Amperometric Biosensors for Tyramine Determination Based on Graphene Oxide and Polyvinylferrocene Modified Screen‐printed Electrodes

A comparison of the analytical characteristics of two tyramine biosensors, based on graphene oxide (GRO) and polyvinylferrocene (PVF) modified screen‐printed carbon electrodes (SPCE), is reported. Diamine oxidase (DAOx) or monoamine oxidase (MAOx) was immobilized onto the PVF/GRO modified SPCE to fabricate the biosensors. Surface characteristics and electrochemical behaviour of the modified SPCEs were investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM), energy dispersive X‐ray spectroscopy (EDX) and cyclic voltammetry (CV). Electrode surface composition and experimental variables such as pH and working potential were optimized in order to ensure a high performance. Under optimum experimental conditions, both DAOx/PVF/GRO/SPCE and MAOx/PVF/GRO/SPCE biosensors exhibited wide linear dynamic ranges for tyramine from 9.9×10^?7 to 1.2×10^?4 M and from 9.9×10^?7 to 1.1×10^?4 M, respectively. MAOx/PVF/GRO/SPCE biosensor showed higher sensitivity (11.98 μA mM^?1) for tyramine determination than the DAOx/PVF/GRO/SPCE biosensor (7.99 μA mM^?1). The substrate specifity of the biosensors to other biogenic amines namely histamine, putrescine, spermine, spermidine, tryptamine, β‐phenylethylamine and cadaverine was also investigated. The developed biosensors were successfully used for tyramine determination in cheese sample.     

Electrocatalytic Reduction and Determination of Iodate and Periodate at Silicomolybdate‐Incorporated‐Glutaraldehyde‐ Cross‐Linked Poly‐L‐lysine Film Electrodes

The present work describes reduction of iodate (IO₃^?), and periodate (IO₄^?) at silicomolybdate‐doped‐glutaraldehyde‐cross‐linked poly‐L ‐lysine (PLL‐GA‐SiMo) film coated glassy carbon electrode in 0.1 M H₂SO₄. In our previous study, we were able to prepare the PLL‐GA‐SiMo film modified electrode by means of electrostatically trapping SiMo₁₂O₄₀^4? mediator in the cationic film of PLL‐GA, and the voltammetric investigation in pure supporting indicated that the charge transport through the film was fast. Here, the electrocatalytic activity of PLL‐GA‐SiMo film electrode towards iodate and periodate was tested and subsequently used for analytical determination of these analytes by amperometry. The two electron reduced species of SiMo₁₂O₄₀^4? anion was responsible for the electrocatalytic reduction of IO₃^? at PLL‐GA‐SiMo film electrode while two and six electron reduced species were showed electrocatalytic activity towards IO₄^? reduction. Under optimized experimental conditions of amperometry, the linear concentration range and sensitivity are 2.5×10^?6 to 1.1×10^?2 M and 18.47 μA mM^?1 for iodate, and 5×10^?6 to 1.43×10^?4 M and 1014.7 μA mM^?1 for periodate, respectively.     

Construction of an Amperometric Glucose Biosensor by Immobilization of Glucose Oxidase on Nanocomposite at the Surface of FTO Electrode

Fluorine? tin oxide (FTO) nanostructure was developed on the surface of a glass plate using spray payroliziz method. A new electrochemical biosensor was fabricated based on a layer by layer process. In this process chitosan? Fe₃O₄ (CH? Fe₃O₄) nanocomposite film was prepared at the surface of FTO electrode by dip? coating method. In the next step, the glucose oxidase (GOx) was immobilized on the CH? Fe₃O₄/FTO nanocomposite electrode. The GOx/CH? Fe₃O₄/FTO bioelectrode has a linear range of 10–270 µM and a detection limit of 5 µM. The highest sensitivity was obtained at 1.2 µA mM^?1 cm^?2.     

Silicomolybdate‐Incorporated‐Glutaraldehyde‐Cross‐Linked Poly‐L‐Lysine Film Modified Glassy Carbon Electrode as Amperometric Sensor for Bromate Determination

Silicomolybdate‐doped‐glutaraldehyde‐cross‐linked poly‐L ‐lysine (PLL‐GA‐SiMo) film modified glassy carbon electrode was successfully prepared by means of electrostatically trapping the silicomolybdate anion in PLL‐GA cationic coating. The PLL‐GA‐SiMo film was stable and the charge transport through the film was fast. The modified electrode shows excellent electrocatalytic activity towards bromate reduction with significant reduction of overpotential. In amperometric determination of bromate, the calibration plot was linear over the concentration range of 5×10^?5 to 1.2×10^?3 M with a sensitivity of 3.6 μA mM^?1. Furthermore, PLL‐GA‐SiMo film electrode showed fast response and good stability.     

