozymes are regarded as potential alternatives to natural enzymes. Compared to protein-based enzymes, nanozymes exhibit attractive characteristics of low preparation cost, robust activity, flexible performance adjustment, and versatile functionalization. These advantages endow them with wide use from biochemical sensing and environmental remediation to medical theranostics. Especially in biomedical diagnosis, the feature of catalytic signal amplification provided by nanozymes makes them function as emerging labels for the detection of biomarkers and diseases, with rapid developments observed in recent years. To provide a comprehensive overview of recent progress made in this dynamic field, here an overview of biomedical diagnosis enabled by nanozymes is provided. This review first summarizes the synthesis of nanozyme materials and then discusses the main strategies applied to enhance their catalytic activity and specificity. Subsequently, representative utilization of nanozymes combined with biological elements in disease diagnosis is reviewed, including the detection of biomarkers related to metabolic, cardiovascular, nervous, and digestive diseases as well as cancers. Finally, some development trends in nanozyme-enabled biomedical diagnosis are highlighted, and corresponding challenges are also pointed out, aiming to inspire future efforts to further advance this promising field.

Atom-pair engineering of single-atom nanozyme for boosting peroxidase-like activity

Constructing atom-pair engineering and improving the activity of metal single-atom nanozyme (SAzyme) is significant but challenging. Herein, we design the atom-pair engineering of Zn-SA/CNCl SAzyme by simultaneously constructing Zn-N4 sites as catalytic sites and Zn-N4Cl1 sites as catalytic regulator. The Zn-N4Cl1 catalytic regulators effectively boost the peroxidase-like activities of Zn-N4 catalytic sites, resulting in a 346-fold, 1496-fold, and 133-fold increase in the maximal reaction velocity, the catalytic constant and the catalytic efficiency, compared to Zn-SA/CN SAzyme without the Zn-N4Cl1 catalytic regulator. The Zn-SA/CNCl SAzyme with excellent peroxidase-like activity effectively inhibits tumor cell growth in vitro and in vivo. The density functional theory (DFT) calculations reveal that the Zn-N4Cl1 catalytic regulators facilitate the adsorption of *H2O2 and re-exposure of Zn-N4 catalytic sites, and thus improve the reaction rate. This work provides a rational and effective strategy for improving the peroxidase-like activity of metal SAzyme by atom-pair engineering.

Raspberry-shaped ZIF-8/Au nanozymes with excellent peroxidase-like activity for simple and visual detection of glutathione

Artificial enzymes with high stability, adjustable catalytic activity, controllable preparation, and good reproducibility have been widely studied. Noble metal nanozymes, particularly gold nanoparticles (Au NPs), exhibit good catalytic activity, but their stability is poor. In this study, zeolitic imidazolate framework-8 (ZIF-8) was used as a carrier for Au NPs, thus improving the utilization efficiency and conservation stability of the nanozymes. A ZIF-8/Au nanocomposite with peroxidase activity and a raspberry-shaped structure was synthesized. In the assay, ZIF-8/Au catalyzed the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to a blue product oxidized TMB (oxTMB). Glutathione (GSH) selectively inhibited this reaction, with a detection limit of 0.28 µM and linear range of 0.5-60 µM. Using the photo and chromaticity analysis functions, we developed a portable analysis method using a smartphone equipped with a camera module as a detection terminal for a wide range of rapid screening techniques for GSH. Preparation of raspberry-shaped ZIF-8/Au improved the catalytic activity of Au NPs and good results were demonstrated in serum, which suggests their promising application under physiological conditions.

Breaking the pH Limitation of Nanozymes: Mechanisms, Methods, and Applications

Although nanozymes have drawn great attention over the past decade, the activities of peroxidase-like, oxidase-like, and catalase-like nanozymes are often pH dependent with elusive mechanism, which largely restricts their application. Therefore, a systematical discussion on the pH-related catalytic mechanisms of nanozymes together with the methods to overcome this limitation is in need. In this review, various nanozymes exhibiting pH-dependent catalytic activities are collected and the root causes for their pH dependence are comprehensively analyzed. Subsequently, regulatory concepts including catalytic environment reconstruction and direct catalytic activity improvement to break this pH restriction are summarized. Moreover, applications of pH-independent nanozymes in sensing, disease therapy, and pollutant degradation are overviewed. Finally, current challenges and future opportunities on the development of pH-independent nanozymes are suggested. It is anticipated that this review will promote the further design of pH-independent nanozymes and broaden their application range with higher efficiency.

