Ionic liquid modified GC electrode for the direct electrochemistry of chloroperoxidase

Chloropcroxidase （CPO） was immobilized by konjac glucomannan （KGM） on the 1-butyl-3-methyl imidazolium tetrafluoroborate [BMIM][BF4]/Nafion modified glassy carbon eloctrode. The electrochemical behaviors of the immobilized CPO were investigated by cyclic voltammetry. The results showed that CPO was successfully immobilized on the GCE and underwent fast direct electron transfer reactions with the formal potential at -0.3 V vs. SCE. The modified electrode showed a good catalytic activity for elcctrocatalytical reduction of O2 and H2O2.

Predominating stable adsorption and direct electrochemistry of glucose oxidase on carbon nanotubes by oxygen-containing groups

Stable adsorption and direct electrochemistry of glucose oxidase （COx） occurred on nitric acid （HNO3）-treated multi-walled carbon nanotubcs （MWNTs） instead of as-received MWNTs, demonstrating the critical roles of oxygen-containing groups in stable adsorption and direct electrochemistry of GOx on carbon nanotubcs （CNTs）.

Direct Electrochemistry of Hemoglobin Immobilized in Sodium Alginate Film on the Ionic Liquid [BMIM]PF_6 Modified Carbon Paste Electrode

Room temperature ionic liquid （RTILs） [BMIM]PF6 was used as a new kind of binder to construct a chemical modified carbon paste electrode （CPE） and the direct electrochemistry of hemoglobin （Hb）, which was immobilized on the surface of RTIL/CPE with the film of sodium alginate hydrogel, was studied by cyclic voltammetry. The presence of RTILs improved the direct electron transfer of Hb and a pair of well-defined quasi-revesible redox peaks appeared in pH 7.0 B-R buffer solution. The cathodic and anodic peak potentials were located at -0.383 V and -0.305 V with the formal potential （E^0） at -0.344 V （vs. SCE）. In addition the immobilized Hb showed good electrocatalytic activity to the reduction of H2O2.

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 excellent electrocatalytic response to the reduction of hydrogen peroxide. The catalytic current increased linearly with H2O2 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（Km^app） was 2.95 mmol/L.

Direct Electrochemistry Transfer and Electrocatalysis of Hemoglobin Immobilized in Porous Mn_2O_3

Novel porous Mn2O3 with good crystallinity was synthesized via hard-template method. Hb-Mn2O3 na-nocomposite was prepared and used for biosensor construction. The Hb-Mn2O3-Nafion modified electrode shows fast direct electron transfer and displays good electrocatalytic response to the reduction of H2O2. The response time is less than 5 s, the sensitivity is as high as 493 μA·L·mmol-1·cm-2 in a linear range of 1-100 μmol/L, and the detection limit is 0.16 μmol/L. This modified electrode also shows good stability and reproducibility. This indicates that the porous Mn2O3 provides a good matrix for enzyme immobilization and biosensor construction.

Direct Electrochemistry of Hemoglobin in Layer-by-layer {PDDA/Hb}_n Films Assembled on Pyrolytic Graphite Electrodes

Layer-by-layer {PDDA/Hb}(n) films were assembled by means of alternate adsorption of positively charged poly(diallyldimethyl ammonium) (PDDA) and negatively charged hemoglobin (Hb) at pH 9.2 from their aqueous solutions on pyrolytic graphite (PG) electrodes. Film growth during adsorption cycles was demonstrated by cyclic voltammetry and UV-Vis spectroscopy. Direct electrochemistry of Hb in {PDDA/Hb}(n) films on PG was studied.

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.

PROMOTION EFFECT OF PYRIDINE FOR THE DIRECT ELECTROCHEMISTRY OF CYTOCHROME C AT GOLD ELECTRODES

It was found for the first time that the compounds with only one functional group, such as pyridine, can show the promotion effect for the electrochemical reaction of cytochrome C at gold electrodes.

