Amperometric determination of sulfide ion by glassy carbon electrode modified with multiwall carbon nanotubes and copper (II) phenanthroline complex

Electrocatalytic oxidation of sulfide ion on a glassy carbon electrode (GCE) modified with multiwall carbon nanotubes (MWCNTs) and a copper (II) complex was investigated. The Cu(II) complex was used due to the reversibility of the Cu(II)/Cu(III) redox couple. The MWCNTs are evaluated as a transducer, stabilizer and immobilization matrix for the construction of amperometric sensor based on Cu(II) complex adsorbed on MWCNTs immobilized on the surface of GCE. The modified GCE was applied to the selective amperometric detection of sulfide at a potential of 0.47 V (vs. Ag/AgCl) at pH 8.0. The calibration graph was linear in the concentration range of 5 µM–400 µM; while the limit of detection was 1.2 µM, the sensitivity was 34 nA µM^?1. The interference effects of SO₃ ^2?, SO₄ ^2?, S₂O₃ ^2?, S₄O₆ ^2?, Cysteine, and Cystein were negligible at the concentration ratios more than 40 times. The modified electrode is more stable with time and more easily restorable than unmodified electrode surface. Also, modified electrode permits detection of sulfide ion by its oxidation at lower anodic potentials.      

Glassy carbon electrode modified with a film composed of Ni(II), quercetin and graphene for enzyme-less sensing of glucose

We present a modified glassy carbon electrode as a sensing platform for glucose. It is based on a composite film prepared from Ni(II) ion, quercetin and graphene. The sensor was characterized by cyclic voltammetry. The electron transfer coefficient, reaction rate constant and catalytic rate constant were determined and found to be 0.53, 5.4?s^?1 and 2.93?×?10³?M^?1 s^?1, respectively. The catalytic current depends linearly on the concentration of glucose in the range from 3 to 900???M, with a detection limit of 0.5???M (at an S/R of 3). The sensor exhibits good reproducibility, stability, fast response, and high sensitivity.

A study of the electrochemical behavior of an oxadiazole derivative electrodeposited on multi-wall carbon nanotube-modified electrode and its application as a hydrazine sensor

In this study, an oxadiazole multi-wall carbon nanotube-modified glassy carbon electrode (OMWCNT?GCE) was used as a highly sensitive electrochemical sensor for hydrazine determination. The surface charge transfer rate constant, k _s, and the charge transfer coefficient, ??, for electron transfer between GCE and electrodeposited oxadiazole were calculated as 19.4?±?0.5?s^?1 and 0.51, respectively at pH?=?7.0. The obtained results indicate that hydrazine peak potential at OMWCNT?GCE shifted for 14, 109, and 136?mV to negative values as compared with oxadiazole-modified GCE, MWCNT?GCE, and activated GCE surface, respectively. The electron transfer coefficient, ??, and the heterogeneous rate constant, k??, for the oxidation of hydrazine at OMWCNT?GCE were also determined by cyclic voltammetry measurements. Two linear dynamic ranges of 0.6 to 10.0???M and 10.0 to 400.0???M and detection limit of 0.17???M for hydrazine determination were evaluated using differential pulse voltammetry. In addition, OMWCNT?GCE was shown to be successfully applied to determine hydrazine in various water samples.     

Direct electrochemistry of glucose oxidase immobilized on TiO2–graphene/nickel oxide nanocomposite film and its application

A novel electrochemical platform based on nickel oxide (NiO) nanoparticles and TiO₂–graphene (TiO₂–Gr) was developed for the direct electrochemistry of glucose oxidase (GOD). The electrochemical behavior of the sensor was studied using cyclic voltammetry and chronoamperometry. The experimental results demonstrated that the nanocomposite well retained the activity of GOD and the modified electrode GOD/NiO/TiO₂–Gr/GCE exhibited excellent electrocatalytic activity toward the redox of GOD as evidenced by the significant enhancement of redox peak currents in comparison with bare GCE. The biosensor responded linearly to glucose in the range of 1.0–12.0?mM, with a sensitivity of 4.129?μA?mM^?1 and a detection limit of 1.2?×?10^?6?M under optimized conditions. The response time of the biosensor was 3?s. In addition, the developed biosensor possessed good reproducibility and stability, and there was negligible interference from other electroactive components.     

