Carbon Nanotube-modified Electrode Research Articles

Electrochemical Sensing of Guanine and Adenine Based on the Boron-doped Carbon Nanotubes Modified Electrode

Electrochemical Sensing of Guanine and Adenine Based on the Boron-doped Carbon Nanotubes Modified Electrode

Electrocatalysis and determination of pyridine-2-aldoxime methochloride using carbon nanotube-modified gold electrode

A multi-walled carbon nanotube-modified gold electrode (MWCNT/Au) was prepared and its external morphology was characterised by scanning electron microscope and surface area study. The electrochemical behaviour of pyridine-2-aldoxime methochloride (PAM chloride) at this electrode was examined by square wave voltammetry. At the MWCNT/Au electrode, PAM chloride exhibited a well-defined anodic peak at 584 mV in pH 8 phosphate buffer solution with a 15 times enhancement in anodic peak current. The peak current was linear to PAM chloride concentration over the range of 8×10−7–1×10−5 M with a detection limit of 1×10−7 M. The MWCNT/Au electrode showed good stability, selectivity and can be used to quantify PAM chloride in a urine sample.

Electrochemistry of Metoclopramide at Multi-walled Carbon Nanotube Modified Electrode and Its Voltammetric Detection

A simple, sensitive and inexpensive electrochemical method was developed for the determination of metoclopramide (MCP) with a multi-wall carbon nanotube (MWNT) modified glassy carbon electrode (GCE). MWNT was dispersed into polyacrylic acid (PAA); the aqueous suspension was then cast on GCE electrodes, forming MWNT-PAA films after evaporation of the solvent. The electrochemical behavior of MCP at the MWNT-modified electrode was investigated in detail. Compared with the bare GCE, the MWNT-modified electrode exhibits electrocatalytic activity to the oxidation of MCP because of the significant oxidation peak-current enhancement. Furthermore, various experimental parameters, such as the solution pH value, the amount of MWNT-PAA suspension and accumulation conditions were optimized for the determination of MCP. Based on the electrocatalytic effect of the MWNT-modified electrode, linear sweep voltammetry (LSV) was developed for the determination of MCP with the linear response in the range from 1.0 × 10(-7) to 1.0 × 10(-5) mol L(-1) and a detection limit of 5.0 × 10(-8) mol L(-1). The method has been successfully applied to the determination of MCP in commercial MCP tablets.

Electrochemical Detection of Alkaline Phosphatase Using Ionic Liquid Modified Carbon Nanotubes Electrode

An electrochemical method to continuously detect alkaline phosphatase (AP) was developed. Using home-made ionic liquid modified carbon nanotubes electrode (CNTs-ILE), on the basis of the characteristics of CNTs-ILE and the substrate p-nitrophenyl phosphate (PNPP) and product p-nitrophenol (PNP), the continuous detection of the process of AP enzymatic reaction with amperometry was achieved. The results indicated that the cyclic voltammetry feature of the CNTs-ILE was superior to conventional glassy carbon electrode, also a good anti-passivation characteristic was achieved for the detection of PNP. When the concentration of AP was in the range of 1.0 −100 U L−1, the current showed a good linear relationship to the concentrations of AP. This method was quick to detect AP, and detection time was less than 20 min.

NADH Oxidation Catalyzed by Electropolymerized Azines on Carbon Nanotube Modified Electrodes

AbstractElectropolymerizing azines on a carbon nanotube (CNT) modified electrode yields a high‐surface area interface with excellent electrocatalytic activity towards NADH oxidation. Electrodeposition of poly(methylene green) (PMG) and poly(toluidine blue) (PTBO) on the carboxylated CNT‐modified electrodes was achieved by cyclic voltammetry. The PMG‐CNT interface demonstrates 5.0 mA cm−2 current density for NADH oxidation at 50 mV vs. Ag|AgCl in 20 mM NADH solution. The kinetics of NADH electrocatalysis were analyzed using a quantitative mass‐transport‐corrected model with NADH bulk concentration and applied potential as independent variables. This high‐rate poly(azine)‐CNT interface is potentially applicable to high‐performance bioconversion, bioenergy and biosensors involving NADH‐dependent dehydrogenases.