Single-site iron-anchored amyloid hydrogels as catalytic platforms for alcohol detoxification

Constructing effective antidotes to reduce global health impacts induced by alcohol prevalence is a challenging topic. Despite the positive effects observed with intravenous applications of natural enzyme complexes, their insufficient activities and complicated usage often result in the accumulation of toxic acetaldehyde, which raises important clinical concerns, highlighting the pressing need for stable oral strategies. Here we present an effective solution for alcohol detoxification by employing a biomimetic-nanozyme amyloid hydrogel as an orally administered catalytic platform. We exploit amyloid fibrils derived from β-lactoglobulin, a readily accessible milk protein that is rich in coordinable nitrogen atoms, as a nanocarrier to stabilize atomically dispersed iron (ferrous-dominated). By emulating the coordination structure of the horseradish peroxidase enzyme, the single-site iron nanozyme demonstrates the capability to selectively catalyse alcohol oxidation into acetic acid, as opposed to the more toxic acetaldehyde. Administering the gelatinous nanozyme to mice suffering from alcohol intoxication significantly reduced their blood-alcohol levels (decreased by 55.8% 300 min post-alcohol intake) without causing additional acetaldehyde build-up. Our hydrogel further demonstrates a protective effect on the liver, while simultaneously mitigating intestinal damage and dysbiosis associated with chronic alcohol consumption, introducing a promising strategy in effective alcohol detoxification.

The Identification of Oral Cariogenic Bacteria through Colorimetric Sensor Array Based on Single-Atom Nanozymes

Effective identification of multiple cariogenic bacteria in saliva samples is important for oral disease prevention and treatment. Here, a simple colorimetric sensor array is developed for the identification of cariogenic bacteria using single-atom nanozymes (SANs) assisted by machine learning. Interestingly, cariogenic bacteria can increase oxidase-like activity of iron (Fe)─nitrogen (N)─carbon (C) SANs by accelerating electron transfer, and inversely reduce the activity of Fe─N─C further reconstruction with urea. Through machine-learning-assisted sensor array, colorimetric responses are developed as "fingerprints" of cariogenic bacteria. Multiple cariogenic bacteria can be well distinguished by linear discriminant analysis and bacteria at different genera can also be distinguished by hierarchical cluster analysis. Furthermore, colorimetric sensor array has demonstrated excellent performance for the identification of mixed cariogenic bacteria in artificial saliva samples. In view of convenience, precise, and high-throughput discrimination, the developed colorimetric sensor array based on SANs assisted by machine learning, has great potential for the identification of oral cariogenic bacteria so as to serve for oral disease prevention and treatment.

Elucidating the catalytic mechanism of Prussian blue nanozymes with self-increasing catalytic activity

Although Prussian blue nanozymes (PBNZ) are widely applied in various fields, their catalytic mechanisms remain elusive. Here, we investigate the long-term catalytic performance of PBNZ as peroxidase (POD) and catalase (CAT) mimetics to elucidate their lifespan and underlying mechanisms. Unlike our previously reported Fe3O4 nanozymes, which exhibit depletable POD-like activity, the POD and CAT-like activities of PBNZ not only persist but slightly enhance over prolonged catalysis. We demonstrate that the irreversible oxidation of PBNZ significantly promotes catalysis, leading to self-increasing catalytic activities. The catalytic process of the pre-oxidized PBNZ can be initiated through either the conduction band pathway or the valence band pathway. In summary, we reveal that PBNZ follows a dual-path electron transfer mechanism during the POD and CAT-like catalysis, offering the advantage of a long service life.

Regulating Second Coordination Shell of Ce Atom Site and Reshaping of Carrier Enable Single-Atom Nanozyme to Efficiently Express Oxidase-like Activity

Single-atom nanozymes (SANs) are considered to be ideal substitutes for natural enzymes due to their high atom utilization. This work reported a strategy to manipulate the second coordination shell of the Ce atom and reshape the carbon carrier to improve the oxidase-like activity of SANs. Internally, S atoms were symmetrically embedded into the second coordination layer to form a Ce-N4S2-C structure, which reduced the energy barrier for O2 reduction, promoted the electron transfer from the Ce atom to O atoms, and enhanced the interaction between the d orbital of the Ce atom and p orbital of O atoms. Externally, in situ polymerization of mussel-inspired polydopamine on the precursor helps capture metal sources and protects the 3D structure of the carrier during pyrolysis. On the other hand, polyethylene glycol (PEG) modulated the interface of the material to enhance water dispersion and mass transfer efficiency. As a proof of concept, the constructed PEG@P@Ce-N/S-C was applied to the multimodal assay of butyrylcholinesterase activity.

