Electrochemical Detection of Epinephrine Using an L-Glutamic Acid Functionalized Graphene Modified Electrode

The development and application of an L-glutamic acid functionalized graphene nanocomposite, modified glassy carbon electrode are reported for the determination of epinephrine. The properties of the nanocomposite were characterized by scanning electron microscopy, ultraviolet-visible absorption spectroscopy, infrared spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. The modified electrode had high sensitivity and strongly catalytic activity for the detection of epinephrine. A linear relationship between the epinephrine concentration and the current response was obtained in the range of 1 × 10^?7 M to 1 × 10^?3 M by differential pulse voltammetry with a limit of detection of 3 × 10^?8 M. The modified electrode was employed to determine epinephrine in urine with satisfactory results.     

Synergistic Effect of Graphene and Multiwalled Carbon Nanotubes on a Glassy Carbon Electrode for Simultaneous Determination of Uric Acid and Dopamine in the Presence of Ascorbic Acid

A poly(diallyldimethylammonium chloride)-graphene-multiwalled carbon nanotube modified glassy carbon electrode was fabricated and evaluated by cyclic voltammetry and differential pulse voltammetry. The modified electrode offered high sensitivity, selectivity, excellent long-term stability, and electrocatalytic activity for uric acid and dopamine. This sensor showed wide linear dynamic ranges of 5.0 to 350.0 µmol L^?1 for uric acid and 10.0 to 400.0 µmol L^?1 for dopamine in the presence of 500 µmol L^?1 ascorbic acid. The limits of detection were 0.13 for uric acid and 0.55 µmol L^?1 for dopamine. This functionalized electrode has potential application in bioanalysis and biomedicine.     

Stripping voltammetry method for determination of manganese as complex with oxine at the carbon paste electrode with and without modification with montmorillonite clay

Oxine (8-hydroxyquinoline) was used as an efficient and selective ligand for stripping voltammetry trace determination of Mn(II). A validated square-wave adsorptive cathodic stripping voltammetry method has been developed for determination of Mn(II) selectively as oxine complex using both the bare carbon paste electrode (CPE) and the modified CPE with 7 % (w/w) montmorillonite-Na clay. Modification of carbon paste with montmorillonite clay was found to greatly enhance its adsorption capacity. Limits of detection of 45 ng l^?1 (8.19?×?10^?10 mol L^?1) and 1.8 ng l^?1 (3.28?×?10^?11 mol L^?1) Mn(II) were achieved using the bare and modified CP electrodes, respectively. The achieved limits of detection of Mn(II) as oxine complex using the modified CPE are much sensitive than the detection limits obtained by most of the reported electrochemical methods. The developed stripping voltammetry method using both electrodes was successfully applied for trace determination of Mn(II) in various water samples without interferences from various organic and inorganic species.     

Evaluation of a Multi-Walled Carbon Nanotube-Hemin Composite for the Voltammetric Determination of Hydrogen Peroxide in Dental Products

A simple, low cost sensor was developed for the voltammetric determination of hydrogen peroxide in mouthwash and dental whitening gel based on multi-walled carbon nanotubes incorporated with hemin. The sensor showed electrocatalytic activity toward the reduction of hydrogen peroxide in 0.05 mol L^?1 Tris-HCl buffer solution (pH 7.0) using cyclic voltammetry. The optimum composition of paste was 20:10:70% (m/m/m) (multi-walled carbon nanotubes:hemin:mineral oil). A linear plot of the square root of scan rate vs. cathodic peak current showed that reduction of hydrogen peroxide is diffusion controlled. Using linear sweep voltammetry, the analytical curve ranged from 0.2 up to 1.4 mmol L^?1 (r = 0.9996) with a sensitivity of 3.62 × 10^?2 mA mol^?1 L. The limits of detection and quantification were found to be 12.5 µmol L^?1 and 41.7 µmol L^?1, respectively. The developed method was applied for hydrogen peroxide determination in dental formulations. The results were compared with a volumetric method as a reference technique. No significant differences at the 95% level (paired student t test) were observed, thus demonstrating the accuracy of the sensor for the analysis of real samples.     

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.     

