Direct Electrochemistry of Horseradish Peroxidase Embedded in Nano-Fe_3O_4 Matrix on Paraffin Impregnated Graphite Electrode and Its Electrochemical Catalysis for H_2O_2

Fe_3O_4particles coated with acrylic copolymer (ACP) of about5—8 nm in diameter were synthesized and used for immobiliza-tion of horseradish peroxidase (HRP). Direct electrochemistryof HRP embedded in the nanosized Fe_3O_4 solid matrix modifiedparaffin impregnated graphite electrode (PIGE) was achieved,which is related to the heme Fe(Ⅲ)/Fe(Ⅱ) conversion ofHRP. Cyclic voltammetry gave a pair of reproducible and well-defined redox peaks at about E_m of-0.295 V vs. SCE. Thestandard rate constant k_s was determined as 2.7 s~(-1). It demon-     

Direct electrochemistry and electrocatalysis of horseradish peroxidase immobilized on L-glutathione self-assembled monolayers

A novel hydrogen peroxide biosensor has been fabricated based on covalently linked horseradish peroxidase （HRP） onto L- glutathione self-assembled monolayers （SAMs）. The SAMs-based electrode was characterized by electrochemical methods, and direct electrochemistry of HRP can be achieved with formal potential of-0.242 V （vs. saturated Ag/AgCl） in pH 7 phosphate buffer solution （PBS）, the redox peak current is linear to scan rate and rate constant can be calculated to be 0.042 s^-1. The HRP-SAMs- based biosensors show its better electrocatalysis to hydrogen peroxide in the concentration range of 1 × 10^-6 mol/L to 1.2 × 10^-3 mol/L with a detection limit of 4 × 10^-7 mol/L. The apparent Michealis-Menten constant is 3.12 mmol/L. The biosensor can effectively eliminate the interferences of dopamine, ascorbic acid, uric acid, catechol and p-acetaminophen.     

Amplified Electrochemical Immunoassay Using HRP Labeled Protein as an Inhibitor to Silver Deposition in the Presence of H2O2

A novel electrochemical immunosensor with amplification effect based on the enzyme inhibition of silver deposition was proposed. In this method, the capture antibody was first immobilized onto a gold electrode via a self-assembled layer. After a sandwich immunoreaction, HRP labeled antibody was bound to the gold electrode. The HRP on the electrode inhibited silver deposition when the electrode was incubated in hydroquinone-H2O2 solution and silver ion solution. The linear sweep voltammetry was chosen to detect the deposited silver and the result showed that the peak current was linearly proportional to the content of IgG in the range of 50 to 2500 ng/mL with a detection limit of 35 ng/mL.     

Direct Electrochemistry and Electrocatalysis of Hemoglobin at PAMAM Dendrimer-MWNTs-Au Nanoparticles Composite Film Modified Glassy Carbon Electrode

The direct electron transfer of hemoglobin at the PAMAM-MWNTs-AuNPs composite film modified glassy carbon electrode was studied. In a phosphate buffer solution(PBS, pH=7.0), the formal potential(E 0' ) of Hb was –0.105 V versus SCE, the electron transfer rate constant was 4.66 s –1 . E 0′ of Hb at the modified electrode was linearly varied in a pH range of 5.0—8.0 with a slope of –49.2 mV/pH. The Hb/PAMAM-MWNTs-AuNPs/GCE gave an ex-cellent electrocatalytic response to the reduction of hydrogen peroxide. The catalytic current increased linearly with H 2 O 2 concentration in a range of 1.0×10 ?6 to 2.2×10 ?3 mol/L. The detection limit was 2.0×10 ?7 mol/L at a signal to noise ratio of 3. The Michaelis-Menten constant(K ma pp ) was 2.95 mmol/L.     

