Electrochemistry and electrocatalysis of hemoglobin on multi-walled carbon nanotubes modified carbon ionic liquid electrode with hydrophilic EMIMBF4 as modifier

The direct electrochemistry of hemoglobin (Hb) on multi-walled carbon nanotubes (MWCNTs) modified carbon ionic liquid electrode (CILE) was achieved in this paper. By using a hydrophilic ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF₄) as the modifier, a new CILE was fabricated and further modified with MWCNTs to get the MWCNTs/CILE. Hb molecules were immobilized on the surface of MWCNTs/CILE with polyvinyl alcohol (PVA) film by a step-by-step method and the modified electrode was denoted as PVA/Hb/MWCNTs/CILE. UV-vis and FT-IR spectra indicated that Hb remained its native structure in the composite film. Cyclic voltammogram of PVA/Hb/MWCNTs/CILE showed a pair of well-defined and quasi-reversible redox peaks with the formal potential (E^0′) of −0.370 V (vs. SCE) in 0.1 mol/L pH 7.0 phosphate buffer solution (PBS), which was the characteristic of the Hb heme Fe^III/Fe^II redox couples. The redox peak currents increased linearly with the scan rate, indicating the direct electron transfer was a surface-controlled process. The electrochemical parameters of Hb in the film were calculated with the results of the electron transfer coefficient (α) and the apparent heterogeneous electron transfer rate constant (k_s) as 0.49 and 1.054 s⁻¹, respectively. The immobilized Hb in the PVA/MWCNTs composite film modified CILE showed excellent electrocatalytic activity to the reduction of trichloroacetic acid (TCA) and hydrogen peroxide. So the proposed electrode showed the potential application in the third generation reagentless biosensor.     

Activation of glassy carbon electrodes by photocatalytic pretreatment

This paper describes a simple and rapid photocatalytic pretreatment procedure that removes contaminants from glassy carbon (GC) surfaces. The effectiveness of TiO₂ mediated photocatalytic pretreatment procedure was compared to commonly used alumina polishing procedure. Cyclic voltammetric and chronocoulometric measurements were carried out to assess the changes in electrode reactivity by using four redox systems. Electrochemical measurements obtained on photocatalytically treated GC electrodes showed a more active surface relative to polished GC. In cyclic voltammograms of epinephrine, Fe(CN)₆^3−/4− and ferrocene redox systems, higher oxidation and reduction currents were observed. The heterogeneous electron transfer rate constants (k^o) were calculated for Fe(CN)₆^3−/4− and ferrocene which were greater for photocatalytic pretreatment. Chronocoulometry was performed in order to find the amount of adsorbed methylene blue onto the electrode and was calculated as 0.34 pmol cm⁻² for photocatalytically pretreated GC. The proposed photocatalytic GC electrode cleansing and activating pretreatment procedure was more effective than classical alumina polishing.     

Immobilization, direct electrochemistry and electrocatalysis of hemoglobin on colloidal silver nanoparticles-chitosan film

This paper reports on the fabrication and characterization of hemoglobin (Hb)-colloidal silver nanoparticles (CSNs)-chitosan film on the glassy carbon electrode and its application on electrochemical biosensing. CSNs could greatly enhance the electron transfer reactivity of Hb as a bridge. In the phosphate buffer solution with pH value of 7.0, Hb showed a pair of well-defined redox peaks with the formal potential (E^0′) of −0.325 V (vs. SCE). The immobilized Hb in the film maintained its biological activity, showing a surface-controlled process with the heterogeneous electron transfer rate constant (k_s) of 1.83 s⁻¹ and displayed the same features of a peroxidase in the electrocatalytic reduction of oxygen and hydrogen peroxide (H₂O₂). The linear range for the determination of H₂O₂ was from 0.75 μM to 0.216 mM with a detection limit of 0.5 μM (S/N = 3). Such a simple assemble method could offer a promising platform for further study on the direct electrochemistry of other redox proteins and the development of the third-generation electrochemical biosensors.     

