Carbon Nanotube-modified Electrode Research Articles

Fabrication and Electrocatalysis of Self-Assembly Directed Gold Nanoparticles Anchored Carbon Nanotubes Modified Electrode

A self-assembly directed approach was adopted to modify glassy carbon electrode (GC) with gold nanoparticles incorporation and the electrocatalytic performance of self-assembly modified electrode, GC/SA-Au-ME was critically evaluated for the oxidation of ascorbic acid (AA). The modification involves the dispersion of multi-wall carbon nanotube (MWNT) and an inclusion complex, beta-cyclodextrin-4-aminothiophenol on the surface of GC electrode in the presence of cetyltrimethylammonium bromide (CTAB). Gold nanoparticles were deposited into the self-assembled sites to fabricate the modified electrode, GC/SA-Au-ME. Another electrode (GC-Au-ME) was fabricated under similar conditions in the absence of CTAB. The electrocatalytic activity of the modified electrodes (GC/SA-Au-ME and GC-Au-ME) towards the oxidation of AA was critically compared. Cyclic voltammetry, chronoamperometry, and double potential chronoamperometry were used to evaluate the characteristics of the modified electrodes. The self-assembled electrode (GC/SA-Au-ME) shows excellent electrocatalytic activity over the other electrode, GC-Au-ME. Augmented current response, faster electron transfer kinetics (with a rate constant for electron transfer process as 3.25 x 10(4) cm3 mol(-1) s(-1)), linear range of response for the analyte (1-50 mM with an extended detection limit to 1 microM), better sensitivity, and selectivity were witnessed for the self-assembly directed modified electrode.

Immobilization and direct electrochemistry of cytochrome c at a single-walled carbon nanotube-modified electrode

A single-walled carbon nanotube (SWNT)-modified electrode was fabricated and characterized by SEM and ac impedance techniques. The direct electrochemistry of cytochrome c (Cyt c), which was adsorbed on the surface of the SWNT, was studied by cyclic voltammetry. The results from cyclic voltammetry and infrared spectroscopy indicated that Cyt c remained in its original structure and did not undergo structural change after its immobilization on the SWNT. Further results demonstrated that the SWNT had promotional effects on the direct electron transfer of Cyt c and also indicated that the immobilized Cyt c retained its electrocatalytic activity to the reduction of H2O2. This modified electrode might be used in development of new biosensors and the biofuel cells.

β-Cyclodextrin incorporated carbon nanotubes-modified electrodes for simultaneous determination of adenine and guanine

Abstract A simple and reliable method based on electrochemical technique at β-cyclodextrin incorporated carbon nanotubes-modified electrodes (β-CD-CNT/E) was proposed for simultaneous or individual determination of guanine and adenine. After accumulation on β-CD-CNT/E at open circuit for 1 min, guanine and adenine produced well-defined oxidation peaks at about +0.79 and +1.09 V in pH 4.5 acetate buffer. The electrocatalytic mechanism was firstly discussed and revealed in detail from the point of the interface layer microstructure of the composite electrode. The novel modified electrode brings new capabilities for electrochemical devices by combining the advantages of carbon nanotubes and supramolecular cyclodextrins. The results demonstrated that the utility of β-CD-CNT/E clearly provides an effective methodology for the estimations of guanine and adenine. Further, the marked electrocatalytic activity permits effective low-potential amperometric biosensing of DNA with the detection limits of 0.1 and 0.2 μg ml −1 for guanine and adenine, respectively.

Determination of carbamates in nature water based on the enhancement of electrochemiluminescent of Ru(bpy) 32+ at the multi-wall carbon nanotube-modified electrode

A multi-wall carbon nanotube (MWNT)/Nafion composite film-modified electrode was developed in this paper, and its chemical and electrochemiluminescent (ECL) behavior of tris(2,2′-bipyridyl)ruthenium (Ru(bpy) 3 2+) on this electrode has been investigated in detail. It has been also found that some carbamates were able to enhance the ECL intensity of Ru(bpy) 3 2+ greatly at this modified electrode. Based on which, a sensitive and simple method for determination of pirimicarb, methomyl, aldicarb and carbofuran were developed, and the proposed method has been applied to determine the carbamates in the nature water.

