MWCNT-modified Glassy Carbon Electrode Research Articles

Highly sensitive determination of tetracycline in chicken meat and eggs using AuNP/ MWCNT-modified glassy carbon electrodes

Glassy carbon electrodes (GCE) were modified with gold nanoparticles (AuNPs) and multi-walled carbon nanotubes (MWCNTs) by means of sputtering and electrodeposition. The electrodeposited MWCNT on gold coated GCE exhibited the optimum performance as characterized using cyclic voltammetry. The limit of detection and limit of quantitation were found to be 42 ppb and 139 ppb, respectively. The modified electrode was used as working electrode in differential pulse voltammetry to detect tetracycline (TET) residues in the eggs, wings, liver, breast, and thigh, of organic as well as non-organic chicken bought from a local supermarket. The highest concentration in the eggs, wings, liver, breast, and thigh were found to be 5.9 ppm, 2.0 ppm, 1.4 ppm, 1.3 ppm, and 1.2 ppm for organic chicken and 8.70 ppm, 4.8 ppm, 4.3 ppm, 3.3 ppm, and 2.7 ppm for the corresponding parts in non-organic chicken, respectively. The obtained concentrations were remarkably greater compared to the maximum residual limit released by the Codex Alimentarius Commission.

Sensitive and selective molecularly imprinted electrochemical sensor based on multi-walled carbon nanotubes for doxycycline hyclate determination

An electrochemical sensor for doxycycline hyclate (DC) detection with high sensitivity and good selectivity is reported. The sensor was fabricated by electro-polymerization of molecularly imprinted polymers (MIPs) in the presence of DC onto multi-walled carbon nanotubes modified glassy carbon electrode (MWCNTs/GCE). The MWCNTs can significantly increase the current response of the sensor, leading to enhanced sensitivity. The MIPs provide selective recognition sites for DC detection. The experimental parameters, such as the polymer monomer concentration, supporting electrolyte pH, the time for electro-polymerization and the incubation time of the sensor with DC were optimized. Under optimized experimental conditions, the sensor displayed a linear range of 0.05 μmol/L–0.5 μmol/L towards DC detection, with the detection limit of 1.3 × 10−2 μmol/L. The sensor was successfully applied for recovery test of DC in human serum samples.

Enhanced Sensing of 4-Nitroso-N,N–Dimethyl Aniline using Multi-Walled Carbon Nano Tube Modified Glassy Carbon Electrode

The voltammetric behaviour of 4-nitroso-N,N–dimethylaniline (4-NDMA) was investigated on plain glassy carbon electrode (GCE) and multi-walled carbon nanotube modified GCE (MWCNT/GCE) using cyclic voltammetry. Effects of pH, scan rate and concentration were studied. The surface morphology of the modified electrode in the absence and presence of 4-NDMA molecules was characterized by atomic force microscope (AFM). A systematic study on the variation of experimental parameters with differential pulse stripping voltammetry (DPSV) was carried out and the optimized experimental conditions were arrived. MWCNT/GCE performed well compared with the plain GCE system and the limit of detection (LOD) was found to be 7.5 ng/mL 0.1056 ng/mL for 4-NDMA on plain GCE and MWCNT/GCE respectively.

Role of Au(NPs) in the enhanced response of Au(NPs)-decorated MWCNT electrochemical biosensor.

