Peroxidase-like catalytic activity of cubic Pt nanocrystals

Monodispersed cubic platinum (Pt) nanocrystals with an average size of approximately 10 nm were prepared by a reduction method with cetyltrimethylammonium bromide (CTAB) serving as steric stabilizer. The resulting Pt nanocrystals exhibit a peroxidase-like activity and catalyze the H₂O₂-mediated oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to produce two colored products with high catalytic activity. The color-generating activity of this system may be influenced by several factors, and we examined several factors to optimize this colorimetric system including buffer types, pH, and concentrations of both H₂O₂ and Pt nanocrystals. The effect of agglomeration of Pt nanocrystals was also investigated, and we find that agglomeration of Pt nanocrystals in aqueous solution distinctly affects Pt nanocrystals catalytic activity. We attribute the catalytic activity of Pt nanocrystals to their acceleration of the electron-transfer process and the consequent facilitation of radical generation.     

Structural characterization of magnetoferritin

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Peroxidase-like activity of cytochrome c in the presence of anionic surfactants

Peroxidase-like activity of cytochrome c is significantly higher in the presence of anionic surfactants, sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and sodium n-dodecyl sulphate (SDS). The enhancement is due to the higher reaction rate of the cytochrome c with H₂O₂, which is the rate determining step in the peroxidase cycle of cytochrome c. An intermediate formed in the cycle rapidly oxidizes the substrates or reacts with further molecule(s) of H₂O₂, causing heme degradation. Thus, the specific microenvironment provided by anionic surfactants facilitates also degradation of heme iron by H₂O₂.     

Peroxidase-like activity of mesoporous silica encapsulated Pt nanoparticle and its application in colorimetric immunoassay

Nanomaterial-based artificial enzymes have received great attention in recent year due to their potential application in immunoassay techniques. However, such potential is usually limited by poor dispersion stability or low catalytic activity induced by the capping agent essentially required in the synthesis. In an attempt to address these challenges, here, we studied the novel Pt nanoparticles (NPs) based peroxidase-like mimic by encapsulating Pt NP in mesoporous silica (Pt@mSiO₂ NPs). Compared with other nanomaterial-based artificial enzymes, the obtained Pt@mSiO₂ NPs not only exhibit high peroxidase-like activity but also have good dispersion stability in buffer saline solution when grafted with spacer PEG. Results show that when the thickness of silica shell is about 9 nm the resulting Pt@mSiO₂ NPs exhibit the catalytic activity similar to that of Pt NPs, which is approximately 26 times higher than that of Fe₃O₄ NPs (in terms of K_cat for H₂O₂). Due to the protection of silica shell, the subsequent surface modification with antibody has little effect on their catalytic activity. The analytical performance of this system in detecting hCG shows that after 5 min incubation the limit of detection can reach 10 ng mL⁻¹ and dynamic linear working range is 5–200 ng mL⁻¹. Our findings pave the way for design and development of novel artificial enzyme labeling.     

Influence of synthesis temperature on structural and magnetic properties of magnetoferritin

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Peroxidase-like catalytic activity of copper ions and its application for highly sensitive detection of glypican-3

Glypican-3 (GPC3) might be used as new biomarker of liver cancer for the development of new diagnostic methods. The most commonly used methods for protein detection are based on natural enzymes, which are easily affected by environmental conditions and suffer from the rigorous preparation conditions. Thus, the development of new enzyme mimetics with high and stable catalytic activity is of great significance in diagnostic applications. In this paper, copper ions (Cu²⁺) was found to possess the peroxidase-like catalytic activity, which can catalyze H₂O₂-mediated oxidation of peroxidase substrate and obtain the oxidation product with color change. This catalytic activity is much more stable than other nanomaterials based peroxidase mimetics, and can significantly increase by increasing the concentration of H₂O₂. It is worth mentioning that the absorbance signal induced by 5 nM Cu²⁺ can be easily detected. This Cu²⁺-catalyzed reaction can be also applied in the detection of GPC3 by using the anti-GPC3 antibody functionalized CuO NPs, which can release the Cu²⁺ by dissolved in HCl solution. This method permits detection of as low as 0.26 pg mL⁻¹ GPC3. This sensitivity is about one or several magnitudes higher than that of ELISA or other peroxidase mimetics based methods. The high catalytic activity of Cu²⁺ and the signal amplification process of CuO NPs into high amount of Cu²⁺ also make this method more simple and effective.     