A New Amperometric Biosensor Based on HRP/Nano-Au/L-Cysteine/Poly（o-Aminobenzoic acid）-Membrane-Modified Platinum Electrode for the Determination of Hydrogen Peroxide

The third generation amperometric biosensor for the determination of hydrogen peroxide （H2O2） has been described. For the fabrication of biosensor, o-aminobenzoic acid （oABA） was first electropolymerized on the surface of platinum （Pt） electrode as an electrostatic repulsion layer to reject interferences. Horseradish peroxidase （HRP） absorbed by nano-scaled particulate gold （nano-Au） was immobilized on the electrode modified with polymerized o-aminobenzoic acid （poABA） with L-cysteine as a linker to prepare a biosensor for the detection of H2O2. Amperometric detection of H2O2 was realized at a potential of ＋20 mV versus SCE. The resulting biosensor exhibited fast response, excellent reproducibility and sensibility, expanded linear range and low interferences. Temperature and pH dependence and stability of the sensor were investigated. The optimal sensor gave a linear response in the range of 2.99×10^-6 to 3.55×10^-3 mol·L^-1 to H2O2 with a sensibility of 0.0177 A·L^-1·mol^-1 and a detection limit （S/N = 3） of 4.3×10^-7 mol·L^-1. The biosensor demonstrated a 95% response within less than 10 s.     

Fe3O4@SiO2‐PANI‐Au Nanocomposite Prepared for Electrochemical Determination of Quercetin in Food Samples and Biological Fluids

A new electrochemical sensor based on Fe₃O₄@SiO₂‐PANI‐Au nanocomposite was fabricated for modification of glassy carbon electrode (Fe₃O₄@SiO₂‐PANI‐Au GCE). The Fe₃O₄@SiO₂‐PANI‐Au nanocomposite was characterized by TEM, FESEM‐EDS‐Mapping, XRD, and TGA methods. The Fe₃O₄@SiO₂‐PANI‐Au GC electrode exhibited an acceptable sensitivity, fast electrochemical response, and good selectivity for determination of quercetin. Under optimal conditions, the linear range for quercetin concentrations using this sensor was 1.0×10^?8 to 1.5×10^?5 mol L^?1, and the limit of detection was 3.8×10^?9 mol L^?1. The results illustrated that the offered sensor could be a possible alternative for the measurement of quercetin in food samples and biological fluids.     

Direct Electrochemistry and Electrocatalysis of Hemoglobin/ZnO‐Chitosan/nano‐Au Modified Glassy Carbon Electrode

The highly efficient H₂O₂ biosensor was fabricated on the basis of the complex films of hemoglobin (Hb), nano ZnO, chitosan (CHIT) dispersed solution and nano Au immobilized on glassy carbon electrode (GCE). Biocompatible ZnO‐CHIT composition provided a suitable microenvironment to keep Hb bioactivity (Michaelis‐Menten constant of 0.075 mmol L^?1). The presence of nano Au in matrix could effectively enhance electron transfer between Hb and electrode. The electrochemical behaviors and effects of solution pH values were carefully examined in this paper. The (ZnO‐CHIT)‐Au‐Hb/GCE demonstrated excellently electrocatalytical ability for H₂O₂. This biosensor had a fast response to H₂O₂ less than 4 s and excellent linear relationships were obtained in the concentration range from1.94×10^?7 to 1.73×10^?3 mol L^?1 with the detection limit of 9.7×10^?8 mol L^?1 (S/N=3) under the optimum conditions. Moreover, the stability and reproducibility of this biosensor were evaluated with satisfactory results.     

Iodate Sensing Electrodes Based on Phosphotungstate‐ Doped‐Glutaraldehyde‐Cross‐Linked Poly‐L‐lysine Coatings

Glassy carbon electrode modified with phosphotungstate‐doped‐glutaraldehyde‐cross‐linked poly‐L ‐lysine (PLL‐GA‐PW) film was employed for iodate determination. The PLL‐GA‐PW film electrode shows excellent electrocatalytic activity towards iodate reduction with significant reduction of overpotential. Under optimized experimental conditions, a linear range from 5×10^?8 to 2.27×10^?2 M with a sensitivity of 61.75 μA mM^?1 was obtained. Possible interfering species, in iodate determination, were evaluated and the applicability of proposed sensor for iodate estimation in table salt was also demonstrated. The PLL‐GA‐PW film electrode shows fast response, wider linear range, and good selectivity and stability.     

