Use of Cationic Surfactants Film Carbon Paste Electrodes Modified with Multiwalled Carbon Nanotubes in Electrochemical Analysis of dsDNA

Direct electrochemistry of dsDNA based on the enhancement effect of cationic surfactants such as dodecyltrimethylammonium bromide (DTAB) and tetradecyltrimethylammonium bromide (TTAB) was achieved by using a carbon paste electrode modified with multiwalled carbon nanotubes (MWCNTs/CPE) as the basal electrode. The results indicated that the dsDNA molecules have been adsorbed quite strongly on the cationic surfactants’ film and very well developed peaks which were attributed to the oxidation of guanine residues on the dsDNA molecule structure were obtained from both electrodes. The electrochemical behavior of dsDNA at the surface of the modified electrodes was also evaluated. Based on the signal of guanine, under the optimal conditions, very low levels of dsDNA were detected following short accumulation times with detection limits of 0.650 mg L^?1 and 0.119 mg L^?1 for DTAB/MWCNTs/CPE and TTAB/MWCNTs/CPE, respectively.     

Amperometric Lactate Biosensor Based on Carbon Paste Electrode Modified with Benzo[c]cinnoline and Multiwalled Carbon Nanotubes

Amperometric lactate biosensor based on a carbon paste electrode modified with benzo[c]cinnoline and multiwalled carbon nanotubes is reported. Incorporation of benzo[c]cinnoline acting as a mediator and multiwalled carbon nanotubes providing a conduction pathway to accelerate electron transfer due to their excellent conductivity into carbon paste matrix resulted in a high performance lactate biosensor. The resulting biosensor exhibited a fast response, high selectivity, good repeatability and storage stability. Under the optimal conditions, the enzyme electrode showed the detection limit of 7.0×10^?8 M with a linear range of 2.0×10^?7 M–1.1×10^?4 M. The usefulness of the biosensor was demonstrated in serum samples.     

Novel Lu3+ Carbon Paste Electrode Based on Functionalized Multiwalled Carbon Nanotubes

A novel carbon paste ion selective electrode for determination of trace amount of lutetium was prepared. Modified (functionalized) multiwalled carbon nanotubes (f‐MWCNTs) were used for improvement of a lutetium carbon paste sensor response. MWCNTs have a good conductivity which helps the transduction of the signal in carbon paste electrode. In this work it is shown that introducing certain functional groups on MWCNTs can improve the electrode signals. The electrode composition of 20 % paraffin oil, 56 % graphite powder, 18 % ionophore and 6 % f‐MWCNTs showed the stable potential response to Lu³⁺ ions with the Nernstian slope of 21.1 (±0.3) mV decade^?1 over a wide linear concentration range of 1.0×10^?6–1.0×10^?1 mol L^?1. The electrode has fast response time (<15 s) and long term stability (about one month).     

Multi‐Wall Carbon Nanotube Paste Electrode for Adsorptive Stripping Determination of Quercetin: A Comparison with Graphite Paste Electrode via Voltammetry and Chronopotentiometry

Adsorptive‐stripping voltammetry and chronopotentiometry were used to study the adsorption and oxidation of quercetin at both graphite‐nujol paste electrode (GPE) and carbon nanotubes‐nujol paste electrode (CNTPE) for the potential application of carbon nanotube to flavonoids determination. As compared with GPE, CNTPE showed very great power to adsorb quercetin and resulted in a considerable signals enhancement. The adsorption isotherm of quercetin on CNTPE was of Langmuir type, and the stripping of quercetin adsorbed on CNTs showed a quasi‐reversible oxidation reaction involving two‐electron and two‐proton. The high adsorbtive activity of CNTPE was contributed to the high specific surface area and the special surface characteristics of carbon nanotubes. The peak current response of differential pulse voltammetry depended linearly on quercetin concentration. A linear equation I_p(μA)=0.987c(μmol L^?1)+0.023 with a correlation coefficient of 0.994 was obtained over the concentration range 0.1–1.0 μmol L^?1.     

