Voltammetric determination of captopril using a novel ferrocene-based polyamide as a mediator and multi-wall carbon nanotubes as a sensor

A modified carbon paste electrode was prepared by incorporating multi-wall carbon nanotubes with a ferrocene-based polyamide (FDADO-IPC). A mixture of fine graphite powder with 10 wt % of multi-wall carbon nanotubes was applied to the preparation of the carbon paste (by dispersing in paraffin) that was finally modified with a ferrocene polyamide complex. The electrocatalytic oxidation of captopril (CAP) was investigated on the surface of the FDADO-IPC multi-wall carbon nanotubes modified carbon paste electrode (FDADO-IPC-MCNTPE) using cyclic voltammetry (CV), differential pulse voltammetry (DPV), chronoamperometry (CHA) and chronocoloumetry (CHC). Using the modified electrode, the kinetics of CAP electrooxidation was considerably enhanced by lowering the anodic overpotential through a catalytic fashion. A linear dynamic range of 0.2–200 μM for CAP was obtained in buffered solutions at pH 7.0. The detection limit was 0.08 μM. Differential pulse voltammetry as a simple, rapid, sensitive, and selective method was developed for the determination of CAP in tablet and human urine without any treatment.     

Detection of salicylic acid by electrocatalytic oxidation at a nickel-modified glassy carbon electrode

An electrochemical biosensor for the accurate determination of salicylic acid (SA) is prepared by potentiostatic deposition of nickel on the glassy carbon electrode (GCE). The electrochemical performance of the Ni/GCE film and the parameters affecting its activity are investigated by cyclic voltammetry, amperometry and electrochemical impedance spectroscopy (EIS). The electrooxidation of SA is significantly enhanced on Ni/GCE, compared to GCE. Indeed, the modified electrode has a fast response (less than 3 s) and excellent linear behavior over a wide SA concentration range (2 μM-0.55 mM) with a detection limit (LD) of 0.5 μM (signal/noise = 3) under the optimal conditions. Moreover, the stability and the reproducibility of the biosensor are satisfactorily evaluated.     

Glassy carbon electrode modified with hemin and new melamine compounds for H<Subscript>2</Subscript>O<Subscript>2</Subscript> amperometric detection

In an attempt to increase the stability and efficiency of hemin-modified electrodes, the present work reports the preparation of a new modified glassy carbon electrode obtained by immobilization of hemin (Hm) on the electrode surface together with a new N-substituted melamine (2,4,6-triamino-1,3,5-triazine) based G-2 dendrimer comprising p-aminophenol as peripheral unit (Den) or with one of its analogues, a melamine G-0 dimer (Dim). Basic structural features, able to determine intimate relationships between Hm and Dim (or Den) at room temperature in solid state, were evidenced with the use of vibrational analysis carried out by FT-IR. This method revealed contacts between Hm and Dim or Den respectively as H-bond interactions, proton-interchange, and π-π stacking interactions. The new modified electrodes were characterized by cyclic voltammetry and electrochemical impedance spectroscopy and tested for amperometric detection of H₂O₂. In this purpose, GC/Hm-Dim electrode exhibited better catalytic properties than GC/Hm-Den electrode, but lower stability.     

A sensitive and selective nitrite sensor based on a glassy carbon electrode modified with gold nanoparticles and sulfonated graphene

We describe a highly sensitive and selective amperometric sensor for the determination of nitrite. A glassy carbon electrode was modified with a composite made from gold nanoparticles (AuNPs) and sulfonated graphene (SG). The modified electrode displays excellent electrocatalytic activity in terms of nitrite oxidation by giving much higher peak currents (at even lower oxidation overpotential) than those found for the bare electrode, the AuNPs-modified electrode, and the SG-modified electrode. The sensor has a linear response in the 10 μM to 3.96 mM concentration range, a very good detection sensitivity (45.44 μA mM^?1), and a lower detection limit of 0.2 μM of nitrite. Most common ions and many environmental organic pollutants do not interfere. The sensor was successfully applied to the determination of nitrite in water samples, and the results were found to be consistent with the values obtained by spectrophotometry.

Graphene sheet for improving the electrocatalytic activity of a benzofuran derivative modified electrode for determination of epinephrine in the presence of serotonin

A nanocomposite system based on coumarin derivative and graphene sheet was used to prepare a new electrochemical sensor. The objective of the mentioned nanocomposite was to investigate novel electrochemical properties enabling the quantification of epinephrine (Ep). Cyclic voltammetry was used to study the redox properties of the mentioned modified electrode at different scan rates. Henceforward, the electrocatalytic oxidation of Ep at the surface of the modified electrode was considered. The data has shown excellent catalytic activity of the modified electrode for the electrooxidation of Ep, which leads to a reduction of overpotential for more than 238 mV. According to differential pulse voltammetry (DPV), the oxidation of Ep showed a dynamic range between 0.1 and 1000.0 μM and the detection limit (3s) of 0.011 μM. Besides, DPV was used for the determination of Ep at the mentioned modified electrode in the presence of serotonin.     