BackgroundThe combination of Au-metallic-NPs and CNTs are a new class of hybrid nanomaterials for the development of electrochemical biosensor. Concentration of Au(nanoparticles [NPs]) in the electrochemical biosensor is crucial for the efficient charge transfer between the Au-NPs-MWCNTs modified electrode and electrolytic solution.MethodsIn this work, the charge transfer kinetics in the glassy carbon electrode (GCE) modified with Au(NPs)–multiwalled carbon nanotube (MWCNT) nanohybrid with varied concentrations of Au(NPs) in the range 40–100 nM was studied using electrochemical impedance spectroscopy (EIS). Field emission scanning electron microscopy and transmission electron microscopy confirmed the attachment of Au(NPs) on the surface of MWCNTs.ResultsThe cyclic voltammetry and EIS results showed that the charge transfer mechanism was diffusion controlled and the rate of charge transfer was dependent on the concentration of Au(NPs) in the nanohybrid. The formation of spherical diffusion zone, which was dependent on the concentration of Au(NPs) in nanohybrids, was attributed to result in 3 times the increase in the charge transfer rate ks, 5 times increase in mass transfer, and 5% (9%) increase in Ipa (Ipc) observed in cyclic voltammetry in 80 nM Au(NP) nanohybrid-modified GCE from MWCNT-modified GCE. The work was extended to probe the effect of charge transfer rates at various concentrations of Au(NPs) in the nanohybrid-modified electrodes in the presence of Escherichia coli. The cyclic voltammetry results clearly showed the best results for 80 nM Au(NPs) in nanohybrid electrode.ConclusionThe present study suggested that the formation of spherical diffusion zone in nanohybrid-modified electrodes is critical for the enhanced electrochemical biosensing applications.

Sensitive warfarin sensor based on cobalt oxide nanoparticles electrodeposited at multi-walled carbon nanotubes modified glassy carbon electrode (CoxOyNPs/MWCNTs/GCE)

In this work, cobalt oxide nanoparticles were electrodeposited on multi-walled carbon nanotubes modified glassy carbon electrode (MWCNTs/GCE) to develop a new sensor for warfarin determination. The modified electrodes were characterized by cyclic voltammetry, scanning electron microscopy (SEM) along with energy dispersive x-ray spectroscopy (EDS), and electrochemical impedance spectroscopy (EIS). The presence of cobalt oxide nanoparticles on the electrode surface enhanced the warfarin accumulation and its result was the improvement in the electrochemical response. The effect of various parameters such as pH, scan rate, accumulation potential, accumulation time and pulse amplitude on the sensor response were investigated. Under optimal conditions, the differential pulse adsorptive anodic stripping voltammetric (DPASV) response of the modified electrode was linear in the ranges of 8nM to 50μM and 50μM to 800μM with correlation coefficients greater than 0.998. The limit of detection of the proposed method was 3.3nM. The proposed sensor was applied to determine warfarin in urine and plasma samples.

Electrochemical determination of food colorants in soft drinks using MWCNT-modified GCEs

Food colorants are chemicals added to foods and soft drinks during manufacturing or processing. However, some of these chemicals represent potential risks to human health, especially if they are consumed in excess. Here, we modified a glassy carbon electrode (GCE) with multi-walled carbon nanotubes (MWCNTs) using 1,3-dioxolane as a dispersant agent, resulting in a stable and reproducible electrochemical sensor. The resulting sensor was applied to study the food dyes tartrazine, sunset yellow and carmoisine, showing high sensitivity and reproducibility. The influences of the scan rate, pH, amount of MWCNTs and accumulation time were studied. Moreover, the developed method was successfully applied in the determination of colorants in commercial soft drinks and compared with a chromatographic method. The resulting concentrations were compared based on the maximum amount of soft drink that a child and an adult can consume before reaching the admissible daily intake (ADI) of each colorant.

Amperometric sensor based on carbon nanotubes and electropolymerized vanillic acid for simultaneous determination of ascorbic acid, dopamine, and uric acid

This paper describes the development of a simple and efficient nanostructured platform based on multi-walled carbon nanotubes (MWCNT) functionalized with an in situ generated vanillic acid (VA) polymer. It was used as an analytical sensor for the simultaneous determination of ascorbic acid (AA), dopamine (DA), and uric acid (UA). The electropolymerization process of VA, performed on MWCNT-modified glassy carbon electrode, produces three redox systems based on quinone/hydroquinone functionality, as observed by cyclic voltammetry. The amperometric sensor has as figures of merit for the simultaneous determination of AA, DA, and UA the following values: for AA, a linear range of 5–120 μM and detection limit of 3.5 μM; for DA, a linear range of 5–120 μM and detection limit of 4.5 μM; and for UA, a linear range of 5–120 μM and a detection limit of 1.5 μM. From the obtained performance, the development of the platform based on MWCNT/poly-VA is justified for the simultaneous determination of AA, DA, and UA.

