Size-dependent peroxidase-like catalytic activity of Fe_3O_4 nanoparticles

Peroxidase-like catalytic properties of Fe3O4 nanoparficles （NPs） with three different sizes, synthesized by chemical coprecipitation and sol-gel methods, were investigated by UV-vis spectrum analysis. By comparing Fe3O4 NPs with average diameters of 11, 20, and 150 nm, we found that the catalytic activity increases with the reduced nanoparticle size. The electrochemical method to characterize the catalytic activity of Fe3O4 NPs using the response currents of the reaction product and substrate was also developed.

Large scale and controllable preparation of W2C nanorods or WC nanodots with peroxidase-like catalytic activity

WC nanorods or WC nanodots are prepared via an easy,shape-controllable and large-scale preparation technique.Results reveal that each of the WC nanorods and WC nanodots has a peroxidase-like activity.Besides,the peroxidase-like activity of WC is the first time to be demonstrated.The catalytic efficiency of WC nanorods is much higher than that of WC nanodots and chemical condition range of WC can be wider than that of WC,which indicates that WC is likely to be used as artificial mimetic peroxidase or in-situ amplified colorimetric immunoassay.

Silicon dioxide-protection boosting the peroxidase-like activity of Fe single-atom catalyst for combining chemo-photothermal therapy

Carbon-based single-atom catalysts(SACs)have been widely studied in the field of biomedicine due to their excellent catalytic performance.However,carbon-based SACs usually aggregate during pyrolysis,which leads to the reduction of catalytic activity.Here,we describe a method to improve the monodispersion of SACs using silicon dioxide as a protective layer.The decoration of silicon dioxide serves as a buffer layer for individual nanoparticles,which is not destroyed during the pyrolysis process,ensuring the single-particle dispersion of the nanoparticles after etching.This approach increased the hydroxyl groups on the surface of Fe-SAC(Fe-SAC-SE)and improved its water solubility,resulting in a four times enhancement of the peroxidase(POD)-like activity of Fe-SAC-SE(58.4 U/mg)than that of non-protected SACs(13.9 U/mg).The SiO_(2)-protection approach could also improve the catalytic activities of SACs with other metals such as Mn,Co,Ni,and Cu,indicating its generality for SACs preparation.Taking advantage of the high POD-like activity,photothermal properties,and large specific surface area of Fe-SAC-SE,we constructed a synergistic therapeutic system(Fe-SAC-SE@DOX@PEG)for combining the photothermal therapy,catalytic therapy,and chemotherapy.It was verified that the photothermal properties of Fe-SAC-SE@DOX@PEG could effectively improve its POD-like activity,exhibiting excellent tumor-killing performance at the cellular level.This work may provide a general approach to improve the performances of SACs for disease therapy and diagnosis.

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.

Biocompatible carbon nitride quantum dots nanozymes with high nitrogen vacancies enhance peroxidase-like activity for broadspectrum antibacterial

Nanozyme antibacterial agents with high enzyme-like catalytic activity and strong bacteria-binding ability have provided an alternative method to efficiently disinfect drug-resistance microorganism.Herein,the carbon nitride quantum dots(CNQDs)nanozymes with high nitrogen vacancies(NVs)were mass-productively prepared by a simple ultrasonic-crushing method assisted by propylene glycol.It was found that the NVs of CNQDs were stemmed from the selective breaking of surface N-(C)_(2)sites,accounting for 6.2%.Experiments and density functional theory(DFT)simulations have demonstrated that the presence of NVs can alter the local electron distribution and extend theπ-electron delocalization to enhance the peroxidase-like activity.Biocompatible CNQDs could enter inside microorganisms by diffusion and elevate the bacteria-binding ability,which enhanced the accurate and rapid attack of·OH to the microorganisms.The sterilization rate of CNQDs against Gram-negative bacteria(E.coli),Gram-positive bacteria(S.aureus,B.subtilis),fungi(R.solani)reaches more than 99%.Thus,this work showed great potential for engineered nanozymes for broad-spectrum antibacterial in biomedicine and environmental protection.