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

Fe3O4 particles coated with acrylic copolymer (ACP) of about 5-8 nm in diameter were synthesized and used for immobilization of horseradish peroxidase (HRP). Direct electrochemistry of HRP embedded in the nanosized Fe3O4 solid matrix modified paraffin impregnated graphite electrode (PIGE) was achieved, which is related to the heme Fe(III)/Fe(II) conversion of HRP. Cyclic voltammetry gave a pah- of reproducible and well-defined redox peaks at about Em of -0.295 V vs. SCE. The standard rate constant k, was determined as 2.7 s-1. It demonstrated that the nano-Fe3O4 solid matrix offers a friendly platform to assemble the HRP protein molecules and enhance the electron transfer rate between the HRP and the electrode. UV-Vis absorption spectra and FTIR spectra studies revealed that the embedded HRP retained its native-like structure. The HRP/Fe3O4/PIGE showed a strong catalytic activity toward H2O2. The voltammetric response was a linear function of H2O2 concentration in the range of 10-140 μmol/L with detection limit of 7.3 μmol/L (s/n = 3). The apparent Michaelis-Menten constant is calculated to be 0.42 mmol/L.

Direct Electrochemistry of Cytochrome c on EDTA-ZrO_2 Organic-inorganic Hybrid Film Modified Electrodes

A composite film of ethylenediamine tetraacetic acid (EDTA)-ZrO2 organic-inorganic hybrid was prepared based on the chelation between Zr(IV) and EDTA. The direct electrochemical behavior of cytochrome c (cyt. c) at the hybrid film modified glassy carbon electrodes was investigated. The immobilized EDTA can promote the redox of heme in horse heart cyt. c which gives rise to a pair of reversible redox peaks with a formal potential of 40 mV (vs. SCE). The peak current increased linearly with the increase of cyt. c concentration in the range of 1.6×10-6—8.0×10-5 mol昄-1 with the correlation coefficient of 0.996. Further investigation shows that metal ions can impede the electron transfer of cyt. c. The impediment capability of metal ions depends on their coordination capability with EDTA and their valence number.

Promotion of the Direct Electron Transfer of Hemoglobin by the Carbon Nanotube

It is reported that the direct electron transfer of hemoglobin (Hb) can be effectively promoted by carbon nanotubes when Hb was immobilized on the surface of the carbon nanotubes modified electrode. The results indicated that the conversion of Hb-Fe(Ⅲ)/Hb-Fe(Ⅱ) is a one-electron coupled one-proton reaction process. The method presented can be easily extended to study the direct electrochemistry of other proteins or enzymes.

Direct Electron－transfer Reaction of Cytochrome C at a Bare Spectrographic Graphite Electrode

he electrochemistry of cytochrome C was investigated at a spectrographicgraphite electrode. In phosphate buffer solution (pH= 7. 0) , cytochrome C showedstable and quasi-reversible response. The formal potential E￣(o') was 0. 015 V (at25℃ , vs. SCE) and the heterogeneous electron transfer rate constant k_s obtainedvaried form 1. 10×10￣(-3) cm · s￣(-1) to 1. 80k×10￣(-3) cm · s￣(-1). The thermodynamic pa-rameters of the electron transfer reaction of cvtochrome C was also estimated. Fur-thermore, the effect of the various electrode surface states on the electrochemistryof cytochrome C was discussed.

Electrochemical studies of chloroperoxidase on poly-L-lysine film modified GC electrode

Poly-L-lysine(PLL) was first electrodeposited onto the surface of a glassy carbon(GC) electrode.The PLL modified electrode was used to immobilize chloroperoxidase(CPO) via 1-[(3-dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride(EDC).The electrochemical behaviors of immobilized CPO on PLL/GC electrode were investigated by cyclic voltammetry(CV).The CV results obtained showed that CPO was successfully immobilized on the PLL/GC electrode and a fast direct electron transfer between CPO and PLL-GC electrod...