Peroxidase-like catalytic activity of Mn-octabromo-tetrakis(4-sulfophenyl)porphine on linoleate hydroperoxide and its analytical application

To reveal an enzyme-like catalytic activity of metal-octabromo-tetrakis(sulfophenyl)porphines (M-OBPSs), their peroxidease-like catalytic activity on linoleate hydroperoxide (LOOH) were evaluated on the basis of dye-formation in the coloring reaction between N,N-diethylaniline and 4-aminoantipyrine that yields a quinoid-type dye. Among M-OBPSs tested, Mn³⁺-OBPS allowed to produce the largest amount of dye. The optimal conditions of the coloring reaction catalyzed by Mn³⁺-OBPS for the determination of LOOH were determined. A good linear calibration curve was obtained in the concentration range of 0.025-0.4 μmole LOOH with good reproducibility (coefficient of variance = 1.23%), suggesting that Mn³⁺-OBPS is a good artificial mimesis of the peroxidase for LOOH. In addition, Mn³⁺-OBPS was highly specific for LOOH even in the presence of cumene hydroxyperoxide or hydrogen peroxide. It was revealed that the peroxidase-like activity of Mn³⁺-OBTP is attributable to the redox cycle of Mn³⁺ ↔ Mn⁴⁺.     

Peroxidase-like activity of water-soluble cupric oxide nanoparticles and its analytical application for detection of hydrogen peroxide and glucose

Water-soluble cupric oxide nanoparticles are fabricated via a quick-precipitation method and used as peroxidase mimetics for ultrasensitive detection of hydrogen peroxide and glucose. The water-soluble CuO nanoparticles show much higher catalytic activity than that of commercial CuO nanoparticles due to their higher affinity to hydrogen peroxide. In addition, the as-prepared CuO nanoparticles are stable over a wide range of pH and temperature. This excellent stability in the form of aqueous colloidal suspensions makes the application of the water-soluble CuO nanoparticles easier in aqueous systems. A colorimetric assay for hydrogen peroxide and glucose has been established based on the catalytic oxidation of phenol coupled with 4-amino-atipyrine by the action of hydrogen peroxide. This analytical platform not only confirms the intrinsic peroxidase-like activity of the water-soluble cupric oxide nanoparticles, but also shows its great potential applications in environmental chemistry, biotechnology and medicine.     

Peroxidase-like catalytic activity of anion-exchange resins modified with metal-porphyrins in oxidative reaction of hetrocyclic amines with hydrogen peroxide

To elucidate the peroxidase (POD)-like catalytic activity of anion-exchange resins modified with metal-tetrakis(sulfophenyl)porphine (M-TSPP(r)s), an oxidative reaction of seven mutagenic heterocyclic amines (HCAs) with hydrogen peroxide, which reaction is catalyzed by horse radish POD, was investigated in the presence of M-TSPP(r)s. Among six M-TSPP(r)s tested, Mn- and Fe-TSPP(r)s were found to have a relatively strong POD-like activity for HCAs, in particular for a typical HCA, 2-amino-3-methyl-imidazo[4,5-f]quinoline (IQ). The optimal condition for the POD-like activity was selected using Fe- and Mn-TSPP(r)s. For evaluation of an oxidation product of IQ produced in the presence of Fe-TSPP(r), the absorption, NMR and FAB-mass spectra thereof were compared with those of an oxidation product of IQ produced by horse radish POD or a chemical oxidizing agent, sodium hypochlorite. When Fe-TSPP(r) was present as a catalysts, IQ was converted into the dimmer (hydorazone type) which has no mutagenic activity in umu-test. It was revealed that Fe- and Mn-TSPP(r)s exhibit a POD-like catalytic activity in oxidative reaction of HCAs with hydrogen peroxide.     

Peroxidase-like activity on organic hydroperoxides of ion-exchange resins modified with metal-porphine analogues and analytical application for determination of linoleate hydroperoxide

The ion-exchange resins modified with metal-porphyrins and -phthalocyanines (M-P(r)) have been found to exhibit a peroxidase (POD)-like activity on organic peroxides in a reaction wherein a quinoid dye is formed from phenol and 4-aminoantipyrine. Among them, Mn- and Co-P(r) exhibited stronger activity than hemoglobin and Fe-P(r), and hence were expected to be practically useful as a solid catalyst for the determination of linoleate hydroperoxide (LOOH). In addition, a resin modified with Co(3+)-phthalocyanine tetrasulfonate (Co-PCS(r)) lacks POD-like activity on hydrogen peroxide in contrast with Mn-P(r). We, therefore, concluded that Co-PCS(r) is superior to both Mn-P(r) and hemoglobin as a solid catalyst on organic hydroperoxides, and developed a new method for the determination of LOOH.     

