Direct Electrochemistry and Electrocatalysis of Hemoglobin Based on Nafion‐Room Temperature Ionic Liquids‐Multiwalled Carbon Nanotubes Composite Film

A robust and effective composite film combined the benefits of Nafion, room temperature ionic liquid (RTIL) and multi‐wall carbon nanotubes (MWNTs) was prepared. Hemoglobin (Hb) was successfully immobilized on glassy carbon electrode surface by entrapping in the composite film. Direct electrochemistry and electrocatalysis of immobilized Hb were investigated in detail. A pair of well‐defined and quasi‐reversible redox peaks of Hb was obtained in 0.10 mol·L^?1 pH 7.0 phosphate buffer solution (PBS), indicating that the Nafion‐RTIL‐MWNTs film showed an obvious promotion for the direct electron transfer between Hb and the underlying electrode. The immobilized Hb exhibited an excellent electrocatalytic activity towards the reduction of H₂O₂. The catalysis current was linear to H₂O₂ concentration in the range of 2.0×10^?6 to 2.5×10^?4 mol·L^?1, with a detection limit of 8.0×10^?7 mol·L^?1 (S/N=3). The apparent Michaelis‐Menten constant (K_m^app) was calculated to be 0.34 mmol·L^?1. Moreover, the modified electrode displayed a good stability and reproducibility. Based on the composite film, a third‐generation reagentless biosensor could be constructed for the determination of H₂O₂.     

Electrocatalysis of Hemoglobin in ZnO Nanoparticle/Ionic Liquid Composite Film Modified Glassy Carbon Electrode

A nanobiocompatible composite containing hemoglobin (Hb), ZnO nanoparticles (nano‐ZnO) and ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIMPF₆) was fabricated and further modified on the glassy carbon electrode (GCE). The electrochemical behaviours of Hb in the composite film were carefully studied and a pair of quasi‐reversible redox peaks appeared in pH 7.0 phosphate buffer solution, which was attributed to the electrode reaction of Hb heme Fe(III)/Fe(II) redox couple. The presences of nano‐ZnO and BMIMPF₆ in the film can retain the bioactivity of Hb and greatly enhance the direct electron transfer of Hb. The immobilized Hb showed high stability and good electrocatalytic ability to the reduction of hydrogen peroxide and O₂.     

Selective isolation of hemoglobin by use of imidazolium-modified polystyrene as extractant

Ionic liquids have attracted much attention in the analysis of a variety of species. The functional groups in ionic liquids can result in highly efficient separation and enrichment and, because of their typical lack of volatility, they are environmentally benign. We grafted imidazole cations onto the surface of chloromethyl polystyrene, denoted PS-CH₂-[MIM]⁺Cl^?, and this modified polymer was used to selectively extract the protein hemoglobin (Hb). The prepared extractant PS-CH₂-[MIM]⁺Cl^?, containing 2 mmol immobilized imidazole groups per gram polymer, was characterized by FT-IR, surface charge analysis, and elemental analysis. The adsorption efficiency was 91 %. The adsorption capacity of the PS-CH₂-[MIM]⁺Cl^? for Hb was 23.6 μg mg^?1, and 80 % of the retained Hb could be readily recovered by use of 0.5 % (m/v) aqueous sodium dodecyl sulfate (SDS) solution as eluate. The activity of the eluted Hb was approximately 90 %. The prepared imidazole-containing solid phase polymer was used for direct adsorption of Hb without use of any other solid matrix as support of the ionic liquid. The material was used in practice to isolate Hb from human whole blood.

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 tetra?uoroborate ([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 ?lm on the surface of glassy carbon electrode (GCE) were investigated. UV‐vis spectroscopy demonstrated that Hb in the IL‐carrageenan composite ?lm could retain its native secondary structure. A pair of well‐de?ned redox peaks of Hb was obtained at the Hb‐IL‐carrageenan composite ?lm modi?ed electrode through direct electron transfer between the protein and the underlying electrode. The heterogeneous electron transfer rate constant (k_s) was 2.02 s^?1, indicating great facilitation of the electron transfer between Hb and IL‐carrageenan composite film modi?ed electrode. The modi?ed 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 K_M^app for hydrogen peroxide was estimated to be 0.02 mmol/L, indicating that the biosensor possessed high af?nity to hydrogen peroxide. In addition, the proposed biosensor showed good reproducibility and stability.     

