Double enzyme mimetic activities of multifunctional Ag nanoparticle-decorated Co_(3)V_(2)O_(8)hollow hexagonal prismatic pencils for application in colorimetric sensors and disinfection

Since the catalytic activity of most nanozymes is still far lower than the corresponding natural enzymes,there is urgent need to discover novel highly efficient enzyme-like materials.In this work,Co_(3)V_(2)O_(8)with hollow hexagonal prismatic pencil structures were prepared as novel artificial enzyme mimics.They were then decorated by photo-depositing Ag nanoparticles(Ag NPs)on the surface to further improve its catalytic activities.The Ag NPs decorated Co_(3)V_(2)O_(8)(ACVPs)showed both excellent oxidase-and peroxidase-like catalytic activities.They can oxidize the colorless 3,3’,5,5’-tetramethylbenzidine rapidly to induce a blue change.The enhanced enzyme mimetic activities can be attributed to the surface plasma resonance(SPR)effect of Ag NPs as well as the synergistic catalytic effect between Ag NPs and Co_(3)V_(2)O_(8),accelerating electron transfer and promoting the catalytic process.ACVPs were applied in constructing a colorimetric sensor,validating the occurrence of the Fenton reaction,and disinfection,presenting favorable catalytic performance.The enzyme-like catalytic mechanism was studied,indicating the chief role of⋅O_(2)-radicals in the catalytic process.This work not only discovers a novel functional material with double enzyme mimetic activity but also provides a new insight into exploiting artificial enzyme mimics with highly efficient catalytic ability.

Ceria Nanoparticles as Enzyme Mimetics

In the past decades, enzyme mimetics based on ceria nanoparticles （nanoceria） have been developed as potential substitutes for nature enzymes. The mixed valence states of cerium and the patterns of oxygen vacancies on crystal planes result in different enzyme mimetic activities. In this review we survey the bio-applications of nanoceria-based enzyme mimetics as well as the underlying mechanisms. Factors influencing the enzyme mimetic activities and future perspective of nanoceria-based enzyme mimetics are also addressed.

Research progress of nanoparticles as enzyme mimetics

Natural enzymes as biological catalysts possess remarkable advantages,especially their highly efficient and selective catalysis under mild conditions.However,most natural enzymes are proteins,thus exhibiting an inherent low durability to harsh reaction conditions.Artificial enzyme mimetics have been pursued extensively to avoid this drawback.Quite recently,some inorganic nanoparticles(NPs) have been found to exhibit unique enzyme mimetics.In addition,their much higher stability overcomes the inherent disadvantage of natural enzymes.Furthermore,easy mass-production and low cost endow them more benefits.As a new member of artificial enzyme mimetics,they have received intense attention.In this review article,major progress in this field is summarized and future perspectives are highlighted.

Application of Mn(Ⅱ) as a Mimetic Enzyme of Horseradish Peroxidase

In this study, Mn(Ⅱ) as a mimetic enzyme of horseradish peroxidase (HRP) was applied to the determination of hydrogen peroxide (H2O2). The method introduced in this paper is based on Mn(Ⅱ)’s catalytic effect on the oxidation of 4-aminoantipyrine(4-AAP) with modified Trinder’s reagent N-ethyl-N-(2-hydroxy-3-sulfopropyl)-3, 5-dimethoxyaniline(DAOS) by H2O2. By coupling this mimetic catalytic reaction with the catalytic reaction of glucose oxidase (GOD), glucose can be detected. Under optimum conditions, the calibration graphs for the determination of H2O2 and glucose are in the range of 1.0×10-3?1.0×10-1 mol/L and 1.0×10-3?14×10-3 mol/L respectively. The detection limit is 5.9×10-4 mol/L for H2O2 and is 9.2×10-4 mol/L for glucose. The feasibility of Mn ( II ) as a HRP mimetic enzyme in practical clinical analysis has been proven in the determination of glucose in human serum. So far, Mn ( II ) is the simplest and the most inexpensive mimetic enzyme.

Myoglobin as Mimetic Enzyme and Its Analytical Application in Determination of H_2O_2

The characteristic of Myoglobin as mimetic enzyme was studied and applied in the determination of HeO2 with o-phenylenediamine as substrate. The absorbanee obtained at 40 ℃ was found to be proportional to the concentration of H2O2 in the range of 2.0×10^-5- 2.0×10^-7 mol/L, with a correlation coefficient of 0.999 1. The proposed meth od is simple and highly sensitive to a detection limit of 2.7 × 10^-8 mol/L. The relative standard deviations were within 5% for the determination of different concentrations of H2O2. Satisfied results were obtained in the determination of H2O2 in rainwater by this method, and the recoveries were at the range of 97.2%-105.4%.