Bimetallic synergistic Pd-Pt icosahedra as highly active peroxidase-like mimics for colorimetric analysis

Thanks to the synergistic effect,the bimetallic catalysts show better catalytic activity than the single metal cat-alysts and become a focus of research in heterogeneous catalysis.In this study,we successfully prepared Pd-Pt icosahedra which show high peroxidase-like activity under the synergistic effects of Pd and Pt.V max of the Pd-Pt icosahedra was significantly enhanced by 1.66 times for 3,3’,5,5’-tetramethylbenzidine(TMB)as the substrate and 1.23 times for H_(2)O_(2) as the substrate,compared to that of the Pd icosahedra alone.By harnessing the supe-rior peroxidase-like activity of Pd-Pt icosahedra,we successfully utilized Pd-Pt icosahedral nanozymes in various biological analyses based on colorimetry.In most cases,using a Pd-Pt icosahedra/H_(2)O_(2)/TMB system,glucose,glutathione(GSH),acid phosphatase(ACP),and alkaline phosphatase(ALP)were detected over a wide range of 0.05∼0.20 mM,0∼20 mM,0∼10 U/L and 0∼12 U/L.In this study,we prepared a novel bimetallic nanozyme that exhibited excellent peroxidase-like activity owing to the bimetallic synergistic effect,thus demonstrating the promising potential of Pd-Pt icosahedra in the field of bioanalysis.

One-pot synthesis of bimetallic Fe/Co incorporated silica hollow spheres with superior peroxidase-like activity

Mesoporous silica hollow spheres with a homogenous and high content distribution of Fe and Co were synthesized by a facile one-pot hydrothermal process. The sub-nanometer bimetallic components inside the silica framework facilitate the stable fixation and the open accessibility to active sites. The co-doped Fe/Co in the spheres showed excellent peroxidase-like activity and much higher catalytic performance than their monometallic-supported spheres. The synergistic effect between Fe and Co promotes the continuous formation of functional radicals during the oxidation process and thus accelerates the reaction rate. When used for colorimetric detection of hydrogen peroxide(H_(2)O_(2)), the Fe/Co incorporated silica hollow spheres show the capability of detection of H_(2)O_(2) in a wide range(10-250 μmol/L) and with the low detection limit of 0.012 ppm.

A peroxidase-like single-atom Fe-N_(5)active site for effective killing human lung adenocarcinoma cells

Single-atom catalyst(SAC)is one of the newest catalysts,and attracts people’s wide attention in cancer therapy based on their characteristics of maximum specific catalytic activity and high stability.We designed and synthesized a Fe-N decorated graphene nanosheet(Fe-N5/GN SAC)with the coordination number of five.Through enzymology and theoretical calculations,the Fe-N5/GN SAC has outstanding intrinsic peroxidase-like catalytic activity due to single-atom Fe site with five-N-coordination structure.We explored its potential on lung cancer therapy,and found that it could kill human lung adenocarcinoma cells(A549)by decomposing hydrogen peroxide(H_(2)O_(2))into toxic reactive oxygen species(ROS)under acidic microenvironment in threedimensional(3D)lung cancer cell model.Our study demonstrates a promising application of SAC with highly efficient single-atom catalytic sites for cancer treatment.

Diatomic active sites nanozymes:Enhanced peroxidase-like activity for dopamine and intracellular H2O2 detection