Direct Electron Transfer of Hemoglobin on a Carbon Ionic Liquid Electrode with TiO2 Nanopatricle as Enhancer

Room temperature ionic liquids (RTILs) N‐butylpyridinium hexafluorophosphate (BPPF₆) modified carbon paste electrode (CILE) was fabricated and applied to adsorb the hemoglobin (Hb) and TiO₂ nanoparticles on the electrode surface step by step to form a Hb modified electrode noted as TiO₂/Hb/CILE. UV‐Vis and FT‐IR spectra showed that Hb in the film retained its native conformations. Cyclic voltammetric experiments indicated that a pair of well‐defined quasi‐reversible redox peaks appeared with the formal potential (E^0′) located at ?0.251 V (vs. SCE) at pH 7.0 phosphate buffer solution (PBS), which was the characteristic of heme Fe(III)/Fe(II) redox couples. Electrochemical parameters of the Hb in the film such as the electron transfer coefficient (α), the electron transfer number (n) and the standard electron transfer rate constant (k_s) were estimated as 0.469, 0.87 and 0.635 s^?1, respectively.     

Direct Electrochemistry of Hemoglobin on Single‐Walled Carbon Nanotubes Modified Carbon Ionic Liquid Electrode and Its Electrocatalysis

In this article we report on the fabrication of a carbon ionic liquid electrode (CILE) by using a room temperature ionic liquid of 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIMPF₆) as binder. It was further modified by single‐walled carbon nanotubes (SWCNTs) to get a SWCNTs modified CILE denoted as SWCNTs/CILE. The redox protein of hemoglobin (Hb) was further immobilized on the surface of SWCNTs/CILE with the help of Nafion film. UV‐vis and FT‐IR spectra indicated that the immobilized Hb retained its native conformation in the composite film. The direct electrochemistry of Hb on the SWCNTs/CILE was carefully studied in pH 7.0 phosphate buffer solution (PBS). Cyclic voltammetric results indicated that a pair of well‐defined and quasireversible voltammetric peaks of Hb heme Fe(III)/Fe(II) was obtained with the formal potential (E°') at ?0.306 V (vs. SCE). The electrochemical parameters such as the electron transfer coefficient (α), the electron transfer number (n) and the apparent heterogeneous electron transfer rate constant (k_s) were calculated as 0.34, 0.989 and 0.538 s^?1, respectively. The fabricated Hb modified electrode showed good electrocatalytic ability to the reduction of trichloroacetic acid (TCA) in the concentration range from 20.0 to 150.0 mmol/L with the detection limit of 10.0 mmol/L (3σ).     

A Carbon Nanotube Layered Electrode for the Construction of the Wired Bilirubin Oxidase Oxygen Cathode

Oxidatively treated carbon nanotubes were coated on a glassy carbon surface to form a CNT‐layer. On the CNT‐layered GC surface, a redox hydrogel film of the copolymer, of polyacryamide and poly(N‐vinylimidazole) complexed with [Os(4,4′‐dichloro‐2,2′‐bipyridine)₂Cl]^+/2+ wiring bilirubin oxidase was immobilized. A good contact was achieved between the hydrogel film and the hydrophilic CNT‐layer with carboxylated CNTs. The prepared bilirubin oxidase cathode on the CNT‐layer was employed for the electrocatalytic reduction of O₂, and enhanced current and stability were observed. Electron transfers from the electrode surface O₂ molecules were analyzed. The optimal composition of the enzyme, redox polymer, and cross‐linker in the catalyst and the thickness of the CNT‐layer were determined.     