Nonenzymatic electrochemical glucose sensor based on MnO2/MWNTs nanocomposite

In this communication, an amperometric glucose biosensor based on MnO₂/MWNTs electrode was reported. MnO₂ was homogeneously coated on vertically aligned MWNTs by electrodeposition. The MnO₂/MWNTs electrode displayed high electrocatalytic activity towards the oxidation of glucose in alkaline solution, showing about 0.30 V negative shift in peak potential with oxidation starting at ca. −0.20 V (vs. 3 M KCl–Ag/AgCl) as compared with bare MWNTs electrode. At an applied potential of +0.30 V, the MnO₂/MWNTs electrode gives a linear dependence (R = 0.995) in the glucose concentration up to 28 mM with a sensitivity of 33.19 μA mM⁻¹. Meanwhile, the MnO₂/MWNTs electrode is also highly resistant toward poisoning by chloride ions. In addition, interference from the oxidation of common interfering species such as ascorbic acid, dopamine, and uric acid is effectively avoided. The MnO₂/MWNTs electrode allows highly sensitive, low-potential, stable, and fast amperometric sensing of glucose, which is promising for the development of nonenzymatic glucose sensor.     

Enzyme-free impedimetric glucose sensor based on gold nanoparticles/polyaniline composite film

A non-enzymatic impedimetric glucose sensor was fabricated based on the adsorption of gold nanoparticles (GNPs) onto conductive polyaniline (PANI)-modified glassy carbon electrode (GCE). The modified electrode (GCE/PANI/GNPs) was characterized by using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). The determination of glucose concentration was based on the measurement of EIS with the mediation of electron transfer by ferricyanide ([Fe(CN)₆]^3?). The [Fe(CN)₆]^3? is reduced to ferrocyanide ([Fe(CN)₆]^4?), which in turn is oxidized at GCE/PANI/GNPs. An increase in the glucose concentration results in an increase in the diffusion current density of the [Fe(CN)₆]^4? oxidation, which corresponds to a decrease in the faradaic charge transfer resistance (R _ct). A wide linear concentration range from 0.3 to 10 mM with a lower detection limit of 0.1 mM for glucose was obtained. The proposed sensor shows high sensitivity, good reproducibility, and stability. In addition, the sensor exhibits no interference from common interfering substances such as ascorbic acid, acetaminophen, and uric acid.     

Simultaneous determination of levodopa and carbidopa by a novel nanostructure modified carbon paste electrode

The electrochemical behavior of levodopa (LD) was investigated on the surface of a carbon paste electrode modified with TiO₂ nanoparticles and 2,2??-(1,2 butanediylbis(nitriloethylidyne))-bis-hydroquinone (BNH). The prepared modified electrode showed an efficient catalytic role in the electrochemical oxidation of LD, leading to a remarkable decrease in oxidation overpotential and enhancement of the kinetics of the electrode reaction. The mechanism of the electrocatalytic process on the surface of the modified electrode was analyzed by obtaining the cyclic voltammograms in various potential sweep rates. This modified electrode exhibited well-separated oxidation peaks for LD and carbidopa (CD). The differential pulse voltammetry was applied as a very sensitive analytical method for the determination of LD and CD. A linear dynamic range of 2.0?C600.0 and 20.0?C400.0???M with a detection limit of 0.2???M (with sensitivity of 0.199 ??A ??M^?1) and 10???M (with sensitivity of 0.024???A???M^?1) was obtained for LD and CD, respectively. The modified electrode was prepared quite easily and renewed on the surface by simple polishing.     

