Electrodeposition CaCO3 Nanoparticles‐chitosan Composite Film on Carbon Ionic Liquid Electrode as a Platform for Hemoglobin Electrochemical Biosensor

By one‐step co‐electrodeposition CaCO₃ nanoparticles‐chitosan composite film on carbon ionic liquid electrode (CILE), and then by spreading the composition of hemoglobin (Hb) and chitosan on the nanoCaCO₃‐chi/CILE, a Hb‐chi/nanoCaCO₃‐chi/CILE was fabricated and the direct electrochemistry and electrocatalysis of Hb at the electrode was investigated. The electrochemical impedance spectroscopy of the modified electrode showed the electron transfer resistance was 1166 Ω. Investigation results of cyclic voltammetrys showed a pair of well‐defined and quasireversible redox peak of Hb with the formal potentials of ‐0.295 V (vs. SCE) in 0.1 mol·L^‐1 pH 7.0 PBS; the response time of the reduction peak currents of Hb was lower than 3s; a linear range for determination of H₂O₂ was from 5.0 μmol·L^‐1 to 1.3 mmol·L^‐1 with a detection limit of 1.6 μmol·L^‐1 (S/N = 3) and a sensitivity of 0.16 A·M^‐1·cm^‐2; the electron transfer rate constant and the apparent Michaelis‐Menten constant of Hb were 1.98 s^‐1 and 0.81 mmol·L^‐1, respectively. As a result, the case of the one‐step co‐electrodeposition and the promising feature of biocomposite could serve as a versatile platform for the fabrication of electrochemical biosensors.     

Haemoglobin immobilized on nafion modified multi-walled carbon nanotubes for O2, H2O2 and CCl3COOH sensors

A conductive biocomposite film (MWCNTs-NF-Hb) containing multi-walled carbon nanotubes (MWCNTs) incorporated with entrapped haemoglobin (Hb) in nafion (NF) has been synthesized on glassy carbon electrode (GCE), gold (Au), indium tin oxide (ITO) and screen printed carbon electrode (SPCE) separately by potentiostatic methods. The presence of both MWCNTs and NF in the biocomposite film enhances the surface coverage concentration (Γ), and increases the electron transfer rate constant (K_s) to 132%. The biocomposite film exhibits a promising enhanced electrocatalytic activity towards the reduction of O₂, H₂O₂ and CCl₃COOH. The cyclic voltammetry has been used for the measurement of electrocatalysis results of analytes by means of biocomposite film-modified GCEs. The MWCNTs-NF-Hb-modified GCEs’ sensitivity values are higher than the values obtained for other film modified GCEs. The surface morphology of the biocomposite films which have been deposited on ITO has been studied using scanning electron microscopy and atomic force microscopy. The studies have revealed that there was an incorporation of NF and immobilization of Hb on MWCNTs. Finally, the flow injection analysis has been used for the amperometric studies of analytes at MWCNTs-Hb and MWCNTs-NF-Hb film modified SPCEs. The amperometric study results have shown higher slope values for MWCNTs-NF-Hb biocomposite film.     

An Amperometric Glucose Biosensor Based on Poly (Pyrrole‐2‐Carboxylic Acid)/Glucose Oxidase Biocomposite

A newly developed amperometric glucose biosensor based on graphite rod (GR) working electrode modified with biocomposite consisting of poly (pyrrole‐2‐carboxylic acid) (PCPy) particles and enzyme glucose oxidase (GOx) was investigated. The PCPy particles were synthesized by chemical oxidative polymerization technique using H₂O₂ as initiator of polymerization reaction and modified covalently with the GOx (PCPy‐GOx) after activation of carboxyl groups located on the particles surface with a mixture of N‐(3‐dimethylaminopropyl)‐N′‐ethylcarbodiimide hydrochloride (EDC) and N‐hydroxysuccinimide (NHS). Then the PCPy‐GOx biocomposite was dispersed in a buffer solution containing a certain amount of bovine serum albumin (BSA). The resulting biocomposite suspension was adsorbed the on GR electrode surface with subsequent solvent airing and chemical cross‐linking of the proteins with glutaraldehyde vapour (GR/PCPy‐GOx). It was determined that the current response of the GR/PCPy‐GOx electrodes to glucose measured at +300 mV vs Cl reference electrode was influenced by the duration of the PCPy particles synthesis, pH of the GOx solution used for the PCPy particles modification and the amount of immobilized PCPy‐GOx biocomposite. An optimal pH of buffer solution for operation of the biosensor was found to be 8.0. Detection limit was determined as 0.039 mmol L⁻¹ according signal to noise ratio (S/N: 3). The proposed glucose biosensor was tested in human serum samples.     

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.     

