Novel sensor based on carbon paste/Nafion? modified with gold nanoparticles for the determination of glutathione

Several problems for the direct electrochemical oxidation of reduced glutathione (GSH) challenge the usage of electroanalytical techniques for its determination. In this work, the electrochemical oxidation of GSH catalyzed by gold nanoparticles electrodeposited on Nafion modified carbon paste electrode in 0.04?mol?L^?1 universal buffer solution (pH?7.4) is proved successful. The effect of various experimental parameters including pH, scan rate and stability on the voltammetric response of GSH was investigated. At the optimum conditions, the concentration of GSH was determined using differential pulse voltammetry (DPV) in two concentration ranges: 0.1?×?10^?7 to 1.6?×?10^?5?mol?L^?1 and 2.0?×?10^?5 to 2.0?×?10^?4?mol?L^?1 with correlation coefficients 0.9988, 0.9949 and the limit of detections (LOD) are 3.9?×?10^?9?mol?L^?1 and 8.2?×?10^?8?mol?L^?1, respectively, which confirmed the sensitivity of the electrode. The high sensitivity, wide linear range, good stability and reproducibility, and the minimal surface fouling make this modified electrode useful for the determination of spiked GSH in urine samples and in tablet with excellent recovery results obtained.     

多臂碳纳米管/Nafion复合材料修饰玻碳电极测定痕量的铅离子

A composite material of nitric acid oxidized multiwalled carbon nanotube （MWNT） and Nation was prepared. Such composite was modified on a glassy carbon electrode to determine trace of lead by differential pulsed voltammetry. In pH=6.47 NaNO3 solution, Pb^2＋ ions were accumulated on the modified electrode at -0.4 V. Compared with a bare and a Nation film coated electrode, the composite coated GC electrode can reduce the accumulating potential and eliminate the toxic character of mercury. The calibration plots were linear at low concentration of 5.0× 10^-9-2.0× 10^-8 mol/L and high concentration of 2.5× 10^-8-5.0× 10^-6 mol/L. The performances characteristics indicate that the electrode can be used to determine trace Pb^2＋ ions.     

Graphene‐Nafion Composite Film Modified Electrode for Voltammetric Sensor for Determination of Dihydromyricetin

A simple but highly snesitive electrochemical sensor for the determination of dihydromyricetin (DMY) based on graphene‐Nafion nanocomposite film modified Glassy carbon electrode (GCE) was reported. The characteristic of the sensor was examined by scanning electron microscopic (SEM) and electrochemical impedance spectroscopy (EIS). Compares with bare GCE, pre‐anodized glassy carbon electrode (GCE(ox)) and Nafion modified electrode, the sensor exhibited the more superior ability of detecting DMY, due to the synergetic graphene and Nafion. Other, the dependence of the current on pH, instrumental parameters, accumulation time and potential were investigated to optimize the experimental conditions in the determination of DMY. Under the selected conditions, the response peak currents were linear relationship with the DMY concentrations in the range of 8.0 × 10^?8 ～ 2.0 × 10^?5 mol L^?1 with a detection limit of 2.0 × 10^?8 mol L^?1. And, the method was also applied successfully to detect DMY in Ampelopsis grossedentata samples.     

Simultaneous Determination of Pb and Cd Traces in Water Samples by Anodic Stripping Voltammetry Using a Modified GC Electrode

The determination of Pb and Cd with a Nafion‐modified glassy carbon electrode and Cu‐DPABA complex (Cu‐DPABA–NA/GCE; DPABA is methyl 3,5‐bis{bis‐[(pyridin‐2‐yl)methyl]amino}methyl‐benzoate) as an alternative electrode for anodic stripping voltammetry was described. Pb and Cd were accumulated in acetate buffer pH 4 at a potential of ?1.4 V (vs. Ag/AgCl electrode) for 120 s followed by a DPASV scan from ?1.2 to ?0.2 V. Under optimum conditions the calibration curves were linear in the range of 4.8×10^?9–5.0×10^?5 and 5.0×10^?9–5×10^?5 mol L^?1 for Pb and Cd, respectively. Detection limits were 1.8×10^?9 and 1.2×10^?9 mol L^?1 for Pb and Cd, respectively. Different parameters and conditions, such as membrane ingredients, accumulation time, potential and pH value were optimized. A study of interfering substances was also performed. A significant increase in current was achieved at the modified electrode in comparison with the bare glassy carbon electrode. The validation of the proposed method was made by Pb and Cd determination in the certified reference material Groundwater CRM 610 (BCR, Community Bureau of Reference, Brussels, Belgium). The electrode was successfully applied for determination of Pb and Cd in river water with a high content of organic contaminants without any pretreatment.     