Amperometric determination of the insecticide fipronil using batch injection analysis: comparison between unmodified and carbon-nanotube-modified electrodes

The electrochemical oxidation of fipronil is investigated on unmodified and multi-walled carbon-nanotube (MWCNT)-modified glassy carbon electrodes (GCEs), and its amperometric determination using batch injection analysis (BIA) is demonstrated. An oxidation peak was observed at 1.5 V in a 0.1 mol L−1 HClO4/acetone solution (50:50, v/v) on both surfaces. Although MWCNT-modified GCE provided greater sensitivity, the unmodified GCE showed low RSD value, wider linear range, and reduced adsorption of fipronil or its oxidized products on the electrode surface. A detection limit of 4.7 μmol L−1 and linear range of 25–300 μmol L−1 were obtained using a bare GCE. The method was applied in veterinary formulations with results in agreement with those obtained by high-performance liquid chromatography.

Chronocoulometry of wine on multi-walled carbon nanotube modified electrode: Antioxidant capacity assay

Phenolic antioxidants of wine were electrochemically oxidized on multi-walled carbon nanotubes modified glassy carbon electrode (MWNT/GCE) in phosphate buffer solution. Three oxidation peaks were observed at 0.39, 0.61 and 0.83V for red dry wine and 0.39, 0.80 and 1.18V for white dry wine, respectively, using differential pulse voltammetry at pH 4.0. The oxidation potentials for individual phenolic antioxidants confirmed the integral nature of the analytical signals for the wines examined. A one-step chronocoulometric method at 0.83 and 1.18V for red and white wines, respectively, has been developed for the evaluation of wine antioxidant capacity (AOC). The AOC is expressed in gallic acid equivalents per 1L of wine. The AOC of white wine was significantly less than red wine (386±112 vs. 1224±184, p<0.0001), as might be expected. Positive correlations were observed between gallic acid equivalent AOC of wine and total antioxidant capacity, based on coulometric titration with electrogenerated bromine (r=0.8957 at n=5 and r=0.8986 at n=4 for red and white wines, respectively).

Multidimensional voltammetry: Four-way multivariate calibration with third-order differential pulse voltammetric data for multi-analyte quantification in the presence of uncalibrated interferences

A four-way multivariate calibration approach based on the combination of differential pulse voltammetric (DPV) data and four-way algorithms is described for the first time. To achieve this goal, the DPV response of each sample was recorded thirty-six times. Six current-potential matrices were recorded at six different pulse durations. Each matrix consists of six vectors which have been recorded at six different pulse heights. The three-way data array obtained for the calibration set and for each of the test samples were joined into a single four-way data array. The recorded four-way data array was nonlinear, thus, the non-linearities were tackled by potential shift correction using correlation-optimized warping (COW) algorithm and subsequently was analyzed with unfolded-partial least squares/residual trilinearization (U-PLS/RTL) and multi-way-PLS/RTL (N-PLS/RTL) as third-order multivariate calibration algorithms. A comprehensive and systematic strategy for comparing the performance of the two algorithms was presented in this work, in particular with a view of practical applications. This comparison was developed to identify which algorithm offers the best predictions for the simultaneous determination of levodopa (LD), carbidopa (CD), methyldopa (MD), acetaminophen (AC), tramadol (TRA), lidocaine (LC), tolperisone (TOP), ofloxacin (OF), levofloxacin (LOF), and norfloxacin (NOF) in the presence of benserazide (BA), dopamine (DP), and ciprofloxacin (COF) as uncalibrated interferences using a multi-walled carbon nanotubes modified glassy carbon electrode (MWCNTs/GCE). This study demonstrated the more superiority of U-PLS/RTL to resolve the complex systems. The results of applying U-PLS/RTL for the simultaneous determination of the studied analytes in human serum samples as experimental cases were also encouraging.