Selective Detection of Ascorbic Acid Using Octacyanomolybdate‐Doped‐Glutaraldehyde‐Cross‐Linked Poly‐L‐Lysine Film Modified Glassy Carbon Electrode

The present work describes oxidation of ascorbic acid (AA) at octacyanomolybdate‐doped‐glutaraldehyde‐cross‐linked poly‐L ‐lysine (PLL‐GA‐Mo(CN) film modified glassy carbon electrode in 0.1 M H₂SO₄. The modified electrode has been successfully prepared by means of electrostatically trapping Mo(CN) mediator in the cationic film of glutaraldehyde‐cross‐linked poly‐L ‐lysine. The dependence of peak current of modified electrode in pure supporting indicates that the charge transfer in the film was a mixed process at low scan rates (5 to 200 mV s^?1), and kinetically restrained at higher scan rates (200 to 1000 mV s^?1). Cyclic voltammetry and rotating disk electrode (RDE) techniques are used to investigate the electrocatalytic oxidation of ascorbic acid and compared with its oxidation at bare and undoped PLL‐GA film coated electrodes. The rate constant of catalytic reaction k obtained from RDE analysis was found to be 9.5×10⁵ cm³ mol^?1 s^?1. The analytical determination of ascorbic acid has been carried out using RDE technique over the physiological interest of ascorbic acid concentrations with a sensitivity of 75 μA mM^?1. Amperometric estimation of AA in stirred solution shows a sensitivity of 15 μA mM^?1 over the linear concentration range between 50 and 1200 μM. Interestingly, PLL‐GA‐Mo(CN) modified electrode facilitated the oxidation of ascorbic acid but not responded to other electroactive biomolecules such as dopamine, uric acid, NADH, glucose. This unique feature of PLL‐GA‐Mo(CN) modified electrode allowed for the development of a highly selective method for the determination of ascorbic acid in the presence of interferents.     

An Ethanol Biosensor Based on Simple Immobilization of Alcohol Dehydrogenase on Fe3O4@Au Nanoparticles

An ethanol biosensor based on alcohol dehydrogenase (ADH) attached to Au seeds decorated on magnetic nanoparticles (Fe₃O₄@Au NPs) is presented. ADH was immobilized on Fe₃O₄@Au NPs, which were subsequently fixed by a magnet on a carbon paste electrode modified with 5 % (m : m) MnO₂. Optimum conditions for the amperometric determination of ethanol with the biosensor were as follows: working potential +0.1 V (vs. Ag/AgCl); supporting electrolyte: 0.1 M phosphate buffer solution at pH 6.8 containing 0.25 mM of the coenzyme (NAD⁺); working electrode: carbon paste with magnetically attached Fe₃O₄@Au NPs (0.012 mg ? cm^?2 electrode area) with immobilized alcohol dehydrogenase (120 units per cm² of electrode area). Linearity between signal and concentration was found for the range from 0.1 to 2.0 M ethanol (r²=0.995) with a detection limit of 0.07 M, a sensitivity of 0.02 µA ? mM^?1 ? cm^?2, a reproducibility of 4.0 % RSD, and a repeatability of 2.7 % RSD. The results for the determination of ethanol in alcoholic beverages showed good agreement with gas chromatography (GC) with recovery of 96.0 – 108.8 %.     

Research on WPU‐RGO/ATP‐Fe3O4/chitosan composites with excellent electrical and magnetic properties

First, attapulgite‐Fe₃O₄ magnetic filler (ATP‐Fe₃O₄) was prepared by using a chemical precipitation method. Subsequently, graphite oxide (GO) was prepared through Hummer method, and then reduced GO (RGO) was prepared through GO reduced by chitosan (CS). Finally, a series of WPU‐RGO/ATP‐Fe₃O₄/CS composites were prepared by introduced RGO/ATP‐Fe₃O₄/CS to waterborne polyurethane. The structure and properties were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR), X‐ray diffraction (XRD), vibrating sample magnetometry (VSM), thermogravimetric analysis TGA, conductivity test, and tensile test. The experimental results indicated that thermal stability and tensile strength of nanocomposites were improved with the increase of the content of RGO/ATP‐Fe₃O₄/CS. Meanwhile, with the increase of the RGO/ATP‐Fe₃O₄/CS content, the electrical and magnetic properties of WPU‐RGO/ATP‐Fe₃O₄/CS composites were improved. When the content of RGO/ATP‐Fe₃O₄/CS was 8 wt%, the electrical conductivity and the saturation magnetic strength of WPU‐RGO/ATP‐Fe₃O₄/CS composites were 3.1 × 10^?7 S·cm^?1 and 1.38 emu/g, respectively. WPU‐RGO/ATP‐Fe₃O₄/CS composites have excellent electrical and magnetic properties.     