Peroxidase-like catalytic activity of aqueous- and immobilized-Mn(3+)-octabromo-porphyrins on ion-exchange resin supplied as mimetic of horseradish peroxidase

In order to explore the capability of metal porphyrins as an alternative of horseradish peroxidase (HRP), HRP-like activity of three manganese-porphyrins (Mn-Ps) and three Mn-octabromo-porphyrins (Mn-OBPs) was examined in both aqueous and immobilized states. It was found that Mn(3+)-octabromotetrakis(1-methyl-pyridinium-4yl)porphine (Mn-OBTMPyP) has an activity of at least 90% of HRP in an aqueous solution. Mn-OBTMPyP exhibited a catalytic activity even in the presence of hydrogen peroxide without suicide reaction. In addition, Mn-OBTMPyP was revealed to function as an alternative to HRP in the quantitative determination of serum uric acid. These results are of great interest because they indicate that metal-octabromo-porphyrins possibly include promising candidates of artificial enzyme capable of substituting for HRP.     

增强氯化血红素催化活性用于水胺硫磷比色检测研究

建立了一种基于增强氯化血红素(Hemin)过氧化物酶催化活性比色检测水胺硫磷的方法.在H2O2存在下, Hemin催化氧化底物3,3′,5,5′-四甲基联苯胺(TMB), 使其失去1个电子, 导致反应体系由无色变为蓝绿色.水胺硫磷的加入可提高Hemin对底物亲和力, 进一步增强其催化活性, 使底物氧化失去2个电子, 反应体系由蓝绿色变为黄色, 且颜色变化程度与水胺硫磷浓度成正比.在最优条件下, 本方法的动态检测范围为2～100 μg/L, 检出限为1.2 μg/L(3σ).其它有机磷农药对水胺硫磷检测无明显干扰, 实际样品中水胺硫磷的加标回收率为93.0％～113.0％. 本方法可应用于农产品中水胺硫磷残留的检测.     

Peroxidase-like catalytic activities of ionic metalloporphyrins supported on functionalised polystyrene surface

Metalloderivatives of anionic tetrasulphonated tetraphenylporphyrin (MTPPS, M = Mn(III), Fe(III) and Co(III)) were synthesized and immobilized on cationically functionalised divinylbenzene(DVB)-crosslinked polystyrene(PS). These supported catalysts (PS-MTPPS) were found to exhibit peroxidase-like activity. The co-oxidation of 4-aminoantipyrine and phenol by H₂O₂ was attempted with these catalysts to mimic this enzyme function. The catalytic efficiency of all these immobilized MTPPS was found to be superior to the corresponding unsupported MTPPS in solution. The effect of the central metal ion of the porphyrin, pH of the reaction medium and also the temperature effect are investigated. The ideal pH was seen to be in the 8.0–8.5 range, with maximum effect at 8.2. The efficiency order for the various PS-MTPPS was seen to be Co>Mn>Fe, with CoTPPS showing efficiency comparable to that of horseradish peroxidase. The catalytic efficiency was found to be increasing with temperature for all the catalysts. The re-usability of these PS-MTPPS systems for peroxidase-like activity was also studied and it was found that they exhibited a very high degree of recyclability without much poisoning.     

Peroxidase-like catalytic activity of Mn- and Fe-tetrakis(4-carboxyphenyl)porphines bound to aminopropyl-glass bead in oxidative reaction of heterocyclic amines

Fe- or Mn-tetrakis(4-carboxyphenyl)porphine (Fe- and Mn-TCPP) bound to aminopropyl-glass bead (Fe- and Mn-TCPP_gs) was examined for the peroxidase (POD)-like function in order to develop a solid catalyst which can exhibit POD-like activity without adsorbing heterocyclic amines (HCAs). Mn-TCPP in aqueous solution had only a slight POD-like catalytic activity on HCAs (IQ and MeIQ). As for Fe-TCPP, it was impossible to examine the POD-like activity since it reacted with hydrogen peroxide in a liquid reaction system. However, both Fe- and Mn-TCPP when immobilized on aminopropyl-glass bead via peptide bond (Fe- and Mn-TCPP_gs), catalyzed the oxidative reaction of mutagenic HCAs with hydrogen peroxide. The catalytic activity of Fe- and Mn-TCPP_gs was investigated in more detail using as a substrate IQ and MeIQ which were oxidized more rapidly among the tested HCAs. Consequently, the optimal conditions for the oxidative reaction catalyzed by Fe- and Mn-TCPP_gs were determined. In addition, ESI-mass and absorption spectra of oxidation products of IQ and MeIQ showed that they are dimers. Thus, it was demonstrated that a solid catalyst with POD-like activity can be obtained by immobilizing Fe- and Mn-TCPPs on aminopropyl-glass beads.     