Electroanalysis of Mefenamic Acid in Pharmaceutical Formulation and Spiked Biological Fluids on Modified Carbon Nanotube Electrode

The development of an electrochemical sensor for determination of mefenamic acid is the main purpose of this work. The determination was performed in pharmaceutical formulations, spiked urine and human plasma samples by multi-walled carbon nanotube-graphite/Ag (MWCNTs-G/Ag) electrode. Hence some voltammetric methods were investigated to determination of mefenamic acid. The dependence of peak currents and potentials on pH and voltammetric parameters was investigated for the optimization of electrochemical method. The porous structure of MWCNTs-graphite mixture improves the electroactive surface area. As a result, a remarkable increasing in the peak currents was observed. The prepared mixture displayed an electrocatalytic effect in anodic oxidation of mefenamic acid with a sensitivity augmentation. The best electrochemical response was obtained from square wave voltammetry with a sensitive peak at 0.68 V in pH 5. The prepared electrode showed good standard calibration curves during 3 days over a wide concentration range with RSD values ranging from 1.6-8%. The limits of quantification and detection were 50 and 16 ng/mL, respectively.

Electro-Assisted Immobilization of Methylviologen Cation on Multiwalled Carbon Nanotube Modified Electrode and its Unusual pH Sensing Behavior: A Preliminary Study

Electro-Assisted Immobilization of Methylviologen Cation on Multiwalled Carbon Nanotube Modified Electrode and its Unusual pH Sensing Behavior: A Preliminary Study

Electro-oxidation and adsorptive stripping voltammetric determination of ephedrine and pseudoephedrine at carboxylated multi-walled carbon nanotube-modified electrode

Carboxylated multi-walled carbon nanotubes (MWCNTs) were directly cast onto a glassy carbon electrode to fabricate a MWCNT-modified electrode. The modified electrode exhibited good promotion towards the electrochemical oxidation of ephedrine and pseudoephedrine with greatly enhanced peak currents. Adsorptive stripping voltammetry (AdSV) with accumulation at open circuit potential has been used for quantification of these alkaloids. The method was validated and linear over the concentration range of 1–100 μM for both ephedrine and pseudoephedrine. Under optimal experimental conditions, the limits of detection (based on 3σ) for ephedrine and pseudoephedrine were determined as 0.75 μM and 0.82 μM respectively. The proposed method was successfully applied to pseudoephedrine determination in the presence of acetaminophen or cetirizine. This method has also been used for the determination of pseudoephedrine in some pharmaceutical preparations. In addition the proposed method has been successfully used for determination of ephedrine in diluted urine as a real sample.

Critical evaluation of electrode design and matrix effects on monitoring organophosphate pesticides using composite carbon nanotube-modified electrodes

Carbon nanotubes (CNT)/Nafion-modified glassy carbon (GC) electrodes were used to immobilize the enzyme acetylcholinesterase (AChE) by crosslinking with glutaraldehyde. The CNT-modified electrodes exhibited a sensitive and stable electrocatalytic behavior towards thiocholine (TCh). Compared to ordinary GC electrodes modified with Nafion, a substantial (500-mV) decrease in the overvoltage of the TCh oxidation reaction is observed, along with a tenfold enhancement in the amperometric response. The CNT/Nafion/AChE electrode has very good stability of at least a month compared to surfaces made without crosslinking in the absence and presence of Nafion. Under optimal loadings of CNT, Nafion, AChE, and glutaraldehyde, a solution of CNT/Nafion in N,N-dimethylformamide (DMF) containing 4 mg/mL CNT and 0.01% Nafion was used to construct the electrodes in order to maximize the sensitivity of the biosensor for inhibition studies. An optimal enzyme loading of 0.137 U and crosslinking in 0.01% glutaraldehyde for 1 h was also needed to achieve this goal. The prepared electrodes had very good reproducibility to 1.0 mM acetylthiocholine (ATCh) (relative standard deviation [RSD] <5% for eight electrodes). Using paraoxon as a model pesticide, the biosensor was able to detect as low as 1.0 nM after 30 min of incubation at 30 °C. Using a log scale, the biosensor had good linearity in the concentration range 50–800 nM, with a correlation coefficient of 0.99. The prepared biosensor was used to test real water samples spiked with paraoxon and showed good correlation with a calibration curve using phosphate buffer.