Considering intracellular hydrogen peroxide(H_(2)O_(2))plays pivotal roles in the regulation of serial biological processes,the in-situ detection of intracellular H2O2 has attracted an extensive attention.In the present work,an atomically dispersed diatomic active sites Nanozymes(FeN_(3)/PtN_(4)-single-atom nanozymes(SAzyme))was prepared exhibiting enhanced peroxidase-like activity.The obvious synergistic effect between Fe-Pt heteronuclear diatomic active sites was confirmed by series of characterization and density functional theory(DFT).The peroxidase-like activity of Fe-sites could be substantially enhanced by the bonded Pt-sites via the modulation effect.As a consequence,the gap between the d-band centre(εd)of Fe 3d orbitals and the Fermi energy level was narrowed and the electronic interaction could be strengthened,leading to a lower free energy barrier and a lower activation energy as well as fortified metal-O bonding in the kinetic pathway.Therefore,the constructed FeN3/PtN4-SAzyme exhibited higher peroxidase-like activity than that of FeN4-SAzyme.The FeN3/PtN4-SAzyme-assisted oxidation of 3,3',5,5'-tetramethylbenzidine(TMB)facilitated the colorimetric detection of dopamine(DA),an important biomolecule.The linear detection range and limit of detection(LOD)of DA and H_(2)O_(2) were 1-10 μM,0.01-1.0 mM and 0.109 μM,7.97 μM,respectively.In addition,the constructed SAzymes were also applied for the in-situ detection of intracellular H2O2,expanding the application scope of the newborn SAzymes.

Palladium Nanoparticles/Graphdiyne Oxide Nanocomposite with Excellent Peroxidase-like Activity and Its Application for Glutathione Detection

In this study, palladium nanoparticles loaded graphdiyne oxide (Pd/GDYO) nanocomposite were fabricated by in-situ reduction of palladium chloride in the dispersion of GDYO, and characte-rized by Raman spectra, transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The synthesized Pd/GDYO was first found to have catalytic activities similar to those of the peroxidase enzyme, which can catalyze the oxidation of peroxidase substrate 3,3',5,5'-tetramethylbenzidine(TMB) in the presence of hydrogen peroxide(H2O2). Steady-state kinetic studies showed that the catalytic reaction of Pd/GDYO follows a ping-pong mechanism, and Pd/GDYO has a stronger activity to TMB with a Michaelis constant(Km) value of 5.32×10-4 mmol/L. Based on the shielding effect of glutathione(GSH) on the Pd/GDYO-H2O2-TMB reaction system, a colorimetric detection method for GSH was deve-loped with a wide linear range from 0.1 μmol/L to 40 μmol/L and a limit of detection of 0.1 μmol/L. The method was successfully applied for fast and accurate detection of GSH in injection powder drugs. It was expected that this peroxidase-like Pd/GDYO nano- composite would have wide applications in the fields of biomedicine and environmental chemistry.

Synergistic Lewis acid-base sites of ultrathin porous Co_(3)O_(4)nanosheets with enhanced peroxidase-like activity

Surface Lewis acid-base sites in crystal structure may influence the physicochemical properties and the catalytic performances in nanozymes.Understanding the synergistic effect mechanism of Co_(3)O_(4)nanozymes towards substances(3,3’,5,5’-tetramethylbenzidine(TMB)and hydrogen peroxide(H2O2))induced by surface Lewis acid-base sites is important to enhance the efficiency for peroxidase-like reaction.Herein,ultrathin porous Co_(3)O_(4)nanosheets with abundant Lewis acid-base sites were prepared by sodium borohydride(NaBH4)reduction treatment,which exhibited high-efficiency peroxidase-like activity compared with original Co_(3)O_(4)nanosheets.The Lewis acid-base sites for ultrathin porous Co_(3)O_(4)nanosheets nanozyme were owing to the coordination unsaturation of Co ions and the formation of defect structure.Ultrathin porous Co_(3)O_(4)nanosheets had 18.26-fold higher catalytic efficiency(1.27×10^(-2)s^(-1)·mM^(-1))than that of original Co_(3)O_(4)(6.95×10^(-4)s^(-1)·mM^(-1))in oxidizing TMB substrate.The synergistic effect of surface acid and base sites can enhance the interfacial electron transfer process of Co_(3)O_(4)nanosheets,which can be a favor of absorption substrates and the generation of reactive intermediates such as radicals.Furthermore,the limit of detection of hydroquinol was 0.58μM for ultrathin porous Co_(3)O_(4)nanosheets,965-fold lower than original Co_(3)O_(4)(560μM).Besides,the linear range of ultrathin porous Co_(3)O_(4)nanosheets was widely with the concentration of 5.0-1,000μM.Colorimetric detection of hydroquinol by agarose-based hydrogel membrane was provided based on excellent peroxidase-like properties.This study provided insights into designing high-performance nanozymes for peroxidase-like catalysis via a strategy of solid surface acid-base sites engineering.