Phosphomolybdic acid functionalized graphene loading copper nanoparticles modified electrodes for non-enzymatic electrochemical sensing of glucose

A sensitive non-enzymatic glucose electrochemical biosensor (Cu/PMo₁₂-GR/GCE) was developed based on the combination of copper nanoparticles (CuNPs) and phosphomolybdic acid functionalized graphene (PMo₁₂-GR). PMo₁₂-GR films were modified on the surface of glassy carbon electrode (GCE) through electrostatic self-assembly with the aid of poly diallyl dimethyl ammonium chloride (PDDA). Then CuNPs were successfully decorated onto the PMo₁₂-GR modified GCE through electrodeposition. The morphology of Cu/PMo₁₂-GR/GCE was characterized by scanning electron microscope (SEM). Cyclic voltammetry (CV) and chronoamperometry were used to investigate the electrochemical performances of the biosensor. The results indicated that the modified electrode displayed a synergistic effect of PMo₁₂-GR sheets and CuNPs towards the electro-oxidation of glucose in the alkaline solution. At the optimal detection potential of 0.50 V, the response towards glucose presented a linear response ranging from 0.10 μM to 1.0 mM with a detection limit of 3.0 × 10⁻² μM (S/N = 3). In addition, Cu/PMo₁₂-GR/GCE possessed a high selectivity, good reproducibility, excellent stability and acceptable recovery, which indicating the potential application in clinical field.     

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.

Hydrogen peroxide biosensor based on the immobilization of horseradish peroxidase on ��-Al2O3 nanoparticles/chitosan film-modified electrode

An amperometric biosensor based on horseradish peroxidase (HRP) and ??-Al₂O₃/chitosan composite film at a glassy carbon electrode has been developed. Hydrogen peroxide (H₂O₂) was detected with the aid of ferrocene monocarboxylic acid mediator to transfer electrons between the electrode and HRP. The morphology and composition of the modified electrode were characterized by scanning electron microscopy and electrochemical impedance spectroscopy. The electrochemical characteristics of the biosensor were studied by cyclic voltammetry and amperometry. The effects of HRP concentration, the applied potential, and the pH values of the buffer solution on the response of the sensor were investigated for optimum analytical performance. The proposed biosensor showed high sensitivity (0.249?A M^?1?cm^?2) and a fast response (<5?s) to H₂O₂ with the detection limit of 0.07???M. The linear response range of the enzyme electrode to H₂O₂ concentration was from 0.5 to 700???M with a correlation coefficient of 0.9998. The apparent Michaelis-Menten constant of the biosensor was calculated to be 0.818?mM, exhibiting a high enzymatic activity and affinity for H₂O₂.     

Electrode Modified with Langmuir–Blodgett (LB) Film of Calixarenes for Preconcentration and Stripping Analysis of Hg(II)

A new type of current sensor, Langmuir–Blodgett (LB) film of calixarene on the surface of glassy carbon electrode (GCE) was prepared for determination of mercury by anodic stripping voltammetry (ASV). An anodic stripping peak was obtained at 0.15 V (vs. SCE) by scanning the potential from ?0.6 to +0.6 V. Compared with a bare GCE, the LB film coated electrode greatly improves the sensitivity of measuring mercury ion. The fabricated electrode in a 0.1 M H₂SO₄+0.01 M HCl solution shows a linear voltammetric response in the range of 0.07–40 μg L^?1 and detection limit of 0.04 μg L^?1 (ca. 2×10^?10 M). The high sensitivity, selectivity, and stability of this LB film modified electrode demonstrates its practical application for a simple, rapid and economical determination of Hg²⁺ in a water sample.     