Development and application of the tartrazine voltammetric sensors based on molecularly imprinted polymers

A modified glassy carbon electrode was prepared as an electrochemical voltammetric sensor based on molecularly imprinted polymer film for tartrazine (TT) detection. The sensitive film was prepared by copolymerization of tartrazine and acrylamide on the carbon nanotube-modified glassy carbon electrode. The performance of the imprinted sensor was investigated by cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy in detail. Under the optimum conditions, two dynamic linear ranges of 8?×?10^?8 to 1?×?10^?6?mol?L^?1 and 1?×?10^?6 to 1?×?10^?5?mol?L^?1 were obtained, with a detection limit of 2.74?×?10^?8?mol?L^?1(S/N?=?3). This sensor was used successfully for tartrazine determination in beverages.     

One-step construction of an electrode modified with electrodeposited Au/SiO2 nanoparticles, and its application to the determination of NADH and ethanol

A new electrode was developed by one-step potentiostatic electrodeposition (at ?2.0 V for 20 s) of Au/SiO₂ nanoparticles on a glassy carbon electrode. The resulting electrode (nano-Au/SiO₂/GCE) was characterized by scanning electronic microscopy, X-ray photoelectron spectroscopy and electrochemical techniques. The electrochemical behavior of dihydronicotinamide adenine dinucleotide (NADH) at the nano-Au/SiO₂/GCE were thoroughly investigated. Compared to the unmodified electrode, the overpotential decreased by about 300 mV, and the current response significantly increased. These changes indicated that the modified electrode showed excellent catalytic activity in the oxidation of NADH. A linear relationship was obtained in the NADH concentration range from 1.0?×?10^?6 to 1.0?×?10^?4 mol?L^?1. In addition, amperometric sensing of ethanol at the nano-Au/SiO₂/GCE in combination with alcohol dehydrogenase and nicotinamide adenine dinucleotide was successfully demonstrated. A wide linear response was also found for ethanol in the range from 5.0?×?10^?5 to 1.0?×?10^?3 mol?L^?1 and 1.0?×?10^?3 to 1.0?×?10^?2 mol?L^?1, respectively. The method was successfully applied to determine ethanol in beer and biological samples.     

Determination of ferulic acid in Chinese proprietary medicine based on a poly-glutamic acid film sensor

The poly-glutamic acid modified electrode has been prepared by direct electro-polymerization of D-glutamic acid on the surface of glassy carbon electrode. In pH 4.2, 0.1 mol L^?1 HAc-NaAc buffer solution, the film modified electrode exhibited remarkable enhancement effect to the electrochemical responses of ferulic acid. The action mechanism was preliminarily explored. In the range of 2.0 × 10^?7 to 1.0 × 10^?5 mol L^?1, and 1.0 × 10^?5 to 3.0 × 10^?4 mol L^?1, the oxidation peak current has a linear relationship to the concentration, and the detection limit was estimated to be 7.0 × 10^?8 mol L^?1. This method has been adopted to detect trace amount of ferulic acid in Chinese proprietary medicine, and the recovery was from 97.8 to 102.4%.     

Construction of a modified carbon paste electrode based on TiO2 nanoparticles for the determination of gallic acid

A modified carbon paste electrode was prepared by incorporating the TiO₂ nanoparticles in the carbon paste matrix. The electrochemical behavior of gallic acid (GA) is investigated on the surface of the electrode using cyclic voltammetry and differential pulse voltammetry. The surface morphology of the prepared electrode was characterized using the scanning electron microscopy. The results indicate that the electrochemical response of GA is improved significantly at the modified electrode compared with the unmodified electrode. Furthermore, the capabilities of electron transfer on these two electrodes were also investigated by electrochemical impedance spectroscopy. Under the optimized condition, a linear dynamic range of 2.5?×?10^?6 to 1.5?×?10^?4?mol?L^?1 with detection limit of 9.4?×?10^?7?mol?L^?1 for GA is obtained in buffered solutions with pH 1.7. Finally, the proposed modified electrode was successfully used in real sample analysis.     

