Carbon Nanotube Paste Electrode Research Articles

Carbon nanotubes paste electrodes modified with a melanic polymer: Analytical applications for the sensitive and selective quantification of dopamine

This work describes the advantages of carbon nanotubes paste electrodes (CNTPE) modified with a melanic polymer for the highly sensitive and selective quantification of dopamine. The polymer is electrogenerated from a 3.0 × 10 −3 M l-dopa solution (in a 0.050 M phosphate buffer pH 7.40) by applying 0.80 V for 120 min. Two strategies for dopamine quantification are described, the amperometric detection at 0.200 V using 1.0 × 10 −3 M ascorbic acid in the measurement solution to improve the sensitivity of the assay; and the adsorptive stripping detection with medium exchange using differential pulse voltammetry (DPV) as transduction mode. Detection limits of 2.0 nM and 20 nM were obtained with amperometry and adsorptive stripping, respectively. The interference of 5.0 × 10 −4 M ascorbic acid and 5.0 × 10 −5 M dopac was really negligible in both cases, demonstrating the advantages of the melanic polymer as permselective layer.

Characterization and sensing properties of a carbon nanotube paste electrode for acetaminophen

A carbon nanotube paste electrode was prepared by dispersion of multi-wall carbon nanotubes in mineral oil. An electrochemical study on acetaminophen showed that the peak current had increased and that the peak potential was negatively shifted compared to a carbon paste electrode without nanotubes, thus resulting in an electrode for acetaminophen. The linear range for the response ranges from 0.15 µM to 126 µM, and the detection limit is 43 nM (at S/N = 3). Electron transfer number, diffusion coefficient and proton number have been calculated. The relative standard deviation (n = 10; at 20 µM of acetaminophen) is 1.9%. The electrode was applied to determine acetaminophen in effervescent dosage samples.

A Comparative Study of Carbon Nanotube paste Electrode for Development of Indicator-free DNA Sensors Using DPV and EIS: Human Interleukin-2 Oligonucleotide as a Model

A Comparative Study of Carbon Nanotube paste Electrode for Development of Indicator-free DNA Sensors Using DPV and EIS: Human Interleukin-2 Oligonucleotide as a Model

Anodic stripping voltammetric determination of copper(II) using a functionalized carbon nanotubes paste electrode modified with crosslinked chitosan

The development and application of a functionalized carbon nanotubes paste electrode (CNPE) modified with crosslinked chitosan for determination of Cu(II) in industrial wastewater, natural water and human urine samples by linear scan anodic stripping voltammetry (LSASV) are described. Different electrodes were constructed using chitosan and chitosan crosslinked with glutaraldehyde (CTS-GA) and epichlorohydrin (CTS-ECH). The best voltammetric response for Cu(II) was obtained with a paste composition of 65% (m/m) of functionalized carbon nanotubes, 15% (m/m) of CTS-ECH, and 20% (m/m) of mineral oil using a solution of 0.05 mol L −1 KNO 3 with pH adjusted to 2.25 with HNO 3, an accumulation potential of −0.3 V vs. Ag/AgCl (3.0 mol L −1 KCl) for 300 s and a scan rate of 100 mV s −1. Under these optimal experimental conditions, the voltammetric response was linearly dependent on the Cu(II) concentration in the range from 7.90 × 10 −8 to 1.60 × 10 −5 mol L −1 with a detection limit of 1.00 × 10 −8 mol L −1. The samples analyses were evaluated using the proposed sensor and a good recovery of Cu(II) was obtained with results in the range from 98.0% to 104%. The analysis of industrial wastewater, natural water and human urine samples obtained using the proposed CNPE modified with CTS-ECH electrode and those obtained using a comparative method are in agreement at the 95% confidence level.