掺杂双(N-2-甲基苯基-水杨醛亚胺)合铜(II)配合物的碳糊电极电催化测量过氧化氢(英文)

The electrochemical behavior of a bis (N-2-methylphenyl-salicyldenaminato)copper (II) complex spiked in a carbon paste electrode (BMPSCu-CPE) and its electrocatalytic reduc-tion of H2 O2 were examined using cyclic voltammetry, chronoamperometry, and differen-tial pulse voltammetry. Cyclic voltammetry was used to study the redox properties of BMPSCu-CPE at various potential scan rates. The apparent charge transfer rate constant and the transfer coefficient for the electron transfer between BMPSCu and the carbon paste electrode (CPE) were 1.9 ± 0.1 s–1 and 0.43, respectively. BMPSCu-CPE had excel-lent electrocatalytic activity for H2 O2 reduction in 0.1 mol/L phosphate buffer solution (pH 5.0), and it decreased the overpotential by 300 mV as compared to CPE alone. The diffusion coefficient and kinetic parameters such as the heterogeneous catalytic electron transfer rate constant and electron transfer coefficient for the reduction of H2 O2 at the BMPSCu-CPE surface were also determined using electrochemical methods. Differential pulse voltammetry showed two linear dynamic ranges of 1.0–10.0 and 10.0–300.0 μmol/L and a detection limit of 0.63 μmol/L H2 O2. The BMPSCu-CPE has excellent repro-ducibility and long term stability, and it was successfully applied for the determination of H2 O2 in two pharmaceutical samples: an antiseptic solution and a hair dying cream.     

以方沸石负载Ni(Ⅱ)催化剂修饰的电极电氧化甲醇(英文)

There is a high overvoltage in the oxidation of methanol in fuel cells,and so modified electrodes are used to decrease it.A modified electrode that used Ni(II) loaded analcime zeolite to catalyze the electrooxidation of methanol in alkaline solution was proposed.Analcime zeolite was synthesized by hydrothermal synthesis,and Ni(II) ions were incorporated into the analcime structure,which was then mixed with carbon paste to prepare modified electrode.The electrocatalytic oxidation of methanol on the surface of the modified electrode in alkaline solution was investigated by cyclic voltammetry and chronoamperometry.The effects of the scan rate of the potential,concentration of methanol,and amount of zeolite were investigated.The rate constant for the catalytic reaction of methanol was 6 × 103 cm3 mol-1 s-1 from measurements using chronoamperometry.The proposed electrode significantly improved the electron transfer rate and decreased the overpotential for methanol oxidation.     

在3,4-二羟基肉桂酸介质中以多壁碳纳米管为传感器电催化检测L-半胱氨酸(英文)

A highly sensitive electrochemical sensor was prepared for the determination of L-cysteine using a modified multiwall carbon nanotubes paste electrode in the presence of 3,4-dihydroxycinnamic acid(3,4-DHCA) as a mediator, based on an electrocatalytic process. The results indicate that the electrode is electrocatalytically efficient for the oxidation of L-cysteine in the presence of 3,4-DHCA. The interaction between the mediator and L-cysteine can be used for its sensitive and selective determination. Using chronoamperometry, the catalytic reaction rate constant was calculated to be 2.37 × 102 mol–1 L s–1. The catalytic peak current was linearly dependent on the L-cysteine concentration in the range of 0.4–115 μmol/L. The detection limit obtained by linear sweep voltammetry was 0.25 μmol/L. Finally, the modified electrode was examined as a selective, simple, and precise new electrochemical sensor for the determination of L-cysteine in real samples.     

A Novel Composite Electrode of Photocatalyst—TiO2／C Loading on the Surface of the Air （Oxygen） Electrode

The methods for preparing the H2O2 generating air (oxygen) electrode and the composite electrode of photocatalyst-TiO2/C loading on the surface of the air (oxygen) electrode were introduced.In the case of the composite electrode,the current efficiency of electro-generated H2O2 is higher than 80%(J≤15mA/cm^2).The degradation of aniline was used as an example to measure the influence of the composite electrode and compared with the system in which the air (oxygen) electrode and the photocatalyst-TiO2 were sqparated.The results confirmed that the composite electrode played an active role on accelerating the degradation rate of aniline.According to the measurement of the polarization curves of composite electrode and TiO2 photo anode,and of the adsorbing amount of aniline on the surface of the composite electrode,the principle of descending the recombination reta of photo-generated electron and hole and of enhancing the oxidation rate of organic molecule was described.The mechanism about the degradation of aniline was also discussed.     