β‐Cyclodextrin Incorporated Carbon Nanotube Paste Electrode as Electrochemical Sensor for Nifedipine

In this work a carbon paste electrode modified with multiwalled carbon nanotubes/β‐cyclodextrin (MWCNTs/β‐CD) was constructed and applied to the determination of nifedipine. The electrochemical behavior of nifedipine at this electrode was investigated using cyclic voltammetry and differential pulse voltammetry. Characterization of the modified electrode was conducted with electrochemical impedance spectroscopy and scanning electron microscopy. After adsorption of nifedipine on the MWCNTs/β‐CD paste electrode at 0.0 V for 6 min, a well defined reduction peak was produced in sodium hydroxide of 0.05 M. The calibration curve was linear from 7.0×10^?8 to 1.5×10^?5 M. The detection limit was obtained as 2.5×10^?8 M. The results demonstrated that this electrochemical sensor has excellent sensitivity and selectivity. This sensor was applied for determination of nifedipine in drug dosage and blood serum with excellent recoveries.     

Adsorptive Stripping Voltammetry of Rifamycins at Unmodified and Surfactant‐Modified Carbon Paste Electrodes

The electrochemical behavior of the antibiotics rifampicin and rifamycin SV is investigated by cyclic voltammetry at carbon paste and in situ surfactant modified carbon paste electrodes. Both antibiotics adsorb on the unmodified electrodes and show a reversible redox process due to the oxidation of the 6,9‐dihydroxynaphthalene moiety to the corresponding naphthoquinone. This process is used as analytical signal for developing adsorptive voltammetric methods for the determination of the antibiotics. Experimental parameters, such as pH of the supporting electrolyte, accumulation potential and time are optimized. After accumulation from acidic solutions (0.1 M KCl pH 2 or HCl 0.2 M) at ?0.1 or 0 V for 3 min, the differential pulse oxidation peak current changes linearly with the antibiotic concentration in the range 3.5×10^?10 M ?5.4×10^?9 M or 5×10^?11 M ?1.0×10^?9 M for rifampicin and rifamycin SV, respectively. Rifamycin SV is not accumulated on carbon paste electrodes modified in situ with the anionic surfactant sodium dodecyl sulfate, whereas rifampicin is readily accumulated on this modified electrodes resulting in a signal enhancement and allowing rifampicin determinations without interference from rifamycin SV. On the other hand, selective determination of rifamycin SV in the presence of rifampicin is achieved by using carbon paste electrodes in situ modified with the cationic surfactant cetyltrimethylammonium chloride.     

Acetylferrocene Modified Carbon Paste Electrode; A Sensor for Electrocatalytic Determination of Hydrazine

The electrocatalytic oxidation of hydrazine at a carbon paste electrode spiked with acetylferrocene as a mediator was studied by cyclic voltammetry, differential pulse voltammetry, and chronoamperometry. In contrast to other ferrocenic compounds, acetylferrocene exhibits a chemical irreversible behavior, but it can act as an effective mediator for electrocatalytic oxidation of hydrazine, too. The heterogeneous electron transfer rate constant between acetylferrocene and the electrode substrate (carbon paste) and the diffusion coefficient of spiked acetylferrocene in silicon oil were estimated to be about 3.45×10^?4 cm s^?1 and 4.45×10^?9 cm² s^?1, respectively. It has been found that under the optimum conditions (pH 7.5) the oxidation of hydrazine occurs at a potential of about 228 mV less positive than that of an unmodified carbon paste electrode. The catalytic oxidation peak current of hydrazine was linearly dependent on its concentration and the obtained linear range was 3.09×10^?5 M–1.03×10^?3 M. The detection limit (2σ) has been determined as 2.7×10^?5 M by cyclic voltammetry. Also, the peak current was increased linearly with the concentration of hydrazine in the range of 1×10^?5 M–1×10^?3 M by differential pulse voltammetry with a detection limit of 1×10^?5 M. This catalytic oxidation of hydrazine has been applied as a selective, simple, and precise new method for the determination of hydrazine in water samples.     

An electrochemiluminescent sensor for glucose employing a modified carbon nanotube paste electrode

A carbon nanotube paste (CNTP) electrode and a carbon nanotube paste/glucose oxidase (CNTP/GOx) electrode were prepared, and the electrochemiluminescent (ECL) behavior of luminol in the presence of glucose was investigated in detail at each of these electrodes. Compared to the classical carbon paste (CP) electrode, the CNTP electrode incorporating glucose oxidase greatly enhanced the response of the ECL sensor to glucose due to the electrocatalytic activity of the carbon nanotubes, the specificity of the enzymatic reaction, and the sensitivity of the luminol ECL reaction. Under optimal conditions, the electrode was found to respond linearly to glucose in the concentration range 1.0x10(-6) approximately 2.0x10(-3) mol/L, and the detection limit (defined as the concentration that can be detected at a signal-to-noise ratio of 3) was found to be a glucose concentration of 5.0x10(-7) mol/L. The method used to prepare the CNTP/GOx electrode was very convenient, and the electrode surface could be renewed in the case of fouling by simply polishing or cutting it to expose a new and fully active surface. The relative standard deviations (RSD) were found to be 6.8% and 8.9% for the CNTP electrode and the CNTP/GOx electrode (n=6). The electrode retained 95% of its initial response after two weeks.     