Accelerating the electron transfer of choline oxidase using ionic-liquid/NH2-MWCNTs nano-composite

A nano-composite consisting of amine functionalized multi-walled carbon nanotubes and a room temperature ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) was prepared and used for modification of glassy carbon electrode. By immobilizing choline oxidase (ChOx) on the modified electrode, the enzyme direct electron transfer has been achieved. The modified electrode exhibited a pair of well-defined cyclic voltammetric peaks at a formal potential of ?0.395?V versus Ag/AgCl in 0.2?M phosphate buffer solution at pH 7.0. This peak was characteristic of ChOx-FAD/FADH₂ redox couple. The electrochemical parameters such as charge transfer coefficient (??) and apparent heterogeneous electron transfer rate constant (k _s) were estimated to be 0.36 and 2.74?s^?1, respectively. When the enzyme electrode was examined for the detection of choline, a relatively high sensitivity (2.59???A?mM^?1) was obtained. Under the optimized experimental conditions, choline was detected in the concentration range from 6.9?×?10^?3 to 6.7?×?10^?1?mM with a detection limit of 2.7???M. The peak currents of ChOx were reasonably stable and retained 90% of its initial current after a period of 2?months.     

Promotion Effect of Bismuth on Nickel Electrodeposition and Its Electrocatalysis to Glucose Oxidation

Metallic Bi and Ni were co‐deposited onto the surface of glass carbon electrode (GCE) from the electrolyte solution containing their respective nitrate to fabricate a Bi/Ni alloy modified GCE (Bi/Ni‐GCE). The purpose is to study the influence of Bi³⁺ on the deposition of Ni and that of deposited Bi on the electrocatalytic performance of Ni to glucose in alkali solution. The results show that both redox signal of Ni(OH)₂/NiOOH and Ni(OH)₂/NiOOH mediated electrocatalysis to glucose is remarkably increased in the presence of Bi. It seems that there is a synergistic effect between Bi and Ni on each other’s redox electrochemistry. It’s possible that the firstly deposited Bi on GCE surface helps to the following nucleation and growth of Ni, leading to the deposition of more metallic Ni on GCE surface. An extremely attractive feature of Bi/Ni‐GCE is reflected by the fast response time to the electrocatalytic oxidation of glucose. The electrode nearly responses immediately after glucose is added and it reaches a steady‐state level within only 2 seconds, demonstrating a good electrocatalytic property of Bi/Ni‐GCE. The calibration plot is linear over the wide concentration range of 0–5.8 mM with a sensitivity of 33.96 µA/mM and a correlation coefficient of 0.9985. The detection limit of the glucose was found to be 0.59 µM at a signal‐to‐noise ratio of 3. The fabricated Bi/Ni‐GCE was successfully employed to analyze the glucose level in blood samples, exhibiting high accuracy, strong resistance against inference and good reliability in the practical applications.     

Preparation and characterization of Ni(II)/polyacrylonitrile and carbon nanotube composite modified electrode and application for carbohydrates electrocatalytic oxidation

A nickel(II) into porous polyacrylonitrile–carbon nanotubes composite modified glassy carbon electrode (Ni/PAN-CNT/GCE) was fabricated by simple drop-casting and immersing technique. The unique electrochemical activity of Ni/PAN-CNT composite modified glassy carbon electrode was illustrated in 0.10?M NaOH using cyclic voltammetry. The Ni/PAN-CNT/GCE exhibits the characteristic of improved reversibility and enhanced current responses of the Ni(III)/Ni(II) couple compared with Ni/PAN/GCE and Ni/CNT/GCE. The results of electrochemical impedance spectroscopy and scanning electron microscopy indicated the successful immobilization for PAN-CNT composite film. Kinetic parameters such as the electron transfer coefficient, α, and rate constant, k _s, of the electrode reaction were determined. Ni/PAN-CNT/GCE also shows good electrocatalytic activity toward the oxidation of carbohydrates (glucose, sucrose, fructose, and sorbitol). The electrocatalytic response showed a wide linear range (10–1,500, 12–3,200, 7–3,500, and 16–4,200?μM for glucose, sucrose, fructose, and sorbitol, respectively) as well as its experimental limit of detection can be achieved 6, 7, 5, and 11?μM for glucose, sucrose, fructose, and sorbitol, respectively. The modified electrode for carbohydrates determination is of the property of simple preparation, good stability, and high sensitivity.     