Immobilization and electro-oxidation of calf thymus deoxyribonucleic acid at alkylamine modified carbon nanotube electrode and its interaction with promethazine hydrochloride

Abstract Immobilization and electro-oxidation of calf thymus double-stranded deoxyribonucleic acid (dsDNA) were investigated at carbon nanotube (CNT) electrode modified with ethylene diamine. Well-defined oxidation peak and large peak current of dsDNA oxidation have been observed even at very low dsDNA concentration (40 ng mL −1 ). Interaction between promethazine hydrochloride and immobilized dsDNA was also investigated. The intercalative binding of promethazine hydrochloride with dsDNA results in an increase of electrochemical impedance and a decrease of dsDNA oxidation peak current. The possibility using functional CNT electrode immobilized dsDNA to sense promethazine hydrochloride was also explored.

Electrocatalytic oxidation and sensitive detection of cysteine at layer-by-layer assembled carbon nanotube-modified electrode

Electrocatalytic oxidation of cysteine (CySH) at multilayer films of carbon nanotube (CNT)-modified electrode was studied. The CNT-modified electrode was fabricated through layer-by-layer electrostatic deposition of positively charged poly(diallyldimethylammonium chloride) (PDDA) and negatively charged shortened multi-walled carbon nanotubes (MWNTs) on glassy carbon (GC) electrode surface. The multilayer film was characterized by scanning electron microscopy and cyclic voltammetry. Effect of scan rate on CySH oxidation was also investigated. Sensitive detection for CySH at (PDDA/MWNT) 5/GC electrode in 0.16 mol L −1 phosphate buffer solution (pH 7.4) was carried out. A linear calibration curve was observed in the range of 20 μmol L −1 to 1.3 mmol L −1 with differential pulse voltammetry (DPV). The detection limit (signal/noise, 3) of 0.3 μmol L −1 was obtained at 0.8 V in steady-current response.

Electrocatalytic and Analytical Response of β-Cyclodextrin Incorporated Carbon Nanotubes-Modified Electrodes Toward Guanine

The utility of β-cyclodextrin incorporated carbon nanotubes-modified electrodes (β-CD/CNT/E) for electrocatalytic oxidation of guanine in aqueous solution is demonstrated. Compared to the conventional electrode, it lowers the overpotential and enhances the peak current significantly. The action mechanism of β-CD/CNT/E was discussed systemically. The results demonstrated that the use of β-CD/CNT/E clearly provides an effective methodology for the determination of guanine. Based on the signal of guanine, an estimate of DNA concentration can be recognized with a limit of detection of 10 ng mL−1.

β-Cyclodextrin incorporated carbon nanotube-modified electrode as an electrochemical sensor for rutin

An electrochemical sensor modified with multi-walled carbon nanotubes/β-cyclodextrin (MWNTs/β-CD) film was fabricated for the determination of rutin. The electrochemical behavior of rutin at the chemically modified electrode was investigated by cyclic voltammetry (CV). The response mechanism of MWNTs/β-CD film for rutin was based on the inclusion interaction of β-CD for rutin. The MWNTs/β-CD film showed preferably analytical performance characteristics in electrocatalytic oxidation and reduction for rutin compared with the MWNTs film and bare glassy carbon electrode (GCE). A linear calibration plot was obtained covering the range from 4.0 × 10 −7 to 1.0 × 10 −3 mol L −1 with a detection limit of 2.0 × 10 −7 mol L −1. This electrochemical sensor showed excellent sensitivity, selectivity, stability and recovery for the determination of rutin in urine samples.

Electrocatalysis at Graphite and Carbon Nanotube Modified Electrodes: Edge‐Plane Sites and Tube Ends Are the Reactive Sites

AbstractFor Abstract see ChemInform Abstract in Full Text.

Electrochemical Combustion of Phenol at the Carbon Nanotube Electrode

The carboxyl modified carbon nanotubes were obtained by treating them in the concentrated nitric acid with a little surfactant. The complete electrochemical combustion of phenol has been found under 5 M at the carboxyl modified carbon nanotube electrode in phosphate buffer solution. The reaction was discussed in details. Due to the porous tubule of the structure of the carbon nanotube and large quantity of hydroxyl exists in the carboxyl modified carbon nanotube electrode, which were necessary for the continually electrochemical combustion of phenol. Long time potentiostatic oxidation showed that the phenol could be eliminated from the aqueous media without any foul at the carbon nanotube electrode.