Direct Electron Transfer and Electrocatalysis of Hemoglobin on Chitosan‐TiO2 Nanorods‐Glass Carbon Electrode

The direct electron transfer between hemoglobin (Hb) and the glassy carbon electrode (GC) can be readily achieved via a high biocompatible composite system based on biopolymer chitosan (CHT) and TiO₂ nanorods (TiO₂‐NRs). TiO₂‐NRs greatly promote the electron transfer between Hb and GC, which contribute to the higher redox peaks. UV‐vis spectra result indicated the Hb entrapped in the composite film well keep its native structure. The immobilized Hb remains its bioelectrocatalytical activity to the reduction of H₂O₂ with a lower detection limit. A novel, sensitive, reproducible and stable electrochemical biosensing platform of H₂O₂ based on Hb‐TiO₂‐CHT electrode is explored.     

Direct Electrochemistry and Electrocatalysis of the Hemoglobin Immobilized on Diazonium‐Functionalized Aligned Carbon Nanotubes Electrode

A simple and efficient electrochemical method is utilized to functionalize aligned carbon nanotubes (ACNTs) by the electrochemical reduction of 4‐carboxyphenyl diazonium salt. Thus hemoglobin (Hb) molecules were covalently immobilized on the diazonium‐ACNTs surface via carbodiimide chemistry. Direct electrochemistry and bioelectrocatalytic activity of the immobilized Hb were then investigated by cyclic voltammetry (CV) and amperometry techniques. It is showed that the Hb film on the diazonium‐ACNTs electrode had well‐defined redox peaks with a formal potential (E°) at ?312 mV (vs. Ag/AgCl), and the Hb‐ACNTs electrode displayed good electrocatalytic activity to H₂O₂ reduction. Owing to the high Hb covering on the ACNTs surface (Γ*=2.7×10^?9 mol cm^?2), the catalytic current were significantly improved when compared to the current measured at an Hb‐tangled carbon nanotubes electrode. The Hb‐ACNTs electrode exhibited high sensitivity, long‐term stability and wide concentration range from 40 μM to 3 mM for the amperometric detection of H₂O₂. The heterogeneous reaction rate constant (k_s) was 0.95±0.05 s^?1 and the apparent Michaelis–Menten constant (K was 0.15 mM.     

Reagentless Biosensor for Hydrogen Peroxide Based on the Immobilization of Hemoglobin in Platinum Nanoparticles Enhanced Poly(chloromethyl thiirane) Cross‐linked Chitosan Hybrid Film

An unmediated hydrogen peroxide (H₂O₂) biosensor was prepared by co‐immobilizing hemoglobin (Hb) with platinum nanoparticles enhanced poly(chloromethyl thiirane) cross‐linked chitosan (CCCS‐PNs) hybrid film. CCCS could provide a biocompatible microenvironment for Hb and PNs could accelerate the electron transfer between Hb and the electrode. Spectroscopic analysis indicated that the immobilized Hb could maintain its native structure in the CCCS‐PNs hybrid film. Entrapped Hb exhibited direct electrochemistry for its heme Fe(III)/Fe(II) redox couples at ?0.396 V in the CCCS‐PNs hybrid film, as well as peroxidase‐like activity to the reduction of hydrogen peroxide without the aid of an electron mediator.     

Electrochemistry and Electrocatalysis of a Nafion/Nano‐CaCO3/Hb Film Modified Carbon Ionic Liquid Electrode Using BMIMPF6 as Binder

In this paper a room temperature ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIMPF₆) was used as binder for the construction of carbon ionic liquid electrode (CILE) and a new electrochemical biosensor was developed for determination of H₂O₂ by immobilization of hemoglobin (Hb) in the composite film of Nafion/nano‐CaCO₃ on the surface of CILE. The Hb modified electrode showed a pair of well‐defined, quasi‐reversible redox peaks with E_pa and E_pc as ?0.265 V and ?0.470 V (vs. SCE). The formal potential (E°′) was got by the midpoint of E_pa and E_pc as ?0.368 V, which was the characteristic of Hb Fe(III)/Fe(II) redox couples. The peak to peak separation was 205 mV in pH 7.0 Britton–Robinson (B–R) buffer solution at the scan rate of 100 mV/s. The direct electrochemistry of Hb in the film was carefully investigated and the electrochemical parameters of Hb on the modified electrode were calculated as α=0.487 and k_s=0.128 s^?1. The Nafion/nano‐CaCO₃/Hb film electrode showed good electrocatalysis to the reduction of H₂O₂ in the linear range from 8.0 to 240.0 μmol/L and the detection limit as 5.0 μmol/L (3σ). The apparent Michaelis–Menten constant (K_M^app) was estimated to be 65.7 μmol/L. UV‐vis absorption spectroscopy and FT‐IR spectroscopy showed that Hb in the Nafion/nano‐CaCO₃ composite film could retain its native structure.     