Iridium nanoparticles supported on polyaniline nanotubes for peroxidase mimicking towards total antioxidant capacity assay of fruits and vegetables

In this study, a straightforward approach is presented for the first time to anchor Ir nanoparticles on the surface of uniform polyaniline (PANi) nanotubes (NTs), which can be used as an efficient peroxidase (POD)-like catalyst. The morphology and chemical structure of the PANi-Ir nanocomposite are characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffractometer (XRD), Raman and X-ray photoelectron spectroscopy (XPS) measurements. Owing to the strong interaction between Ir nanoparticles and PANi, a remarkable catalytic enhancement is achieved compared to the bare Ir black catalyst and individual PANi NTs, dominating withan electron transfer mechanism. Furthermore, an efficient colorimetric sensor for ascorbic acid (AA) is developed with a low detection limit of 1.0 μM (S/N = 3), and a total antioxidant capacity (TAC) sensing platform is also constructed for the rigorous detection and analysis of fruits and vegetables.

3D-Printed Flexible Microfluidic Health Monitor for In Situ Sweat Analysis and Biomarker Detection

Wearable sweat biosensors have shown great progress in noninvasive, in situ, and continuous health monitoring to demonstrate individuals' physiological states. Advances in novel nanomaterials and fabrication methods promise to usher in a new era of wearable biosensors. Here, we introduce a three-dimensional (3D)-printed flexible wearable health monitor fabricated through a unique one-step continuous manufacturing process with self-supporting microfluidic channels and novel single-atom catalyst-based bioassays for measuring the sweat rate and concentration of three biomarkers. Direct ink writing is adapted to print the microfluidic device with self-supporting structures to harvest human sweat, which eliminates the need for removing sacrificial supporting materials and addresses the contamination and sweat evaporation issues associated with traditional sampling methods. Additionally, the pick-and-place strategy is employed during the printing process to accurately integrate the bioassays, improving manufacturing efficiency. A single-atom catalyst is developed and utilized in colorimetric bioassays to improve sensitivity and accuracy. A feasibility study on human skin successfully demonstrates the functionality and reliability of our health monitor, generating reliable and quantitative in situ results of sweat rate, glucose, lactate, and uric acid concentrations during physical exercise.

Immobilized Multi-Enzyme/Nanozyme Biomimetic Cascade Catalysis for Biosensing Applications

Multiple enzyme-induced cascade catalysis has an indispensable role in the process of complex life activities, and is widely used to construct robust biosensors for analyzing various targets. The immobilized multi-enzyme cascade catalysis system is a novel biomimetic catalysis strategy that immobilizes various enzymes with different functions in stable carriers to simulate the synergistic catalysis of multiple enzymes in biological systems, which enables high stability of enzymes and efficiency enzymatic cascade catalysis. Nanozymes, a type of nanomaterial with intrinsic enzyme-like characteristics and excellent stabilities, are also widely applied instead of enzymes to construct immobilized cascade systems, achieving better catalytic performance and reaction stability. Due to good stability, reusability, and remarkably high efficiency, the immobilized multi-enzyme/nanozyme biomimetic cascade catalysis systems show distinct advantages in promoting signal transduction and amplification, thereby attracting vast research interest in biosensing applications. This review focuses on the research progress of the immobilized multi-enzyme/nanozyme biomimetic cascade catalysis systems in recent years. The construction approaches, factors affecting the efficiency, and applications for sensitive biosensing are discussed in detail. Further, their challenges and outlooks for future study are also provided.

FeSA‐Ir/Metallene Nanozymes Induce Sequential Ferroptosis‐Pyroptosis for Multi‐Immunogenic Responses Against Lung Metastasis

For cancer metastasis inhibition, the combining of nanozymes with immune checkpoint blockade (ICB) therapy remains the major challenge in controllable reactive oxygen species (ROS) generation for creating effective immunogenicity. Herein, new nanozymes with light-controlled ROS production in terms of quantity and variety are developed by conjugating supramolecular-wrapped Fe single atom on iridium metallene with lattice-strained nanoislands (FeSA-Ir@PF NSs). The Fenton-like catalysis of FeSA-Ir@PF NSs effectively produced •OH radicals in dark, which induced ferroptosis and apoptosis of cancer cells. While under second near-infrared (NIR-II) light irradiation, FeSA-Ir@PF NSs showed ultrahigh photothermal conversion efficiency (𝜂, 75.29%), cooperative robust •OH generation, photocatalytic O2 and 1O2 generation, and caused significant pyroptosis of cancer cells. The controllable ROS generation, sequential cancer cells ferroptosis and pyroptosis, led 99.1% primary tumor inhibition and multi-immunogenic responses in vivo. Most importantly, the inhibition of cancer lung metastasis is completely achieved by FeSA-Ir@PF NSs with immune checkpoint inhibitors, as demonstrated in different mice lung metastasis models, including circulating tumor cells (CTCs) model. This work provided new inspiration for developing nanozymes for cancer treatments and metastasis inhibition.

