Direct electrochemical sensing of glucose using glucose oxidase immobilized on functionalized carbon nanotubes via a novel metal chelate-based affinity method

We report on a novel amperometric glassy carbon biosensing electrode for glucose. It is based on the immobilization of a highly sensitive glucose oxidase (GOx) by affinity interaction on carbon nanotubes (CNTs) functionalized with iminodiacetic acid and metal chelates. The new technique for immobilization is exploiting the affinity of Co(II) ions to the histidine and cysteine moieties on the surface of GOx. The direct electrochemistry of immobilized GOx revealed that the functionalized CNTs greatly improve the direct electron transfer between GOx and the surface of the electrode to give a pair of well-defined and almost reversible redox peaks and undergoes fast heterogeneous electron transfer with a rate constant (k _s) of 0.59?s^?1. The GOx immobilized in this way fully retained its activity for the oxidation of glucose. The resulting biosensor is capable of detecting glucose at levels as low as 0.01?mM, and has excellent operational stability (with no decrease in the activity of enzyme over a 10?days period). The method of immobilizing GOx is easy and also provides a model technique for potential use with other redox enzymes and proteins.

Mediatorless amperometric bienzyme glucose biosensor based on horseradish peroxidase and glucose oxidase cross-linked to multiwall carbon nanotubes

We report on a bienzyme-channeling sensor for sensing glucose without the aid of mediator. It was fabricated by cross-linking horseradish peroxidase (HRP) and glucose oxidase (GOx) on a glassy carbon electrode modified with multiwalled carbon nanotubes (MWNTs). The bienzyme was cross-linked with the MWNTs by glutaraldehyde and bovine serum albumin. The MWNTs were employed to accelerate the electron transfer between immobilized HRP and electrode. Glucose was sensed by amperometric reduction of enzymatically generated H₂O₂ at an applied voltage of ?50 mV (vs. Ag/AgCl). Factors influencing the preparation and performance of the bienzyme electrode were investigated in detail. The biosensor exhibited a fast and linear response to glucose in the concentration range from 0.4 to 15 mM, with a detection limit of 0.4 mM. The sensor exhibited good selectivity and durability, with a long-term relative standard deviation of <5 %. Analysis of glucose-spiked human serum samples yielded recoveries between 96 and 101 %.

Preparation and characterization of methylene blue-SDS- multiwalled carbon nanotubes nanocomposite for the detection of hydrogen peroxide

A nanocomposite was prepared by physical adsorption of?(cationic) methylene blue (MB) on (anionic) sodium dodecylsulfate (SDS) that was wrapped on multiwalled carbon nanotubes (MWCNTs) on the surface of a glassy carbon electrode. This electrostatic interaction enables electrical communication between the electrode and analyte. Horseradish peroxidase was then immobilized in a film of gelatin on the nanocomposite to form a biosensor for hydrogen peroxide. Scanning electron microscopy, transmission electron microscopy, Fourier transform infrared and UV?Cvis spectrometry, and cyclic voltammetry were applied to characterize the electrode. The addition of both MWCNTs and MB causes a synergistic effect and leads to a large signal enhancement. The prepared nanocomposite material modified sensor shows better response in presence of several interferences. The biosensor has detection limit of 5 nM of hydrogen peroxide (at S/N?=?3) with a linear response between 0.2???M and 1.4?mM. Its lifetime is >4?months under dry conditions at 4?°C.

Electrocatalytic oxidation of hydrazine at a glassy carbon electrode modified with nickel ferrite and multi-walled carbon nanotubes

A hydrothermal technique was used to synthesize nickel ferrite nanoparticles (NF-NPs) deposited on multi-walled carbon nanotubes (MWCNTs). The material was characterized by scanning electron microscopy, energy dispersive spectrometry, and X-ray powder diffraction which showed that the NF-NPs are located on the surface of the carboxylated MWCNTs. The material was used to modify a glassy carbon electrode which then was characterized via cyclic voltammetry, electrochemical impedance spectroscopy, and amperometry. The electrode displays strong electrochemical response to hydrazine. A potential hydrazine sensing scheme is suggested.

Examination of incubation time of bare gold electrode inside cysteamine solution for immobilization of multi-walled carbon nanotubes on a gold electrode modified with cysteamine

A cysteamine (CysAm) nanostructure was generated to act as an intermediate layer between gold electrode and carbon nanotubes. A bare gold electrode was placed in a solution of CysAm to create a self-assembled monolayer on its surface. The modified electrode was then incubated with a solution of multi-walled carbon nanotubes. Cyclic voltammetry and atomic force microscopy were used to characterize the modified electrode. The results indicated that the number of functionalized MWCNTs on the surface of the electrodes increased by enhancing incubation time.

