Coordinatively unsaturated cobalt single-atom nanozymes for visual pesticides detection by smartphone-based platform

By adjusting the coordination environment of single-atom catalysts,the enzyme-like activity can be finely tuned for highly sensitive biosensing.Herein,we demonstrated that coordinatively unsaturated cobalt-nitrogen sites doped within porous carbon(SA-CoN_(3))could serve as highly efficient oxidase mimic.Compared with the typical planar four-coordination structure(SA-CoN_(4)),the as-obtained single-atom Co nanozymes anchored by three nitrogen atoms are found to display much higher oxidase-like catalytic efficiency.Combined theoretical and experimental analysis revealed that the coordinatively unsaturated Co sites could facilitate adsorption and activation of O_(2) molecule and thus improve their oxidase-like activity.Based on the enhanced oxidase-like activity of SA-CoN_(3),a paper/smartphone sensor for organophosphorus pesticides(OPs)was successfully constructed and used to quantify glyphosate in environmental and food samples with a low detection limit of 0.66μM.This work not only highlights the important role of coordination unsaturation of SA nanozymes for promoting oxidase-like activity,but also provides an easy and cost-effective way to conduct effective quantification of OPs in the field.

D-band center coordination modulated enzyme-like activity in Fe-Cu dual-metal single-atom nanozymes

After explorations in a diversity of single-atom nanozymes(SAzymes),developing dual-centered SAzymes becomes a promising approach for superior catalytic performance.But confusing mechanisms including atomic coordination,spatial configuration,and metal–metal atom interaction hinder the development and design of SAzymes.Herein,a dual-centered Fe-Cu-N_(x)SAzyme exhibits excellent peroxidase(POD)-and catalase(CAT)-like activities with d-band center(ε_(d))coordination of Fe and Cu in multiple reaction stages,which plays a critical role in the adsorption of H_(2)O_(2)molecule and H_(2)O and O_(2)release.Therefore,the dband center coordination,which can be represented byε_(d)(Fe)–ε_(d)(Cu)shifts,leads to the competition between one-side and bilateral adsorption,which determines the favorable reaction path with lower energy barriers.Based on experimental statistics,simulated formation energies,and reaction barriers,3 configurations,Fe-Cu-N6-I,Fe-Cu-N_(8)-II,and Fe-Cu-N_(8)-III,are modeled and validated.Impressively,configuration-dependent catalytic selectivity and the competition between one-side and bilateral adsorption can be unveiled by d-band center coordination paradigm analysis.Theoretical simulations suggest that the unsymmetrical charge distribution over the three Fe-Cu configurations could tune the adsorption strength compared with the counterparts FeN_(4)and CuN_(4).The present work provides a potential route for optimizing enzyme-like catalysis by designing the dual-or even triple-metal SAzymes,which demonstrates the large space to modulate the metal atomic configuration and interaction.

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.

Dual-active-site Fe/Cu single-atom nanozymes with multifunctional specific peroxidase-like properties for S^(2-)detection and dye degradation

Designing single-atom nanozymes with densely exposed metal atom active sites and enhancing catalytic activity to detect pollutants remain a serious challenge.Herein,we reported a single-atom nanozyme with layered stacked Fe/Cu dual active sites(Fe/Cu-NC SAzyme)synthesized via hydrothermal and hightemperature pyrolysis using folic acid as a template.Compared with Fe-NC and Cu-NC SAzyme,Fe/Cu-NC SAzyme has higher peroxidase-like activity,which indicates that the doping of synthesized Fe/Cu bimetals can improve the catalytic activity and that the atomic loading of Fe and Cu in Fe/Cu-NC is 5.5 wt%and 2.27 wt%,respectively.When S^(2-)is added to the Fe/Cu-NC catalytic system,a high-sensitivity and high-selectivity S^(2-)colorimetric sensing platform can be established,with a wide linear range(0.09-6μmol/L)and a low detection limit(30 nmol/L),which can be used to detect S^(2-)in environmental water samples.What’s more,the Fe/Cu-NC SAzyme can activate peroxymonosulfate(PMS)to degrade 99.9%of rhodamine B(Rh B)within 10 min with a degradation kinetics of 0.5943 min^(-1).This work details attractive applications in Fe/Cu-NC SAzyme colorimetric sensing and dye degradation.