Voltammetric Determination of Methylparaban in Cosmetics Using a Multi-Wall Carbon Nanotubes/Nafion Composite Modified Glassy Carbon Electrode

A novel voltammetric sensor using multi-wall carbon nanotubes (MWNTs) coupled with Nafion modified glassy carbon electrode (GCE) was developed for the detection of methylparaben (MP). The sensor exhibited good electrocatalytic activity toward the oxidation of MP in the phosphate buffer solution (PBS, pH 6.5). It displayed good sensitivity, repeatability, reproducibility, and long-term stability. Under the optimized conditions, the anodic peak current was linear with the concentration of MP in the range of 3 × 10^?6 mol L^?1 to 1 × 10^?4 mol L^?1. The detection limit was 1 × 10^?6 mol L^?1. The proposed method was successfully applied to determine MP in cosmetics with satisfactory results.     

Electrochemical Properties of the Oxo‐Manganese‐Phenanthroline Complex Immobilized on Ion‐Exchange Polymeric Film and Its Application as Biomimetic Sensor for Sulfite Ions

A biomimetic sensor containing the oxo‐bridged dinuclear manganese‐phenanthroline complex incorporated into a cation‐exchange polymeric film deposited onto glassy carbon electrode for detection of sulfite was studied. Cyclic voltammetry at the modified electrode in universal buffer showed a two electron oxidation/reduction of the couple Mn^IV(μ‐O)₂Mn^IV/Mn^III(μ‐O)₂Mn^III. The sensor exhibited electrocatalytic property toward sulfite oxidation with a decrease of the overpotential of 450 mV compared with the glassy carbon electrode. A plot of the anodic current versus the sulfite concentration for potential fixed (+0.15 V vs. SCE) at the sensor was linear in the 4.99×10^?7 to 2.49×10^?6 mol L^?1 concentration range and the concentration limit was 1.33×10^?7 mol L^?1. The mediated mechanism was derived by Michaelis? Menten kinetics. The calculated kinetics values were Michaelis? Menten rate constant= =1.33 µmol L^?1, catalytic rate constant=6.06×10^?3 s^?1 and heterogeneous electro‐chemical rate constant=3.61×10^?5 cm s^?1.     

The electrochemistry of uric acid at a gold electrode modified with L-cysteine, and its application to sensing uric urine

The electrochemistry of uric acid at a gold electrode modified with a self-assembled film of L-cysteine was studied by cyclic voltammetry and differential pulse voltammetry. Compared to the bare gold electrode, uric acid showed better electrochemical response in that the anodic peak current is stronger and the peak potential is negatively shifted by about 100 mV. The effects of experimental conditions on the oxidation of uric acid were tested and a calibration plot was established. The differential pulse response to uric acid is linear in the concentration range from 1.0?×?10^?6 to ~?1.0?×?10^?4 mol?L^?1 (r?=?0.9995) and from 1.0?×?10^?4 to ~?5.0?×?10^?4 mol?L^?1 (r?=?0.9990), the detection limit being 1.0?×?10^?7 mol?L^?1 (at S/N?=?3). The high sensitivity and good selectivity of the electrode was demonstrated by its practical application to the determination of uric acid in urine samples.

Electrochemiluminescence Biosensor for Glucose Based on Graphene/Nafion/GOD Film Modified Glassy Carbon Electrode

Glucose oxidase(GOD) was encapsulated in the Graphene/Nafion film modified glassy carbon electrode(GCE) and used as an ECL sensor for glucose. The GOD retains its bioactivity after being immobilized into the composite film. The sensor gives a linear response for glucose in the range of 2.0×10^?6–1.0×10^?4 mol/L with a detection limit of 1.0×10^?6 mol/L. The sensor showed good stability, the RSD for continuous scanning for 5.0×10^?5 mol/L glucose was 4.21 % (n=5). After being stored in 0.05 mol/L pH 7.4 PBS in 4 °C for two weeks, the modified electrode maintains 80 % of its initial activity. The glucose sensor provides new opportunity for clinical diagnosis applications.     