Electrochemical Study of Interaction Between Clozapine and DNA and Its Analytical Application

Abstract

The interaction between clozapine (CLZ) as an orally administrated antipsychotic drug with double stranded calf thymus DNA (dsDNA) was investigated at electrode surface using differential pulse voltammetry (DPV). Activated carbon paste electrode (CPE) was modified with dsDNA and used for monitoring the changes of the characteristics peak of CLZ in 0.05 M acetate buffer (pH 4.3). The adsorptive stripping voltammetry on dsDNA‐modified carbon paste electrode (dsDNA‐CPE) was used for determination of very low concentration of CLZ. Under optimal conditions, the oxidation peak current is proportional to CLZ concentration in the range of 7×10^?9?1.2×10^?6 mol l^?1 with a detection limit of 1.5×10^?9 mol l^?1 for 180 s accumulation time by DPV. The proposed dsDNA‐CPE was successfully used for determination of CLZ in human serum samples with recovery of 97.0±2.5%.     

High Sensitive Sensor Based on Carbon Nanotube Electrode for Determination of Lanthanum in the Presence of Calcon Carboxylic Acid

In this paper we have investigated the electrochemical activity of lanthanum chloride (La (III)) in the presence of calcon carboxylic acid (CCA) using a multi-walled carbon nano tube/carbon paste electrode (CNT/CPE). The peak current increases linearly with increasing of the La (III) concentration. For this purpose, a few electrochemical methods such as cyclic, differential pulse voltammetry, linear sweep and hydrodynamic voltammetry, and chronoamperometry were used. The results show that calcon carboxylic acid as a ligand was useful for determination of La (III) and was able to improve its sensitivity. Cyclic voltammetry was used for study of reduction reaction of La (III) at the surface of modified electrode. The electrochemical parameters for La (III) at the surface of CNT/CPE, such as diffusion coefficient (D/ cm² s ^?1 = 5.26 × 10^?6), the electron transfer coefficient, (α = 0. 43), and the reduction rate constant, (k/ M s^?1 = 2.33 (±0.015) × 10²), were determined using voltammetry methods, which with the detection limit of La (III) by differential pulse voltammetry was found to be 1.3 nM. The combination of CCA with CNT as mediators in carbon paste electrode showed that this electrode is capable, sensitive, and simple to quantify La (III) in real samples with an average recovery of 97.64%.     

Electrocatalytic Oxidation of Sulfite on a Cobalt Pentacyanonitrosylferrate Film Modified Glassy Carbon Electrode

The electrocatalytic oxidation of sulfite has been studied on the cobalt pentacyanonitrosylferrate modified glassy carbon electrode (CoPCNF). The CoPCNF films on the glassy carbon electrodes show an excellent electrocatalytic activity toward the oxidation of sulfite in 0.5 M KNO₃. The kinetics of the catalytic reaction was investigated by using cyclic voltammetry, rotating disk electrode (RDE) voltammetry and chronoamperometry. The average value of the rate constant, K, for the catalytic reaction and the diffusion coefficient, D, were evaluated by different approaches for sulfite and found to be 2.9×10² M^?1s^?1 and 4.6×10^?6 cm²s^?1, respectively. At a fixed potential under hydrodynamic conditions (stirred solutions), the oxidation current is proportional to the sulfite concentration and the calibration plot was linear over the concentration range 5×10^?6–1×10^?4 M. The detection limit of the method is 3×10^?6 M., low enough for the trace sulfite determination.     

Alizarin-modified sulfonate carbon nanoparticles in vanadium sensing

The adsorption processes of alizarin onto hydrophilic carbon nanoparticles (Emperor 2000?) are investigated. The significant increase in voltammetric responses for pre-adsorbed alizarin compared with those for solution confirms high affinity of alizarin to carbon nanoparticles (possibly due to π–π stacking interaction between aromatic rings of alizarin and surface-sulfonated carbon nanoparticles). To obtain the optimum of adsorption conditions, the effects of pH, agitation rate, and adsorption time are investigated. Under square wave voltammetry conditions, the peak current for the reduction of alizarin shows a linear relationship with concentration in the range from 2.0 to 10.0 nM. The limit of detection is estimated 5.8?×?10^?9 mol L^?1. Next, alizarin is applied as a receptor for sensing of trace vanadium in acetate buffer pH 5. Linear calibration curves are obtained for vanadium in the range of 1.0?×?10^?6 to 1.0?×?10^?4 mol L^?1 and the limit of detection is estimated 9.6?×?10^?8 mol L^?1. Determination of vanadium in real samples such as sea and tap water is demonstrated.     