Heterogeneous Electron-Transfer Kinetics for Flavin Adenine Dinucleotide and Ferrocene through Alkanethiol Mixed Monolayers on Gold Electrodes

The heterogeneous electron-transfer properties of flavin adenine dinucleotide (FAD) were studied at self-assembled monolayer (SAM)-modified gold electrodes and compared to ferrocene-modified SAMs as a reference system. A modified form of FAD, N6-(2-aminoethyl)-FAD, was covalently immobilized onto a mixed self-assembled monolayer (SAMs) formed by two series of alkanethiols (HS−(CH2)n−COOH with a diluent HS−(CH2)n−CH3 where n = 5, 7, 10, or 15 and HS−(CH2)n−COOH with a diluent HS−(CH2)n−CH2OH where n = 5, 7, 10, or 11). The electron-transfer (ET) rates followed an exponential decay with the increasing thickness of the SAM (ket = A exp(−βn); n = number of bonds) with an attenuation factor (β) of 1.0 per bond for FAD with both diluents. Despite the similarity in β the apparent rate constant for electron transfer was 2 orders of magnitude greater with the alcohol-terminated diluent relative to the methyl-terminated SAM. In comparison the ferrocenyl SAMs also had β values of 1.0−1.2 per bond, depending on the composition of the diluent layer, with the apparent rate constant for electron transfer being significantly faster with the alcohol-terminated diluent layer. The reconstitution of apo-glucose oxidase (apo-GOx) onto a FAD-modified gold electrode was also carried out; however, no biocatalytic activity was observed. Based on the β value for the FAD-modified electrodes and the magnitude of the apparent rate of electron transfer, rate constants for direct electron transfer to glucose oxidase at carbon nanotube-modified electrodes and graphite electrodes suggest the enzyme has been partially denatured from its native configuration, thus bringing the redox-active center of the enzyme closer to the electrode and allowing appreciable ET to be observed.

Electrocatalysis of Tryptophan at Multi-Walled Carbon Nanotube Modified Electrode

Acid-treated multi-walled carbon nanotubes (MWNTs) were immobilized on the surface of a glassy carbon electrode to form an MWNT-modified electrode. The electrocatalytic response of the modified electrode towards tryptophan (Trp) was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The results demonstrated that the modified electrode exhibited a high degree of catalytic activity towards the oxidation of Trp. An oxidation peak was obtained in Trp solution at the MWNT-modified electrode. Compared with a bare electrode, the peak current had obviously increased, and the peak potential had shifted in a negative direction. However, under the same conditions, no response was observed for other amino acids. The oxidation peak currents were proportional linearly to the concentration of Trp, a property which could be utilized to detect Trp. The determination conditions, such as the concentration, the composition and the pH values of the supporting electrolyte, accumulation time, as well as scan rate etc. were optimized. Under the chosen conditions, the DPV peak current is linear to the concentration of Trp in the range of 2.5 × 10−7 to 1.0 × 10−4 mol L−1, and the detection limit is 2.7 × 10−8 mol L−1. Moreover, the detection is free of interference from other amino acids. The modified electrode has been successfully applied to determine the concentration of Trp in composite amino acid injections, and it displays excellent repeatability and higher sensitivity.

Indicator Free DNA Hybridization Detection by Impedance Measurement Based on the DNA‐Doped Conducting Polymer Film Formed on the Carbon Nanotube Modified Electrode

AbstractA new biosensing strategy for direct electrochemical detection of DNA hybridization by AC impedance measurement is described. The indicator or label free approach was developed on the basis of the carbon nanotubes coupled with a conductive polymer polypyrrole (PPy). Multi‐walled carbon nanotubes functionalized with carboxylic group (MWNTs‐COOH) were modified on the glassy carbon electrode (GCE) and the oligonucleotide probes were doped within the electro‐polymerized PPy films by serving as the sole counter anion during the growth of the conducting films. Before and after hybridization reaction with the complementary DNA sequences, a decrease of impedance values was observed as a result of the reduction of the electrode resistance. Hybridization amounts of the one‐base, two‐base and three‐base mismatched sequences were obtained only in a 51%, 18% and 8.2% response when compared to that for the complementary matched sequence. Such unique response is attributed to the concomitant conductivity changes of the PPy‐polymerized carbon nanotubes, and offers great promise for reagentless DNA hybridization analysis.