Gold Catalysts Supported on Crystalline Fe_2O_3 and CeO_2/Fe_2O_3 for Low-temperature CO Oxidation

High active and stable gold catalysts supported on crystalline Fe2O3 and CeO2/Fe2O3 were prepared via the deposition-precipitation method. The catalyst with a Au load of 1.0% calcined at 180 °C showed a CO conversion of 100% at -8.9 °C, while Au/CeO2/Fe2O3 converted CO completely at -16.1 °C. Even having been calcined at 500 °C, Au/Fe2O3 still exhibited significant catalytic activity, achieving full conversion of CO at 61.6 °C. The catalyst with a low Au load of 0.5% could convert CO completely at room temperature and kept the activity unchanged for at least 150 h. N2 adsorption-desorption measurements show that the crystalline supports possessed a high specific surface area of about 200 m2/g. Characterizations of X-ray diffraction and transmission electron microscopy indicate that gold species were highly dispersed as nano or sub-nano particles on the supports. Even after the catalyst was calcined at 500 °C, the Au particles remained in a nano-size of about 6―10 nm. X-ray photoelectron spectra reveal that the supported Au existed in metallic state Au0. The modification of Au/Fe2O3 by CeO2 proved to be beneficial to the inhibition of crystallization of Fe2O3 and the stabilization of gold particles in dispersed state, consequently promoting catalytic activity.     

Electrochemical behavior of [UO_2Cl_4]~(2-) in 1-ethyl-3-methylimidazolium based ionic liquids

In order to examine the chemical form of uranyl species in 1-ethyl-3-methylimidazolium(EMI) based ionic liquids,UV-visible absorption spectra of solutions prepared by dissolving [EMI] 2 [UO2Cl4] into a mixture of EMICl and EMIBF 4(50:50 mol%) were measured.As a result,it was confirmed that uranyl species in the mixture of EMICl and EMIBF 4 existed as [UO2Cl4]2-.Cyclic voltammograms(CVs) of [UO2Cl4]2-in the mixture were measured at 25 ℃ using a Pt working electrode,a Pt wire counter electrode,and an Ag/Ag + reference electrode(0.01 M AgNO 3,0.1 M tetrabutylammonium perchlorate in acetonitrile) in a glove box under an Ar atmosphere.Peaks corresponding to one redox couple were observed around-1.05 V(Epc) and-0.92 V(Epa) vs.ferrocene/ferrocenium ion(Fc/Fc +).The potential differences between two peaks(Ep) increased from 101 to 152 mV with an increase in the scan rate from 50 to 300 mV s-1,while the(Epc+Epa)/2 value was constant,-0.989 V vs.Fc/Fc + regardless of the scan rate.Furthermore,the diffusion coefficient of [UO2Cl4]2-and the standard rate constant were estimated to be 3.7 × 10-8 cm 2 s-1 and(2.7-2.8) × 10-4 cm s-1 at 25 oC.By using the diffusion coefficient and the standard rate constant,the simulation of CVs was performed based on the reaction,[UO2Cl4]2-+ e = [UO2Cl4]3-.The simulated CVs were found to be consistent with the experimental ones.From these results,it is concluded that [UO2Cl4]2-in the mixture of EMICl and EMIBF 4 is reduced to [UO2Cl4]3-quasi-reversibly at-0.989 V vs.Fc/Fc +.     