Determination of Epinephrine at Different Types of Carbon Paste Electrodes

The voltammetric behavior of epinephrine was investigated by differential pulse voltammetry (DPV) at a carbon paste electrodes (CPE) made of different carbon powders – CR-2, glassy carbon (GC) microparticles, and single-wall carbon nanotubes (SWNT). In Briton-Robinson (BR) buffer solution pH 6, the linear dependence was found for the determination of epinephrine by the given method in the concentration ranges of 1·10^?6–1·10^?4 (CR-2), 1·10^?6–1·10^?4 (GC microparticles) and 4·10^?6–1·10^?4 (SWNT) mol·dm^?3. Limits of detection were 8·10^?7, 8·10^?7, and 2·10^?6 mol·dm^?3, respectively. The best results were obtained employing CPE containing carbon paste with 50% (m/m) of SWNT, a linear dynamic range being 4·10^?7–1·10^?4 mol·dm^?3 and a limit of detection 2·10^?7 mol·dm^?3. The attempt to increase the sensitivity by adsorptive accumulation of epinephrine was not successful.     

Carbon Paste Electrode Modified with Functionalized Nanoporous Silica Gel as a New Sensor for Determination of Silver Ion

A new dipyridyl‐functionalized silica gel (DPSG) was synthesized. The potentiometric response of silver ion was investigated at a carbon paste electrode chemically modified with functionalized nanoporous silica gel. The electrodes with a DPSG proportions of 10.1% (w/w), showed very stable potential. Calibration plots with Nernstian slopes for Ag⁺ were observed, 58.7 (±0.9) mV decade^?1, over a wide linear range of concentration (5.0×10^?7 to 1.0×10^?1 M). The electrode has a detection limit of 1.0×10^?7 M. The selectivity coefficients measured by the match potential method in acetate buffer, pH 5.5, were investigated. The electrode has fast response time, high performance, high sensitivity in wide cation activity ranges, and good long term stability (more than 6 months). The method was satisfactory and used to determine the concentration of silver ion in waste waters contaminated by this metal.     

Flow Injection Analysis of Maleic Hydrazide Using an Electrochemical Sensor Based on Palladium‐Dispersed Carbon Paste Electrode

A new analytical methodology for the electrochemical detection of the herbicide maleic hydrazide (3,6‐dihydroxypyridazine) by flow injection analysis is presented. This method is supported by the novel application of a palladium‐dispersed carbon paste electrode as an amperometric sensor for this herbicide. Maleic hydrazide shows anodic electrochemical activity on carbon‐based electrodes (glassy carbon or carbon paste electrodes) in all the pH range. This electrochemical activity is enhanced using metal‐dispersed carbon paste electrodes, especially at Pd‐dispersed CPE which displays good oxidation signals at 690 mV (0.050 M phosphate buffer pH 7.0), 140 mV lower than at unmodified electrodes. Under the optimized conditions, the electroanalytical performance of Pd‐dispersed CPE in flow injection analysis was excellent, with good reproducibility (RSD 3.3%) and a wide linear range (1.9×10^?7 to 1.0×10^?4 mol L^?1). A detection limit of 1.4×10^?8 mol L^?1 (0.14 ng maleic hydrazide) was obtained for a sample loop of 100 μL at a fixed potential of 700 mV in 0.050 M phosphate buffer solution at pH 7.0 and a flow rate of 2.0 mL min^?1. The proposed method was applied for the maleic hydrazide detection in natural drinking water samples.     