Application of a Carbon Nanotube Modified Electrode in Anodic Stripping Voltammetry for Determination of Trace Amounts of 6-Benzylaminopurine

Carbon nanotubes were modified on the surface of a glassy carbon electrode (GC) and initially applied in semi-derivative anode stripping voltammetry for the determination of 6-benzylaminopurine. The experiments demonstrated that the presence of the carbon nanotube greatly increased the current of the oxidation peak of benzylaminopurine. Cyclic voltammetry (CV) and semi-derivative voltammetry were used in a comparative investigation into the electrochemical oxidation of benzylaminopurine with the modified electrode. Studies on the effect of pH on the peak current and potential were carried out over the pH range of 9.0 ∼ 13.0 with the NH3–NH4Cl buffer solution. A pH of 10.0 was chosen as the optimum pH. Other experimental parameters, such as film thickness, accumulation potential, temperature etc. were optimized. The anodic peak current was found to be linearly related to the concentration of benzylaminopurine over the range of 4.0×10−8 to 1.0×10−5 mol·L−1 with a detection limit of 5.0×10−9 mol·L−1 in an accumulation time of 5 min. Interferences of some inorganic and organic species on the response have been studied.

An Amperometric Biosensor Based on the Coimmobilization of Horseradish Peroxidase and Methylene Blue on a Carbon Nanotubes Modified Electrode

AbstractA novel hydrogen peroxide biosensor has been constructed based on the characteristics of the carbon nanotube. The multiwall carbon nanotube (MWNT) was used as a coimmobilization matrix to incorporate horseradish peroxidase (HRP) and electron transfer mediator methylene blue (MB) onto a glassy carbon electrode surface. Cyclic voltammetry and amperometric measurements were employed to demonstrate the feasibility of methylene blue as an electron carrier between the immobilized peroxidase and the surface of glassy carbon electrode. The amperometric response of this resulting biosensor to H2O2 shows a linear relation in the range from 4 μM to 2 mM. The detection limit was 1 μM when the signal to noise ratio is 3. The presence of dopamine and ascorbic acid hardly affects the sensitive determination of H2O2. This biosensor also possesses very good stability and reproducibility.

Carbon nanotube-modified electrodes for the simultaneous determination of dopamine and ascorbic acid.

The voltammetric separation of dopamine and ascorbic acid was studied with cyclic voltammetry at two kinds of carbon nanotube-modified electrodes (coated and intercalated). The anodic peak difference reached 270 mV under the present conditions. The separation mechanism and effect factors were carefully studied. Using various types of surfactants as coating dispersants of carbon nanotubes, it was demonstrated that the charge nature of the surfactants had a strong effect on the electrochemical behavior of dopamine and ascorbic acid. When the oxidation solution of carbon nanotubes was changed from the most commonly used mixed concentrated nitric acid and sulfuric acid (1 + 3 v/v) to dilute nitric acid and to hydrochloric acid, the anodic peak separation value of dopamine and ascorbic acid increased significantly, and it was shown that carboxylic acid groups attached to the carbon nanotubes were an adverse factor for the discrimination of DA from AA. These results indicated that the resolution of DA and AA was mainly attributable to the stereo porous interfacial layer formed from aggregated pores and inner cavities of the carbon nanotubes. The modified electrodes exhibited an attractive ability to measure DA and AA simultaneously and showed good stability and reproducibility.

A selective voltammetric method for uric acid detection at beta-cyclodextrin modified electrode incorporating carbon nanotubes.

A beta-cyclodextrin-coated electrode incorporating carbon nanotubes was constructed and applied to the detection of uric acid in the presence of high concentration of ascorbic acid. The major obstacle of the overlapped oxidation potential of ascorbic acid was overcome owing to the distinct ability of the carbon nanotubes-modified electrode to yield a large anodic peak difference ca. 400 mV. The sensitive detection of uric acid has been further improved by the formation of a supramolecular complex between beta-cyclodextrin and uric acid. A linear calibration curve was obtained for 5 x 10(-7) to 5 x 10(-5) M in 0.2 M HAc-NaAc buffer (pH 4.5) with correlation coefficient of 0.998 and detection limit of 0.2 microM. The practical analytical application was illustrated by a selective measurement of uric acid in human urine without any preliminary treatment.