An enzymatic glucose biosensor based on a glassy carbon electrode modified with manganese dioxide nanowires

A glassy carbon electrode was modified with β-manganese dioxide (β-MnO₂), and glucose oxidase (GOx) was immobilized on its surface. The β-MnO₂ nanowires were prepared by a hydrothermal method and characterized by scanning electron microscopy and powder X-ray diffraction. They were then dispersed in Nafion solution and cast on the glassy carbon electrode (GCE) to form an electrode modified with β-MnO₂ nanowires that exhibits improved sensitivity toward hydrogen peroxide. If GOx is immobilized in the surface, the β-MnO₂ acts as a mediator, and Nafion as a polymer backbone. The fabrication process was characterized by electrochemical impedance spectroscopy, and the sensor and its materials were characterized by cyclic voltammetry and amperometry. The biosensor enables amperometric detection of glucose with a sensitivity of 38.2 μA?·?mM^?1?·?cm^?2, and a response time of?<?5 s. This study also demonstrates the feasibility of realizing inexpensive, reliable, and high-performance biosensors using MnO₂ nanowires.

Biosensor based on a glassy carbon electrode modified with tyrosinase immmobilized on multiwalled carbon nanotubes

We describe a biosensor for phenolic compounds that is based on a glassy carbon electrode modified with tyrosinase immobilized on multiwalled carbon nanotubes (MWNTs). The MWNTs possess excellent inherent electrical conductivity which enhances the electron transfer rate and results in good electrochemical catalytic activity towards the reduction of benzoquinone produced by enzymatic reaction. The biosensor was characterized by cyclic voltammetry, and the experimental conditions were optimized. The cathodíc current is linearly related to the concentration of the phenols between 0.4???M and 10???M, and the detection limit is 0.2???M. The method was applied to the determination of phenol in water samples.

A glassy carbon electrode modified with the nickel(II)-bis(1,10-phenanthroline) complex and multi-walled carbon nanotubes, and its use as a sensor for ascorbic acid

A glassy carbon electrode (GCE) was modified with the nickel(II)-bis(1,10-phenanthroline) complex and with multi-walled carbon nanotubes (MWCNTs). The nickel complex was electrodeposited on the MWCNTs by cyclic voltammetry. The modified GCE displays excellent electrocatalytic activity to the oxidation of ascorbic acid (AA). The effects of fraction of MWCNTs, film thickness and pH values were optimized. Response to AA is linear in the 10 to 630 μM concentration range, and the detection limit is 4 μM (at a signal-to-noise ratio of 3:1). The modified electrode was applied to determine AA in vitamin C tablets and in spiked fruit juice.

Direct electrochemistry of glucose oxidase and sensing glucose using a screen-printed carbon electrode modified with graphite nanosheets and zinc oxide nanoparticles

We have studied the direct electrochemistry of glucose oxidase (GOx) immobilized on electrochemically fabricated graphite nanosheets (GNs) and zinc oxide nanoparticles (ZnO) that were deposited on a screen printed carbon electrode (SPCE). The GNs/ZnO composite was characterized by using scanning electron microscopy and elemental analysis. The GOx immobilized on the modified electrode shows a well-defined redox couple at a formal potential of ?0.4 V. The enhanced direct electrochemistry of GOx (compared to electrodes without ZnO or without GNs) indicates a fast electron transfer at this kind of electrode, with a heterogeneous electron transfer rate constant (K_s) of 3.75 s^?1. The fast electron transfer is attributed to the high conductivity and large edge plane defects of GNs and good conductivity of ZnO-NPs. The modified electrode displays a linear response to glucose in concentrations from 0.3 to 4.5 mM, and the sensitivity is 30.07 μA mM^?1 cm^?2. The sensor exhibits a high selectivity, good repeatability and reproducibility, and long term stability. Figure

Graphical representation for the fabrication of GNs/ZnO composite modified SPCE and the immobilization of GOx     

Simple construction of an enzymatic glucose biosensor based on a nanocomposite film prepared in one step from iron oxide, gold nanoparticles, and chitosan

The one-step synthesis is reported of a nanofilm composed of iron oxide and gold nanoparticles in a chitosan matrix that can act as a novel matrix for the immobilization of glucose oxidase (GOx) to fabricate a glucose biosensor. The use for the composite film strongly increased the effective electrode surface for loading of GOx. The size and shape of the iron oxide nanoparticles were examined by transmission electron micrograph. Direct electron transfer and electrocatalysis by GOx was investigated via cyclic voltammetry and chronoamperometry. Under optimized conditions, the biosensor has a response time of 6?s and a linear response in the range between 3???M and 0.57?mM of glucose, with a detection limit of 1.2???M at a signal-to-noise ratio of 3. This novel and disposable mediatorless glucose biosensor may form the basis for a future mass-produced glucose biosensor.