Application of silica gel as an effective modifier for the voltammetric determination of dopamine in the presence of ascorbic acid and uric acid

Amorphous silica gel modified carbon paste electrode (CPE) offers substantial improvements in voltammetric sensitivity and selectivity towards determination of dopamine (DA). Cyclic voltammetry of Fe(CN)₆^3−/4− as a negatively charged probe revealed that the surface of the silica gel modified carbon paste electrode had a high density of negative charge at pH 8.0. Therefore, the modified electrode adsorbed DA (pK_a = 8.9) and enhanced its voltammetric response while repulsed ascorbic acid (AA) (pK_a = 4.2) and uric acid (UA) (pK_a = 5.4) and inhibited their interfering effects. The influence of various experimental parameters including percent of silica gel in the CPE, pH of solution, and accumulation time and potentials, on the voltammetric response of DA was investigated. At the optimum conditions, the analytical curve was linear for dopamine concentrations from 2.0 × 10⁻⁷ to 1.0 × 10⁻⁶ mol L⁻¹ and 2.0 × 10⁻⁶ to 1.5 × 10⁻⁴ mol L⁻¹ with a detection limit (3σ) of 4.8 × 10⁻⁸ mol L⁻¹. The prepared electrode was used for determination of DA spiked into DA injection and human serum samples, and very good recovery results were obtained over a wide concentration range of DA.     

Direct electron transfer from glucose oxidase immobilized on a nano-porous glassy carbon electrode

A pair of well-defined and reversible redox peaks was observed for the direct electron transfer (DET) reaction of an immobilized glucose oxidase (GOx) on the surface of a nano-porous glassy carbon electrode at the formal potential (E°′) of −0.439 V versus Ag/AgCl/saturated KCl. The electron transfer rate constant (k_s) was calculated to be 5.27 s⁻¹. The dependence of E°′ on pH indicated that the direct electron transfer of the GOx was a two-electron transfer process, coupled with two-proton transfer. The results clearly demonstrate that the nano-porous glassy carbon electrode is a cost-effective and ready-to-use scaffold for the fabrication of a glucose biosensor.     

Direct electrochemistry and electrocatalysis of hemoglobin with carbon nanotube-ionic liquid-chitosan composite materials modified carbon ionic liquid electrode

A novel composite biomaterial was prepared by combining chitosan, multi-walled carbon nanotubes (MWCNTs), hemoglobin (Hb) and ionic liquid (IL) 1-butyl-3-methyl-imidazolium bromide together, which was further modified on the surface of a carbon ionic liquid electrode (CILE) with another ionic liquid 1-ethyl-3-methylimidazolium ethylsulphate as the binder. Ultraviolet-visible and Fourier transform infrared spectroscopic results indicated that Hb molecules in the composite film retained the native structure. Cyclic voltammetric results showed that a pair of well-defined redox peaks appeared in 0.1 mol/L phosphate buffer solution, indicating that the direct electron transfer of Hb in the composite film with the underlying electrode was realized. The results were attributed to the synergistic effect of MWCNTs and IL in the composite film, which promoted the electron transfer rate of Hb. The composite material modified electrode showed excellent electrocatalytic ability towards the reduction of different substrates such as trichloroacetic acid and NaNO₂ with good stability and reproducibility.     