Sensitive and Selective Detection of Dopamine Using a DNA Immobilized Ethylenedidamine/Polyglutamic Modified Electrode

DNA was attached on the surface of an ethylenedidamine/polyglutamic(En/PGA) modified glassy carbon electrode (GCE) to create a novel voltammetric sensor (DNA/En/PGA/GCE) for dopamine (DA). This modified electrode exhibited a linear voltammetric response for DA in the range from 1.0×10^?7 mol L^?1 to 1×10^?5 mol L^?1, with a detection limit of 2×10^?8 mol L^?1. The detection of DA was found to be unaffected by the presence of ascorbic acid, uric acid, serotonin and folic acid. The method proposed was applied to detect DA in pharmaceutical dosage and human blood serum with good satisfactory results.     

Simultaneous determination of dopamine and serotonin by use of covalent modification of 5-hydroxytryptophan on glassy carbon electrode

An electrochemical biosensor was fabricated by covalent modification of 5-hydroxytryptophan (5-HTP) on the surface of glassy carbon electrode (GCE). The electrode, denoted as 5-HTP/GCE, was characterized by X-ray photoelectron spectroscopy, cyclic voltammetry and differential pulse voltammetry. For comparison, tryptophan modified GCE (TRP/GCE) and serotonin modified GCE (5-HT/GCE) were prepared by the same method. It was found that electrocatalytic ability of these electrodes was in the order of 5-HTP/GCE?>?TRP/GCE?>?5-HT/GCE for the oxidation of dopamine (DA) and 5-HT. The sensor was effective to simultaneously determine DA and 5-HT in a mixture. It can resolve the overlapping anodic peaks into two well-defined voltammetric peaks at 0.24 and 0.39 V (versus SCE). The linear response is in the range of 5.0?×?10^?7–3.5?×?10^?5 mol L^?1 with a detection limit of 3.1?×?10^?7 mol L^?1 for DA, and in the range of 5.0?×?10^?6–3.5?×?10^?5 mol L^?1 with a detection limit of 1.7?×?10^?6 mol L^?1 for 5-HT (s/n?=?3), respectively.     

Determination of 1-hydroxypyrene in human urine by a multi-wall carbon nanotubes-modified glassy carbon electrode

A multi-walled carbon nanotubes (MWNTs) modified glassy carbon electrode (MWNT-GCE) was used to study the electrochemical behaviour of1-hydroxypyrene (1-OHP) and applied to its determination. The results showed that the modified electrode had a strong adsorptive ability to 1-OHP and enhances its electrochemical signal. By square wave voltammetry, the linear relationship of 1-OHP was 6?×?10^?9???8?×?10^?7?mol?L^?1 with a linear correlation coefficient of 0.996, and the detection limit was 1?×?10^?10?mol?L^?1. Compared with other published methods, this newly proposed method possesses many advantages such as very low detection limit, fast response, low cost and simplicity. And this method was applied successfully in the determination of 1‐OHP in real human urine samples.     

Simultaneous Determination of Iron and Copper in Ethanol Fuel Using Nafion/Carbon Nanotubes Electrode

This work presents the analytical method development for iron and copper determination in ethanol fuel. This method was developed using stripping voltammetry with a glassy carbon electrode modified with Nafion/Carbon‐nanotubes. With linear sweep stripping voltammetry was achieved a limit of detection of 7.1×10^?7 mol L^?1 for Fe³⁺ and 5.1×10^?8 mol L^?1 for Cu²⁺. The amperometric sensitivities were 2.0×10⁶ µA mol^?1 L for Fe³⁺ and 2.8×10⁷ µA mol^?1 L for Cu²⁺. The recovery study showed that the method has good accuracy and repeatability, with recovery of 108 and 103 % for Fe³⁺ and Cu²⁺ respectively.     