A Comparison of a Nanostructured Enzymeless Au/Fe2O3/MWCNTs/GCE Electrode and a GOx Modified One in Electrocatalytic Detection of Glucose

Acid functionalized multi‐walled carbon nanotubes (f‐MWCNTs) were decorated with Au and Fe₂O₃ nanoparticles (FeONPs) and deposited on glassy carbon electrode (GCE). The resulting hybrid Au/Fe₂O₃/f‐MWCNTs/GCE electrode and the one further modified by glucose oxidase were compared for detection of glucose. FeONPs and Au were deposited on the f‐MWCNTs by sonication‐assisted precipitation and deposition‐precipitation methods, respectively. The morphology and structure of the samples were characterized by transmission electron microscopy, scanning electron microscopy, X‐ray diffraction and Raman spectroscopy. A uniform distribution of FeONPs with an average size of 5 nm increased the surface area of functionalized nanotubes from 39 to 50 m²/g. The electrocatalytic glucose detection on the modified electrodes was evaluated using cyclic voltammetry and chronoamperometry in 0.1 M phosphate buffer solution at pH 7.0. The non‐enzymatic and enzymatic electrodes show sensitivity of 512.4 and 921.4 mA/mM.cm² and detection limit of 1.7 and 0.9 mM, respectively. The enzymatic and enzymeless electrodes retained more than 70 % and 80 % of their cathodic faradic current after 70 days, respectively. The sensing mechanism of the non‐enzymatic biosensor is described through the reaction of glucose with iron (III) ions, while in the case of enzymatic electrode, glucose is oxidized by glucose oxidase.     

Resonance Character of Copper/Silver/Gold Bonding in Small Molecule⋅⋅⋅MX (X=F,Cl, Br,CH3, CF3) Complexes

The resonance character of Cu/Ag/Au bonding is investigated in B???M?X (M=Cu, Ag, Au; X=F, Cl, Br, CH₃, CF₃; B=CO, H₂O, H₂S, C₂H₂, C₂H₄) complexes. The natural bond orbital/natural resonance theory results strongly support the general resonance‐type three‐center/four‐electron (3c/4e) picture of Cu/Ag/Au bonding, B:M?X?B⁺?M:X^?, which mainly arises from hyperconjugation interactions. On the basis of such resonance‐type bonding mechanisms, the ligand effects in the more strongly bound OC???M?X series are analyzed, and distinct competition between CO and the axial ligand X is observed. This competitive bonding picture directly explains why CO in OC???Au?CF₃ can be readily replaced by a number of other ligands. Additionally, conservation of the bond order indicates that the idealized relationship b_B???M+b_MX=1 should be suitably generalized for intermolecular bonding, especially if there is additional partial multiple bonding at one end of the 3c/4e hyperbonded triad.     

Sensitive Determination of Terbutaline Using a Platform Based on Nanoparticles of Europium Oxide and Carbon Nanotubes

This study presents a sensitive voltammetric determination of terbutaline (TER) on a platform based on carbon nanotubes (CNTs) and europium oxide nanoparticles (Eu₂O₃NPs) coated glassy carbon electrodes (GCEs). An ultrasonic bath was performed for the preparation of composite material. The material was characterized by energy dispersive X‐ray spectroscopy (EDX), X‐ray diffraction method (XRD) and scanning electron microscopy (SEM). The Eu₂O₃NPs/CNTs/GCE system was assessed for the oxidation of terbutaline (TER). A broad oxidation peak was appeared at 0.71 V using a bare GCE. However, the voltammetry of TER has been improved at a GCE coated with CNTs and a well‐defined anodic peak exhibited at 0.61 V. Furthermore, the nanoparticles of Eu₂O₃ and CNTs coated GCE has greatly improved the electrochemical behaviour of TER and a sharp peak was appeared at 0.59 V. Cyclic voltammetry at Eu₂O₃NPs/CNTs/GCE also reveals a high catalytic effect for the oxidation of TER with an oxidation peak that is distinctly enhanced compared to GCE and CNTs/GCE. Eu₂O₃ nanoparticles were utilized to enhance the surface area of GCE and then improve the sensitivity of the procedure. The response of TER was linear over a concentration range of 2.0×10^?8 M ?9.5×10^?6 M with an LOD of 3.7×10^?9 M. Square wave voltammetric analysis of tablets by Eu₂O₃NPs/CNTs/GCE yielded a recovery of 99.2 % with an RSD% of 3.2. The modified electrode (EuO₂NPs/CNTs/GCE) provides accuracy and precision to the analysis of samples.     