Direct Electrochemistry of Hemoglobin and its Electrocatalysis Based on a Carbon Nanotube Paste Electrode

AbstractA new hemoglobin (Hb) and carbon nanotube (CNT) modified carbon paste electrode was fabricated by simply mixing the Hb, CNT with carbon powder and liquid paraffin homogeneously. To prevent the leakage of Hb from the electrode surface, a Nafion film was further applied on the surface of the Hb‐CNT composite paste electrode. The modified electrode was characterized by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). Direct electrochemistry of hemoglobin in this paste electrode was easily achieved and a pair of well‐defined quasi‐reversible redox peaks of a heme Fe(III)/Fe(II) couple appeared with a formal potential (E0′) of −0.441 V (vs. SCE) in pH 7.0 phosphate buffer solution (PBS). The electrochemical behaviors of Hb in the composite electrode were carefully studied. The fabricated modified bioelectrode showed good electrocatalytic ability for reduction of H2O2 and trichloroacetic acid (TCA), which shows potential applications in third generation biosensors.

Nickel(II)–baicalein complex modified multiwall carbon nanotube paste electrode and its electrocatalytic oxidation toward glycine

A modified electrode, nickel(II)–baicalein complex modified multiwall carbon nanotube paste electrode (Ni(II)–BA–MWCNT–PE), has been fabricated by electrodepositing Ni(II)–BA complex on the surface of MWCNT–PE in alkaline solution. The Ni(II)–BA–MWCNT–PE exhibits the characteristic of improved reversibility and enhanced current responses of the Ni(III)/Ni(II) couple compared with Ni(II)–BA–carbon paste electrode (CPE). It also shows better electrocatalytic activity toward the oxidation of glycine than Ni(II)–MWCNT–PE. Kinetic parameters such as the electron transfer coefficient α, rate constant k s of the electrode reaction, the diffusion coefficient D of glycine, and the catalytic rate constant k cat of the catalytic reaction are determined. Moreover, the catalytic currents present linear dependence on the concentration of glycine from 20 μM to 1.0 mM by amperometry. The detection limit and sensitivity are 9.2 μM and 3.92 μA mM −1, respectively. The modified electrode for glycine determination is of the property of simple preparation, fast response, and good stability.

Speciation of Sb(III) and Sb(V) in meglumine antimoniate pharmaceutical formulations by PSA using carbon nanotube electrode

A new and simple electroanalytical method for speciation of Sb(III) and Sb(V) in pharmaceutical formulation by potentiometric stripping analysis (PSA) using a multiwall carbon nanotube paste electrode was developed. All instrumental and chemical parameters influencing the performance of the method were carefully assessed and optimized. Trivalent antimony was determined in acid medium (pH 3.6) under the optimized condition (deposition potential of −0.7 V, deposition time of 180 s, ionic strength of 0.3 M and oxidant mercury concentration of 10 mg l −1). Total antimony was determined after quantitative reduction of Sb(V) with l-cysteine (1.5%, w/v) and its concentration was calculated from difference between the total antimony and Sb(III). The developed method provided two distinct linear calibration one ranging from 10 up to 50 μg l −1 and other from 100 up to 800 μg l −1 with respective correlation coefficient of 0.9978 and 0.9993, presenting a detection limit of 6.2 μg l −1. Repeatability for the six independent samples expressed in terms of relative standard deviation was found to be 3.01 and 1.39% for 40.0 and 300.0 μg l −1 antimony concentration, respectively. Results on the effect of foreign substances [Al(III), Mg(II), Fe(III), Cd(II), Zn(II) and meglumine] on analytical signal of antimony showed no interference even using high content of foreign ions in the analyte:interferent ratio up to 1:100. The proposed method was successfully applied for the speciation of Sb(III) and Sb(V) in pharmaceutical formulation and the accuracy was assessed from addition and recovery tests as well as comparing with graphite furnace atomic absorption spectrometry (GF AAS) technique used as reference analytical method.