Iron(Ⅱ) tetrasulfophthalocyanine mimetic enzymatic synthesis of conducting polyaniline in micellar system

Iron(Ⅱ) tetrasulfophthalocyanine(FeTSPc) ,as a novel mimetic enzyme of peroxidase,was used in the synthesis of a conducting polyaniline(PANI) /sodium dodecylsulfate(SDS) complex in SDS aqueous micellar solutions. The effects of pH,concentrations of aniline,SDS and H2O2,and reaction time on polymerization of aniline were studied in this case as shown by UV-Vis absorption spectroscopy. The results show that a wide range of pH(0.5-4.0) is required to produce the conducting PANI,and the optimal pH is 1.0 in SDS micelle. The optimal concentrations of aniline,SDS and H2O2 in feed,and reaction time in this case for the production of conducting PANI are respectively 10 mmol/L,10 mmol/L,25 mmol/L,and 15 h. FT-IR spectrum,elemental analysis,conductivity,cyclic voltammetry and thermogravimetric analysis confirm the thermal stability and electroactive form of PANI.

Effect of Solvents on Oxidation of 1,1′-Bi-2-naphthol

A novel biomimetic catalyst of complex Cu(p-OTs) 2/ethanolamine(1∶1) was used to oxidize 1,1′-bi-2-naphthol into xanthene derivatives with a relative high yield in a mixed solvents of dimethyl sulfoxide(DMSO) and CH 3OH. The studies on the effect of some solvents on the yield of xanthene derivatives indicates that the yield reduces dramatically with the increase of the content of H 2O in the mixed solvents of H 2O and DMSO. No product can be obtained when the content of H 2O is up to 70%. The cyclic voltammetric study demonstrated that the copper ion in complex Cu(p-OTs) 2/ethanolamine(1∶1) is reduced via a two-step one-electron reduction process from Cu(Ⅱ) to Cu in the mixture of DMSO and H 2O. Water as a poor solvent in respect to the reactants probably hampered the coordination of 1,1′-bi-2-naphthol to copper/amine complex and led to the insufficient catalytic efficiency of complex Cu(p-OTs) 2/ethanolamine(1∶1).

Study on the Intermediate in the o-Phenylenediamine Oxidative Reaction Using Hemoglobin as A Mimetic Peroxidase in Aqueous-Organic Two Phase

Hemoglobin was used as a mimetic enzyme for peroxidase to catalyze the oxidative reaction of o-phenylenediamine with H2O2 which functioned as an oxidant. The relationship between physicochemical properties of the intermediate and enzymatic activity of hemoglobin was studied. Since the solubility of the intermediate in the reaction is higher in butanol phase than in water phase, the intermediate itself diffused from the aqueous phase to the butanol phase. The experimental results showed that the rate of product and the stability of intermediate were associated with the temperature and the pH value of the buffer. The formation rate of intermediate and half-life period reveal the maximal in pH7, nevertheless, the whole rate of the catalytic reaction is the greatest in pH5, which the ratio of the initial rate in final product formation compared to that intermediate formation is the greatest.

Fluorescence Spectra and Enzymatic Property of Hemoglobin as Mimetic Peroxidase

Intrinsic fluorescence emission maxima of hemoglobin(Hb) was investigated in relation to peroxidase property of Hb. The peroxidase activity of Hb was based on its ca\| talytic activity for oxidation of o \|phenylenediamine by hydrogen peroxide. Hb was treated in the condition (temperature, ethanol and salt) that tetramer\|dimer equilibrium of Hb is shifted to the dimer state and its fluorescence spectrum was measured . When Hb treated in temperature (60\|70 ℃), ethanol concentration (60%\|70%) and NaCl concentration (2.5\|3.0 mol/L), the fluorescence emission maxima of Hb shifted towards red wavelength and its activity decreased quickly. Experimental results revealed that the activity and stability of Hb as mimetic peroxidase was closely relative to the hydrophobic environment of active center of Hb, and when Hb (Fe Ⅱ ) converted into met Hb (Fe Ⅲ ), its activity was 1.6 times as much as that of Hb.