Tin disulfide nanoflakes decorated with gold nanoparticles for direct electrochemistry of glucose oxidase and glucose biosensing

Previously, we have prepared nanoflake-like tin disulfide (SnS2) and used for the immobilization of proteins and biosensing. We have now modified an electrode with a composite consisting of nanoflake-like SnS2 decorated with gold nanoparticles (Au-NPs) and have immobilized glucose oxidase (GOx) on its surface in order to study its direct electrochemistry. Scanning electron microscopy, electrochemical impedance spectroscopy, Fourier transform IR spectroscopy and cyclic voltammetry were used to examine the interaction between GOx and the AuNP-SnS2 film. It is shown that the composite film has a larger surface area and offers a microenvironment that facilitates the direct electron transfer between enzyme and electrode surface. The immobilized enzyme retains its bioactivity and undergoes a surface-controlled, reversible 2-proton and 2-electron transfer reaction, with an apparent electron transfer rate constant of 3.87 s ^-1. Compared to the nanoflake-like SnS2-based glucose sensor, the GOx-based biosensor exhibits a lower detection limit (1.0 :M), a better sensitivity (21.8 mA?M ^-1 ?cm ^-2), and a wider linear range (from 0.02 to 1.3 mM). The sensor displays excellent selectivity, good reproducibility, and acceptable stability. It was successfully applied to reagentless sensing of glucose at ?0.43 V.

Direct electrodeposition of a biocomposite consisting of reduced graphene oxide, chitosan and glucose oxidase on a glassy carbon electrode for direct sensing of glucose

We have electrodeposited a composite film consisting of graphene oxide, chitosan and glucose oxidase directly on a glassy carbon electrode (GCE) through electrochemical reduction of a solution of the 3 components under controlled direct electrical potential. The procedure takes only several minutes, and the thickness of the resulting film is uniform and controllable. The GOx has uncompromised bioactivity and exhibits reversible 2-proton and 2-electron transfer in presence of glucose. It therefore can be used amperometric sensing of glucose. The biosensor has a fast response (<3 s), a detection limit of 0.4 μM (which is 50-fold lower compared to the biosensor prepared by drop-casting solutions of the same materials onto an GCE), and a linear response in the 0.4 μM to 2 mM concentration range (which again is much better than that of the biosensor prepared by the drop-casting method). Other features include high reproducibility, long-time storage stability, and satisfactory selectivity. We presume that the direct single-step electrodeposition of this nanocomposite offers a promising approach towards novel types of highly sensitive and stable electrochemical biosensors.

Performance of dye-sensitized solar cells with various carbon nanotube counter electrodes

Double-wall carbon nanotubes (DWCNTs), single-wall carbon nanotubes (SWCNTs), and multi-wall carbon nanotubes (MWCNTs) were investigated as an alternative for platinum in counter-electrodes for dye-sensitized solar cells. The counter-electrodes were prepared on fluorine-doped tin oxide glass substrates by the screen printing technique from pastes of carbon nanotubes and organic binder. The solar cells were assembled from carbon nanotubes counter-electrodes and screen printed anodes made from titanium dioxide. The cells produced with DWCNTs, SWCNTs or MWCNTs have overall conversion efficiencies of 8.0%, 7.6% and 7.1%, respectively. Electrochemical impedance spectroscopy measurements revealed that DWCNTs displayed the highest catalytic activity for the reduction of tri-iodide ions. The large surface area and superior chemical stability of the DWCNTs facilitated the electron-transfer kinetics at the interface between counter-electrode and electrolyte and yielded the lowest transfer resistance, thereby improving the photovoltaic activity. A short-term stability test at moderate conditions confirmed the robustness of solar cells based on the use of DWCNTs, SWCNTs or MWCNTs.

Hydrogen peroxide sensor based on a stainless steel electrode coated with multi-walled carbon nanotubes modified with magnetite nanoparticles

Multi-walled carbon nanotubes (MWCNTs) were decorated with magnetite (Fe₃O₄) nanoparticles and then used to modify a stainless steel electrode. The Fe₃O₄/MWCNTs composite was characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and X-ray diffraction patterns. Electrochemical properties of the modified electrode revealed a substantial catalytic activity for the reduction of hydrogen peroxide. The relationship between peak current and the concentration of hydrogen peroxide was linear in the range from 0.06?mmol?L^?1 to 0.36?mmol?L^?1, and the lowest detectable concentration is 0.01?mmol·L^?1 (S/N?=?3). The modified stainless steel electrode displays excellent stability.