Ni(II)–baicalein complex modified multi-wall carbon nanotube paste electrode toward electrocatalytic oxidation of hydrazine

A modified electrode Ni(II)–BA–MWCNT-PE has been fabricated by electrodepositing nickel(II)–baicalein [Ni(II)–BA] complex on the surface of multi-wall carbon nanotube paste electrode (MWCNT-PE) in alkaline solution. The Ni(II)–BA–MWCNT-PE exhibits the characteristic of improved reversibility and enhanced current responses of the Ni(III)/Ni(II) couple compared with Ni(II)–BA–CPE. It also shows good electrocatalytic activity toward the oxidation of hydrazine. Kinetic parameters such as the electron transfer coefficient α, rate constant k s of the electrode reaction, the diffusion coefficient D of hydrazine and the catalytic rate constant k cat of the catalytic reaction are determined. Moreover, the catalytic currents present linear dependence on the concentration of hydrazine from 2.5 μM to 0.2 mM by amperometry. The detection limit and sensitivity are 0.8 μM and 69.9 μA mM −1, respectively. The modified electrode for hydrazine determination is of the property of simple preparation, good stability, fast response and high sensitivity.

Electrocatalytic oxidation of methanol and other short chain aliphatic alcohols at Ni(II)–quercetin complex modified multi-wall carbon nanotube paste electrode

A modified electrode Ni(II)–Qu–MWCNT-PE has been fabricated by electrodepositing nickel(II)–quercetin [Ni(II)–Qu] complex on the surface of multi-wall carbon nanotube paste electrode (MWCNT-PE) in alkaline solution. Ni(II)–Qu–MWCNT-PE exhibits the characteristic of improved reversibility and enhanced current responses of the Ni(III)/Ni(II) couple compared with Ni(II)–MWCNT-PE and Ni(II)–Qu-carbon paste electrode. It also shows electrocatalytic activity toward the oxidation of methanol and other short chain aliphatic alcohols, such as ethanol, 1-propanol, and 1-butanol. The catalytic peak current and peak potential decrease in exponential form with the increase of carbon number of the chains. Kinetic parameters such as the electron transfer coefficient, α, rate constant, ks, of the electrode reaction, and the catalytic rate constant, kcat, for oxidation of methanol are determined. The stability and reproducibility of the Ni(II)–Qu–MWCNT-PE are good for practical applications.

Voltammetric Bioassay of Caffeine using Sensor Implant

In this article, we examined the performance of the voltammetric assay of caffeine using DNA immobilized onto a carbon nanotube paste electrode (DPE) and compared it with that of an ordinary carbon nanotube paste electrode (PE). Under optimal conditions, the working ranges for caffeine were from 0.1 to 12 mg l(-1) (for DPE) and 30-230 mg l(-1) (for PE). Detection limits (DLs) of 0.068 mg l(-1) (3.50 x 10(-7) M) DPE and 9.94 mg l(-1) (5.12 x 10(-5) M) PE were obtained and the relative standard deviation at the caffeine concentration of 5.0 mg l(-1) was 0.064% (n = 15) DPE under optimum conditions. The sensor could be implanted in a leaf skin or animal brain cell, which can then be interfaced with an electrochemical workstation. It can be used in real-time in vivo caffeine analysis in a live cell or leaf skin.

Electrochemical and catalytic investigations of dopamine and uric acid by modified carbon nanotube paste electrode

The redox response of a modified carbon nanotube paste electrode of 2,2′-[1, 2-ethanediylbis(nitriloethylidyne)]-bis-hydroquinone was investigated. Mixture of dopamine (DA) and uric acid (UA), can be separated from one another with a potential difference of 180 mV between them at a scan rate of 25 mVs − 1 by cyclic voltammetry. These conditions are sufficient to allow determination of DA and UA both individually and simultaneously. The electrocatalytic currents increases linearly with the DA and UA concentrations in the ranges of 0.1–900 μM and 20–650 μM, and the detection limits for DA and UA, were 0.087 and 15 μM, respectively. The diffusion coefficient ( D/cm 2 s − 1 = 7.3 × 10 − 6 ) and the kinetic parameters such as the electron transfer coefficient, ( α = 0.32) and the heterogeneous rate constant, ( k′/cm s − 1 = 2.21 × 10 − 3 ) for DA were determined using electrochemical approaches.