Characterization of polymeric film of a new manganese phthalocyanine complex octa-substituted with 2-diethylaminoethanethiol, and its use for the electrochemical detection of bentazon

Manganese acetate octakis-(2-diethyaminoethanethiol) phthalocyanine (AcMnODEAETPc) was newly synthesized and characterized by spectroscopic and electrochemical methods. Solution electrochemistry of the complex showed three redox processes assigned to Mn^IIIPc⁻¹/Mn^IIIPc⁻², Mn^IIIPc⁻²/Mn^IIPc⁻² and Mn^IIPc⁻²/Mn^IIPc⁻³ species. The new molecule was polymerized onto a glassy carbon electrode (GCE) to form thin films of different thickness, giving poly-10-AcMnODEAETPc-GCE, poly-20-AcMnODEAETPc-GCE and poly-30-AcMnODEAETPc-GCE, where 10, 20 and 30 represent the number of voltammetry scans during polymerization. Three distinct redox processes were observed on the modified electrode in 0.1 M phosphate buffer solution, pH 5, which confirmed the formation of the polymer. The current signal due to the herbicide, bentazon, was dependent on film thickness; the best signal was obtained on poly-20-AcMnODEAETPc-GCE while poly-10-AcMnODEAETPc-GCE gave the least signal. However, the signals due to the herbicide were better on the different films compared to the bare electrode. Electrochemical impedance spectroscopy (EIS) technique revealed that differences in film thickness offered different charge transfer resistances, R_ct, hence difference in current signals for bentazon oxidation were observed on these films. A Tafel slope of 77 mV/decade, obtained for the herbicide on poly-20-AcMnODEAETPc-GCE, denotes a fast one electron transfer followed by a slow chemical step in the electro-oxidation of bentazon. The voltammetry signals of the herbicide on the films indicated the likely involvement of ring-based redox processes in the detection of the herbicide. A plot of background corrected current response, on this film, versus the concentration of bentazon was linear within the range 50–750 μM with a detection limit of 2.48 × 10⁻⁷ M.     

Enhanced direct electron transfer reactivity of hemoglobin in cationic gemini surfactant-room temperature ionic liquid composite film on glassy carbon electrodes

A novel composite film comprising cationic gemini surfactant butyl-α,ω-bis(dimethylcetylammonium bromide) (C₁₆H₃₃N(CH₃)₂-C₄H₈-N(CH₃)₂C₁₆H₃₃, C₁₆-C₄-C₁₆) and ionic liquid 1-octyl-3-methylimidazolium hexafluorophate (OMIMPF₆) has been prepared. The composite film shows good biocompatibility and it can promote the direct electron transfer between hemoglobin (Hb) and glassy carbon (GC) electrode. On the C₁₆-C₄-C₁₆ (dissolved in ethanol)-OMIMPF₆ film coated GC electrode, the immobilized Hb can exhibit a pair of well-defined, quasi-reversible and stable redox peaks with a formal potential of −0.317 V (vs SCE) in 0.10 M pH 7 phosphate buffer solutions. The electron transfer coefficient (α) of Hb is calculated to be 0.44 and the heterogeneous electron transfer rate constant is 6.08 s⁻¹. With the length of alkyl chains of gemini surfactant increasing and the ethanol concentration rising, the redox peaks of the resulting electrode C₁₆-C₄-C₁₆-OMIMPF₆-Hb/GC become bigger. The electrode presents good electrocatalytic response to peroxide hydrogen. The kinetic parameters I_max and k_m for the catalytic reaction are estimated. In addition, UV-vis spectra and reflectance absorption infrared spectra demonstrate that the Hb immobilized in the C₁₆-C₄-C₁₆-OMIMPF₆ film almost retains the structure of native Hb.     

Direct electrochemistry of chemically modified catalase immobilized on an oxidatively activated glassy carbon electrode

Catalase (Ct) was modified using Woodward’s reagent K (WRK) as a specific modifier of carboxyl residues. The modified Ct was immobilized on an oxidatively activated glassy carbon electrode surface to investigate its direct electrochemistry. Using cyclic voltammetry an irreversible reduction peak was obtained at approximately −0.362 V vs. Ag/AgCl in buffer solution, pH 7, and at a scan rate of 0.1 V s⁻¹. The electrochemical parameters, including charge-transfer coefficient (0.27), apparent heterogeneous electron transfer rate constant (13.51 ± 0.42 s⁻¹) and formal potential of the Ct film (−0.275 V) were determined. The prepared enzyme electrode exhibited a response to H₂O₂.     