Superior oxidase-mimetic activity of FeCo-NC dual-atom nanozyme for smartphone-based visually colorimetric assay of organophosphorus pesticides

A colorimetric analysis platform has been successfully developed based on FeCo-NC dual-atom nanozyme (FeCo-NC DAzyme) for the detection of organophosphorus pesticides (OPPs). The FeCo-NC DAzyme exhibited exceptional oxidase-like activity (OXD), enabling the catalysis of colorless TMB to form blue oxidized TMB (oxTMB) without the need for H2O2 involvement. By combining acid phosphatase (ACP) hydrolase with FeCo-NC DAzyme, a "FeCo-NC DAzyme + TMB + ACP + SAP" colorimetric system was constructed, which facilitated the rapid detection of malathion. The chromogenic system was applied to detect malathion using a smartphone-based app and an auxiliary imaging interferogram device for colorimetric measurements, which have a linear range of 0.05-4.0 µM and a limit of detection (LOD) as low as 15 nM in real samples, comparable to UV-Vis and HPLC-DAD detection methods. Overall, these findings present a novel approach for convenient, rapid, and on-site monitoring of OPPs.

A lateral flow assay for miRNA-21 based on CRISPR/Cas13a and MnO2 nanosheets-mediated recognition and signal amplification

The point-of-care testing (POCT) of miRNA has significant application in medical diagnosis, yet presents challenges due to their characteristics of high homology, low abundance, and short length, which hinders the achievement of quick detection with high specificity and sensitivity. In this study, a lateral flow assay based on the CRISPR/Cas13a system and MnO2 nanozyme was developed for highly sensitive detection of microRNA-21 (miR-21). The CRISPR/Cas13a cleavage system exhibits the ability to recognize the specific oligonucleotide sequence, where two-base mismatches significantly impact the cleavage activity of the Cas13a. Upon binding of the target to crRNA, the cleavage activity of Cas13a is activated, resulting in the unlocking of the sequence and initiating strand displacement, thereby enabling signal amplification to produce a new sequence P1. When applying the reaction solution to the lateral flow test strip, P1 mediates the capture of MnO2 nanosheets (MnO2 NSs) on the T zone, which catalyzes the oxidation of the pre-immobilized colorless substrate 3,3',5,5'-tetramethylbenzidine (TMB) on the T zone and generates the blue-green product (ox-TMB). The change in gray value is directly proportional to the concentration of miR-21, allowing for qualitative detection through visual inspection and quantitative measurement using ImageJ software. This method achieves the detection of miR-21 within a rapid 10-min timeframe, and the limit of detection (LOD) is 0.33 pM. With the advantages of high specificity, simplicity, and sensitivity, the lateral flow test strip and the design strategy hold great potential for the early diagnosis of related diseases.

Targeting starvation therapy for diabetic bacterial infections with endogenous enzyme-triggered hyaluronan-modified nanozymes in the infection microenvironment

The high-glycemic microenvironment of diabetic wounds promotes bacterial proliferation, leading to persistent infections and delayed wound healing. This poses a significant threat to human health, necessitating the development of new nanodrug visualization platforms. In this study, we designed and synthesized cascade nano-systems modified with targeted peptide and hyaluronic acid for diabetic infection therapy. The nano-systems were able to target the site of infection using LL-37, and in the microenvironment of wound infection, the hyaluronic acid shell of the nano-systems was degraded by endogenous hyaluronidase. This precise degradation released a cascade of nano-enzymes on the surface of the bacteria, effectively destroying their cytoskeleton. Additionally, the metals in the nano-enzymes provided a photo-thermal effect, accelerating wound healing. The cascade nano-visualization platform demonstrated excellent bactericidal efficacy in both in vitro antimicrobial assays and in vivo diabetic infection models. In conclusion, this nano-system employs multiple approaches including targeting, enzyme-catalyzed therapy, photothermal therapy, and chemodynamic therapy to kill bacteria and promote healing. The Ag@Pt-Au-LYZ/HA-LL-37 formulation shows great potential for the treatment of diabetic wounds.