Electrochemical Behavior of a Glassy Carbon Electrode Chemically Modified with Nickel Pentacyanonitrosylferrate in Presence of Sulfur Compounds

The glassy carbon electrode was modified with a nickel pentacyanonitrosylferrate film by electrodeposition of Ni and subsequent derivatization with NaPCNF. The film was characterized by XPS and electrochemical methods. Cyclic voltammetry of the NiPCNF onto the GC shows a redox couple (Fe^III/Fe^II) with E°′ of 538 mV (I_pa/I_pc around 1) and ΔE_p of 93 mV in 0.5 mol L^?1 KNO₃, with a diffusion‐controlled process. There was a decrease of anodic peak currents of the film in the presence of sulfide and 2‐propanethiol due to a precipitation reaction on the film surface by nucleophilic attack.     

The Effect of Ionic Liquid Covalent Bonding to Sol‐Gel Processed Film on Ion Accumulation and Transfer

Accumulation of electroactive anions into a silicate film with covalently bonded room temperature ionic liquid film deposited on an indium tin oxide electrode was studied and compared with an electrode modified with an unconfined room temperature ionic liquid. A thin film containing imidazolium cationic groups was obtained by sol‐gel processing of the ionic liquid precursor 1‐methyl‐3‐(3‐trimethoxysilylpropyl)imidazolium bis(trifluoromethylsulfonyl)imide together with tetramethylorthosilicate on the electrode surface. Profilometry shows that the obtained film is not smooth and its approximate thickness is above 1 μm. It is to some extent permeable for a neutral redox probe – 1,1′‐ferrocene dimethanol. However, it acts as a sponge for electroactive ions like Fe(CN)₆^3?, Fe(CN)₆^4? and IrCl₆^3?. This effect can be traced by cyclic voltammetry down to a concentration equal to 10^?7 mol dm^?3. Some accumulation of the redox active ions also occurs at the electrode modified with the ionic liquid precursor, but the voltammetric signal is significantly smaller compare with the bare electrode. The electrochemical oxidation of the redox liquid t‐butyloferrocene deposited on silicate confined ionic liquid film is followed by the expulsion of the electrogenerated cation into an aqueous solution. On the other hand, the voltammetry obtained with the electrode modified with t‐butyloferrocene solution in the ionic liquid precursor exhibits anion sensitive voltammetry. This is explained by anion insertion into the unconfined ionic liquid deposit following t‐butylferricinium cation formation.     

Direct Electron Transfer Reactivity of Hemoglobin in Cationic Gemini Surfactant–Poly (Allylamine) Hydrochloride Composite Film on Glassy Carbon Electrode

A new composite film comprising cationic gemini surfactant butane-α,ω-bis(dimethyl dodeculammonium bromide) (BDDA, C₁₂-C₄-C₁₂) and poly (allylamine) hydrochloride(PAH) have been prepared. The composite film showed good biocompatibility and could promote the direct electron transfer between hemoglobin (Hb) and glassy carbon (GC) electrode. The immobilized Hb exhibited a pair of well-defined, quasi-reversible, and stable redox peaks with a formal potential of ?0.158 V (vs. SCE) in 0.10 M pH 7 phosphate buffer solutions, and showed high affinity to hydrogen peroxide. The cathodic peak current of the electrode was linear with increasing concentration of H₂O₂ in the range of 5.14 to 200 μM.     