Nanomolar and Selective Determination of Epinephrine in the Presence of Norepinephrine Using Carbon Paste Electrode Modified with Carbon Nanotubes and Novel 2-(4-Oxo-3-phenyl-3,4-dihydro-quinazolinyl)-N′-phenyl-hydrazinecarbothioamide

A novel modified carbon nanotube paste electrode of 2-(4-oxo-3-phenyl-3,4-dihydro-quinazolinyl)-N'-phenyl-hydrazinecarbothioamide (2PHC) was fabricated, and the electro-oxidation of epinephrine (EP), norepinephrine (NE), and their mixture has been studied using electrochemical methods. The modified electrode displayed strong catalytic function for the oxidation of EP and NE and resolved the overlap voltammetric response of EP and NE into two well-defined voltammetric peaks of about 240 mV with square wave voltammetry (SWV). A linear response in the range of (5 x 10(-8))-(5.5 x 10(-4)) M with a detection limit (S/N = 3) of 9.4 nM for EP was obtained.

Simultaneous Diagnostic Assay of Catechol and Caffeine Using an in vivo Implanted Neuro Sensor

Catechol and caffeine were simultaneously analyzed with a bismuth-immobilized carbon nanotube paste electrode (BPE) using square wave (SW) stripping voltammetry. Optimum analytical conditions were determined. Simultaneous working ranges of 100-1,500 <TEX>$mgL^{-1}$</TEX> for caffeine and 5-75 <TEX>$mgL^{-1}$</TEX> for catechol were obtained. In the separated cell systems, a working range of 0.1-2.1 <TEX>$mgL^{-1}$</TEX> catechol with a correlation coefficient of 0.9935, and a working range of 10-210 <TEX>$mgL^{-1}$</TEX> caffeine with a correlation coefficient of 0.9921 were obtained. A detection limit (S/N) of 0.15 <TEX>$mgL^{-1}$</TEX> (7.7 <TEX>${\times}$</TEX> <TEX>$10^{-7}$</TEX> M) and a detection limit of 0.02 <TEX>$mgL^{-1}$</TEX> (1.82 <TEX>${\times}$</TEX> <TEX>$10^{-7}$</TEX> M), respectively, manifested for catechol and caffeine. It was found that three macro-type electrode systems could be implanted in fish and rat neuro cells. For both ions, the ion currents were observed. The physiological impulse conditions and the neuronal thinking current were also obtained.

Comparison of the Electrochemical Reactivity of Carbon Nanotubes Paste Electrodes with Different Types of Multiwalled Carbon Nanotubes

AbstractCarbon nanotubes (CNTs) are widely used in electrochemical studies. It is reported that CNTs with different source and dispersed in different agents [1] yield significant difference of electrochemical reactivity. Here we report on the electrochemical performance of CNTs paste electrodes (CNTPEs) prepared by multiwalled carbon nanotubes (MWNTs) with different diameters, lengths and functional groups. The resulting electrodes exhibit remarkable different electrochemical reactivity towards redox molecules such as NADH and K3[Fe(CN)6]. It is found that CNTPEs prepared by MWNTs with 20–30 nm diameter show highest catalysis to NADH oxidation, while CNTPEs prepared by MWNTs with carboxylate groups have best electron‐transfer rate (The peak‐peak separation (ΔEp) is +0.108 V for MWNTs with carboxylate groups, +0.155 V for normal MWNTs, and +0.174 V for short MWNTs) but weak catalysis towards oxidation of NADH owing to the hydrophilicity of carboxylate groups. The electrochemical reactivity depends on the lengths of CNTs to some extent. The ‘long’ CNTs perform better in our study (The oxidation signals of NADH appear below +0.39 V for ‘long’ CNTs and above +0.46 V for the ‘short’ one totally). Readers may get some directions from this article while choose CNTs for electrochemical study.