Amperometric detection of hydrogen peroxide at nano-nickel oxide/thionine and celestine blue nanocomposite-modified glassy carbon electrodes

A simple procedure was developed to prepare a glassy carbon (GC) electrode modified with nickel oxide (NiOx) nanoparticles and water-soluble dyes. By immersing the GC/NiOx modified electrode into thionine (TH) or celestine blue (CB) solutions for a short period of time (5–120 s), a thin film of the proposed molecules was immobilized onto the electrode surface. The modified electrodes showed stable and a well-defined redox couples at a wide pH range (2–12), with surface confined characteristics. In comparison to usual methods for the immobilization of dye molecules, such as electropolymerization or adsorption on the surface of preanodized electrodes, the electrochemical reversibility and stability of these modified electrodes have been improved. The surface coverage and heterogeneous electron transfer rate constants (k_s) of thionin and celestin blue immobilized on a NiOx-GC electrode were approximately 3.5 × 10⁻¹⁰ mol cm⁻², 6.12 s⁻¹, 5.9 × 10⁻¹⁰ mol cm⁻² and 6.58 s⁻¹, respectively. The results clearly show the high loading ability of the NiOx nanoparticles and great facilitation of the electron transfer between the immobilized TH, CB and NiOx nanoparticles. The modified electrodes show excellent electrocatalytic activity toward hydrogen peroxide reduction at a reduced overpotential. The catalytic rate constants for hydrogen peroxide reduction at GC/NiOx/CB and GC/NiOx/TH were 7.96 (±0.2) × 10³ M⁻¹ s⁻¹ and 5.5 (±0.2) × 10³ M⁻¹ s⁻¹, respectively. The detection limit, sensitivity and linear concentration range for hydrogen peroxide detection were 1.67 μM, 4.14 nA μM⁻¹ nA μM⁻¹ and 5 μM to 20 mM, and 0.36 μM, 7.62 nA μM⁻¹, and 1 μM to 10 mM for the GC/NiOx/TH and GC/NiOx/CB modified electrodes, respectively. Compared to other modified electrodes, these modified electrodes have many advantages, such as remarkable catalytic activity, good reproducibility, simple preparation procedures and long-term stabilities of signal responses during hydrogen peroxide reduction.     

Effects of microwave radiation on electrodeposition processes at tin-doped indium oxide (ITO) electrodes

In situ microwave activation is investigated for the electrodeposition of a metal (gold) and for a metal oxide (hydrous Ti(IV) oxide) onto tin-doped indium oxide (ITO) film electrodes. It is demonstrated that localized microwave heating of the ITO film can be exploited to affect electrodeposition processes.The electrochemically reversible and temperature sensitive one-electron redox system Fe(CN)₆^3−/4− was employed in aqueous solution in order to calibrate the average surface temperature at the ITO film electrode. In the presence of microwave radiation the average electrode surface temperature reached ca. 363 K whereas under the same conditions the bulk solution temperature reached ca. 313 K. Therefore localized heating of the ITO film appears to be important.The rate of electrodeposition of gold from an aqueous 1 mM tetrachloroaurate(III) solution in 0.1 M KCl (adjusted to pH 2) is enhanced by microwave activation. However, the morphology of deposits remains un-effected. Hydrous titanium (IV) oxide films were electrodeposited from an aqueous solution of 1 mM TiCl₃ in 0.1 M acetate buffer pH 4.7. Dense films with blocking character were obtained with conventional heating but a fibrous more open deposit forms in the presence of microwaves.     