Application of Titanium Dioxide Nanowires for the Direct Electrochemistry of Hemoglobin and Electrocatalysis

Titanium dioxide (TiO₂) nanowires were synthesized and used for the realization of direct electrochemistry of hemoglobin (Hb) with carbon ionic liquid electrode (CILE) as the substrate electrode. TiO₂‐Hb composite was casted on the surface of CILE with a chitosan film and spectroscopic results confirmed that Hb retained its native structure in the composite. Direct electron transfer of Hb on the modified electrode was realized with a pair of quasi‐reversible redox waves appeared, indicating that the presence of TiO₂ nanowires could accelerate the electron transfer rate between the electroactive center of Hb and the substrate electrode. Electrochemical behaviors of Hb on the modified electrode were carefully investigated with the values of the electron transfer coefficient (α), the electron transfer number and the heterogeneous electron transfer rate constant (k_s) as 0.58, 0.98 and 1.62 s^‐1. The Hb modified electrode showed excellent electrocatalytic activity to the reduction of trichloroacetic acid and NaNO₂ with wider linear range and lower detection limit, indicating the successful fabrication of a new third‐generation biosensor.     

Carbon Nanostructured Screen‐printed Electrodes Modified with CuO/Glucose Oxidase/Maltase/SiO2 Composite Film for Maltose Determination

A sensitive voltammetric method was developed to determine maltose in beverage products using a carbon nanostructured screen‐printed electrode modified with CuO/glucose oxidase/maltase/SiO₂ biocomposite film. Adding CuO particles was done to possess catalytic activity toward hydrogen peroxide. Electrode modified by glucose oxidase and maltase shows a good response to maltose. A well‐defined reduction peak was registered at the potential of ?0.55 V (vs. Ag/AgCl) which intensity increases linearly with the concentration of maltose ranging from 0.01 to 0.1 mmol L^?1. The calculated limit of detection was 0.005 mmol L^?1. Tested on the beer samples, the developed CuO/glucose oxidase/maltase/SiO₂ biocomposite film covered carbon nanostructured screen‐printed electrode is showed to be a prospective sensitive element of the third generation biosensor for maltose.     

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.     

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 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.     

High Performance Oxide Functionalized Nitrogen‐Doped Mesocellular Carbon Foam for Biosensor Construction

Nitrogen‐doped mesocellular carbon foam (denoted as MCF? CN_x) with high surface area and large pore volume was prepared and characterized in detail. The MCF? CN_x was further functionalized by oxidation with HNO₃ (denoted as MCF? CN_x‐O) in order to effectively improve its hydrophilicity and biocompatibility. Both MCF? CN_x and MCF? CN_x‐O were used for immobilization of Hb and design of electrochemical biosensors. The activity of Hb immobilized on MCF? CN_x‐O is two times higher than that of Hb immobilized on MCF? CN_x. The Hb‐MCF? CN_x‐O‐Nafion modified electrode displays fast response, high sensitivity and low detection limit to the detection of hydrogen peroxide. The sensitivity of Hb‐MCF? CN_x‐O‐Nafion modified electrode (477 μA mM^?1 cm^?2) is twice that of Hb‐MCF? CN_x‐Nafion modified electrode.     

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.     

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).     

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.     

Direct Electrochemistry of Hemoglobin Immobilized on Carbon‐Coated Iron Nanoparticles for Amperometric Detection of Hydrogen Peroxide

A novel method for preparation of hydrogen peroxide biosensor was presented based on immobilization of hemoglobin (Hb) on carbon‐coated iron nanoparticles (CIN). CIN was firstly dispersed in a chitosan solution and cast onto a glassy carbon electrode to form a CIN/chitosan composite film modified electrode. Hb was then immobilized onto the composite film with the cross‐linking of glutaraldehyde. The immobilized Hb displayed a pair of stable and quasireversible redox peaks and excellent electrocatalytic reduction of hydrogen peroxide (H₂O₂), which leading to an unmediated biosensor for H₂O₂. The electrocatalytic response exhibited a linear dependence on H₂O₂ concentration in a wide range from 3.1 μM to 4.0 mM with a detection limit of 1.2 μM (S/N=3). The designed biosensor exhibited acceptable stability, long‐term life and good reproducibility.     

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.     

Reduced Graphene Oxide|Carbon Ceramic Electrode Modified with CdS‐Hemoglobin as a Sensitive Hydrogen Peroxide Biosensor

A sensitive hydrogen peroxide (H₂O₂) biosensor was developed based on a reduced graphene oxide|carbon ceramic electrode (RGO|CCE) modified with cadmium sulfide‐hemoglobin (CdS‐Hb). The electron transfer kinetics of Hb were promoted due to the synergetic function of RGO and CdS nanoparticles. The transfer coefficient (α) and the heterogeneous electron transfer rate constant (k_s) were calculated to be 0.54 and 2.6 s^?1, respectively, indicating a great facilitation achieved in the electron transfer between Hb and the electrode surface. The biosensor showed a good linear response to the reduction of H₂O₂ over the concentration range of 2–240 µM with a detection limit of 0.24 µM (S/N=3) and a sensitivity of 1.056 µA µM^?1 cm^?2. The high surface coverage of the CdS‐Hb modified RGO|CCE (1.04×10^?8 mol cm^?2) and a smaller value of the apparent Michaelis? Menten constant (0.24 mM) confirmed excellent loading of Hb and high affinity of the biosensor for hydrogen peroxide.     