Electrochemical sensor for hazardous food colourant quinoline yellow based on carbon nanotube-modified electrode

A novel electrochemical method using multi-wall carbon nanotube (MWNT) film-modified electrode was developed for the detection of quinoline yellow. In pH 8 phosphate buffer, an irreversible oxidation peak at 0.71V was observed for quinoline yellow. Compared with the unmodified electrode, the MWNT film-modified electrode greatly increases the oxidation peak current of quinoline yellow, showing notable enhancement effect. The effects of pH value, amount of MWNT, accumulation potential and time were studied on the oxidation peak current of quinoline yellow. The linear range is from 0.75 to 20mgL−1, and the limit of detection is 0.5mgL−1. It was applied to the detection of quinoline yellow in commercial soft drinks, and the results consisted with the value that obtained by high-performance liquid chromatography.

Electroreduction of Oxygen on Nitrogen-Doped Carbon Nanotube Modified Electrodes

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Electrocatalytic Oxidation of Hydrazine at Rutin Carbon Nanotubes Modified Electrode

Electrocatalytic Oxidation of Hydrazine at Rutin Carbon Nanotubes Modified Electrode

Cannabinoid receptor gene detection by electrochemical genosensor

This paper describes the investigation of two aspects which play a fundamental role in the development of an enzyme-linked electrochemical genosensor: the labelling step and the electrode surface. Biotinylated locked nucleic acid (LNA) signalling probes were investigated in order to design a sandwich hybridisation format able to detect PCR amplified samples with high specificity. After labelling the biotinylated hybrid with a streptavidin–enzyme conjugate, the electrochemical detection of the enzymatic product was performed onto the surface of disposable carbon nanotube-modified electrode. In this way, the sensor coupled the high stability and specificity of LNA with the unique electrical properties of carbon nanotubes (high surface area, fast heterogeneous electron transfer, chemical stability, and ease of miniaturisation). After characterisation, the sensor was applied to the detection of PCR amplicons related to a region of the CB2 cannabinoid receptor gene (CNR2), which is relevant for the study of a mutation suspected to account for altered receptor activity. To our knowledge, this is the first example of recognition of this particular gene in real samples, using a LNA-based electrochemical genosensor. A linear response was obtained over a wide concentration range (0–100 nmol/L) and a detection limit of 0.4 nmol/L was achieved (RDS = 9%).

The 2011 H. H. Uhlig Summer Research Fellowship -- Summary Report: Catechol-encapsulated Multi-walled Carbon Nanotube Modified Electrode as a New Generation Electrocatalyst for NADH Oxidation

The 2011 H. H. Uhlig Summer Research Fellowship -- Summary Report: Catechol-encapsulated Multi-walled Carbon Nanotube Modified Electrode as a New Generation Electrocatalyst for NADH Oxidation

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, α, 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, α, 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 μM and 10.0 to 400.0 μM and detection limit of 0.17 μM 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.

Study on electroactive and electrocatalytic surfaces of single walled carbon nanotube-modified electrodes

An investigation of the electrocatalysis of single-walled carbon nanotubes modified electrodes has been performed in this work. Nanotube-modified electrodes present a surface area much higher than the bare glassy carbon surfaces as determined by capacitance measurements. Several redox probes were selected for checking the reactivity of specific sites at the carbon nanotube surface. The presence of carbon nanotubes on the electrode improves the kinetics for all the reactions studied compared with the bare glassy carbon electrode with variations of the heterogeneous electron transfer rate constant up to 5 orders of magnitude. The most important effects are observed for the benzoquinone/hydroquinone and ferrocene/ferricinium redox couples, which show a remarkable improvement of their electron transfer kinetics on SWCNT-modified electrodes, probably due to strong π–π interaction between the organic molecules and the walls of the carbon nanotubes. For many of the reactions studied, less than 1% of the nanotube-modified electrode surface is transferring charge to species in solution. This result suggests that only nanotube tips are active sites for the electron transfer in such cases. On the contrary, the electroactive surface for the reactions of ferrocene and quinone is higher indicating that the electron transfer is produced also from the nanotube walls.

Electroanalytical studies of sulfentrazone in protic medium, its degradation by the electro-Fenton process, and toxicity assessment using ss-DNA

Sulfentrazone is an herbicide used as a pre-plant incorporated or pre-emergence treatment. The electrochemical oxidation of sulfentrazone was studied, by cyclic, differential and square-wave voltammetry on unmodified and on glassy carbon nanotube-modified electrodes, and by controlled-potential coulometry and electrolysis. The voltammograms of sulfentrazone showed a main irreversible diffusion-controlled pH-dependent oxidation peak. The in situ DNA-damaging capacity of sulfentrazone was also investigated, employing double stranded ds-DNA-modified glassy carbon electrode, without evidence of interaction. On the other hand, in a solution of sulfentrazone and single stranded ss-DNA, the oxidation signals of the respective bases decreased concentration-dependently, indicating binding of sulfentrazone to guanine and adenine. The electro-Fenton method was employed to promote decontamination by eliminating the herbicide, resulting in almost 60% of mineralization.