Fabrication of a novel electrochemical sensor for determination of hydrogen peroxide in different fruit juice samples

A new hydrogen peroxide (H2O2) sensor is fabricated based on a multiwalled carbon nanotube-modified glassy carbon electrode (MWCNT-GCE) and reactive blue 19 (RB). The charge transfer coefficient, α, and the charge transfer rate constant, ks, of RB adsorbed on MWCNT-GCE were calculated and found to be 0.44 ± 0.01 Hz and 1.9 ± 0.05 Hz, respectively. The catalysis of the electroreduction of H2O2 by RB-MWCNT-GCE is described. The RB-MWCNT-GCE shows a dramatic increase in the peak current and a decrease in the overvoltage of H2O2 electroreduction in comparison with that seen at an RB modified GCE, MWCNT modified GCE, and activated GCE. The kinetic parameters such as α and the heterogeneous rate constant, k', for the reduction of H2O2 at RB-MWCNT-GCE surface were determined using cyclic voltammetry. The detection limit of 0.27μM and three linear calibration ranges were obtained for H2O2 determination at the RB-MWCNT-GCE surface using an amperometry method. In addition, using the newly developed sensor, H2O2 was determined in real samples with satisfactory results.

Multi-walled carbon nanotubes: Size-dependent electrochemistry of phenolic compounds

The electrochemical activity of functionalized multi-walled carbon nanotubes (MWCNTs) of different sizes (D×L: 100–170nm×5–9μm and 6–9nm×5μm, corresponding to LD- and SD-MWCNTs, respectively) towards the electro-oxidation of hydroquinone (HQ), tert-butylhydroquinone (TBHQ), catechol (CT), and dopamine (DP) was investigated. The electrochemical response for all phenolic compounds at MWCNT-modified glassy-carbon electrodes (GCEs) presented a short decrease in the overpotential of the oxidation reactions (<100mV); however, the values of ΔEp (peak-to-peak separation) were considerably reduced at the LD-MWCNT surface and even more at the SD-MWCNT-modified GCE in comparison with the unmodified GCE. This result indicates the higher electrocatalytic activity of SD-MWCNTs, which is in agreement with the nanotube diameter and the increased defect density, as revealed by XRD and Raman spectroscopic measurements, respectively. Additionally, a substantial increase (three-fold) in the current for the oxidation of HQ, TBHQ, and DP at the SD-MWCNT-modified GCE was obtained. Amperometric measurements also revealed the improved performance of SD-MWCNT-modified GCE (up to four-fold increase in sensitivity).

Fabrication of novel redox-active poly (4,5-dihydro-1,3-thiazol-2-ylsulfanyl-3-methyl-1,2-benzenediol)-gold nanoparticles film on MWCNTs modified electrode: Application as the electrochemical sensor for the determination of hydrazine

In this study, a hybrid nanocomposite consisting of a conducting polymer and gold nanoparticles (AuNPs) is fabricated on a multi-walled carbon nanotubes modified glassy carbon electrode (MWCNTs/GCE). First, dihydroxy-benzene derivative (4,5-dihydro-1,3-thiazol-2-ylsulfanyl-1,2-benzenediol) containing sulphur and nitrogen groups was electrochemically synthesized and used as a monomer. Then, a thin layer of conducting polymer is coated electrochemically on a MWCNTs/GCE and the effective parameters have been optimized. Afterward, the nano-sized AuNPs are embedded by physical adsorption from colloidal solution of AuNPs. The resultant nanocomposite modified electrode is characterized by electrochemical methods and transmission electron microscopy. Finally, the potential application of nanocomposite film modified electrode has been investigated for the electrocatalytic oxidation of hydrazine. The experimental results showed that the response of modified electrode is linear in the range of 2.0–350.0μM with detection limit (S/N=3) of 0.6μM for hydrazine.

Chemometrics: An important tool for monitoring interactions of vitamin B7 with bovine serum albumin with the aim of developing an efficient biosensing system for the analysis of protein