Effect of Al content on the electrochemical properties of Mg2−xAlxNi thin film hydride electrodes

Thin films of Mg_2−xAl_xNi alloys have been prepared by magnetron sputtering, and the effects of partial substitution of Al for Mg on the electrochemical properties of the films were studied. EIS results indicate the rate-limiting process for the thin film hydride electrode is the charge transfer reaction during the process of total discharge. A theoretical model has been derived for the impedance of a thin film hydride electrode based upon the assumption that hydrogen diffusion is neglected in the electrode. The charge-transfer reaction rate at the electrode surface and hydrogen diffusivity in the Mg_2−xAl_xNi thin film hydride electrodes were observed to initially decrease then increase with increasing Al content. Results from capacitance measurements indicate n-type semiconductor properties for the corrosion layer during the charge–discharge process. Hydrogen atom and OH⁻ transfer became more difficult with increasing Al content until x = 0.3, after which a significant drop in the barrier resistance was observed.     

Electrochemical behaviors of thymine on a new ionic liquid modified carbon electrode and its detection

A new electrochemical method was proposed for the determination of thymine, which relied on the oxidation of thymine at a carbon ionic liquid electrode (CILE) in a pH 5.0 Britton-Robinson buffer solution. CILE was fabricated by using ionic liquid 1-(3-chloro-2-hydroxy-propyl)-3-methylimidazole acetate as the binder, which showed strong electrocatalytic ability to promote the oxidation of thymine. A single well-defined irreversible oxidation peak appeared with adsorption-controlled process and enhanced electrochemical response on the CILE, which was due to the presence of high conductive ionic liquid on the electrode. The reaction parameters of thymine were calculated with the electron transfer coefficient (α) as 0.27, the electron transfer number (n) as 1.23, the apparent heterogeneous electron transfer rate constant (k_s) as 6.87 × 10⁻⁶ s⁻¹ and the surface coverage (Г_T) as 5.71 × 10⁻⁸ mol cm⁻². Under the selected conditions the oxidation peak current was proportional to thymine concentration in the range from 3.0 to 3000.0 μM with the detection limit as 0.54 μM (3σ) by differential pulse voltammetry. The proposed method showed good selectivity to the thymine detection without the interferences of coexisting substances.     

Preparation and electrochemical properties of functionalized ionic liquid self-assembled modified graphite electrode

A modified graphite electrode with functionalized ionic liquid (IL) pyridinium derivative of β-cyclodextrin ([CDbPy]BF₄) was prepared by layer-by-layer self-assembly technique. With ferrocene as probe, the characterization of the (CDIL/PDDA)_n/GE SAMs in the solution of phosphate (PBS, pH 7.0) was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronocoulometry. The electrochemical behavior of p-chloronitrobenzene (p-CNB) at the modified electrode was studied. It was found that the modified electrode could catalyze the reduction of p-CNB and made the cathode peak move about 100 mV in positive direction in the solution of 0.1 mol/L PBS (pH 7.0). Differential pulse voltammetry (DPV) was applied to the determination of p-CNB in waste water with satisfactory results. The detection limit and the linear range of the concentration of p-CNB to the reduction peak current were 8.0 × 10⁻⁸ mol/L and 3.0 × 10⁻⁷–1.0 × 10⁻⁵ mol/L, respectively.     

Adsorption thermodynamics and kinetics study for the self-assembly of 1,8,15,22-tetraaminophthalocyanatocobalt(II) on glassy carbon surface