Ultrasensitive cortisol electrochemical immunosensor amplifying by Au single-atom nanozymes and HRP enzymes

Cortisol, a corticosteroid hormone as a primary stress hormone response to internal and external stress, has been regarded as a gold standard reliable biomarker to evaluate human mental stress. The double enzymes strategy, using nanozyme and enzyme amplifying the electrochemical signal, has been widely used to improve the performance of electrochemical biosensors. An ultra-sensitive electrochemical cortisol sensor based on Au single-atom nanozymes had been fabricated through HRP labeled anti-cortisol antibody binding with Au by Au-S bond. Based on the high catalytic activity of Au single-atom nanozymes and the high selectivity of HRP-labeled anti-cortisol antibodies, the cortisol electrochemical sensor-based Au single-atom nanozymes had an excellent response to cortisol, such as high electrochemical activity, high sensitivity, high selectivity, and wide linear range (0.15-300 ng mL-1) and low detection (0.48 pg mL-1) through the four-parameter logistic model with 95% confidence. The electrochemical cortisol sensor was used to determine the cortisol concentration of human saliva at different times.

Transition-Metal-Based Nanozymes: Synthesis, Mechanisms of Therapeutic Action, and Applications in Cancer Treatment

Cancer, as one of the leading causes of death worldwide, drives the advancement of cutting-edge technologies for cancer treatment. Transition-metal-based nanozymes emerge as promising therapeutic nanodrugs that provide a reference for cancer therapy. In this review, we present recent breakthrough nanozymes for cancer treatment. First, we comprehensively outline the preparation strategies involved in creating transition-metal-based nanozymes, including hydrothermal method, solvothermal method, chemical reduction method, biomimetic mineralization method, and sol-gel method. Subsequently, we elucidate the catalytic mechanisms (catalase (CAT)-like activities), peroxidase (POD)-like activities), oxidase (OXD)-like activities) and superoxide dismutase (SOD)-like activities) of transition-metal-based nanozymes along with their activity regulation strategies such as morphology control, size manipulation, modulation, composition adjustment and surface modification under environmental stimulation. Furthermore, we elaborate on the diverse applications of transition-metal-based nanozymes in anticancer therapies encompassing radiotherapy (RT), chemodynamic therapy (CDT), photodynamic therapy (PDT), photothermal therapy (PTT), sonodynamic therapy (SDT), immunotherapy, and synergistic therapy. Finally, the challenges faced by transition-metal-based nanozymes are discussed alongside future research directions. The purpose of this review is to offer scientific guidance that will enhance the clinical applications of nanozymes based on transition metals.

A Pt1Pd Single-Atom Alloy Nanozyme with Boosted Enzyme-Like Activity for Efficient Photo-Mediated Tumor Therapy

Single-atom nanozymes (SAzymes) are emerging natural enzyme mimics and have attracted much attention in the biomedical field. SAzymes with Metal─Nx sites designed on carbon matrixes are currently the mainstream in research. It is of great significance to further expand the types of SAzymes to enrich the nanozyme library. Single-atom alloys (SAAs) are a material in which single-atom metal sites are dispersed onto another active metal matrix, and currently, there is limited research on their enzyme-like catalytic performance. In this work, a biodegradable Pt1Pd SAA is fabricated via a simple galvanic replacement strategy, and for the first time reveals its intrinsic enzyme-like catalytic performance including catalase-, oxidase-, and peroxidase-like activities, as well as its photodynamic effect. Experimental characterizations demonstrate that the introduction of single-atom Pt sites contributes to enhancing the affinity of Pt1Pd single-atom alloy nanozyme (SAAzyme) toward substrates, thus exhibiting boosted catalytic efficiency. In vitro and in vivo experiments demonstrate that Pt1Pd SAAzyme exhibits a photo-controlled therapeutic effect, with a tumor inhibition rate of up to 100%. This work provides vital guidance for opening the research direction of SAAs in enzyme-like catalysis.