Hierarchical micro-nanostructures from polyoxometalates and polydopamine:Characterization,electrochemical and intrinsic peroxidase-like properties

Hybrid composite materials with hierarchical structures have attracted continuing attention for their enhanced features and various applications.The new hybrid composites XW_(9)@PDA(XW_(9) means Na_(8)H[α-PW_(9)O_(34)],Na_(10)[α-SiW_(9)O_(34)]and Na_(10)[α-GeW_(9)O_(34)];PDA means polydopamine)have been synthesized for potential sensing applications.The effect of polyoxometalates on the formation of the hybrid composites was investigated.Scanning electron microscopy(SEM)supported the obtained XW_(9)@PDA were hierarchical microsphere.By monitoring the reaction of classical peroxidase substrate o-phenylenediamine(OPD)to form yellow 2,3-diaminophenazine(DAB)in the presence of H_(2)O_(2),the peroxidase-like activity of XW_(9)@PDA was calculated.The results showed that XW_(9)@PDA still keep the peroxidase-like activity and have 505.98%,208.58%and 582.78%enhancement in intrinsic catalytic activity for PW_(9)@PDA,SiW_(9)@PDA and GeW_(9)@PDA.Among the three composites,PW_(9)@PDA showed the highest peroxidase-like activity.Therefore,PW_(9)@PDA was applicable to the colorimetric and electrochemical sensing for H_(2)O_(2).

Green synthesis of Au@WSe_(2) hybrid nanostructures with the enhanced peroxidase-like activity for sensitive colorimetric detection of glucose

We report a colorimetric method for glucose detection based on Au nanoparticle-decorated WSe_(2)(Au@WSe_(2))hybrid nanostructures.These hybrid structures are easily synthesized by simply stirring HAuCl_(4) precursor with WSe_(2) nanosheets in aqueous solution.Owing to strong synergistic catalytic effects of Au nanoparticles and WSe_(2) nanosheets,the Au@WSe_(2) hybrid nanostructures exhibit enhanced peroxidase-like activity(about 2-fold higher compared to WSe_(2) nanosheets alone)for 3,3',5,5'-tetramethylbenzidine oxidation by H_(2)O_(2).Based on the highly catalytical property,the colorimetric method for glucose detection is established by coupling glucose oxidase(GOx).The detection limit of glucose is 3.66 pM.Moreover,the proposed colorimetric method is applicable to glucose detection in serum samples and is promising for applications in biomedical fields.

CNT-Modified MIL-88(NH_(2))-Fe for Enhancing DNA-Regulated Peroxidase-Like Activity

Over the past few decades,the enzyme-mimicking activity of metal-organic frameworks(MOFs)accompanied with struc-tural characteristics has aroused much attention.However,pure MOFs have low affinity with DNA.Here,iron-based MOFs with acidized carbon nanotubes(CNTs)via a simple hydrothermal process have been synthesized,named as MIL-88(NH_(2))-Fe@CNTs.CNTs can enhance the affinity between MOF and DNA,achieving flexible regulation of their catalytic activity benefiting from the strongπ−πstacking between CNTs and DNA.Meanwhile,in comparison with conventional iron-based MOFs,the addition of CNTs,which contributes to the acceleration of electron transfer,endowing as-prepared nanocomposites remarkably enhanced peroxidase-like activity to achieve an ultrasensitive detection of H_(2)O_(2) with the LOD of 17.64μg/L.Notably,the as-prepared nanocomposites with adsorbed DNA displayed excellent affinity towards both TMB(3,3′,5,5′-tetramethylbenzidine)substrates and H_(2)O_(2) as well as high catalytic velocity.On the basis of their switchable peroxidase-like activity regulated by different length or sequence of ssDNA,it is believed that our-prepared MOF-based nanomaterials would be promising for fabricating versatile and sensitive label-free colorimetric assays for diverse targets.