Spontaneous adsorption of 1,8,15,22-tetraaminophthalocyanatocobalt(II) (4α-Co^IITAPc) on glassy carbon (GC) electrode leads to the formation of a stable self-assembled monolayer (SAM). Since the SAM of 4α-Co^IITAPc is redox active, its adsorption on GC electrode was followed by cyclic voltammetry. SAM of 4α-Co^IITAPc on GC electrode shows two pairs of well-defined redox peaks corresponding to Co^III/Co^II and Co^IIIPc⁻¹/Co^IIIPc⁻². The surface coverage (Γ) value, calculated by integrating the charge under Co^II oxidation, was used to study the adsorption thermodynamics and kinetics of 4α-Co^IITAPc on GC surface. Cyclic voltammetric studies show that the adsorption of 4α-Co^IITAPc on GC electrode has reached the saturation coverage (Γ_s) within 3 h. The Γ_s value for the SAM of 4α-Co^IITAPc on GC electrode was found to be 2.37 × 10⁻¹⁰ mol cm⁻². Gibbs free energy (ΔG_ads) and adsorption rate constant (k_ad) for the adsorption of 4α-Co^IITAPc on GC surface were found to be −16.76 kJ mol⁻¹ and 7.1 M⁻¹ s⁻¹, respectively. The possible mechanism for the self-assembly of 4α-Co^IITAPc on GC surface is through the addition of nucleophilic amines to the olefinic bond on the GC surface in addition to a meager contribution from π stacking. The contribution of π stacking was confirmed from the adsorption of unsubstituted phthalocyanatocobalt(II) (CoPc) on GC electrode. Raman spectra for the SAM of 4α-Co^IITAPc on carbon surface shows strong stretching and breathing bands of Pc macrocycle, pyrrole ring and isoindole ring. Raman and CV studies suggest that 4α-Co^IITAPc is adopting nearly a flat orientation or little bit tilted orientation.     

Ex situ and in situ characterization studies of spin-coated TiO2 film electrodes for the electrochemical ozone production process

An electrode composed of silicon/titanium oxide/platinum/titanium dioxide (Si/TiO_X/Pt/TiO₂) was fabricated by spin-coating TiO₂ multilayers on a Si/TiO_X/Pt substrate and was used in electrochemical ozone production (EOP). EOP was realized when the Si/TiO_X/Pt substrate was completely covered with the TiO₂ film and a current efficiency of 7% was achieved at a low current density of 26.7 mA cm⁻² in 0.01 M HClO₄ at 15 °C. The TiO₂ film was found to be of an anatase-type TiO₂ and that to comprise aperture structures from the X-ray diffraction (XRD) and transmission electron microscopy (TEM) observations. Moreover, the fabricated TiO₂ film was found to be an n-type semiconductor by photoelectrochemical measurements. The high efficiency at a low current density of EOP on the TiO₂ n-type semiconductor was explained to result from the electron transfer through the TiO₂/HClO₄ interface as tunneling current. When the tunneling current passes through a depletion layer of TiO₂, the electrode potential is necessarily high enough to facilitate EOP.     

Direct voltammetry and catalysis of hemoenzymes in methyl cellulose film

Horseradish peroxidase (HRP) and catalase (Cat) immobilized on edge-plane pyrolytic graphite (EPG) electrodes by methyl cellulose (MC). Both the hemoenzymes entrapped in the MC film undergo fast direct electron-transfer reaction, corresponding to hemeFe(III)+e→hemeFe(II). The formal potential (E⁰′), the apparent coverage (Γ), the electron transfer coefficient (α) and the apparent electron transfer rate constant (k_s) were calculated by performing nonlinear regression analysis of square wave voltammetry (SWV) experimental data. E⁰′ are linearly dependent on pH, indicating the electron transfer of Fe(III)/Fe(II) redox couple companied with the transfer of proton. The processes of catalytically reducing oxygen, hydrogen peroxide and nitric oxide by HRP and Cat entrapped in MC film are also explored.     

A novel biosensor based on electro-co-deposition of sodium alginate-Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>-graphene composite on the carbon ionic liquid electrode for the direct electrochemistry and electrocatalysis of myoglobin