A novel method for D-arabinitol determination based on a nano-structured sensing film by one-step electrodeposition

Copper nanoparticles (Cu-NPs) were incorporated into chitosan hydrogel to form a film on the surface of a glassy carbon electrode (GCE) leading to a sensing element for D-arabinitol with excellent oxidative catalytic activity. The electrochemical response to D-arabinitol was studied by cyclic voltammetry and differential pulse voltammetry. Operational parameters affecting the response were examined and optimized, and a simple and sensitive method was established for the determination of D-arabinitol. Response is linear in the concentration range from 10 μmol·L^?1 to 10 mmol·L^?1, and the limit of detection is 1.0 μmol·L^?1. The method may be combined with separation techniques in order to analyze for the ratio of D- and L-arabinitol which is a diagnostic marker for candidiasis.     

Self-assembling of Prussian blue nanocubic particles on nanoporous glassy carbon and its use in the electrocatalytic reduction of hydrogen peroxide

In this paper, self-assembled Prussian blue nanocubic particles on nanoporous glassy carbon was developed. The morphology of the PBNP-modified porous glassy carbon was characterized by scanning electron microscopy. The PBNP-GCE-red film-modified electrode was used for the sensitive detection of hydrogen peroxide. The electrochemical behavior of the resulting sensor was investigated using cyclic voltammetry and chronoamperometry. The value of α, k _cat, and D was calculated as 0.35, 1.7 × 10⁵ cm³ mol^?1 s^?1, and 2.6 × 10^?5 cm² s^?1, respectively. The calibration curve for hydrogen peroxide determination was linear over 0–600 μM with a detection limit (S/N = 3) of 0.51 μM.     

Electrodeposition of zinc oxide nanoparticles on multiwalled carbon nanotube-modified electrode for determination of caffeine in wastewater effluent

We report on the development of an electrochemical sensor based on electrodepositing zinc oxide on multiwalled carbon nanotube-modified glassy carbon electrode for the detection of caffeine in pharmaceutical wastewater effluents. The measurements were carried out using cyclic voltammetry, electrochemical impedance spectroscopy, chronoamperometry and differential pulse voltammetry (DPV). DPV measurements showed a linear relationship between oxidation peak current and concentration of caffeine in 0.1 M HClO₄ (pH 1.0) over the concentration range 0.00388–4.85 mg/L and a detection limit of 0.00194 mg/L. The diffusion coefficient and Langmuir adsorption constant for caffeine were calculated to be 3.25 × 10^?6 cm² s^?1 and 1.10 × 10³ M^?1, respectively. The sensor showed satisfactory results when applied to the detection of caffeine in wastewater effluents.     

Electrochemical sensor for detection of imipramine antidepressant at low potential based on oxidized carbon nanotubes,ferrocenecarboxylic acid,and cyclodextrin: application in psychotropic drugs and urine samples

Imipramine (IMP), a tricyclic antidepressant drug, is commonly prescribed for treatment of psychiatric patients suffering from different forms of depression. The appropriate amount of drug intake is crucial to ensure the optimum therapeutic effects minimizing severe collateral effects and toxicity. Therefore, the monitoring of imipramine is essential for its clinical applications. Herein, we report an electrochemical sensor based on a composite of ferrocenecarboxylic acid (FCA), β-cyclodextrin (CD), and oxidized multi-walled carbon nanotubes (f-CNT) modified glassy carbon electrode for detection of IMP at low potential. The electrochemical behavior of the proposed sensor was characterized by scanning electron microscopy, Raman spectroscopy, and cyclic voltammetry. The results show that imipramine determination using the proposed sensor occurs around 0 V vs Ag/AgCl in phosphate buffer pH 7.0. The calibration curves were obtained by cyclic voltammetry and differential pulse voltammetry, with linear ranges of 10 to 350 μmol L^?1 and 0.1 to 10 μmol L^?1, respectively. A detection limit of 0.03 μmol L^?1 was obtained for the detection of IMP. The sensor was applied for IMP determination in psychotropic drugs and urine samples and the results show a recovery percentage between 99 and 101% for the analyte.     