Hydrogen Peroxide Sensor Based on Horseradish Peroxidase Combined with CaCO_3 Microspheres and Gold Nanoparticles

Direct electrochemistry and electrocatalysis of horseradish peroxidase（HRP） were achieved by entrapping the enzyme between CaCO3 microspheres and gold nanoparticles through forming sandwich configuration （CaCO3-HRP-AuNPs）. Polyanion, poly（styrene sulfonate）（PSS）, was hybrid with CaCO3 microspheres to increase the surface negative charges for binding with HRP through electrostatic interaction. After the bioconjugate CaCO3 PSS-HRP was entrapped in chitosan based sol-gel（CS-GPTMS） film, HRP was encapsulated by in situ formation of an outer layer of AuNPs through electrochemical reduction of HAuCl4. The composite film containing AuNPs, CaCO3-PSS-HRP bioconjugates and CS-GPTMS can provide favorable microenvironment for HRP to perform direct electron transfer at glassy carbon electrode（GCE）. HRP retained its bioelectrocatalytic activity and lead to sensitive and fast amperometric response for the determination of H2O2. H2O2 could be detected in a very wide linear range from 5.0×10-6 mol/L to 7.1×10-2 mol/L. The sandwich configuration of CaCO3-biomolecules-AuNPs could serve as a versatile platform for enzyme immobilization and biosensing.

Amperometric Hydrogen Peroxide Biosensor Based on Multiwall Carbon Nanotubes and Cadmium Sulfide Quantum Dots

A novel third-generation hydrogen peroxide（H2O2） biosensor（Hb/CdS/MWNTs/GCE） was fabricated through hemoglobin（Hb） adsorbed onto the mercaptoacetic acid modified CdS QDs/carboxyl multiwall carbon nanotubes＇（MWNTs） films. Cyclic voltammogram of Hb/CdS/MWNTs/GCE showed a pair of well-defined and quasi-reversible redox peaks with a formal potential（E^0） of-0.230 V（vs. Ag/AgCl） in 0.1 mol/L pH=8.0 phosphate buffer solution（PBS）, which was the characteristic of the Hb heme Fe（Ⅲ）/Fe（Ⅱ） redox couple. The biosensor shows an excellent electrocatalytic activity to the reduction of H2O2. The response time of the designed biosensor to H202 at a potential of-0.30 V was less than 2 s and linear relationships were obtained in the concentration ranges of 2.0×10^-6-2.7×10^-3 mol/L and 2.7×10^-3-7.7×10^-3 mol/L with a detection limit of 3.0×10^-7 mol/L（S/N=3）. The apparent Michaelis-Menten constant Km was estimated to be 1.324 mmol/L that illustrated the excellent biological activity of the fixed Hb.

Studies on the Electron Transfer Centers of Amino Oxidase Immobilized on Self-Asembly Monolayer Using Electrochemical Methods

The direct electron transfer of amino oxidase on electrode surface based on self assembly technique occurs at 505 mV( vs . Ag/AgCl), indicating that copper atoms are the electron transfer centers and catalytic centers of amino oxidase.

Immobilization and Bioelectrochemistry of Hemoglobin Based on Carrageenan and Room Temperature Ionic Liquid Composite Film

A novel biopolymer/room-temperature ionic liquid composite film based on carrageenan, room temperature ionic liquid （IL） [1-butyl-3-methylimidazolium tetrafluoroborate （[BMIM]BF4）] was explored for immobilization of hemoglobin （Hb） and construction of biosensor. Direct electrochemistry and electrocatalytic behaviors of Hb entrapped in the IL-carrageenan composite film on the surface of glassy carbon electrode （GCE） were investigated. UV-vis spectroscopy demonstrated that Hb in the IL-carrageenan composite film could retain its native secondary structure. A pair of well-defined redox peaks of Hb was obtained at the Hb-IL-carrageenan composite film modified electrode through direct electron transfer between the protein and the underlying electrode. The heterogeneous electron transfer rate constant （ks） was 2.02 s 1, indicating great facilitation of the electron transfer between Hb and IL-carrageenan composite film modified electrode. The modified electrode showed excellent electrocatalytic activity toward reduction of hydrogen peroxide with a linear range of 5.0 × 10-6 to 1.5 ×10-4 mol/L and the detection limit was 2.12 ×10 7 mol/L （S/N= 3）. The apparent Michaelis-Menten constant KM^app for hydrogen peroxide was estimated to be 0.02 mmol/L, indicating that the biosensor possessed high affinity to hydrogen peroxide. In addition, the proposed biosensor showed good reproducibility and stability.