Application of NiMoO4 Nanorods for the Direct Electrochemistry and Electrocatalysis of Hemoglobin with Carbon Ionic Liquid Electrode

In this paper NiMoO₄ nanorods were synthesized and used to accelerate the direct electron transfer of hemoglobin (Hb). By using an ionic liquid (IL) 1‐butylpyridinium hexafluorophosphate (BPPF₆) modified carbon paste electrode (CILE) as the basic electrode, NiMoO₄ nanorods and Hb composite biomaterial was further cast on the surface of CILE and fixed by chitosan (CTS) to establish a modified electrode denoted as CTS/NiMoO₄‐Hb/CILE. UV‐vis and FT‐IR spectroscopic results showed that Hb in the film retained its native structures without any conformational changes. Electrochemical behaviors of Hb entrapped in the film were carefully investigated by cyclic voltammetry with a pair of well‐defined and quasi‐reversible redox voltammetric peaks appearing in phosphate buffer solution (PBS, pH 3.0), which was attributed to the direct electrochemistry of the electroactive center of Hb heme Fe(III)/Fe(II). The results were ascribed to the specific characteristic of NiMoO₄ nanorods, which accelerated the direct electron transfer rate of Hb with the underlying CILE. The electrochemical parameters of Hb in the composite film were further carefully calculated with the results of the electron transfer number (n) as 1.08, the charge transfer coefficient (α) as 0.39 and the electron‐transfer rate constant (k_s) as 0.82 s^?1. The Hb modified electrode showed good electrocatalytic ability toward the reduction of trichloroacetic acid (TCA) in the concentration range from 0.2 to 26.0 mmol/L with a detection limit of 0.072 mmol/L (3σ), and H₂O₂ in the concentration range from 0.1 to 426.0 µmol/L with a detection limit of 3.16×10^?8 mol/L (3σ).     

Electrochemical Biosensor Based on Carbon Ionic Liquid Electrode Modified with Nafion/Hemoglobin/DNA Composite Film

A new electrochemical biosensor was constructed by immobilization of hemoglobin (Hb) on a DNA modified carbon ionic liquid electrode (CILE), which was prepared by using 1‐ethyl‐3‐methylimidazolium tetrafluoroborate (EMIMBF₄) as the modifier. UV‐vis absorption spectroscopic result indicated that Hb remained its native conformation in the composite film. The fabricated Nafion/Hb/DNA/CILE was characterized by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). A pair of well‐defined redox peaks was obtained on the modified electrode, indicated that the Nafion and DNA composite film provided an excellent biocompatible microenvironment for keeping the native structure of Hb and promoting the direct electron transfer rate of Hb with the basal electrode. The electrochemical parameters of Hb in the composite film were further calculated with the results of the charge transfer coefficient (α) and the apparent heterogeneous electron transfer rate constant (k_s) as 0.41 and 0.31 s^?1. The proposed electrochemical biosensor showed good electrocatalytic response to the reduction of trichloroacetic acid (TCA), H₂O₂, NO and the apparent Michaelis–Menten constant (K_M^app) for the electrocatalytic reaction was calculated, respectively.     

Fabrication and Electrochemical Behavior of Hemoglobin Modified Carbon Ionic Liquid Electrode

A new hemoglobin (Hb) and room temperature ionic liquid modified carbon paste electrode was constructed by mixing Hb with 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIMPF₆) and graphite powder together. The Hb modified carbon ionic liquid electrode (Hb‐CILE) was further characterized by FT‐IR spectra, scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). Hb in the carbon ionic liquid electrode remained its natural structure and showed good direct electrochemical behaviors. A pair of well‐defined quasireversible redox peaks appeared with the apparent standard potential (E′) as ?0.334 (vs. SCE) in pH 7.0 phosphate buffer solution (PBS). The electrochemical parameters such as the electron transfer number (n), the electron transfer coefficient (α) and the heterogeneous electron transfer kinetic constant (k_s) of the electrode reaction were calculated with the results as 1.2, 0.465 and 0.434 s^?1, respectively. The fabricated Hb‐CILE exhibited excellent electrocatalytic activity to the reduction of H₂O₂. The calibration range for H₂O₂ quantitation was between 8.0×10^?6 mol/L and 2.8×10^?4 mol/L with the linear regression equation as I_ss (μA)=0.12 C (μmol/L)+0.73 (n=18, γ=0.997) and the detection limit as 1.0×10^?6 mol/L (3σ). The apparent Michaelis–Menten constant (K_M^app) of Hb in the modified electrode was estimated to be 1.103 mmol/L. The surface of this electrochemical sensor can be renewed by a simple polishing step and showed good reproducibility.     