Construction of Mn-decorated zeolitic imidazolate framework-90 nanostructure as superior oxidase-like mimic for colorimetric detection of glucose and choline

A Mn decorated zeolitic imidazolate framework-90 (ZIF-90) nanozyme (Mn/ZIF-90) was constructed through an effective and rapid post-synthetic strategy for the first time. The Mn in Mn/ZIF-90 exists in mixed valence states, which is doped to the ZIF-90 through the formation of Mn-O bond. The Zn-N coordination structure of ZIF-90 may change the electronic arrangement of oxygen atoms in the free carbonyl groups (-CHO), allowing the coordination of Mn with O. The prepared Mn/ZIF-90 possesses outstanding oxidase-like activity and remarkable stability. Besides, the catalytic activity of Mn/ZIF-90 can be inhibited in the presence of H2O2. Therefore, using the Mn/ZIF-90-triggered chromogenic reaction of 3,3',5,5'-tetramethylbenzidine (TMB) as an amplifier, a versatile enzyme cascade-based colorimetric method for the detection of glucose and choline with good sensitivity and selectivity was developed. The linear ranges for glucose and choline are 6.25-500 μM and 5-1000 μM, respectively. Furthermore, the developed method was applied in the detection of glucose and choline in rabbit plasma samples, and the recoveries are 89.5-107.3 % and 96.0-109.3 %, respectively. In short, the simple and efficient post-synthetic doping method may provide a new thought for the rational designs of enzyme mimics with improved catalytic performance. Moreover, the colorimetric method based on the excellent catalytic activity of Mn/ZIF-90 may be extended to detect other H2O2-generating or consuming molecules and evaluate the activity of bio-enzymes that can catalyze the generation of glucose or choline.

The Application of Metal-Organic Frameworks in Water Treatment and Their Large-Scale Preparation: A Review

Over the last few decades, there has been a growing discourse surrounding environmental and health issues stemming from drinking water and the discharge of effluents into the environment. The rapid advancement of various sewage treatment methodologies has prompted a thorough exploration of promising materials to capitalize on their benefits. Metal-organic frameworks (MOFs), as porous materials, have garnered considerable attention from researchers in recent years. These materials boast exceptional properties: unparalleled porosity, expansive specific surface areas, unique electronic characteristics including semi-conductivity, and a versatile affinity for organic molecules. These attributes have fueled a spike in research activity. This paper reviews the current MOF-based wastewater removal technologies, including separation, catalysis, and related pollutant monitoring methods, and briefly introduces the basic mechanism of some methods. The scale production problems faced by MOF in water treatment applications are evaluated, and two pioneering methods for MOF mass production are highlighted. In closing, we propose targeted recommendations and future perspectives to navigate the challenges of MOF implementation in water purification, enhancing the efficiency of material synthesis for environmental stewardship.

Single-Mg-Atom Catalyst with a Dual Active Center as an Emerging Promising Sensing Platform

Bisphenol compounds [bisphenol A (BPA), etc.] are one class of the most important and widespread pollutants in food and environment, which pose severe endocrine disrupting effect, reproductive toxicity, immunotoxicity, and metabolic toxicity on humans and animals. Simultaneous rapid determination of BPA and its analogues (bisphenol S, bisphenol AF, etc.) with extraordinary potential resolution and sensitivity is of great significance but still extremely challenging. Herein, a series of single-atom catalysts (SACs) were synthesized by anchoring different metal atoms (Mg, Co, Ni, and Cu) on N-doped carbon materials and used as sensing materials for simultaneous detection of bisphenols with similar chemical structures. The Mg-based SAC enables the potential discrimination and simultaneous rapid detection of multiple bisphenols, showing outstanding analytical performances, outperforming all other SACs and traditional electrode materials. Our experiments and density functional theory calculations show that pyrrolic N serves as the adsorption site for the adsorption of bisphenols and the Mg atom serves as the active site for the electrocatalytic oxidation of bisphenols, which play a synergistic role as dual active centers in improving the sensing performance. The results of this work may pave the way for the rational design of SACs as advanced sensing and catalytic materials.

A Single-Atom Manganese Nanozyme Mn-N/C Promotes Anti-Tumor Immune Response via Eliciting Type I Interferon Signaling

Tumor microenvironment (TME)-induced nanocatalytic therapy is a promising strategy for cancer treatment, but the low catalytic efficiency limits its therapeutic efficacy. Single-atom catalysts (SACs) are a new type of nanozyme with incredible catalytic efficiency. Here, a single-atom manganese (Mn)-N/C nanozyme is constructed. Mn-N/C catalyzes the conversion of cellular H2O2 to ∙OH through a Fenton-like reaction and enables the sufficient generation of reactive oxygen species (ROS), which induces immunogenic cell death (ICD) of tumor cells and significantly promotes CD8+T anti-tumor immunity. Moreover, RNA sequencing analysis reveals that Mn-N/C treatment activates type I interferon (IFN) signaling, which is critical for Mn-N/C-mediated anti-tumor immune response. Mechanistically, the release of cytosolic DNA and Mn2+ triggered by Mn-N/C collectively activates the cGAS-STING pathway, subsequently stimulating type I IFN induction. A highly efficient single-atom nanozyme, Mn-N/C, which enhances anti-tumor immune response and exhibits synergistic therapeutic effects when combined with the anti-PD-L1 blockade, is proposed.