Trans-membrane electron transfer in red blood cells immobilized in a chitosan film on a glassy carbon electrode

We have studied the trans-membrane electron transfer in human red blood cells (RBCs) immobilized in a chitosan film on a glassy carbon electrode (GCE). Electron transfer results from the presence of hemoglobin (Hb) in the RBCs. The electron transfer rate (k _s) of Hb in RBCs is 0.42 s^?1, and <1.13 s^?1 for Hb directly immobilized in the chitosan film. Only Hb molecules in RBCs that are closest to the plasma membrane and the surface of the electrode can undergo electron transfer to the electrode. The immobilized RBCs displayed sensitive electrocatalytic response to oxygen and hydrogen peroxide. It is believed that this cellular biosensor is of potential significance in studies on the physiological status of RBCs based on observing their electron transfer on the modified electrode.

A uric acid sensor based on electrodeposition of nickel hexacyanoferrate nanoparticles on an electrode modified with multi-walled carbon nanotubes

An electrode sensitive to uric acid was prepared by electrodeposition of nickel(II) hexacyanoferrate(III) on the surface of a glassy carbon electrode modified with multi-walled carbon nanotubes. The morphology of the material was characterized by scanning electron microscopy and Fourier transform infrared spectrometry. The modified electrode were characterized via cyclic voltammetry and amperometry (i - t). It exhibited efficient electron transfer ability and a strong and fast (< 3?s) response towards uric acid which is linear in the range from 0.1???M to 18???M, with a lower detection limit of 50 nM (at an S/N ratio of 3). In addition, the electrode exhibited good reproducibility and long-term stability.

A Novel Amperometric Glucose Biosensor Based on Fe3O4-Chitosan-β-Cyclodextrin/MWCNTs Nanobiocomposite

A novel enzymatic biosensing platform toward glucose is achieved with nanocomposite of magnetic nanoparticles (Fe₃O₄−CS−CD) and multi-walled carbon nanotubes (MWCNTs). The synergistic effect of chitosan, β-cyclodextrin and MWCNTs can facilitate electron transfer between enzyme and electrode based on the promoting results of the cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The new biosensors exhibited direct electron transfer (DET) from enzyme to electrode after glucose oxidase (GOx) was immobilized on the modified electrode with the nanocomposite. Consequently, the enzymatic glucose biosensor displayed a considerably wide linear range (40 μM to 1.04 mM) with a high sensitivity of 23.59 μA mM⁻¹cm⁻², low detection limit of 19.30 μM, good selectivity, reproducibility and repeatability for detecting glucose. In addition, the current response still retained at 93.4 % after 25 days. Furthermore, the practical application of glucose biosensor was test in human serum samples with satisfactory accuracy, demonstrating promising and practical potential in biomedical diagnostics.     

Direct electron transfer of glucose oxidase on the carbon nanotube electrode

The direct electrochemistry of redox enzymes (or proteins) has received more and more attention[1—9]. These studies developed an electrochemical basis for the investigation of enzyme structure, mechanisms of redox transformations of enzyme molecules and metabolic processes involving redox transformations. From these studies, one can also find potential appli-cations of enzymes in biotechnology. For example, if an enzyme immobilized on electrode surface is ca-pable of the direct electron tra…     

Direct electron transfer and biocatalytic activity of iron storage protein molecules immobilized on electrodeposited cobalt oxide nanoparticles

Ferritin was immobilized on a glassy carbon electrode with electrodeposited cobalt oxide nanoparticles, and its direct electron transfer behavior was studied. It exhibits a pair of redox peaks due to direct electron transfer between ferritin and the nanoparticles. Electrochemical parameters including the formal potential (E^0??), the charge transfer coefficient (??), and the apparent heterogeneous electron transfer rate constant (k_s) were determined. The sensor displays excellent biocatalytic activity in terms of reduction of hydrogen peroxide, and this was applied to electrochemical sensing of hydrogen peroxide.

Gold nanoparticle-coated multiwall carbon nanotube-modified electrode for electrochemical determination of methyl parathion

We report on an electrochemical sensor for the determination of methyl parathion. It is based on an electrode modified with multi-walled carbon nanotubes that were covered with gold nanoparticles (Au-NPs). The vertically aligned array of MWCNTs on a tantalum substrate was coated with Au-NPs by overhead magnetron sputtering deposition. Scanning and transmission electron microscopy and XRD were used to characterize the Au-NP-MWCNTs composite. Cyclic voltammetry and differential pulse voltammetry were employed to evaluate the suitability of the new electrode for the determination of methyl parathion. Under the optimal conditions, the current response of the electrode to methyl parathion is linear in the range from 0.50 to 16.0 mg mL^-1, with a detection limit of 50 ??g mL^-1 (signal/noise = 3), and the sensitivity is 4.5 times better than that of the plain MWCNTs electrode. We conclude that this method represents a simple, rapid, effective and sensitive approach for the detection of methyl parathion.