Direct electrochemistry of hemoglobin on graphene/Fe3O4 nanocomposite-modified glass carbon electrode and its sensitive detection for hydrogen peroxide

Graphene/Fe₃O₄ nanocomposite was prepared for the immobilization of hemoglobin (Hb) to improve the electron transfer between Hb and glass carbon electrode (GCE). The characterization of nanocomposites was described by transmission electron microscopy, Fourier transform infrared, Raman spectroscopy, and X-ray photoelectron spectroscopy, respectively. The electrochemistry of Hb on the graphene/Fe₃O₄-based GCE was investigated by cyclic voltammetry and amperometric measurement. The modified electrode showed a wide linear range from 0.25 μmol/L to 1.7 mmol/L with a correlation coefficient of 0.9967. The detection limit of the H₂O₂ biosensor was estimated at 6.0?×?10^?6?mol/L at a signal-to-noise ratio of 3.     

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

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

Enzyme Immobilization and Direct Electrochemistry Based on a New Matrix of Phospholipid‐Monolayer‐Functionalized Graphene

A new nanocomposite material for enzyme immobilization and subsequent direct electrochemistry and electrocatalysis was developed by using 1,2‐dimyristoyl‐sn‐glycero‐3‐phospho‐(1‐rac‐glycerol)‐phospholipid‐monolayer‐membrane‐modified graphene (DMPG‐G). Microperoxidase‐11 (MP11) was chosen as a model enzyme to investigate the composite system. Owing to the improved conductivity and biocompatible microenvironment, MP11 that was immobilized in the matrix of the DMPG‐G nanocomposite (DMPG‐G‐MP11) effectively retained its native structure and bioactivity. DMPG‐G‐MP11‐modified glassy carbon electrode (DMPG‐G‐MP11/GCE) exhibited a pair of well‐defined quasi‐reversible redox peaks of MP11 and showed high electrocatalytic activity towards hydrogen peroxide (H₂O₂). The linear response of the developed biosensor for the determination of H₂O₂ ranged from 2.0×10^?6 to 4.5×10^?4 M with a detection limit of 7.2×10^?7 M . This biosensor exhibited high reproducibility and long‐term storage stability. The promising features of this biosensor indicate that these lipid–graphene nanocomposites are ideal candidate materials for the direct electrochemistry of redox proteins and that they could serve as a versatile platform for the construction of a third‐generation biosensor.     

Carbazole‐based conjugated polymer covalently coated Fe3O4 nanoparticle as efficient and reversible Hg2+ optical probe

A type of fluorescent–magnetic dual‐function nanocomposite, Fe₃O₄@SiO₂@P‐2, was successfully obtained by Cu⁺‐catalyzed click reaction between acetylene (C?C? H)‐substituted carbazole‐based conjugated polymer ( P‐2) and azide‐terminated silica‐coated magnetic iron oxide nanoparticles (Fe₃O₄@SiO₂–N₃). Optical and magnetization analyses indicate that Fe₃O₄@SiO₂@P‐2 exhibits stable fluorescence and rapid magnetic response. The fluorescence of Fe₃O₄@SiO₂@P‐2 was quenched significantly in the presence of I^? and gave a detection limit (DL) of ～8.85 × 10^?7 M. Given the high binding constant and matching ratio between Hg²⁺ and I^?, the fluorescence of Fe₃O₄@SiO₂@P‐2/I^? complex recovered efficiently with the addition of Hg²⁺. A DL of ～4.17 × 10^?7 M was obtained by this probing system. Recycling of Fe₃O₄@SiO₂@P‐2 probe was readily achieved by simple magnetic separation. Results indicate that Fe₃O₄@SiO₂@P‐2 can be used as an “on–off–on” fluorescent switchable and recyclable Hg²⁺ probe. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3636–3645     