Development of a facile sensor for the determination of Brilliant Blue FCF in beverages

A facile method was developed for the detection of Brilliant Blue FCF (BB FCF) (E133), a synthetic soluble colorant in common beverages. The method is based on a new composite of multi-walled carbon nanotube (MWCNT)-graphite oxide (GO)-room temperature ionic liquids (MWCNT/GO-RTIL) of 1-butyl-3-methylimidazolium hexafluorophosphate with high dispersibility and strong conductivity. Differential pulse stripping voltammetry (DPSV) and the MWCNT/GO-RTIL composite-modified glassy carbon electrode (GCE) were used to determine the BB FCF in this work. Under the optimum experimental conditions, the oxidation current of BB FCF was proportional to its concentration in two linear ranges, from 6.34 μg kg^?1 to 7.93 × 10² μg kg^?1 and 7.93 × 10² μg kg^?1 to 7.93 × 10³ μg kg^?1.

The detection limit was down to 3.01 μg kg^?1 at signal-to-noise ratio of 3. Also, this method has been successfully applied in the determination of BB FCF in common beverage samples, including RIO cocktail, Bacardi Breezer and Reinnbow rum dinks. The assay results of BB FCF in drink samples obtained by the proposed method were in a good agreement with the reference values detected by high performance liquid chromatography (HPLC). The proposed method provided a useful tool for the assay of BB FCF in drink samples.     

Electrochemical Behavior of Hydrogen Peroxide at a Glassy Carbon Electrode Modified with Nickel Hydroxide–Decorated Multiwalled Carbon Nanotubes

Abstract

The multiwalled carbon nanotube–nickel hydroxide composite film used to modify glassy carbon electrode was prepared and confirmed by transmission electron microscopy and cyclic voltammetry. The process and mechanism of film formation were discussed in detail. The electrode modified with the composite film exhibited good catalytic activity toward electrochemical oxidation of hydrogen peroxide in 0.1 mol/L sodium hydroxide solution. Various factors affecting the electrocatalytic activity of nickel hydroxide film were investigated. The anodic peak current increased with the increased concentration of hydrogen peroxide. The linear range for the determination of hydrogen peroxide was from 1.5 × 10^?6 mol/L to 2.5 × 10^?3 mol/L with the detection limit 6.1 × 10^?7 mol/L (S/N = 3). And the proposed method was applied to the determination of hydrogen peroxide in disinfector with higher sensitivity and lower detection limit.     

Determination of Tyrosine in the Presence of Sodium Dodecyl Sulfate Using a Gold Nanoparticle Modified Carbon Paste Electrode

A carbon paste electrode modified with gold nanoparticles (AuMCPE) was used as a highly sensitive sensor for determination of Tyrosine (Tyr), in the presence of an anionic surfactant, sodium dodecyl sulfate (SDS), in aqueous solution. The measurements were carried out by using of differential pulse voltammetry (DPV), cyclic voltammetry (CV), amd chronocoulometry and chronoamperometry methods. The prepared electrode shows voltammetric responses with high sensitivity and selectivity for Tyr in the presence of SDS. The relationship between the oxidation peak current of Tyr and its concentration was obtained linearly and it was 1.0 × 10^?7 to 1.0 × 10^?5 M with a detection limit of 5.5 × 10^?8 M in the absence of SDS. On the other hand the oxidation peak current of Tyr increased significantly at AuMCPE in the presence of SDS and its detection limit was reduced to 2.7 × 10^?9 M. The proposed voltammetric approach was also applied to the determination of Tyr concentration in human serum.     