Advances in the application of logic gates in nanozymes

Nanozymes are a class of nanomaterials with biocatalytic function and enzyme-like activity, whose advantages include high stability, low cost, and mass production. They can catalyze the substrates of natural enzymes based on specific nanostructures and serve as substitutes for natural enzymes. Their applied research involves a wide range of fields such as biomedicine, environmental governance, agriculture, and food. Molecular logic gates are a new cross-disciplinary discipline, which can simulate the function of silicon circuits on a molecular scale, perform single or multiple input logic operations, and generate logic outputs. A molecular logic gate is a binary operation that converts an input signal into an output signal according to the rules of Boolean logic, generating two signals, a high level, and a low level. The high and low levels represent the "true" and "false" values of the logic gates, and their outputs correspond to "l" and "0" of the molecular logic gates, respectively. The combination of nanozymes and logic gates is a novel and attractive research direction, and the cross-application of the two brings new opportunities and ideas for various fields, such as the construction of efficient biocomputers, intelligent drug delivery systems, and the precise diagnosis of diseases. This review describes the application of logic gates based on nanozymes, which is expected to provide a certain theoretical foundation for researchers' subsequent studies.

Spatial engineering of single-atom Fe adjacent to Cu-assisted nanozymes for biomimetic O2 activation

The precise design of single-atom nanozymes (SAzymes) and understanding of their biocatalytic mechanisms hold great promise for developing ideal bio-enzyme substitutes. While considerable efforts have been directed towards mimicking partial bio-inspired structures, the integration of heterogeneous SAzymes configurations and homogeneous enzyme-like mechanism remains an enormous challenge. Here, we show a spatial engineering strategy to fabricate dual-sites SAzymes with atomic Fe active center and adjacent Cu sites. Compared to planar Fe-Cu dual-atomic sites, vertically stacked Fe-Cu geometry in FePc@2D-Cu-N-C possesses highly optimized scaffolds, favorable substrate affinity, and fast electron transfer. These characteristics of FePc@2D-Cu-N-C SAzyme induces biomimetic O2 activation through homogenous enzymatic pathway, resembling functional and mechanistic similarity to natural cytochrome c oxidase. Furthermore, it presents an appealing alternative of cytochrome P450 3A4 for drug metabolism and drug-drug interaction. These findings are expected to deepen the fundamental understanding of atomic-level design in next-generation bio-inspired nanozymes.

Harmonizing Enzyme-like Cofactors to Boost Nanozyme Catalysis

Engineering isolated metal sites resembling the primary coordination sphere of metallocofactors enables atomically dispersed materials as promising nanozymes. However, most existing nanozymes primarily focus on replicating specific metallocofactors while neglecting other supporting cofactors within active pockets, leading to reduced electron transfer (ET) efficiency and thus inferior catalytic performances. Herein, we report a metal-organic framework UiO-67 nanozyme with atomically dispersed iron sites, which involves multiple tailored enzyme-like nanocofactors that synergistically drive the ET process for enhanced peroxidase-like catalysis. Among them, the linker-coupled atomic iron site plays a critical role in substrate activation, while bare linkers and zirconia nodes facilitate the ET efficiency of intermediates. The synergy of three nanocofactors results in a 4.29-fold enhancement compared with the single effort of isolated metal site-based nanocofactor, holding promise in immunoassay for sensitive detection of chlorpyrifos. This finding opens a new way for designing high-performance nanozymes by harmonizing various nanocofactors at the atomic and molecular scale.

p-d Orbital Hybridization-Engineered PdSn Nanozymes for a Sensitive Immunoassay

Nanozymes with peroxidase-like activity have been extensively studied for colorimetric biosensing. However, their catalytic activity and specificity still lag far behind those of natural enzymes, which significantly affects the accuracy and sensitivity of colorimetric biosensing. To address this issue, we design PdSn nanozymes with selectively enhanced peroxidase-like activity, which improves the sensitivity and accuracy of a colorimetric immunoassay. The peroxidase-like activity of PdSn nanozymes is significantly higher than that of Pd nanozymes. Theoretical calculations reveal that the p-d orbital hybridization of Pd and Sn not only results in an upward shift of the d-band center to enhance hydrogen peroxide (H2O2) adsorption but also regulates the O-O bonding strength of H2O2 to achieve selective H2O2 activation. Ultimately, the nanozyme-linked immunosorbent assay has been successfully developed to sensitively and accurately detect the prostate-specific antigen (PSA), achieving a low detection limit of 1.696 pg mL-1. This work demonstrates a promising approach for detecting PSA in a clinical diagnosis.