Construction of a biointerface for glucose oxidase through diazonium chemistry and electrostatic self-assembly technique

In this study, a new procedure for the fabrication of biosensors was developed. The method is based on the covalent attachment of nitrophenyl groups to the electrode surface via diazonium salt reaction followed by their conversion to amine moieties through electrochemical reduction and electrostatic layer-by-layer (LbL) assembly technique. In this procedure, highly stable iron oxide (Fe₃O₄) nanoparticles (IONPs), chitosan (CHIt), GOx, and Nile blue (NB) were assembled on the surface of aminophenyl modified glassy carbon electrode (AP/GCE) by LbL assembly technique. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to characterize the interfaces. The surface coverage of the active GOx and Michaelis–Menten constant (K _M) of the immobilized GOx were Γ?=?3.38?×?10^?11 mol cm^?2 and 2.54 mM, respectively. The developed biosensor displayed a well-defined amperometric response for glucose determination with high sensitivity (8.07 μA mM^?1) and low limit of detection (LOD) of 19.0 μM. The proposed approach allows simple biointerface regeneration by increasing pH which causes disruption of the ionic interactions and release of the electrostatic attached layers. The biosensor can then be reconstructed again using fresh enzyme. Simple preparation, good chemical and mechanical stabilities, and easy surface renewal are remarkable advantages of the proposed biosensor fabrication procedure.     

Direct Electrochemistry of Hemoglobin Entrapped in Composite Electrodeposited Chitosan‐Multiwall Carbon Nanotubes and Nanogold Particles Membrane and Its Electrocatalytic Application

Hemoglobin was entrapped in composite electrodeposited chitosan‐multiwall carbon nanotubes (MCNTs) film by assembling gold nanoparticles and hemoglobin step by step. In phosphate buffer solution (pH 7), a pair of well‐defined and quasireversible redox peaks appeared with formal potential at ?0.289 V and peak separation of 100 mV. The redox peaks respected for the direct electrochemistry of hemoglobin at the surface of chitosan‐MCNTs‐gold nanoparticles modified electrode. The parameters of experiments have also been optimized. The composite electrode showed excellent electrocatalysis to peroxide hydrogen and oxygen, the peak current was linearly proportional to H₂O₂ concentration in the range from 1×10^?6 mol/L to 4.7×10^?4 mol/L with a detection limit of 5.0×10^?7 mol/L, and this biosensor exhibited high stability, good reproducibility and better selectivity. The biosensor showed a Michaelis–Menten kinetic response as H₂O₂ concentration is larger than 5.0×10^?4 mol/L, the apparent Michaelis–Menten constant for hydrogen peroxide was calculated to be 1.61 μmol/L.     

An Organic Sol‐Gel Film as Modifier to Construct Biosensor

A new amperometric biosensor for hydrogen peroxide (H₂O₂) was developed by adsorbing hemoglobin (Hb) on an organic sol‐gel film. The organic sol‐gel was prepared using resorcinol and formaldehyde as monomers. This sol‐gel film shows a biocompatible microenvironment for retaining the native activity of the adsorbed Hb. The direct electron transfer between Hb and electrode is achieved. Hb adsorbed on the film shows an enzyme‐like catalytic activity for the reduction of H₂O₂. The reduction peak currents are proportional linearly to the concentration of hydrogen peroxide in the range of 6×10^?8 to 3.6×10^?6 M, with a detection limit of 2.4×10^?8 M (S/N=3). This research enlarges the applications of organic sol‐gel materials in biosensor field.     

Amperometric Hydrogen Peroxide Biosensor Based on Horseradish Peroxidase Immobilized on Fe3O4/Chitosan Modified Glassy Carbon Electrode

A new type of amperometric hydrogen peroxide biosensor was constructed based on horseradish peroxidase (HRP) immobilized on Fe₃O₄/chitosan modified glassy carbon electrode. The effects of some experimental variables such as the concentration of supporting electrolyte, pH, enzyme loading, the concentration of the mediator of methylene blue (MB) and the applied potential were investigated. The linear range of the calibration curve for H₂O₂ was 2.0×10^?4–1.2×10^?2 M with a detection limit of 1.0×10^?4 M (S/N=3). The response time was less than 12 s. The apparent Michaelis‐Menten constant K_m was 21.4 mM and it illustrated the excellent biological activity of the fixed enzyme. In addition, the biosensor had long‐time stability and good reproducibility. And this method has been used to determine H₂O₂ concentration in the real sample.