Direct Electrochemistry of Hemoglobin Based on Fe3O4@SiO2 Nanoparticles Modified Electrode

A biosensor based on hemoglobin‐Fe₃O₄@SiO₂ nanoparticle bioconjunctions modified indium‐tin‐oxide (Hb/Fe₃O₄@SiO₂/ITO) electrode was fabricated to determine the concentration of H₂O₂. UV‐vis absorption spectra, fourier transform infrared (FT‐IR) spectroscopy, cyclic voltammetry (CV) and high‐resolution transmission electron microscopy (HRTEM) were used to characterize the bioconjunction of Fe₃O₄@SiO₂ with Hb. Experimental results demonstrate that the immobilized Hb on the Fe₃O₄@SiO₂ matrix retained its native structure well. In addition, Fe₃O₄@SiO₂ nanoparticles (NPs) are very effective in facilitating electron transfer of the immobilized enzyme, which can be attributed to the unique nanostructure and larger surface area of the Fe₃O₄@SiO₂ NPs. The biosensor displayed good performance for the detection of H₂O₂ with a wide linear range from 2.03×10^?6 to 4.05×10^?3 mol/L and a detection limit of 0.32 µmol/L. The resulting biosensor exhibited fast amperometric response, good stability, reproducibility, and selectivity to H₂O₂.     

Direct Electron Transfer of Horseradish Peroxidase in Gellan Gum–Hydrophilic Ionic Liquid Gel Film

A new composite film of microbial exocellular polysaccharide‐gellan gum (GG) and hydrophilic room temperature ionic liquid 1‐butyl‐3‐methyl‐imidazolium tetrafluoroborate (BMIMBF₄) was firstly used as an immobilization matrix to entrap horseradish peroxidase (HRP), and its properties were studied by UV/vis spectroscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The results showed that BMIMBF₄ could promote the electron transfer between HRP and electrode surface, and the existence of GG could successfully immobilize BMIMBF₄ on the electrode surface with improved stability. HRP–BMIMBF₄–GG/GCE exhibited a pair of well‐defined and quasireversible cyclic voltammetric peaks in 0.1 M pH 7.0 phosphate buffer solutions at 1.8 V/s, which was the characteristic of HRP Fe(III)/Fe(II) redox couples. The formal potentials (E°′) was ?0.368 V (vs. SCE) and the peak‐to‐peak potential separation (ΔE_P) was 0.058 V. The peak currents were five times as large as those of HRP–GG/GCE. The average surface coverage (Γ*) and the apparent Michaelis‐Menten constant (K_m) were 4.5×10^?9 mol/cm² and 0.67 μM, respectively. The electron transfer rate constant was estimated to be 15.8 s^?1. The proposed electrode showed excellent electrocatalytic activity towards hydrogen peroxide (H₂O₂). The linear dynamic range for the detection of H₂O₂ was 0.05–0.5 μM with a correlation coefficient of 0.9945 and the detection limit was estimated at about 0.02 μM (S/N=3). BMIMBF₄–GG composite film was promising to immobilize other redox enzymes or proteins and attain their direct electrochemistry.     

Fabrication of a Fe2O3 Nanoparticles Implantation‐modified Electrode and its Applications in Electrochemical Sensing

A novel Fe₂O₃ modified indium tin oxide electrode (Fe₂O₃/ITO) was fabricated by iron ion‐implantation method first, and then annealed at 300 °C. Fe₂O₃/ITO reveals good catalytic performance toward hydrogen peroxide (H₂O₂) in phosphate buffer solution due to the Fe(II)/Fe(III) redox couple. Amperometric response shows a linear dependency on the H₂O₂ concentration ranging up to 360 μM with a detection limit of 0.3 μM. Moreover, electrocatalytic activity based on rarely reported higher oxidation states of iron (tentatively assigned to Fe(IV)) was shown to allow the reliable detection of glucose and cysteine. The results show promising application potential of the proposed electrode.     