Study on Mimetic Peroxidase and Molecular Recognition of Phenols With Inclusion Complex of Ironporphyrin Immobilized by β-CD Polymer

β-Cyclodextrin (β-CD) and its cross-linked polymer (β-CDP) were known as the mimetic models. Metalloporphyrin had been widely used in the enzymatic method of analysis and molecular recognition. In present work, it was investigation that supramolecular recognition for halogenated phenols, three crosols, three nitrophenols and three aminophenols, served respectively as the substrate of the mimetic receptor, iron-5, 10, 15, 20-tetrakis (sulforphenyl)-21H, 23H-porphine (FeTPPS) or FeTPPS-β-CDP. Supramolecular complex, FeTPPS-β-CDP with function of mult i-recognition and induced-fit, was a advanced kind of mimetic peroxidase; Methyl phenol or polyphenol was the substitute of chlorophenic acid, while aminophenols and other phenols were suggested not to be utilized to enzymatic assay of H2O2. Being a mimetic enzyme mimicking the space structure of overall proteinase, beaimed by immobilized mimetic enzyme with a large number of β-CD interior cavities, chlorophenol was identified optimal substrate in the system tested.

Vc-Functionalized Fe3O4 Nanocomposites as Peroxidase-like Mimetics for H2O2 and Glucose Sensing

A simple and efficient colorimetric biosensing for hydrogen peroxide and glucose with peroxidase-like vitamin C（Vc） functionalized Fe3O4 magnetic nanoparticles（Vc/Fe3O4MNPs） as a catalyst is reported. Compared with Fe3O4 MNPs and other catalysts, Vc/Fe3O4 MNPs exhibited superior catalytic properties. Kinetic studies indicated that vitamin C incorporated on Fe3O4 MNPs improved the affinity toward H2O2. As low as 0,29 μmol/L H2O2 can be detected with a wide linear range of 0.5-100 μmol/L H2O2; moreover, as low as 0.288 μmol/L glucose can be detected with a linear range of 0.5-25 μmol/L glucose. The detection method was highly sensitive in sensing H2O2 and glucose. The robustness of Vc/Fe3O4 MNPs rendered them suitable for wide ranging applications.

Enzymatic self-assembly/disassembly turns “ON”/“OFF” the mimetic hydrolytic activity of histidine nanofibers

Mimetic enzymes are devised as alternates or supplements of natural enzymes in broad fields but regulating their activities in a switchable manner remains challenging.Herein,we proposed an enzymatic self-assembly/disassembly strategy to address this issue.A peptide molecule Nap FFEYIH(YH) was rationally designed which,after self-assembling into nanofibers,lined up the histidine moieties to form active hydrolysis centers for mimicking hydrolase activity.Enzymatic dephosphorylation of Nap FFEYp IH(Yp H) by alkaline phosphatase to yield YH also turned “ON” the hydrolase activity.In turn,phosphorylation of YH by phosphokinase epidermal growth factor receptor to yield Yp H disassembled the nanofibers and thus turned the activity “OFF”.As such,the “ON”/“OFF” of the mimetic hydrolase activities could be regulated under physiological conditions through ALP/EGFR-mediated self-assembly/disassembly of histidine nanofibers.This work provides a feasible strategy for the on-demand fabrication of artificial enzymes with controllable and superior activities.

Tunable catalytic activity of FeWO_(4) nanomaterials for sensitive assays of pyrophosphate ion and alkaline phosphatase activity

Alkaline phosphatase(ALP)activity and pyrophosphate ion(PPi)levels are remarkable for the human body functions such as signal transduction pathways and metabolism.Current quantitative methods mainly focus on developing complicated organic substrates or employing unstable metal ions as signal-regulated medium.Herein,we have developed a facile hydrothermal method for preparing Fe WO_(4)nanomaterials with intrinsic peroxidase-like activity and further confirmed that such a catalytic activity could be significantly enhanced by adjusting the size and oxygen vacancy content.More encouragingly,PPi can easily inhibit the catalytic activity of Fe WO_(4),whereas orthophosphate ions(Pi)cannot.Therefore,we constructed an Fe WO_(4)-based colorimetric assay for sensing PPi by means of the classical 3,3′,5,5′-tetramethylbenzidine-peroxidase chromogenic reaction.A facile and reliable ALP activity assay was also designed and developed because of the logical regulation of the peroxidase-like activity of Fe WO_(4)through the ALP-catalyzed hydrolysis of PPi into Pi.Based on the clear mechanism and mimetic-enzyme Fe WO_(4)-catalyzed amplification,the sensing system exhibited excellent performance and was able to evaluate ALP activity in real serum samples and screen for potential ALP inhibitors.The proposed mimetic enzyme-involved colorimetric assay provides an alternative pathway,and Fe WO_(4)nanomaterials with excellent performance have great potential for further biosensing and biomedical applications.