Single-atom nanozymes towards central nervous system diseases

Nanozymes have a similar catalytic mechanism to natural enzymes,with excellent performance,facile synthesis,and better stability.Single-atom nanozymes are developed based on single-atom catalysts due to their advantages in coordination structure and electronic configuration,making them highly enzymatic-like biomimetic catalysts.Central nervous system(CNS)diseases have become one of the biggest killers of human health because they are difficult to diagnose and treat,expensive,and result in serious illness.Single-atom nanozymes have been widely used for biomedical applications,especially in oxidative-stressinduced diseases and most CNS diseases which are closely related to oxidative stress.Therefore,single-atom nanozymes show promising application prospects for the treatment of CNS diseases.In addition,due to the outstanding material properties and sensitivity of single-atom nanozymes,they also exhibit great advantages in detecting various CNS disease markers for diagnosis.

Single-atom nanozymes with axial ligand-induced self-adaptive conformation in alkaline medium boost chemiluminescence

Mimicking the structure of natural enzymes for designing advanced alternatives provides great opportunities to address the bottleneck of enzyme-involved chemiluminescence(CL). Herein, according to theoretical calculations, we found that an endogenous axial ligand of M-N-C single-atom nanozymes(SAzymes), originating from OH-spontaneously bonding to the metal center in an alkaline medium, can self-adaptively change its strength to facilitate intermediate steps. Furthermore, the lowest energy barrier of the rate-determining step and the strongest affinity and fastest electron transfer with luminol anion endow CoN-C with the highest peroxidase-like activity. Guided by the theoretical calculations, a series of M-N-C SAzymes(M=Fe, Co,Ni) were synthesized to boost CL, where Co-N-C SAzymes with superior catalytic activity and high selective generation of O_(2)·- were validated. As a proof-of-concept, Co-N-C SAzymes were employed for sensitive detection of acetylcholinesterase and organophosphorus pesticide.

Atomically dispersed hierarchically ordered porous Fe-N-C single-atom nanozymes for dyes degradation

The development of novel nanozymes for environmental contamination remediation is a worthwhile research direction.However,most of the reported nanozymes cannot degrade efficiently due to the limitation of the internal active sites not being able to come into direct contact with contaminants.Therefore,we reported Fe-N-C single-atom nanozymes(SAzymes)with atomically dispersed FeN4 active sites anchored on a three-dimensional hierarchically ordered microporous-mesoporous-macroporous nitrogen doped carbon matrix(3DOM Fe-N-C)for the degradation of a targeted environmental pollutant(rhodamine B(RhB)).The three-dimensional(3D)hierarchically ordered porous structure may accelerate mass transfer and improve the accessibility of active sites.This structure and high metal atom utilization endow Fe-N-C SAzyme with enhanced tri-enzyme-mimic activities,comprising oxidase-mimic,peroxidase-mimic,and catalase-mimic activities.Based on its excellent peroxidase-mimic activity,3DOM Fe-N-C can degrade RhB by hydroxyl radicals(·OH)generated in the presence of hydrogen peroxide.This study provides a new idea for designing porous Fe-N-C SAzymes for environmental contamination remediation.

Recent progress in single-atom nanozymes research

Single-atom nanozyme(SAzyme)is the hot topic of the current nanozyme research.Its intrinsic properties,such as high activity,stability,and low cost,present great substitutes to natural enzymes.Moreover,its fundamental characteristics,i.e.,maximized atom utilizations and well-defined geometric and electronic structures,lead to higher catalytic activities and specificity than traditional nanozymes.SAzymes have been applied in many biomedical areas,such as anti-tumor therapy,biosensing,antibiosis,and anti-oxidation therapy.Here,we will discuss a series of representative examples of SAzymes categorized by their biomedical applications in this review.In the end,we will address the future opportunities and challenges SAzymes facing in their designs and applications.