Electrochemical characterization of 2, 2′-[1, 2-ethanediylbis (nitriloethylidyne)]-bis-hydroquinone-carbon nanotube paste electrode and its application to simultaneous voltammetric determination of ascorbic acid and uric acid

The preparation and electrochemical characterization of a carbon nanotube paste electrode modified with 2,2′-[1,2-ethanediylbis (nitriloethylidyne)]-bis-hydroquinone, referred to as EBNBH, was investigated. The EBNBH carbon nanotube paste electrode (EBNBHCNPE) displayed one pair of reversible peaks at E pa = 0.18 V and E pc = 0.115 V vs Ag/AgCl. Half wave potential (E 1/2) and ΔE p were 0.148 and 0.065 V vs Ag/AgCl, respectively. The electrocatalytic oxidation of ascorbic acid (AA) has been studied on EBNBHCNPE, using cyclic voltammetry, differential pulse voltammetry and chronoamperometry techniques. It has been shown that the oxidation of AA occurs at a potential where oxidation is not observed at the unmodified carbon paste electrode. The heterogeneous rate constant for oxidation of AA at the EBNBHCNPE was also determined and found to be about 1.07 × 10−3 cm s−1. The diffusion coefficient of AA was also estimated as 5.66 × 10−6 cm2 s−1 for the experimental conditions, using chronoamperometry. Also, this modified electrode presented the property of electrocatalysing the oxidation of AA and uric acid (UA) at 0.18 and 0.35 V vs Ag/AgCl, respectively. The separations of anodic peak potentials of AA and UA reached 0.17 V. Using differential pulse voltammetry, the calibration curves for AA and UA were obtained over the range of 0.1–800 μM and 20–700 μM, respectively. With good selectivity and sensitivity, the present method provides a simple method for selective detection of AA and UA in biological samples.

Ordered Mesoporous Carbon Paste Electrodes for Electrochemical Sensing and Biosensing

AbstractSurface renewable ordered mesoporous carbon paste electrodes (OMCPE) were prepared by mechanical mixing ordered mesoporous carbon (OMC) and mineral oil. Electrochemical behavior of the composite electrode was evaluated and compared with the conventional graphite paste (GPE) and carbon nanotubes paste (CNTPE) electrodes. The OMCPE provided improved electron transfer kinetics and catalytic capabilities in connection with oxidation and/or reduction of different redox systems, such as ferricyanide and some biological species, e. g. ascorbic acid (AA), uric acid (UA), β‐nicotinamide adenine dinucleotide (NADH), dopamine (DA), epinephrine (EP), acetaminophenol (AP) and hydrogen peroxide. The substantial decrease in the over voltage of the hydrogen peroxide oxidation along with the facile incorporation of glucose oxidase (GOD) into the composite matrix allowed us successfully to fabricate a sensitive and selective glucose biosensor. A linear response up to 15 mM glucose was obtained for the OMCPE modified with 10% GOD (w/w) with a detection limit of 0.072 mM. In addition, we also successfully applied the OMCPE to the anodic stripping voltammetric analysis of heavy metal ions with improved sensitivities in comparison with CNTPE and GPE. The excellent experimental results implicate that the new developed paste electrode holds great promise in the design of electrochemical devices, such as sensors and biosensors.

Novel 2,2′-[1,2-ethanediylbis(nitriloethylidyne)]-bis-hydroquinone double-wall carbon nanotube paste electrode for simultaneous determination of epinephrine, uric acid and folic acid

The electro-oxidation of epinephrine (EP), uric acid (UA), folic acid (FA), and their mixture has been studied by modified carbon nanotube paste electrode of 2,2′-[1,2-ethanediylbis(nitriloethylidyne)]-bis-hydroquinone using cyclic voltammetry, chronoamperometry and differential pulse voltammetry. This modified electrode exhibited potent and persistent electron mediating behavior followed by well-separated oxidation peaks towards EP, UA and FA with activation overpotential. For the ternary mixture containing EP, UA and FA the three compounds can be well separated from each other at the scan rate of 20 mV s −1. The obtained catalytic peak current, was linearly dependent on the EP, UA and FA concentrations in the range of 0.7–1200 μM, 25–750 μM and 15–800 μM and the detection limits for EP, UA and FA were 0.216 ± 0.004, 8.8 ± 0.2 and 11.0 ± 0.3 μM, respectively. The diffusion coefficient ( D), and the kinetic parameters such as electron transfer coefficient, ( α) and heterogeneous rate constant, ( k′) for EP were also determined using electrochemical approaches. The modified electrode showed good sensitivity, selectivity and stability, and was employed for the determination of EP, UA and FA in the real samples.