Microwave Activation of Electrochemical Processes in Ionic Liquid Impregnated Ionomer Spheres

The redox system K₄Fe(CN)₆ adsorbed into anion exchanger particles (Dowex 1×2 of typically 200 µm diameter) and impregnated with 1‐butyl‐3‐methyl‐imidazolium tetrafluoroborate ionic liquid (BMIM⁺BF₄^?) in contact to a 50 µm diameter platinum microelectrode show well‐defined Fe(III/II) voltammetric responses. Processes are studied at the ionic liquid sphere | electrode | gas interface in the presence of dry or 80 % relative humidity argon gas flow. Due to the hygroscopic nature of BMIN⁺BF₄^? currents are sensitive to humidity levels. Pulsed and continuous microwave activation (2.45 GHz) is shown to occur locally at the tip of the platinum microelectrode due to focusing of microwave energy. Impedance experiments reveal the presence of a thin active film of ionic liquid.     

Direct electrochemistry and electrocatalysis of hemoglobin in gelatine film modified glassy carbon electrode

Direct electrochemical and electrocatalytic behavior of hemoglobin (Hb) immobilized on glass carbon electrode (GCE) containing gelatine (Gel) films was investigated. The characteristics of Hb/Gel film modified GC electrode were performed by using SEM microscopy, UV-vis spectroscopy and electrochemical methods. The immobilized Hb showed a couple of quasi-reversible redox peak with a formal potential of −0.38 V (versus SCE) in 0.1 M pH 7.0 PBS. The formal potential changed linearly from pH 4.03 to 8.41 with a slope value of −52.0 mV pH⁻¹, which suggested that a proton transfer was accompanied with each electron transfer (ET) in the electrochemical reaction. The Hb/gelatine/GCE displayed a rapid amperometric response to the reduction of H₂O₂ and nitrite.     

Cu(II) Hexacyanoferrate(III) Modified Carbon Paste Electrode; Application for Electrocatalytic Detection of Nitrite

Copper hexacyanoferrate (CuHCF) film‐modified carbon paste electrode (CPE) has been prepared from various electrolytic aqueous solutions using consecutive cyclic voltammetry. The cyclic voltammograms showed the direct deposition of CuHCF films from the mixing of Cu²⁺ and Fe(CN)₆^3? ions and each time with one of the six cations: H⁺, Na⁺, K⁺, NH₄⁺, Mg²⁺, and Al³⁺. The CuHCF film showed a single redox couple that exhibited a cation effect (Na⁺, K⁺, Mg²⁺, and NH₄⁺) and anion effect (Cl^?, NO₃^?, SO₄^2?, ClO₄^?, and BrO₃^?) in the cyclic voltammograms. Voltammetric studies have indicated that in presence of nitrite, the cathodic peak current of CuHCF increases, followed by a decrease in the corresponding anodic current. This indicated that nitrite was reduced by the redox mediator immobilized on the electrode surface via an electrocatalytic mechanism. The process of reduction and its kinetics were investigated by using cyclic voltammetry, differential pulse voltammetry, chronoamperometry and chronocoulometry techniques. The electrocatalytic ability about 800 mV can be seen. The rate constant of the catalytic reduction of nitrite was found to be 7.9×10⁵ cm³ mol^?1 s^?1. Linearity range obtained was 5×10^?5?8.4×10^?3 by cyclic voltammetry and 8×10^?6?1.3×10^?3 and 4×10^?3?2×10^?2 by differential pulse voltammetry.