Voltammetric Determination of Hemoglobin Using a Pencil Lead Electrode

In this paper the electrochemical behavior of hemoglobin (Hb) immobilized on a pencil lead electrode (PLE) was investigated. Immobilization of Hb on the pencil lead electrode was performed by nonelectrochemical and electrochemical methods. In phosphate buffer solution with pH 7.0 Hb showed a pair of well‐defined and nearly reversible redox waves (the anodic and cathodic peak potentials are located at ?0.18 V and ?0.22 V, respectively). The dependence of the anodic peak potential (E_pa) on the pH of the buffer solution indicated that the conversion of Hb? Fe(III)/Hb? Fe(II) is a one‐electron‐transfer reaction process coupled with one‐proton‐transfer. In addition the effect of scan rate on peak currents and peak separation potential was investigated and electrochemical parameters such as α and k_s were calculated. In the second part of this work, the ability of the electrode for determination of Hb concentration was investigated. The results showed a linear dynamic range from 0.15 to 2 µM and a detection limit of 0.11 µM. The relative standard deviation is 4.1 % for 4 successive determinations of a 1 µM Hb solution.     

Facile Synthesis of Poly (N‐isopropylacrylamide) Coated SiO2 Core‐shell Microspheres via Surface‐initiated Atom Transfer Radical Polymerization for H2O2 Biosensor Applications

In this study, inorganic/organic composites containing poly (N‐isopropylacrylamide) coated core‐shell SiO₂ microspheres were prepared via surface‐initiated atom transfer radical polymerization (ATRP). The thermal responsive polymer, N‐isopropylacrylamide was treated with methanol, water and CuBr/CuBr₂/1,1,4,7,7‐pentamethyldiethylenetriamine (PMDETA) at room temperature to form PNIPAM@SiO₂ microspheres. The as‐prepared PNIPAM@SiO₂ microspheres were characterized by FT‐IR, TGA, XPS, SEM, TEM analyses. Hemoglobin (Hb) was immobilized onto the surfaces of PNIPAM@SiO₂ microspheres via hydrophobic and π‐π stacking interactions. The as‐prepared Hb/PNIPAM@SiO₂ electrode exhibits well‐defined redox peak at a formal potential of −0.38 V, validating the direct electrochemistry of Hb. The Hb immobilized composite film retained its bioelectroactivity without any significant loss of catalytic activity. The modified electrode detects H₂O₂ over a wide linear concentration range (0.1 μM to 333 μM) with a detection limit of 0.07 μM. This modified electrode also successfully detects H₂O₂ from food and disinfectant samples with appreciable recovery values, validating its practicality. We believe that PNIPAM@SiO₂ composite has great potential to be used in the detection of H₂O₂ and development of other enzyme based biosensors.     

Direct Electrochemistry of Hemoglobin in Layer‐by‐Layer Films Assembled with DNA and Room Temperature Ionic Liquid

Based on electrostatic interaction and electrodeposition, poly‐anionic deoxyribonucleic acid (DNA), room temperature ionic liquid 1‐butyl‐3‐methyl‐imidazolium tetrafluoroborate (BMIMBF₄), hemoglobin (Hb) and Poly(diallyldimethylammonium chloride) (PDDA) were successfully assembled into Hb/IL/DNA/PDDA layer‐by‐layer complex films on the surface of ITO electrode. FTIR spectroscopy, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) 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 redox peaks of Hb with the formal potentials (E°′) of ?0.180 V (vs. SCE) was appeared in phosphate buffer solution (PBS, pH 7.0). The Hb/IL/DNA/PDDA/ITO modified electrode also showed an excellent electrocatalytic behavior to the reduction of hydrogen peroxide (H₂O₂). Therefore, the IL/DNA/PDDA complex film as a novel matrix open up a possibility for further study on the direct electrochemistry of other proteins and the fabrication of the third‐generation electrochemical biosensors.     

Electrochemical Surface Structuring with Polyaniline Wrapped Hb for Hydrogen Peroxide Biosensing

Through the electrodeposition of aniline with hemoglobin (Hb) on zincoxide‐gold colloidal sols (ZnO‐AuNPs) modified indium oxide electrode, a hydrogen peroxide (H₂O₂) biosensor was constructed. Polyaniline (PANI) form a nano‐cage wrapped Hb, which provided a comfortable and stable site for the immobization of Hb. UV‐vis spectrum was employed to characterize Hb retained original structure in the resulting Hb‐PANI/ZnO‐AuNPs membrane. Electrochemical investigation of the biosensor showed a pair of well‐defined, quasi‐reversible redox peaks with E_pa= ‐0.139 V and E_pc = ‐0.238 V (vs. SCE) in 0.1 M pH 7.0 phosphate buffer solution at the scan rate of 100 mV/s. The biosensor displayed a fast response time (<3 s) and broad linear response to H₂O₂ in the range from 1.5 μM to 1.7 mM with a detection limit of 0.8 μM (S/N = 3).