Peroxidase-Like Reactivity at Iron-Chelation Sites in a Mesoporous Synthetic Melanin

High catalytic activity and substrate specificity make enzymes a rich source of inspiration for catalyst development.Co-opting the advantages of natural materials while tuning them to a modified form and purpose,however,is not a straightforward synthetic task.Polymerization of L-3,4-dihydroxyphenylalanine(L-DOPA)results in amorphous polymer nanoparticles that are similar in many ways to natural eumelanin.Herein,the authors introduce mesoporosity and iron ion chelation to synthesize a variant of the L-DOPA polymer with high peroxidase-like activity.Our results indicate catalytic reaction with peroxide under mildly acidic conditions(pH 5.4 and 6)with a greater maximum reaction velocity(Vmax)than horseradish peroxidase(HRP)at optimal pH 3.5–4.5.Comparison between Fe(Ⅲ)and Fe(Ⅱ)loading indicates that either can be used as a starting point to trigger reactivity,though Fe(Ⅱ)loading leads to materials with twice the Vmax of the Fe(Ⅲ)-loaded sample.The lack of catalyst degradation despite the redox changes and presence of radical species is consistent with the robust nature and redox versatility of polydopamine-based materials and demonstrates strong potential as a versatile redox-catalysis platform.

Peroxidase-like active Cu-ZIF-8 with rich copper(I)-nitrogen sites for excellent antibacterial performances toward drug-resistant bacteria

Bacterial pathogens pose a serious threat to human health,and there is an urgent need to develop highly effective antibacterial materials to eliminate the increasingly serious contamination of drug-resistant bacteria.Here,a Cu-doped ZIF-8 particle with unsaturated copper exhibits high peroxidase-like activity.99.998%antibacterial efficiency against S.aureus can be achieved for 30 min at a low concentration of 50μg·mL^(−1),as well as complete sterilization against E.coli(up to 8 log).99.999%antibacterial efficiency against Methicillin-resistant Staphylococcus aureus can be achieved,performing orders of magnitude higher than Vancomycin.The mechanism shows that the unsaturated Cu-Nx sites are enzyme-like active centers,which could promote the consumption of bacteria reducing substances by H_(2)O_(2),and the generated*OH further aggravates bacterial oxidative stress and membrane damage.More importantly,the oxidation activity of adsorbed oxygen species on Cu-ZIF-8 is enhanced by charge transfer and structural changes between the ligand and copper center like natural enzymes.Cu-doped ZIF-8 with peroxidase-like activity shows great potential in antibacterial application and the revealed catalytic mechanism is helpful for understanding the high antibacterial activity of nanoparticles with Cu-Nx sites.

Tuning Atomically Dispersed Fe Sites in Metal–Organic Frameworks Boosts Peroxidase‑Like Activity for Sensitive Biosensing

Although nanozymes have been widely developed,accurate design of highly active sites at the atomic level to mimic the electronic and geometrical structure of enzymes and the exploration of underlying mechanisms still face significant challenges.Herein,two functional groups with opposite electron modulation abilities(nitro and amino)were introduced into the metal–organic frameworks(MIL-101(Fe))to tune the atomically dispersed metal sites and thus regulate the enzymelike activity.Notably,the functionalization of nitro can enhance the peroxidase(POD)-like activity of MIL-101(Fe),while the amino is poles apart.Theoretical calculations demonstrate that the introduction of nitro can not only regulate the geometry of adsorbed intermediates but also improve the electronic structure of metal active sites.Benefiting from both geometric and electronic effects,the nitro-functionalized MIL-101(Fe)with a low reaction energy barrier for the HO*formation exhibits a superior POD-like activity.As a concept of the application,a nitro-functionalized MIL-101(Fe)-based biosensor was elaborately applied for the sensitive detection of acetylcholinesterase activity in the range of 0.2–50 mU mL−1 with a limit of detection of 0.14 mU mL−1.Moreover,the detection of organophosphorus pesticides was also achieved.This work not only opens up new prospects for the rational design of highly active nanozymes at the atomic scale but also enhances the performance of nanozyme-based biosensors.