Determination of Trace Copper by Adsorptive Voltammetry Using a Multiwalled Carbon Nanotube Modified Carbon Paste Electrode

A new method for the determination of trace copper was described. A multiwalled carbon nanotube modified carbon paste electrode was prepared and the adsorptive voltammetric behavior of copper‐alizarin red S (ARS) complex at the modified electrode was investigated. By use of the second‐order derivative linear sweep voltammetry, it was found that in 0.04 mol/L acetate buffer solution (pH 4.2) containing 4×10^?6 mol/L ARS, when accumulation potential is 0 mV, accumulation time is 60 s and scan rate is 100 mV/s, the complex can be adsorbed on the surface of the electrode, yielding one sensitive reduction peak at ?172 mV (vs. SCE). The peak current of the complex is proportional to the concentration of Cu(II) in the range of 2.0×10^?11–4.0×10^?7 mol L^?1 with a detection limit (S/N=3) of 8.0×10^?12 mol/L (4 min accumulation). The proposed method was successfully applied to the determination of copper in biological samples with satisfactory results, the recoveries were found to be 96%–102%.     

Electrochemical Behavior of 8‐Azaguanine at DNA Langmuir–Blodgett Modified Glassy Carbon Electrode and Its Analytical Application

A highly sensitive electrochemical biosensor for the detection of trace amounts of 8‐azaguanine has been designed. Double stranded (ds)DNA molecules are immobilized onto a glassy carbon electrode surface with Langmuir–Blodgett technique. The adsorptive voltammetric behaviors of 8‐azaguanine at DNA‐modified electrode were explored by means of cyclic voltammetry and square wave voltammetry. Compared with bare glassy carbon electrode (GCE), the Langmuir–Blodgett film modified electrode can greatly improve the measuring sensitivity of 8‐azaguanine. Under the optimum experimental conditions, the Langmuir–Blodgett film modified electrode in pH 3.0 Britton–Robinson buffer solutions shows a linear voltammetric response in the range of 5.0×10^?8 to 1.0×10^?5 mol L^?1 with detection limit 9.0×10^?9 mol L^?1. The method proposed was applied successfully for the determination of 8‐azaguanine in diluted human urine with wonderful satisfactory.     

Amperometric Nitric Oxide Sensor Based on Poly(Thionine)/Nafion‐Modified Electrode and Its Application in Monitoring Nitric Oxide Release from Rat Kidney

Abstract

A novel amperometric nitric oxide (NO) sensor based on a glassy carbon electrode modified with thionine and Nafion films has been developed. The oxidation peak current of NO increased significantly at the poly(thionine)/Nafion‐modified glassy carbon electrode (GCE), which can be used for the detection of NO. The oxidation peak current was linear with the concentration of nitric oxide over the range from 3.6×10^?7 to 6.8×10^?5 mol · L^?1, and the detection limit was 7.2×10^?8 mol · L^?1. This nitric oxide sensor showed high selectivity to nitric oxide determination, and some potential interference could be eliminated effectively. The nitric oxide sensor has been applied to monitor NO release from rat kidney stimulated by L‐arginine. The results indicated the applicability of the NO sensor to biomedical samples.     

Carbon electrode modified with ionic liquid and multi-walled carbon nanotubes for voltammetric sensing of adenine

A voltammetric sensor was fabricated by applying a Nafion and multi-walled carbon nanotubes (MWCNTs) composite film on the surface of a carbon ionic liquid electrode (CILE), which was prepared by mixing 1-butyl-3-methylimidazolium hexafluorophosphate with graphite powder. The electrochemical behavior of adenine on the Nafion-MWCNTs/CILE was investigated in pH 5.5 buffer solution. Adenine showed an irreversible adsorption-controlled oxidation reaction with enhanced electrochemical response, which was due to the presence of high conductive MWCNTs on the CILE surface. The electrochemical parameters of adenine electro-oxidation were determined, and the experimental conditions were optimized. Under the optimal conditions, the oxidation peak current was linear to the adenine concentration over the range of 1.0?×?10^?7 to 7.0?×?10^?5 mol L^?1 with a detection limit of 3.3?×?10^?8 mol L^?1 (signal/noise?=?3). The electrode showed good stability and selectivity, and was further applied to milk powder samples with satisfactory results.