Deep Insight of Design,Mechanism,and Cancer Theranostic Strategy of Nanozymes

Since the discovery of enzyme-like activity of Fe3O4 nanoparticles in 2007,nanozymes are becoming the promising substitutes for natural enzymes due to their advantages of high catalytic activity,low cost,mild reaction conditions,good stability,and suitable for large-scale production.Recently,with the cross fusion of nanomedicine and nanocatalysis,nanozyme-based theranostic strategies attract great attention,since the enzymatic reactions can be triggered in the tumor microenvironment to achieve good curative effect with substrate specificity and low side effects.Thus,various nanozymes have been developed and used for tumor therapy.In this review,more than 270 research articles are discussed systematically to present progress in the past five years.First,the discovery and development of nanozymes are summarized.Second,classification and catalytic mechanism of nanozymes are discussed.Third,activity prediction and rational design of nanozymes are focused by highlighting the methods of density functional theory,machine learning,biomimetic and chemical design.Then,synergistic theranostic strategy of nanozymes are introduced.Finally,current challenges and future prospects of nanozymes used for tumor theranostic are outlined,including selectivity,biosafety,repeatability and stability,in-depth catalytic mechanism,predicting and evaluating activities.

Advances in Single-Atom Nanozymes Research

Nanozymes with intrinsic enzyme-like properties have attracted significant interest owing to their capability to address the limitations of traditional enzymes such as fragility,high cost and dificult mass production.However,the currently reported nanozymes are generally less active than natural enzymes.In recent years,with the rapid development of nanoscience and nanotechnology,single-atom nanozymes(SAzymes)with well-defined electronic and geometric structures have shown a promise to serve as direct surrogates of traditional enzymes by mimicking the highly evolved catalytic center of natural enzymes.In this review,we will introduce the enzymatic characteristics and recent advances of SAzymes,and summarize their significant applications from in vitro detection to in vivo monitoring and therapy.

Emerging single-atom nanozymes for catalytic biomedical uses

The past four years have witnessed booming progress in single-atom nanozymes(SANs),one of the newest generations of nanozymes with atomically dispersed metal sites for catalytic biomedical uses.They show distinct advantages over their nanoparticle-based counterparts,such as well-defined electronic/geometric structures and complete atomic utilization efficiency,thus offering opportunities to develop advanced nanozymes for practical uses.The atomically dispersed active centers in SANs could also facilitate the precise regulation of catalytic performance,while probing structure–activity relationship for in-depth understanding of mechanism.In this review,we first introduce the synthetic approaches,surface engineering,and characterization techniques of SANs.Subsequently,we discuss the enzyme-like properties of SANs,including some strategies for boosting their catalytic activities.Furthermore,we present their biomedical applications,ranging from biosensors,antibacterial uses,antioxidants,to therapeutics.Finally,the challenges and opportunities of SANs are prospected.

A Review on Metal-and Metal Oxide-Based Nanozymes:Properties,Mechanisms,and Applications

Since the ferromagnetic(Fe_(3)O_(4))nanoparticles were firstly reported to exert enzyme-like activity in 2007,extensive research progress in nanozymes has been made with deep investigation of diverse nanozymes and rapid development of related nanotechnologies.As promising alterna-tives for natural enzymes,nanozymes have broadened the way toward clinical medicine,food safety,environmental monitoring,and chemical production.The past decade has witnessed the rapid development of metal-and metal oxide-based nanozymes owing to their remarkable physicochemical proper-ties in parallel with low cost,high stability,and easy storage.It is widely known that the deep study of catalytic activities and mechanism sheds sig-nificant influence on the applications of nanozymes.This review digs into the characteristics and intrinsic properties of metal-and metal oxide-based nanozymes,especially emphasizing their catalytic mechanism and recent applications in biological analysis,relieving inflammation,antibacterial,and cancer therapy.We also conclude the present challenges and provide insights into the future research of nanozymes constituted of metal and metal oxide nanomaterials.