Nanocatalysts for modulating antitumor immunity: fabrication, mechanisms and applications

Immunotherapy harnesses the inherent immune system in the body to generate systemic antitumor immunity, offering a promising modality for defending against cancer. However, tumor immunosuppression and evasion seriously restrict the immune response rates in clinical settings. Catalytic nanomedicines can transform tumoral substances/metabolites into therapeutic products in situ, offering unique advantages in antitumor immunotherapy. Through catalytic reactions, both tumor eradication and immune regulation can be simultaneously achieved, favoring the development of systemic antitumor immunity. In recent years, with advancements in catalytic chemistry and nanotechnology, catalytic nanomedicines based on nanozymes, photocatalysts, sonocatalysts, Fenton catalysts, electrocatalysts, piezocatalysts, thermocatalysts and radiocatalysts have been rapidly developed with vast applications in cancer immunotherapy. This review provides an introduction to the fabrication of catalytic nanomedicines with an emphasis on their structures and engineering strategies. Furthermore, the catalytic substrates and state-of-the-art applications of nanocatalysts in cancer immunotherapy have also been outlined and discussed. The relationships between nanostructures and immune regulating performance of catalytic nanomedicines are highlighted to provide a deep understanding of their working mechanisms in the tumor microenvironment. Finally, the challenges and development trends are revealed, aiming to provide new insights for the future development of nanocatalysts in catalytic immunotherapy.

Copper Nanodots-Based Hybrid Hydrogels with Multiple Enzyme Activities for Acute and Infected Wound Repair

Effectively controlling bacterial infection, reducing the inflammation and promoting vascular regeneration are all essential strategies for wound repair. Nanozyme technology has potential applications in the treatment of infections because its non-antibiotic dependent, topical and noninvasive nature. In wound management, copper-based nanozymes have emerged as viable alternatives to antibiotics. In this study, an ultrasmall cupric enzyme with high enzymatic activity is synthesized and added to a nontoxic, self-healing, injectable cationic guar gum (CG) hydrogel network. The nanozyme exhibits remarkable antioxidant properties under neutral conditions, effectively scavenging reactive nitrogen and oxygen species (RNOS). Under acidic conditions, Cu NDs have peroxide (POD) enzyme-like activity, which allows them to eliminate hydrogen peroxides and produce free radicals locally. Antibacterial experiments show that they can kill bacteria and remove biofilms. It reveals that low concentrations of Cu ND/CG decrease the expression of the inflammatory factors in cells and tissues, effectively controlling inflammatory responses. Cu ND/CG hydrogels also inhibit HIF-1α and promote VEGF expression in the wound with the ability to promote vascular regeneration. In vivo safety assessments reveal a favorable biosafety profile. Cu ND/CG hydrogels offer a promising solution for treating acute and infected wounds, highlighting the potential of innovative nanomaterials in wound healing.

Current Advances on the Single-Atom Nanozyme and Its Bioapplications

Nanozymes, a class of nanomaterials mimicking the function of enzymes, have aroused much attention as the candidate in diverse fields with the arbitrarily tunable features owing to the diversity of crystalline nanostructures, composition, and surface configurations. However, the uncertainty of their active sites and the lower intrinsic deficiencies of nanomaterial-initiated catalysis compared with the natural enzymes promote the pursuing of alternatives by imitating the biological active centers. Single-atom nanozymes (SAzymes) maximize the atom utilization with the well-defined structure, providing an important bridge to investigate mechanism and the relationship between structure and catalytic activity. They have risen as the new burgeoning alternative to the natural enzyme from in vitro bioanalytical tool to in vivo therapy owing to the flexible atomic engineering structure. Here, focus is mainly on the three parts. First, a detailed overview of single-atom catalyst synthesis strategies including bottom-up and top-down approaches is given. Then, according to the structural feature of single-atom nanocatalysts, the influence factors such as central metal atom, coordination number, heteroatom doping, and the metal-support interaction are discussed and the representative biological applications (including antibacterial/antiviral performance, cancer therapy, and biosensing) are highlighted. In the end, the future perspective and challenge facing are demonstrated.

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.

Biosystem-Inspired Engineering of Nanozymes for Biomedical Applications

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