3,4‐Dihydroxy‐L‐phenylalanine for Preparation of Gold Nanoparticles and as Electron Transfer Promoter in H2O2 Biosensor

3,4‐Dihydroxy‐L ‐phenylalanine (dopa) and 2‐(3,4‐dihydroxyphenyl)ethylamine (dopamine) were investigated as reducing agent and stabilizer for synthesis of gold nanoparticles (AuNPs) by one‐pot heating of a solution of HAuCl₄/dopa or dopamine. AuNPs with different sizes were obtained by controlling the mass ratios of HAuCl₄/dopa or dopamine. The formation mechanism for AuNPs was also proposed. Immobilization of horseradish peroxidase (HRP) and promotion of its electron transfer by polydopa film were investigated for preparation of H₂O₂ biosensor. Alkaline dopa solution was dropped onto a gold electrode for the formation of polydopa film. HRP was immobilized on the polydopa film through interactions between heme centre of HRP and the amine and carboxyl groups in polydopa. The AuNPs embedded in the polydopa film improved the electron transfer efficiency. These two factors allowed successful development of a H₂O₂ sensor with HRP@polydopa‐AuNPs electrode. Due to its biocompatibility, the polydopa‐AuNPs film provided good retention of enzyme activity and long‐term stability of the sensor. A rapid catalytic response (3 s) and a linear range from 0.006 to 5.0 mmol L^?1 were obtained for H₂O₂. This facile preparation strategy can be extended to other enzyme‐based biosensors.     

Fabrication of New Magnetic Nanoparticles (Fe3O4) Grafted Multiwall Carbon Nanotubes and Heterocyclic Compound Modified Electrode for Electrochemical Sensor

Magnetic Fe₃O₄ nanoparticles functionalized multiwalled carbon nanotubes (nano‐Fe₃O₄ MWNTs) were prepared for electrochemical sensors. 2‐amino‐5‐mercapto‐1,3,4‐thiadiazole was used as a connecter to form a network that connected nano‐Fe₃O₄ MWNTs to the Au electrode surface. Modified process of the electrode was studied with SEM, TEM and cyclic voltammetry. Cyclic voltammetry and amperometric i‐t curve were used to investigate characteristics of the obtained electrode. The sensor has been successfully used on the direct detection of catechol and showed excellent performances. The linear regression equation was I_pa(μA)=0.07763+0.16739 C (μmol/L); R=0.9993 and the detection limit was 5.38×10^?8 mol/L. The modified electrode showed good reproducibility and stability.     

Carbonized Hemoglobin Nanofibers for Enhanced H2O2 Detection

Electrospun hemoglobin (Hb) microbelts were used as a novel precursor to produce a new class of carbon nanofibers (Hb‐CNFs) containing Fe species (Fe₂O₃ and/or Fe‐N₄ moiety). The Hb‐CNFs modified glassy carbon electrode (Hb‐CNFs/GCE) exhibits significant oxidation/reduction towards H₂O₂. The observed H₂O₂ oxidation/reduction starting at ca. +0.26 V and +0.15 V (vs. Ag/AgCl) are significantly lower than the values observed at other CNFs modified GCE. The Hb‐CNFs/GCE was also applied to the amperometric detection of H₂O₂ and the results showed fast response, high sensitivity, excellent reproducibility, good selectivity, and wide dynamic range with good limit of detection.     

A Novel Biomimetic Hydrogen Peroxide Biosensor Based on Pt Flowers‐decorated Fe3O4/Graphene Nanocomposite

A sensitive and selective amperometric H₂O₂ biosensor was obtained by utilizing the electrodeposition of Pt flowers on iron oxide‐reduced graphene oxide (Fe₃O₄/rGO) nanocomposite modified glassy carbon electrode (GCE). The morphology of Fe₃O₄/rGO and Pt/Fe₃O₄/rGO was characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM), respectively. The step‐wise modification and the electrochemical characteristics of the resulting biosensor were characterized by cyclic voltammetry (CV) and chronoamperometry methods. Thanks to the fast electron transfer at the Pt/Fe₃O₄/rGO electrode interface, the developed biosensor exhibits a fast and linear amperometric response upon H₂O₂. The linear range of Pt/Fe₃O₄/rGO is 0.1∼2.4 mM (R²=0.998), with a sensitivity of 6.875 μA/mM and a detection limit of 1.58 μM (S/N=3). In addition, the prepared biosensor also provides good anti‐interferent ability and long‐term stability due to the favorable biocompatibility of the electrode interface. The proposed sensor will become a reliable and effective tool for monitoring and sensing the H₂O₂ in complicate environment.     