For the first time, interaction of vitamin B7 (VB7) with bovine serum albumin (BSA) was investigated with the aim of developing a method for the analysis of BSA. The interaction of VB7 with BSA was investigated by cyclic voltammetry (CV), linear sweep voltammetry (LSV), and differential pulse voltammetry (DPV) at a multi-walled carbon nanotubes-modified glassy carbon electrode (MWCNTs/GCE). The recorded electrochemical data was combined with UVvis and fluorescence (F) spectroscopic data into a row- and column-wise augmented matrix and resolved by multivariate curve resolution-alternating least squares (MCR-ALS) as an efficient chemometric tool, and this assisted in the further elucidation of the above interaction. Also, with aid of MCR-BANDS method, the absence of rotational ambiguity was verified in the obtained results and we confirmed that the obtained results were unambiguous and reliable. The binding of VB7 to BSA was also modeled by molecular docking methods. Excellent agreement was found between the experimental and computational results. The differences of DPV responses of VB7 in the absence and presence of BSA (ΔI) were found to be linearly related to BSA concentration between 0.5×10−9molL−1 and 35.0×10−9molL−1, and a limit of detection (LOD, 3Sb/b) of 0.22×10−9molL−1 was calculated. Finally, the DPV method was further applied to the determination of serum albumin (SA) in serum samples obtained from Holstein cows and the results were in good agreement with those obtained by a medical diagnostic laboratory whose method was based on traditional cellulose acetate electrophoresis. The MWCNTs/GCE showed enhanced electron transfer kinetics, large electroactive surface area, and was highly sensitive, selective, and stable towards SA determination. The satisfactory analytical performance of the proposed method would make it potentially advantageous for a broad range of biosensing and clinical applications.

Simultaneous determination of mycophenolate mofetil and its active metabolite, mycophenolic acid, by differential pulse voltammetry using multi-walled carbon nanotubes modified glassy carbon electrode

A highly sensitive electrochemical sensor for the simultaneous determination of mycophenolate mofetil (MPM) and mycophenolic acid (MPA) was fabricated by multi-walled carbon nanotubes modified glassy carbon electrode (MWCNTs/GCE). The electrochemical behavior of these two drugs was studied at the modified electrode using cyclic voltammetry and adsorptive differential pulse voltammetry. MPM and MPA were oxidized at the GCE during an irreversible process. DPV analysis showed two oxidation peaks at 0.87V and 1.1V vs. Ag/AgCl for MPM and an oxidation peak at 0.87V vs. Ag/AgCl for MPA in phosphate buffer solution of pH5.0. The MWCNTs/GCE displayed excellent electrochemical activities toward oxidation of MPM and MPA relative to the bare GCE. The experimental design algorithm was used for optimization of DPV parameters. The electrode represents linear responses in the range 5.0×10−6 to 1.6×10−4molL−1 and 2.5×10−6molL−1 to 6.0×10−5molL−1 for MPM and MPA, respectively. The detection limit was found to be 9.0×10−7molL−1 and 4.0×10−7molL−1 for MPM and MPA, respectively. The modified electrode showed a good sensitivity and stability. It was successfully applied to the simultaneous determination of MPM and MPA in plasma and urine samples.

Electrochemical Oxidation of Sulfamethazine on Multi-Walled Nanotube Film Coated Glassy Carbon Electrode

The electrochemical oxidation of sulfamethazine (SMZ) has been studied at a multi-walled carbon nanotubes modified glassy carbon electrode (MWCNT-GCE) by cyclic voltammetry. This modified electrode (MWCNT-GCE) exhibited excellent electrocatalytic behavior toward the oxidation of SMZ as evidenced by the enhancement of the oxidation peak current and the shift in the anodic potential to less positive values (170 mV) in comparison with the bare GCE. The formal potential, E0', of SMZ is pH dependent with a slope of 54 mV per unit of pH, close to the anticipated Nerstian value of 59 mV for a 2-electron and 2-proton oxidation process. A detailed analysis of cyclic voltammograms gave fundamental electrochemical parameters including the electroactive surface coverage (Г), the transfer coefficient (a), the heterogeneous rate constant (ks). Under the selected conditions, the peak current shows two dynamic linear ranges of 10-200 mM and 300-3000 mM with the detection limit of 6.1 mM. The method was successfully applied to analyze SMZ in serum sample

Electrooxidation of Indomethacin at Multiwalled Carbon Nanotubes-Modified GCE and Its Determination in Pharmaceutical Dosage Form and Human Biological Fluids