A novel biosensor based on electro-co-deposition of myoglobin (Mb), sodium alginate (SA), Fe₃O₄-graphene (Fe₃O₄-GR) composite on the carbon ionic liquid electrode (CILE) was fabricated using Nafion as the film forming material to improve the stability of protein immobilized on the electrode surface, and the modified electrode was abbreviated as Nafion/Mb-SA-Fe₃O₄-GR/CILE. FT-IR and UV–vis absorption spectra suggested that Mb could retain its native structure after being immobilized in the SA-Fe₃O₄-GR composite film. The electrochemical behavior of the modified electrode was studied by cyclic voltammetry, and a pair of symmetric redox peaks appeared in the cyclic voltammograms, indicating that direct electron transfer of Mb was realized on the modified electrode, which was ascribed to the good electrocatalytic capability of Fe₃O₄-GR composite, the good biocompatibility of SA and the synergistic effects of SA and Fe₃O₄-GR composite. The electrochemical parameters of the electron transfer number (n), the charge transfer coefficient (α) and the electron transfer rate constant (k _s) were calculated as 0.982, 0.357 and 0.234 s^?1, respectively. The modified electrode exhibited good electrocatalytic ability to the reduction of trichloroacetic acid (TCA) with wide linear range from 1.4 to 119.4 mmol/L, low detection limit as 0.174 mmol/L (3σ), good stability and reproducibility.     

Direct electron transfer of hemoglobin immobilized in a mesocellular siliceous foams supported room temperature ionic liquid matrix and the electrocatalytic reduction of H2O2

Room temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM·PF₆) has been successfully immobilized on mesocellular siliceous foams (MSFs) by using a specific annealing method. Nitrogen adsorption/desorption isotherms and scanning electron microscopy (SEM) images reveal that most pores of MSFs are filled with the RTIL and the outer surfaces of MSFs are covered with the RTIL. When hemoglobin (Hb) is immobilized with the resulting hybrid material on a glassy carbon electrode (GCE), a pair of well-defined and quasi-reversible voltammetric peaks for Hb Fe(III)/Fe(II) is obtained. Its formal potential is −0.330 V (vs. saturated calomel electrode) in pH 7.0 phosphate buffer solution (PBS). The peak currents are much larger than those of Hb immobilized with MSFs or BMIM·PF₆-MSFs mixture. This indicates that the hybrid material has stronger promotion to the direct electron transfer of Hb, which is related to the effective immobilization of BMIM·PF₆ on MSFs. The electron-transfer rate constant (k_s) is estimated to be 1.91 s⁻¹. The immobilized Hb retains its native conformation and shows high electrocatalysis to the reduction of H₂O₂. Under the optimized experimental conditions, the catalytic current is linear to the concentration of H₂O₂ from 0.2 to 28 μM, and the detection limit is 8 × 10⁻⁸ M (S/N = 3). The linear range is wider than those for Hb immobilized with MSFs or BMIM·PF₆-MSFs mixture. Thus, the MSFs supported RTILs hybrid material is an ideal matrix for protein immobilization and biosensor fabrication.     

Direct electrochemistry and biocatalytic activity of hemoglobin entrapped into gellan gum and room temperature ionic liquid composite system

A new composite film of microbial exocellular polysaccharide-gellan gum (GG) and room temperature ionic liquid (IL) 1-butyl-3-methyl-imidazolium hexafluorophosphate (BMIMPF₆) was firstly used as an immobilization matrix to entrap proteins and its bioelectrochemical properties were studied. Hemoglobin (Hb) was chosen as a model protein to investigate the composite system. UV-vis spectroscopy, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to characterize the composite film. The obtained results demonstrated that the Hb molecule in the film kept its native structure and showed its good electrochemical behavior. A pair of well-defined, quasi-reversible cyclic voltammetric peaks appeared in pH 7.0 phosphate buffer solutions (PBS, 0.1 M), with the formal potential (E°′) of −0.368 V (vs. SCE), which was the characteristic of Hb Fe(III)/Fe(II) redox couples. The Hb-IL-GG-modified electrode also showed an excellent electrocatalytic behavior to the reduction of hydrogen peroxide (H₂O₂). Therefore, this kind of composite film as a novel substrate offers an efficient strategy and a new promising platform for further study on the direct electrochemistry of redox proteins and the development of the third-generation electrochemical biosensors.