Synthesis of graphene oxide nanosheet: A novel glucose sensor based on nickel-graphene oxide composite film

The graphene oxide (GO) nanosheets were produced by chemical conversion of graphite, and were characterized by transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR). An electrochemical sensor based on Ni/graphene (GR) composite film was developed by incorporating Ni²⁺ into the graphene oxide film modified glassy carbon electrode (Ni/GO/GCE) through the electrostatic interactions with negatively charged graphene oxide. The Ni²⁺/graphene modified glassy carbon electrode (Ni/GR/GCE) was prepared by cyclic voltammetric scanning of Ni/GO/GCE in the potential range from ?1.5 to 0.2 V at 50 mV s^?1 for 5 cycles. The electrochemical activity of Ni/GR/GCE was illustrated in 0.10 M NaOH using cyclic voltammetry. The Ni/GR/GCE exhibits the characteristic of improved reversibility and enhanced current responses of the Ni(III)/Ni(II) couple. The introduction of conductive graphene not only greatly facilitates the electron transfer of Ni²⁺, but also dramatically improves the long-term stability of the sensor by providing the electrostatic interactions. Ni/GR/GCE also shows good electrocatalytic activity toward the oxidation of glucose. The Ni/GR/GCE gives a good linear range over 10 to 2700 μM with a detection limit of 5 μM towards the determination of glucose by amperometry. This sensor keeps over 85% activity towards 0.1 mM glucose after being stored in air for a month, respectively. Furthermore, the modified sensor was successfully applied to the sensitive determination of glucose in blood samples.     

Stripping Analysis of Trace Arsenic Based on the MnOx/AuNPs Composite Film Modified Electrode in Alkaline Media

A simple, rapid fabricated and sensitive modified electrode for detection of As(III) in alkaline media was proposed. The modified electrode was prepared by co‐electrodeposition of manganese oxides (MnO_x) and gold nanoparticles (AuNPs) on the glassy carbon electrode (GCE) with cyclic voltammetry. Linear sweep anodic stripping voltammetry (LS‐ASV) was employed for the determination of arsenic (III) without interference from Cu(II), Hg(II), and other coexisting metal ions. A lower detection limit of 0.057 µg L^?1 (S/N=3) were obtained with a accumulation time of 200 s. The proposed method was successfully applied to determine arsenic (III) in real water samples with satisfactory recoveries.     

One-pot solvothermal synthesis of a Cu2O/Graphene nanocomposite and its application in an electrochemical sensor for dopamine

Nanocomposites composed of cuprous oxide (Cu₂O) and graphene were synthesized via reduction of copper(II) in ethylene glycol. This material possesses the specific features of both Cu₂O and graphene. Its morphology was characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. Cyclic voltammetry was used to evaluate the electrochemical response of a glass carbon electrode (GCE) modified with the nanocomposite towards dopamine (DA). Compared to the bare GCE, the Cu₂O nanoparticles modified electrode and the graphene modified electrode, the nanocomposites modified electrode displays high electrocatalytic activity in giving an oxidation peak current that is proportional to the concentration of DA in the range from 0.1 to 10???M,with a detection limit of 10?nM (S/N?=?3). The modified electrode shows excellent selectivity and sensitivity even in the presence of high concentration of uric acid and can be applied to determine DA in real samples with satisfactory results.