Two Heterometallic–Organic Frameworks Composed of Iron(III)‐Salen‐Based Ligands and d10 Metals: Gas Sorption and Visible‐Light Photocatalytic Degradation of 2‐Chlorophenol

Two examples of heterometallic–organic frameworks (HMOFs) composed of dicarboxyl‐functionalized Fe^III‐salen complexes and d¹⁰ metals (Zn, Cd), [Zn₂(Fe‐L)₂(μ₂‐O)(H₂O)₂] ? 4 DMF ? 4 H₂O ( 1 ) and [Cd₂(Fe‐L)₂(μ₂‐O)(H₂O)₂] ? 2 DMF ? H₂O ( 2 ) (H₄L=1,2‐cyclohexanediamino‐N,N′‐bis(3‐methyl‐5‐carboxysalicylidene), have been synthesized and structurally characterized. In 1 and 2 , each square‐pyramidal Fe^III atom is embedded in the [N₂O₂] pocket of an L^4? anion, and these units are further bridged by a μ₂‐O anion to give an (Fe‐L)₂(μ₂‐O) dimer. The two carboxylate groups of each L^4? anion bridge Zn^II or Cd^II atoms to afford a 3D porous HMOF. The gas sorption and magnetic properties of 1 and 2 have been studied. Remarkably, 1 and 2 show activity for the photocatalytic degradation of 2‐chlorophenol (2‐CP) under visible‐light irradiation, which, to the best of our knowledge, is the first time that this has been observed for Fe^III‐salen‐based HMOFs.     

A Fe3O4‐Based Chemical Sensor for Cathodic Determination of Hydrogen Peroxide

A new cathodic scheme for hydrogen peroxide (H₂O₂) measurement by Fe₃O₄‐based chemical sensor was described. The unique characteristic of electrocatalytic property was firstly investigated by voltammetry. And then the amperometric response of H₂O₂ was measured at ?0.2 V (vs. Ag/AgCl) by Fe₃O₄ modified glassy carbon rotating disk electrode. The kinetic parameter was also calculated from Koutecky‐Levich plot, and the value was 6.4×10^?4 cm s^?1 in pH 3 citrate buffer. In order to benefit the possible biomedical applications, Fe₃O₄/chitosan modified electrode was also investigated in this experiment. There were several characteristic enhancements by the coated chitosan thin film for H₂O₂ sensor. The calibration curves were found to be linear up to 4.0 and 5.0 mM (r=0.999) in pH 3 and 7 with the detection limits of 7.6 and 7.4 μM L^?1 (S/N=3). The stability was evaluated by the results of half‐life time (t_50%) for 9 months at room temperature and 24 months at 4 °C.     

Electrochemical synthesis of Fe3O4-PB nanoparticles with core-shell structure and its electrocatalytic reduction toward H2O2

The Fe₃O₄-Prussian blue (PB) nanoparticles with core-shell structure have been in situ prepared directly on a nano-Fe₃O₄-modified glassy carbon electrode by cyclic voltammetry (CV). First, the magnetic nano-Fe₃O₄ particles were synthesized and characterized by X-ray diffraction. Then, the properties of the Fe₃O₄-PB nanoparticles were characterized by CV, electrochemical impedance spectroscopy, and superconducting quantum interference device. The resulting core-shell Fe₃O₄-PB-modified electrode displays a dramatic electrocatalytic ability toward H₂O₂ reduction, and the catalytic current was a linear function with the concentration of H₂O₂ in the range of 1 × 10⁻⁷~5 × 10⁻⁴ mol/l. A detection limit of 2 × 10⁻⁸ (s/n = 3) was determined. Moreover, it showed good reproducibility, enhanced long-term stability, and potential applications in fields of magnetite biosensors.