A Novel Screen-Printed and Carbon Paste Electrodes for Potentiometric Determination of Uranyl(II) Ion in Spiked Water Samples

Four new ion-selective electrodes (ISEs) based on poly-(1-4)-2-amino-2-deoxy-β-D-glucan (chitosan) ionophore were constructed for determination of uranyl ion (UO₂(II)) over wide concentration ranges. The linear concentration range for carbon paste electrodes (CPEs) was 1 × 10^–6–1 × 10^–2 mol/L with a detection limit of 1 × 10^–6 mol/L and that for the screen-printed electrode (SPEs) was 1 × 10^–5–1 × 10^–1 mol/L with a detection limit of 8 × 10^–6 mol/L. The slopes of the calibration graphs were 29.90 ± 0.40 and 29.10 ± 0.60 mV/decade for CPEs with dibutylphthalate (DBP) (electrode I) and o-nitrophenyloctylether (o-NPOE) (electrode II) as plasticizers, respectively. Also, the SPEs showed good potentiometric slopes of 29.70 ± 0.30 and 28.20 ± 1.20 mV/decade with DBP (electrode III) and o-NPOE (electrode IV), respectively. The electrodes showed stable and reproducible potential over a period of 54, 62, 101 and 115 days for electrodes I, II, III, and IV, respectively. The electrodes manifested advantages of low resistance, very fast response and, most importantly, good selectivities relative to a wide variety of other cations except Ce(III) ion which interfere seriously. The results obtained compared well with those obtained using atomic absorption spectrometry.     

Ordered Mesoporous Carbon Paste Electrodes for Electrochemical Sensing and Biosensing

Surface 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.     

Catalytic Effect on Silver Electrodeposition of Gold Deposited on Carbon Electrodes

A new methodology, based on silver electrocatalytic deposition and designed to quantify gold deposited onto carbon paste electrode (CPE) and glassy carbon electrode (GCE), has been developed in this work. Silver (prepared in 1.0 M NH₃) electrodeposition at ?0.13 V occurs only when gold is previously deposited at an adequate potential on the electrode surface for a fixed period of time. When a CPE is used as working electrode, an adequate oxidation of gold is necessary. This oxidation is carried out in both 0.1 M NaOH and 0.1 M H₂SO₄ at oxidation potentials. When a GCE is used as working electrode, the oxidation steps are not necessary. Moreover, a cleaning step in KCN, which removes gold from electrode surface, is included. To obtain reproducibility in the analytical signal, the surface of the electrodes must be suitably pretreated; this electrodic pretreatment depends on the kind of electrode used as working electrode. Low detection limits (5.0×10^?10 M) for short gold deposition times (10 min for CPE and 5 min for GCE) were achieved with this novel methodology. Finally, sodium aurothiomalate can be quantified using silver electrocatalytic deposition and GCE as working electrode. Good linear relationship between silver anodic stripping peak and aurothiomalate concentration was found from 5.0×10^?10 M to 1.0×10^?8 M.     

Determination of Sulfide by Hematoxylin Multiwalled Carbon Nanotubes Modified Carbon Paste Electrode

This study investigates a new approach for the amperometric determination of sulfide using a hematoxylin multiwalled carbon nanotubes modified carbon paste electrode (HM‐MWCNTs/CPE). The experimental results show that HM‐MWCNTs/CPE significantly enhances the electrocatalytic activity towards sulfide oxidation. Cyclic voltammetric studies show that the peak potential of sulfide shifted from +400 mV at unmodified CPE to +175 mV at HM‐MWCNTs/CPE. The currents obtained from amperometric measurements at optimum conditions were linearly correlated with the concentration of sulfide. The calibration curve was obtained for sulfide concentrations in the range of 0.5–150×10^?6 mol L^?1. The detection limit was found to be 0.2×10^?6 mol L^?1 for the amperometric method. The proposed method was successfully applied to a river water sample in Pardubice, Czech Republic.     

Cyclodextrin Modified Carbon Paste Based Electrodes as Sensors for the Determination of Carcinogenic Polycyclic Aromatic Amines

Voltammetric properties and possibility of the determination of carcinogenic aminoderivatives of polycyclic aromatic hydrocarbons, namely 1‐ and 2‐aminonaphthalene and 2‐aminobiphenyl, have been investigated. Carbon paste electrodes (CPE) modified with monomeric α‐, β‐ or γ‐cyclodextrin and carbon‐based screen‐printed electrodes (SPE) surface‐modified with a thin film of β‐cyclodextrin (β‐CDP) or carboxymethylated β‐cyclodextrin (β‐CDPA) condensation polymer were used for that purpose as simple electrochemical biosensors. Analytical procedure for the DPV determination of tested amines using these biosensors was proposed. Linear calibration plots within the concentration range of 2×10^?8 – 2×10^?7 mol dm^?3 and 2×10^?7–1×10^?6 mol dm^?3 with limits of quantification of the order of 10^?9 mol dm^?3 were obtained for the modified CPE and modified SPE.     