Experimental assessment of interactions between liquid crystal 4-cyano-4’-hexylbiphenyl and magnetoferritin

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CuS/Ag2S纳米复合物的制备及类过氧化物酶性质

采用水热法合成了一种微球状的CuS/Ag₂S纳米复合物. 通过透射电子显微镜、 紫外-可见吸收光谱和拉曼光谱等对其形貌及光学性质进行了表征; 考察了其类过氧化物酶性质, 并通过表面增强拉曼散射原位监测了类过氧化物酶催化反应. 以3,3',5,5'-四甲基联苯胺(TMB)为底物进行显色反应, 结果表明, 在H₂O₂存在下CuS/Ag₂S 纳米复合物具有类过氧化物酶的性质, 可以将无色的TMB氧化成蓝色的oxTMB. 基于此实现了对微量H₂O₂的检测.     

2-Methylimidazole-assisted Morphology Modulation of a Copper-based Metal-organic Framework Transducer for Enhanced Electrochemical Peroxidase-like Activity

A tailored metal-organic framework transducer material Cu−BDC(NH₂)@2-MI was synthesized with 2-methylimidazole as competitive ligand for the modulation of its morphology and catalytic activity. 2-MI effectively helped the deprotonation of 2-aminoterephthalic acid and enabled the fast generation of MOF crystals at room temperature. More importantly, this 2-MI-doped MOF exhibited well-tuned morphology and was able to assist efficient redox procedures in electrochemical H₂O₂ reduction. Therefore, a prototype H₂O₂ sensor can present decent linear ranges from 10 μM to 13.28 mM and a detection limit of 0.97 μM. This novel design could boost the utilization of proprietary MOFs materials out of laboratory.     

Selective Hemin Binding by a Non-G-quadruplex Aptamer with Higher Affinity and Better Peroxidase-like Activity

Previous aptamers for porphyrins and metalloporphyrins were all guanine-rich sequences that can fold in G-quadruplex structures. Due to stacking-based binding, these aptamers can hardly tell different porphyrins apart, and they can also bind other planar molecules, hindering their practical applications. In this work, we used the capture selection method to obtain aptamers for hemin and protoporphyrin IX (PPIX). The hemin aptamer (Hem1) features two highly conserved repeating binding loops, and it cannot form a G-quadruplex, which was supported by its Mg²⁺-dependent but K⁺-independent hemin binding and CD spectroscopy. Isothermal titration calorimetry revealed much higher enthalpy change for the new aptamer, and the best aptamer showed a K_d of 43 nM hemin. Hem1 can also enhance the peroxidase-like activity of hemin. This work demonstrates that aptamers have alternative ways to bind porphyrins allowing selective recognition of different porphyrins.     

Electrochemical Enhanced Detection of Uric Acid Based on Peroxidase-like Activity of Fe3O4@Au

Fe₃O₄@Au nanomaterials were prepared by the self-assembly method. An enzyme-free, ultrasensitive electrochemical detection of uric acid was achieved based on the peroxidase-like activity of Fe₃O₄@Au. The proposed procedure has exhibited excellent catalytic activities and achieved significant enhancements of the current responses to uric acid. The detection range was from 0.1 to 10 mmol/L, and the limit of detection was 0.087 μmol/L. Under the action of external magnetic field, the magnetic particles can be easily separated from the bottom liquid, which has the advantages of simple operation and high separation efficiency. Moreover, this detection method combining a simulated enzyme and electrochemical can enhance the effective output of the overall electrochemical signal without modifying the electrode, and excellent reproducibility can be achieved. Compared to colorimetric assay, the electrochemical one has higher sensitivity and selectivity, and was further applied in ultrasensitive detection of uric acid in food samples. In short, the proposed electrochemical assay has great potential in the fields of food quality control and biomedical analysis.     

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(K_m) 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.