Iron-Imprinted Single-Atomic Site Catalyst-Based Nanoprobe for Detection of Hydrogen Peroxide in Living Cells

Fe-based single-atomic site catalysts(SASCs),with the natural metalloproteases-like active site structure,have attracted widespread attention in biocatalysis and biosensing.Precisely,controlling the isolated single-atom Fe-N-C active site structure is crucial to improve the SASCs’performance.In this work,we use a facile ion-imprinting method(IIM)to synthesize isolated Fe-N-C single-atomic site catalysts(IIM-Fe-SASC).With this method,the ion-imprinting process can precisely control ion at the atomic level and form numerous well-defined single-atomic Fe-N-C sites.The IIM-Fe-SASC shows better peroxidase-like activities than that of non-imprinted references.Due to its excellent properties,IIM-Fe-SASC is an ideal nanoprobe used in the colorimetric biosensing of hydrogen peroxide(H_(2)O_(2)).Using IIM-Fe-SASC as the nanoprobe,in situ detection of H_(2)O_(2)generated from MDA-MB-231 cells has been successfully demonstrated with satisfactory sensitivity and specificity.This work opens a novel and easy route in designing advanced SASC and provides a sensitive tool for intracellular H_(2)O_(2)detection.

Highly sensitive nanozyme strip:An effective tool for forensic material evidence identification

During criminal case investigations,blood evidence tracing is critical for criminal investigation.However,the blood stains are often cleaned or covered up after the crime,resulting in trace residue and difficult tracking.Therefore,a highly sensitive and specific method for the rapid detection of human blood stains remains urgent.To solve this problem,we established a nanozyme-based strip for rapid detection of blood evidence with high sensitivity and specificity.To construct reliable nanozyme strips,we synthesized CoFe_(2)O_(4) nanozymes with high peroxidase-like activity by scaling up to gram level,which can be supplied for six million tests,and conjugated antibody as a detection probe in nanozyme strip.The developed CoFe_(2)O_(4) nanozyme strip can detect human hemoglobin(HGB)at a concentration as low as 1 ng/mL,which is 100 times lower than the commercially available colloidal gold strips(100 ng/mL).Moreover,this CoFe_(2)O_(4) nanozyme strip showed high generality on 12 substrates and high specificity to human HGB among 13 animal blood samples.Finally,we applied the developed CoFe_(2)O_(4) nanozyme strip to successfully detect blood stains in three real cases,where the current commercial colloidal gold strip failed to do.The results suggest that the CoFe_(2)O_(4) nanozyme strip can be used as an effective on-scene detection method for human blood stains,and can further be used as a long-term preserved material evidence for traceability inquiry.

Predesigned covalent organic framework with sulfur coordination: Anchoring Au nanoparticles for sensitive colorimetric detection of Hg(Ⅱ)

Targeted construction of new covalent organic frameworks(COFs)with specific purposes and rationalities to build colorimetric assay platform for environmental pollutant monitoring have attracted increasing interest.However,it is still challenging due to lack of available coordination sites inside COFs pores and only a slight bonding ability for anchoring metal.In this work,a two-dimensional(2D)COFs(termed as Tz-COF)with high crystallinity,excellent chemical stability,and abundant sulfur coordination in its skeletons was synthesized and used for the confined growth of Au NPs.It was found that the Au NPs showed significant dispersibility for the support of Tz-COF.The proposed Tz-COF@Au NPs possessed outstanding Hg^(2+)-activated peroxidase-like activity benefited from physicochemical properties of gold amalgam and synergistic effect between COFs and Au NPs to oxidize chromogenic substrate.Based on highly efficient activity and distinctive color evolution,the strategy for detecting Hg^(2+)was developed and successfully applied to determine the content of Hg^(2+)in real environmental samples.This work manifests that a potential strategy to establish a colorimetric assay platform for environmental pollutant monitoring based on the targeted manufacturing of novel COFs with specific functions.