Facile Fabrication of a Graphene-based Electrochemical Biosensor for Glucose Detection

A simple and effective glucose biosensor based on immobilization of glucose oxidase （GOD） in graphene （GR）/Nafion film was constructed. The results indicated that the immobilized GOD can maintain its native structure and bioactivity, and the GR/Nafion film provides a favorable microenvironment for GOD immobilization and promotes the direct electron transfer between the electrode substrate and the redox center of GOD. The electrode reaction of the immobilized GOD shows a reversible and surface-controlled process with the large electron transfer rate constant （ks） of 3.42±0.08 s-1. Based on the oxygen consumption during the oxidation process of glucose catalyzed by the immobilized GOD, the as-prepared GOD/GR/Nafion/GCE electrode exhibits a linear range from 0.5 to 14mmol·L-1 with a detection limit of 0.03 mmol·L-1. Moreover, it displays a good reproducibility and long-term stability.

Microelectrode glucose biosensor based on nanoporous platinum/graphene oxide nanostructure for rapid glucose detection of tomato and cucumber fruits

A microelectrode glucose biosensor based on a three-dimensional hybrid nanoporous platinum/graphene oxide nanostructure was developed for rapid glucose detection of tomato and cucumber fruits.The nanostructure was fabricated by a two-step modification method on a microelectrode for loading a larger amount of glucose oxidase.The nanoporous structure was prepared on the surface of the platinum microelectrode by electrochemical etching,and then graphene oxide was deposited on the prepared nanoporous electrode by electrochemical deposition.The nanoporous platinum/graphene oxide nanostructure had the advantage of improving the effective surface area of the electrode and the loading quantity of glucose oxidase.As a result,the biosensor achieved a wide range of 0.1-20.0 mmol/L in glucose detection,which had the ability to accurately detect the glucose content.It was found that the three-dimensional hybrid nanostructure on the electrode surface realized the rapid direct electrochemistry of glucose oxidase.Therefore,the biosensor achieved high glucose detection sensitivity 11.64μA·L/(mmol.cm^(2)),low detection limit(13μmol/L)and rapid response time(reaching 95%steady-state response within 3 s),when calibrating in glucose standard solution.In agricultural application,the as-prepared biosensor was employed to detect the glucose concentration of tomato and cucumber samples.The results showed that the relative deviation of this method was less than 5%when compared with that of high-performance liquid chromatography,implying high accuracy of the presented biosensor in glucose detection in plants.

Assembly of layer-by-layer films of superoxide dismutase and gold nanorods:A third generation biosensor for superoxide anion

Based on the layer-by-layer self-assembly of positively charged cetyltrimethylammonium bromide （CTAB） wrapped gold na- norods （AuNRs） and negatively charged superoxide dismutase （SOD） from their aqueous solutions on cysteine modified gold electrode （Cys/Au）, a third generation electrochemical biosensor （（SOD/AuNRs）2/Cys/Au） for superoxide anion （02＂-） was developed. The two layers assembly of SOD/AuNRs can significantly enhance the direct electron transfer between SOD and the electrode. The functional enzymatic activities of the SOD offer an electrochemical approach to the determination of 02＂-. In the reductive regions, the proposed sensor exhibits excellent analytical performances, such as wide linear range （200 nM to 0.2 mM O2-）, low detection limit （100 nM O2-）, high sensitivity （22.11 nA cm-2 μM-1）, short response time （less than 5 s）, good stability and reproducibility, while no obvious interferences are caused by commonly met interfering species including hydrogen peroxide （H202）, uric acid （UA） and ascorbic acid （AA）.