Differential pulse voltammetric determination of N-acetylcysteine by the electrocatalytic oxidation at the surface of carbon nanotube-paste electrode modified with cobalt salophen complexes

The preparation and electrochemical performance of the carbon nanotube-paste electrode modified with salophen complexes of cobalt(III) perchlorate, with various substituents on the salophen ligand, as well as their electrocatalytic activity toward the oxidation of N-acetylcysteine (NAC) is investigated. Several Schiff base complexes containing various nucleophilic and electrophilic functional groups were prepared, and their electrochemical characteristics for the electro-oxidation of NAC were evaluated using cyclic and differential pulse voltammetry (CV and DPV). The results revealed, the modified electrodes show an efficient and selective electrocatalytic activity toward the anodic oxidation of NAC among biologically important compounds in buffered solutions at pH of 7.0. The best voltammetric responses were obtained for a carbon-paste electrode (CPE) modified with a salophen complex containing para-methoxy groups on its salicylaldehyde ring. The analytical response of the modified electrode for response to other sulfhydryl compounds (e.g., cysteine, penicillamine, captopril and mercaptopropionyl glycine) in comparison to NAC was investigated by CV and DPV methods. The DPV method was applied as a sensitive method for the quantitative detection of the trace amounts of NAC. A linear dynamic range from 1 × 10−7 to 1 × 10−4 M with calibration sensitivity of 0.0646 μA/μM is resulted for NAC in DPV measurements. The detection limit was 5 × 10−8 M, which is remarkably lower than those reported previously for NAC using other modified electrodes. The results of voltammetric determinations show a very good reproducibility, and the R.S.D. for the slope of the calibration curve, based on 10 measurements in a period of two months, was <3.9%. The detection system provides very stable electrochemical responses toward NAC, makes it very suitable for using in pharmaceutical and clinical measurements.

Determination of concentrated hydrogen peroxide at single-walled carbon nanohorn paste electrode

Single-walled carbon nanohorn (SWCNH) paste electrode was used for amperometric determination of concentrated hydrogen peroxide, and was compared with other carbon electrodes. The calibration plots are linear from 0.5 to 100 mM at activated SWCNH paste electrode and edge plane graphite (EPG) electrode. In contrast, the calibration plots are linear only at concentrations lower than 45 mM at graphite paste electrode, multi-walled carbon nanotube paste electrode, and glassy carbon electrode. Our results show that SWCNH paste electrode and EPG electrode are interesting alternatives to high surface area platinum electrode for determination of concentrated hydrogen peroxide. Because of its high-purity, metal-free SWCNH is a user-friendly and attractive material for electrochemical study.

Administering Pesticide Assays in In Vivo-Implanted Biosensors

An analytical pesticide assay of O-ethyl-O-4-(nitrophenyl)phenyl phosphonothioate (EPN) was carried out using the following: a carbon nanotube paste electrode, a mercury-immobilized carbon nanotube paste electrode, a glassy carbon electrode, a metal–gold electrode, and a DNA-immobilized carbon nanotube paste electrode (DPE), which is two-fold more sensitive than other sensors. The DPE was optimized using cyclic and square wave stripping voltammetry. Linear working ranges approached 5–55 mg L–1 EPN and the nano-range of 10–210 ng L–1 in a 0.1 mol L–1 NH4H2PO4 electrolyte solution, with a speedy analytical time of 30-s stripping. The detection limit was 2.57 ng L–1 (7.94 × 10–12 mol L–1), and the precision was 0.102% relative standard deviation (n = 15) at the 10.0 mg L–1 EPN spike. This indicates that the method is more sensitive than common voltammetric methods. This method was applied to fruit samples using patch- and needle-type electrodes, specifically on the skin tissues of an orange and an apple. Moreover, the implanted electrode was interfaced with a fish brain cell at the electrochemical workstation. Results showed that the aforementioned method can be used to conduct a pesticide assay in neuro-treated and non-treated cell systems.