Nanozymes:Versatile Platforms for Cancer Diagnosis and Therapy

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

Gold Nanozymes:From Concept to Biomedical Applications

In recent years,gold nanoparticles have demonstrated excellent enzyme-mimicking activities which resemble those of peroxidase,oxidase,catalase,superoxide dismutase or reductase.This,merged with their ease of synthesis,tunability,biocompatibility and low cost,makes them excellent candidates when compared with biological enzymes for applications in biomedicine or biochemical analyses.Herein,over 200 research papers have been systematically reviewed to present the recent progress on the fundamentals of gold nanozymes and their potential applications.The review reveals that the morphology and surface chemistry of the nanoparticles play an important role in their catalytic properties,as well as external parameters such as pH or temperature.Yet,real applications often require specific biorecognition elements to be immobilized onto the nanozymes,leading to unexpected positive or negative effects on their activity.Thus,rational design of efficient nanozymes remains a challenge of paramount importance.Different implementation paths have already been explored,including the application of peroxidase-like nanozymes for the development of clinical diagnostics or the regulation of oxidative stress within cells via their catalase and superoxide dismutase activities.The review also indicates that it is essential to understand how external parameters may boost or inhibit each of these activities,as more than one of them could coexist.Likewise,further toxicity studies are required to ensure the applicability of gold nanozymes in vivo.Current challenges and future prospects of gold nanozymes are discussed in this review,whose significance can be anticipated in a diverse range of fields beyond biomedicine,such as food safety,environmental analyses or the chemical industry.

MXene-Based Composites as Nanozymes in Biomedicine: A Perspective

MXene-based nanozymes have garnered considerable attention because of their potential environmental and biomedical applications.These materials encompass alluring and manageable catalytic performances and physicochemical features,which make them suitable as(bio)sensors with high selectivity/sensitivity and efficiency.MXene-based structures with suitable electrical conductivity,biocompatibility,large surface area,optical/magnetic properties,and thermal/mechanical features can be applied in designing innovative nanozymes with area-dependent electrocatalytic performances.Despite the advances made,there is still a long way to deploy MXene-based nanozymes,especially in medical and healthcare applications;limitations pertaining the peroxidaselike activity and sensitivity/selectivity may restrict further practical applications of pristine MXenes.Thus,developing an efficient surface engineering tactic is still required to fabricate multifunctional MXene-based nanozymes with excellent activity.To obtain MXene-based nanozymes with unique physicochemical features and high stability,some crucial steps such as hybridization and modification ought to be performed.Notably,(nano)toxicological and long-term biosafety analyses along with clinical translation studies still need to be comprehensively addressed.Although very limited reports exist pertaining to the biomedical potentials of MXene-based nanozymes,the future explorations should transition toward the extensive research and detailed analyses to realize additional potentials of these structures in biomedicine with a focus on clinical and industrial aspects.In this perspective,therapeutic,diagnostic,and theranostic applications of MXene-based nanozymes are deliberated with a focus on future per-spectives toward more successful clinical translational studies.The current state-of-the-art biomedical advances in the use of MXene-based nanozymes,as well as their developmental challenges and future prospects are also highlighted.In view of the fascinating properties of MXene-based nanozymes,these materials can open significant new opportunities in the future of bio-and nanomedicine.

Nanozymes in Point-of-Care Diagnosis:An Emerging Futuristic Approach for Biosensing

Nanomaterial-based artificial enzymes(or nanozymes) have attracted great attention in the past few years owing to their capability not only to mimic functionality but also to overcome the inherent drawbacks of the natural enzymes.Numerous advantages of nanozymes such as diverse enzyme-mimicking activities,low cost,high stability,robustness,unique surface chemistry,and ease of surface tunability and biocompatibility have allowed their integration in a wide range of biosensing applications. Several metal,metal oxide,metal–organic framework-based nanozymes have been exploited for the development of biosensing systems,which present the potential for point-of-care analysis. To highlight recent progress in the field,in this review,more than 260 research articles are discussed systematically with suitable recent examples,elucidating the role of nanozymes to reinforce,miniaturize,and improve the performance of point-of-care diagnostics addressing the ASSURED(a ordable,sensitive,specific,user-friendly,rapid and robust,equipment-free and deliverable to the end user) criteria formulated by World Health Organization. The review reveals that many biosensing strategies such as electrochemical,colorimetric,fluorescent,and immunological sensors required to achieve the ASSURED standards can be implemented by using enzyme-mimicking activities of nanomaterials as signal producing components. However,basic system functionality is still lacking. Since the enzyme-mimicking properties of the nanomaterials are dictated by their size,shape,composition,surface charge,surface chemistry as well as external parameters such as pH or temperature,these factors play a crucial role in the design and function of nanozyme-based point-of-care diagnostics. Therefore,it requires a deliberate exertion to integrate various parameters for truly ASSURED solutions to be realized. This review also discusses possible limitations and research gaps to provide readers a brief scenario of the emerging role of nanozymes in state-of-the-art POC diagnosis system development for futuristic biosensing applications.