Enzymatic Biosensors Based on Carbon Nanotubes Paste Electrodes

The performance of enzymatic biosensors based on the immobilization of different enzymes within a carbon nanotubes paste electrode (CNTPE) prepared by dispersion of multi‐wall carbon nanotubes (MWNT) and mineral oil is reported in this work. The strong electrocatalytic activity of carbon nanotubes towards the reduction of hydrogen peroxide and quinones and the oxidation of NADH have allowed an effective low‐potential amperometric determination of lactate, phenols, catechols and ethanol, in connection with the incorporation of lactate oxidase, polyphenol oxidase and alcohol dehydrogenase/NAD⁺, respectively, within the composite matrix. Compared to the analogous enzymatic CPEs, a great enhancement in the response is observed at the enzymatic CNTPEs. Therefore, highly sensitive lactate, phenols, catechols and alcohols biosensors without using any metal or redox mediator can be obtained with this new composite material.     

High‐Selective Tramadol Sensor Based on Modified Molecularly Imprinted Polymer?Carbon Paste Electrode with Multiwalled Carbon Nanotubes

We report here a novel carbon paste electrode (CPE) which is able to quantitatively sense tramadol under physiological conditions without sample preparation step. The selectivity of CPE is modified by applying molecularly imprinted polymer (MIP) technology. Multiwalled carbon nanotubes (MWCNTs) are incorporated in the structure of CPE to improve the conductivity and the ion‐to‐electron transduction. The electrode shows a wide dynamic linear range for tramadol from 10^?7 to 10^?3 M. The observed limit of detection and % RSD are 5×10^?7 M and 1.8 %, respectively. Finally, the proposed method is applied to determine tramadol in urine and medicinal tablets.     

Nanocarbon Paste Electrodes

The electrochemical behaviour of carbon paste electrodes prepared using nanocarbon and mineral oil was investigated and the results contrasted with different carbon and carbon pastes electrodes. The composition of carbon paste was studied by performing cyclic voltammetry performed in 0.1 M KCl solution in the presence of 4.0 mM Ru(NH₃)₆Cl₃, a well‐characterized redox system commonly used to test the electrode behaviour. After optimisation of the paste composition, the sensors chosen were tested for the analysis and characterization of three different systems: Ru(NH₃)₆^3+/2+, FcCH₂OH/FcCH₂OH⁺ and acetaminophen. The ability to obtain high quality voltammetry from the nanocarbon electrode was demonstrated and simulation of the voltammetry allowed the extraction of electrode kinetic parameters with high precision.     

Electrochemiluminescent Detection Method for Glyphosate in Soybean on Carbon Fiber-ionic Liquid Paste Electrode

A carbon fiber paste electrode using ionic liquid as the binder (CFILE) was fabricated. The electrochemical characteristics of the electrode was examined in ferro‐/ferricyanide solution and showed better conductivity and reversibility when compared with graphite paste‐ionic liquid electrode (GPILE) and a little better than that on the carbon nanotube paste‐ionic liquid electrode (CNTILE). Glyphosate (GLY), a pesticide, exhibited excellent catalysis to the oxidation of Ru(bpy)²⁺₃ on CFILE and brought an obvious enhancement to the electrochemiluminescence (ECL) intensity of Ru(bpy)²⁺₃. Based on the catalytic ability of GLY, a simple ECL method for GLY detection had been established. Under optimum conditions, the enhanced ECL intensities were found to had linearly respond to the GLY concentration between 3.0×10^?7 and 3.0×10^?5 mol/L, and the detection limit (S/N=3) was 2.0×10^?7 mol/L. The electrode also showed excellent sensitivity in detecting GLY‐spiked soybean samples. The linear range for GLY in soybean samples was 1.0×10^?6–4.0×10^?5 mol/L and the detection limit was 5.0×10^?7 mol/L, equal to 8.45 µg GLY in per gram of soybean. The detection limit in soybean sample was lower than the USA, EU regulation and so on. If the method is coupled with the separation technology, it can be applied to detect the GLY in the contaminated samples.