A simple, rapid, selective, and sensitive electrochemical method for the direct determination of indomethacin was developed. The electrochemical behavior of indomethacin was carried at multiwalled carbon nanotube- (MWCNTs-) modified glassy carbon electrode (GCE). The cyclic voltammetric results indicated that MWCNT-modified glassy carbon electrode remarkably enhanced electrocatalytic activity towards the oxidation of indomethacin in slightly acidic solutions. It led to a considerable improvement of the anodic peak current for indomethacin and could effectively accumulate at this electrode and produce two anodic peaks at 0.720 V and 0.991 V, respectively, and one reduction peak at 0.183 V. The electrocatalytic behavior was further exploited as a sensitive detection scheme for the determination of indomethacin by differential-pulse voltammetry (DPV). Under optimized conditions, the concentration range and detection limit were 0.2 to 6.0 μM and 13.2 nM, respectively. The proposed method was successfully applied to determination of Indomethacine in pharmaceutical samples. The analytical performance of this sensor has been evaluated for detection of analyte in human serum and urine as real samples.

Electro-oxidation and voltammetric determination of oxymetholone in the presence of mestanolone using glassy carbon electrode modified with carbon nanotubes

A new chemically modified electrode was constructed and applied to the electro-oxidation of the oxymetholone. Also, the electrode was applied to the simple, rapid, highly selective and sensitive determination of oxymetholone (OXM) in pharmaceutical and plasma samples using square wave voltammetry (SWV). The multi-walled carbon nanotubes modified glassy carbon electrode (MWCNT/GCE) were prepared by casting of the multi-walled carbon nanotubes (MWCNT) suspension on the glassy carbon electrode surface. The limit of detection and the linear range were found to be 1.36 and 2.00-90.00 ng mL(-1) of OXM, respectively. The effects of potentially interfering substances on the determination of this compound were investigated and found that the electrode is highly selective. The proposed modified electrode was used for the determination of OXM in human plasma and pharmaceutical samples. This reveals that MWCNT/GCE shows excellent analytical performance for the determination of OXM in terms of very low detection limit, high sensitivity, very good repeatability and reproducibility over other methods reported in literature.

Electrochemical behavior of dihydroxybenzene isomers at MWCNTs modified electrode and simultaneous determination in neutral condition

Simultaneous determination of dihydroxybenzene isomers in neutral condition was successfully realized by a simple and easy prepared modified electrode without previous chemical or physical separations. The multi-walled carbon nanotubes modified glassy carbon electrode (MWCNTs/GCE), which was prepared by the drop-coating method, was characterized by FE-SEM and TEM. Then, the electrochemical behavior of dihydroxybenzene isomers at MWCNTs/GCE was systematically studied at different temperature and pH conditions. The oxidation peak potentials were separated in neutral condition with 105 mV to hydroquinone (HQ) and catechol (CC) and 390 mV to CC and resorcinol (RS). And in neutral condition, the amperometric current were found to be linear with concentration of HQ, CC, and RS (20–140 μM) with the presence of 100 μM other isomers. Furthermore, excellent anti-interference, stability, and reproducibility were also presented by this modified electrode.

Graphene versus Multi-Walled Carbon Nanotubes for Electrochemical Glucose Biosensing.

A simple procedure was developed for the fabrication of electrochemical glucose biosensors using glucose oxidase (GOx), with graphene or multi-walled carbon nanotubes (MWCNTs). Graphene and MWCNTs were dispersed in 0.25% 3-aminopropyltriethoxysilane (APTES) and drop cast on 1% KOH-pre-treated glassy carbon electrodes (GCEs). The EDC (1-ethyl-(3-dimethylaminopropyl) carbodiimide)-activated GOx was then bound covalently on the graphene- or MWCNT-modified GCE. Both the graphene- and MWCNT-based biosensors detected the entire pathophysiological range of blood glucose in humans, 1.4–27.9 mM. However, the direct electron transfer (DET) between GOx and the modified GCE’s surface was only observed for the MWCNT-based biosensor. The MWCNT-based glucose biosensor also provided over a four-fold higher current signal than its graphene counterpart. Several interfering substances, including drug metabolites, provoked negligible interference at pathological levels for both the MWCNT- and graphene-based biosensors. However, the former was more prone to interfering substances and drug metabolites at extremely pathological concentrations than its graphene counterpart.