Functional Superoxide Dismutase Mimics Become Diverse: From Simple Compounds on Prebiotic Earth to Nanozymes

Inorganic solids with enzyme-like activity are promising to overcome many restrictions of native enzymes in application.Especially attractive are nanoparticles with superoxide dismutase(SOD)activity,due to their ability to reduce the damaging properties of reactive oxygen species within cells and organism.This review discusses the necessary requirements for nanoparticles to have SOD activity and reveals a close relationship between catalysis on prebiotic earth and the recent SOD mimics.This review also aims to highlight the progress in the development of SOD mimicking nanoparticles.We give a broad overview of nanoparticles with SOD activity,based on their material make-up,to underline their increasing diversity.

Nanozyme‑Engineered Hydrogels for Anti‑Inflammation and Skin Regeneration

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

Boric Acid-Assisted Pyrolysis for High-Loading Single-Atom Catalysts to Boost Oxygen Reduction Reaction in Zn-Air Batteries

The emerging of single-atom catalysts(SACs)offers a great opportunity for the development of advanced energy storage and conversion devices due to their excellent activity and durability,but the actual mass production of high-loading SACs is still challenging.Herein,a facile and green boron acid(H_(3)BO_(3))-assisted pyrolysis strategy is put forward to synthesize SACs by only using chitosan,cobalt salt and H_(3)BO_(3)as precursor,and the effect of H_(3)BO_(3)is deeply investigated.The results show that molten boron oxide derived from H_(3)BO_(3)as ideal high-temperature carbonization media and blocking media play important role in the synthesis process.As a result,the acquired Co/N/B tri-doped porous carbon framework(Co-N-B-C)not only presents hierarchical porous structure,large specific surface area and abundant carbon edges but also possesses high-loading single Co atom(4.2 wt.%),thus giving rise to outstanding oxygen catalytic performance.When employed as a catalyst for air cathode in Zn-air batteries,the resultant Co-N-B-C catalyst shows remarkable power density and long-term stability.Clearly,our work gains deep insight into the role of H_(3)BO_(3)and provides a new avenue to synthesis of high-performance SACs.

Single-atom catalysts for the electrochemical reduction of carbon dioxide into hydrocarbons and oxygenates

The electrochemical reduction of carbon dioxide offers a sound and economically viable technology for the electrification and decarbonization of the chemical and fuel industries.In this technology,an electrocatalytic material and renewable energy-generated electricity drive the conversion of carbon dioxide into high-value chemicals and carbon-neutral fuels.Over the past few years,single-atom catalysts have been intensively studied as they could provide near-unity atom utilization and unique catalytic performance.Single-atom catalysts have become one of the state-of-the-art catalyst materials for the electrochemical reduction of carbon dioxide into carbon monoxide.However,it remains a challenge for single-atom catalysts to facilitate the efficient conversion of carbon dioxide into products beyond carbon monoxide.In this review,we summarize and present important findings and critical insights from studies on the electrochemical carbon dioxide reduction reaction into hydrocarbons and oxygenates using single-atom catalysts.It is hoped that this review gives a thorough recapitulation and analysis of the science behind the catalysis of carbon dioxide into more reduced products through singleatom catalysts so that it can be a guide for future research and development on catalysts with industry-ready performance for the electrochemical reduction of carbon dioxide into high-value chemicals and carbon-neutral fuels.