A sensitive and stable biosensor based on the direct electrochemistry of glucose oxidase assembled layer-by-layer at the multiwall carbon nanotube-modified electrode

A novel strategy for fabricating the sensitive and stable biosensor was present by layer-by-layer (LBL) self-assembling glucose oxidase (GOD) on multiwall carbon nanotube (CNT)-modified glassy carbon (GC) electrode. GOD was immobilized on the negatively charged CNT surface by alternatively assembling a cationic poly(ethylenimine) (PEI) layer and a GOD layer. And the direct electrochemistry of GOD in the self-assembled {GOD/PEI} n film was investigated. CNT as an excellent nanomaterial greatly improved the direct electron transfer between GOD in {GOD/PEI} n film and the electrode. And the ultrathin {GOD/PEI} n film on the CNT surface provided a favorable microenvironment to keep the bioactivity of GOD. Moreover, PEI used as an out-layer was adsorbed on the top of the {GOD/PEI} n film to form the sandwich-like structure (PEI/{GOD/PEI} n ), improving the stability of the enzyme electrode. On basis of these, the developed PEI/{GOD/PEI} n /CNT/GC biosensor has a high sensitivity of 106.57 μA mM −1 cm −2, and can measure as low as 0.05 mM glucose. In addition, the biosensor has excellent operational stability with no decrease in the activity of enzyme over a 1-week period. Therefore, the developed strategy making use of the advantages of CNT and LBL assembly is ideal for the direct electrochemistry of the redox enzymes and the construction of the sensitive and stable enzyme biosensor.

Voltammetric monitoring photodegradation of EDTA based on carbon nanotubes-modified electrode

This work described a fast and sensitive voltammetric method developed for monitoring the photodegradation of ethylenediaminetetraacetic acid (EDTA). Due to the unique properties of carbon nanotubes (CNTs) such as negative charges, large surface area and excellent electron transfer ability, metal ion namely Fe 3+ showed a pair of well-defined redox response peaks on the CNTs-modified electrode. When EDTA was present in the solution, the voltammetric response of Fe 3+ was suppressed due to the chelating interaction between Fe 3+ and EDTA. In acetate buffer solution, the concentration of EDTA was found to be inversely proportional to the decreased cathodic peak current in the range of 1.0 × 10 −6 to 1.0 × 10 −4 mol/L with a detection limit (3S/N) of 6.5 × 10 −7 mol/L. While EDTA was degraded by UV irradiation, the voltammetric response on the CNTs-modified electrode was enhanced due to the reduced amount of EDTA species chelating with Fe 3+. Accordingly, the concentration variation of EDTA during the photodegradation was analyzed. The effects of H 2O 2 and pH on the photodegradation of EDTA were investigated. Thus, the proposed CNTs-based voltammetry provided a useful analytical tool for studying the degradation of EDTA.

Synthesis and identification of organosoluble polyamides bearing a triaryl imidazole pendent: Thermal, photophysical, chemiluminescent, and electrochemical characterization with a modified carbon nanotube electrode

Abstract A novel monomer containing a triaryl imidazole pendent group was successfully synthesized by nucleophilic substitution of bisphenol A with 2-(2-chloro-5-nitrophenyl)-4,5-diphenyl-1H-imidazole (I). A series of new polyamides (PAs) with inherent viscosities of 0.95–1.2 dL/g was prepared by direct polycondensation of the diamine with various dicarboxylic acids. These PAs were readily soluble in many organic solvents and gave tough and flexible films by solution casting. These PAs exhibited Tgs between 189 °C and 252 °C, and 10% weight loss temperatures in excess of 400 °C with up to 68% char yield at 600 °C in air. All of the PAs emitted a greenish-yellow light in dilute THF solution, with photoluminescence (PL) quantum yields in the range of 10–25%. The chemiluminescent activity and electrochemical oxidation of the PAs were also investigated.