Electrocatalytic oxidation of methanol by ZSM-5 nanozeolite-modified carbon paste electrode in alkaline medium

Development of a novel modified electrode for electrocatalytic oxidation of methanol in order to decrease overvoltage is importance. In this paper, carbon paste electrode (CPE) was modified by ZSM-5 nanozeolite. The average diameter of used nanozeolite was 97 nm. Ni²⁺ ions were incorporated to the nanozeolite by immersion of the modified electrode in a 0.1 M nickel chloride solution. Then, electrochemical studies of this electrode were performed by using cyclic voltammetry(CV) in alkaline medium. This modified electrode was used as an anode for the electrocatalytic oxidation of methanol in 0.1 M of NaOH solution. The obtained data demonstrated that ZSM-5 nanozeolite at the surface of CPE improves catalytic efficiency of the dispersed nickel ions toward methanol oxidation. The values of electron transfer coefficient, charge-transfer rate constant, and the electrode surface coverage are obtained 0.61, 0.2342 s^?1, and 4.33 × 10^?8 mol cm^?2, respectively. Also, the mean value of catalytic rate constant between the methanol and redox sites of electrode and diffusion coefficient were found to be 2.54 × 10⁴ cm³ mol^?1 s^?1 and 1.85 × 10^?8 cm² s^?1, respectively. Obtained results from both CV and chronoamperometric techniques indicated that the electrode reaction is a diffusion-controlled process.     

Direct electrochemical behavior of cytochrome c, and its determination on phytic acid modified electrode

Phytic acid (PA) with its unique structure was attached to a glassy carbon electrode (GCE) to form PA/GCE modified electrode which was characterized by electrochemical impedance. The electrochemical behavior of cytochrome c (Cyt c) on the PA/GCE modified electrode was explored by cyclic voltammetry and differential pulse voltammetry. The Cyt c displayed a quasi-reversible redox process on PA modified electrode pH 7.0 phosphate buffer solution with a formal potential (E ^0′) of 57 mV (versus Ag/AgCl). The peak currents were linearly related to the square root of the scan rate in the range of 20–120 mV·s^?1. The electron transfer rate constant was determined to be 12.5 s^?1. The PA/GCE modified electrode was applied to the determination of Cyt c, in the range of 5?×?10^?6 to 3?×?10^?4 M, the currents increase linearly to the Cyt c concentration with a correlation coefficient 0.9981. The detection limit was 1?×?10^?6 M (signal/noise?=?3).     

Sandwich Immunoassay for Hepatitis C Virus Non-Structural 5A Protein Using a Glassy Carbon Electrode Modified with an Au-MoO3/Chitosan Nanocomposite

A novel electrochemical immunosensor was prepared for the detection of the hepatitis C virus non-structural 5A protein. A glassy carbon electrode was modified with an Au-MoO₃/Chitosan nanocomposite that warranted good conductivity and biocompatibility. Mesoporous silica with a large specific surface served as a nanocarrier for horseradish peroxidase and the polyclonal antibody as the reporter probe. The immunosensor was characterized by scanning electron microscopy, electrochemical impedance spectroscopy, and cyclic voltammetry. Following the sandwich-type immunoreaction, horseradish peroxidase was efficiently captured on the surface of the electrode to catalyze the decomposition of hydrogen peroxide. The analytical signal was obtained as an amperometric i-t curve (chronoamperometry). The assay reported here had a wide detection range (1 ng mL^?1 ?50 µg mL^?1) and detection limit as low as 1 ng mL^?1 of hepatitis C virus non-structural 5A protein. The electrochemical biosensor experiments showed excellent reproducibility, high selectivity, and outstanding stability for the determination of hepatitis C virus non-structural 5A protein, and it was successfully applied to the detection of the analyte in real serum samples.     

Application of a sensitive nanocomposite-based electrochemical sensor for voltammetric determination of dicyclomine hydrochloride in real samples

In the present study a glassy carbon electrode, modified with nanocomposite of gold nanoparticles/multiwalled carbon nanotubes (GNPs/MWCNTs/GCE), was used for determination of dicyclomine hydrochloride (DcCl). The results showed that synergetic effects of GNPs and MWCNTs highly improved electrochemical response and sensitivity of the sensor. The electrochemical oxidation of DcCl was investigated by cyclic voltammetry and differential pulse voltammetry. Also, scanning electron microscopy and energy dispersive x-ray spectroscopy were used to evaluate microstructure of electrochemical sensor. The effect of various experimental parameters including pH and scan rate on the voltammetric response of DcCl were investigated. Under the optimal conditions linear response was observed in range of 1.0–1.2 × 10² µmol L^?1 for DcCl. The lower detection limit was found to be 0.40 µmol L^?1 for DcCl. The investigated method showed good stability, reproducibility and repeatability. The proposed sensor was successfully applied to the determination of DcCl in real samples.