Voltammetric determination of paracetamol at NiO nanoparticles-modified carbon paste electrode in bulk and tablet dosage forms

Nickel oxide (NiO) nanoparticles were synthesized by a rapid method and well characterized. The nanoparticles were then used with graphite powder to prepare modified carbon paste electrode (CPE/NiO) for electrocatalytic oxidation of paracetamol (AC). The CPE/NiO showed higher electrocatalytic activity than nickel rod electrode in electrocatalytic oxidation of AC in alkaline media. The assay of AC, mechanism and kinetics of the electrooxidation process were investigated by cyclic voltammetry and chronoamperometry. The catalytic rate constant and the charge transfer coefficient of AC electrooxidation by the active nickel species and the diffusion coefficient of AC were also reported. The linear dependence of the peak current on the concentration of the AC was observed in the range 2–14 mM. This procedure was successfully applied to the determination of AC in tablets. The results showed sufficient precision, accuracy and achieved a mean recovery of 97.2% (RSD = 6.7%).     

Kinetics and mechanism of the electrochemical reduction of [1,2-bis(tert-butylperoxy)ethyl]benzene under conditions of the in situ recovery of a platinum surface

The behavior of [1,2-bis(tert-butylperoxy)ethyl]benzene (I) on Pt electrode is studied by means of cyclic voltammetry (CVA). A comparison of the electrochemical properties of I and the properties of previously studied bridge-type 1,2,4,5-tetraoxane ((1,4)-1,4-dimethyl-7-(4-methylbenzyl)-2,3,5,6-tetraoxabicyclo[2.2.1]heptane) (II) shows that the biperoxide studied in this work is reduced on a Pt electrode at lower cathodic potentials and is resistant to electrooxidation.     

Electrocatalytic performance of cobalt microparticles film-modified platinum disk electrode for amperometric detection of ascorbic acid

Deposited cobalt microparticales (Co-MPs) film onto the platinum disk electrode has been successfully used as a new amperometric sensor for the determination of ascorbic acid (AA). AA is detected by surface catalyzed oxidation involving cobalt(III) oxyhydroxides in alkaline solution. The Co-MPs/Pt electrode exhibits a high electrocatalytic activity toward the AA oxidation. The diffusion coefficient of AA (6.09 × 10⁵ cm²/s) and the catalytic rate constant (k _cat = 6.27 × 10³ M^–1s^–1) have been determined using electrochemical approaches. The amperometric response of the modified electrode is linear against the AA concentration in the range (0.01?0.48 mM). The sensor displays the best activity with a high response signal, a good sensitivity of 74.3 μA/mM, a low detection limit of 2.5 μM (signal/noise = 3) and a fast response time (<3 s). Moreover, the reproducibility, selectivity and applicability of this biosensor are satisfactorily evaluated.     

Amperometric nonenzymatic glucose sensor based on a glassy carbon electrode modified with a nanocomposite made from nickel(II) hydroxide nanoplates and carbon nanofibers

We report on a highly sensitive and selective nonenzymatic glucose sensor based on a glassy carbon electrode modified with a composite prepared from nickel(II) hydroxide nanoplates and carbon nanofibers. The nanocomposite was characterized by scanning electron microscopy and powder X-ray diffraction. Electrodes modified with pure Ni(OH)₂ and with the nanocomposite were characterized by electrochemical impedance spectroscopy. Cyclic voltammetric and amperometric methods were used to investigate the catalytic properties of the modified electrodes for glucose electrooxidation in strongly alkaline solution. The sensor exhibits a wide linear range (from 0.001 to 1.2 mM), a low detection limit (0.76 μM), fast response time (< 5 s), high sensitivity (1038.6 μA?·?mM^?1?·?cm^?2), good reproducibility, and long operational stability. Application of the nonenzymatic sensor for monitoring glucose in real samples was also demonstrated.

Iron nanoparticles decorated graphene-multiwalled carbon nanotubes nanocomposite-modified glassy carbon electrode for the sensitive determination of nitrite

In the present work, we described the preparation of iron nanoparticles decorated graphene-multiwalled carbon nanotubes nanocomposite (GR-MWCNTs/FeNPs) modified glassy carbon electrode (GCE) and its application for the sensitive determination of nitrite. First, GR-MWCNTs/FeNPs nanocomposite has been prepared by a simple solution-based approach via chemical reduction and then it was characterized. Afterwards, GR-MWCNTs/FeNPs/GCE was prepared and employed for the electrocatalysis of nitrite. Electrocatalytic oxidation of nitrite at the GR-MWCNTs/FeNPs/GCE has been significantly improved in terms of both reduction in overpotential and increase in peak current. Therefore, the modified electrode was employed for amperometric determination of nitrite which exhibited excellent analytical parameters with wide linear range of 1?×?10^?7 M to 1.68?×?10^?3 M and very low detection limit of 75.6 (±1.3)?nM. The proposed sensor selectively detects nitrite even in the presence of high concentration of common ions and biological interferrants. Good recoveries achieved for the determination of nitrite in various water samples reveal the promising practicality of the sensor. In addition, the sensor displays an acceptable repeatability and reproducibility along with appreciable storage and excellent operational stabilities.

A nanomaterial composed of cobalt nanoparticles, poly(3,4-ethylenedioxythiophene) and graphene with high electrocatalytic activity for nitrite oxidation

We have investigated the oxidative electrochemistry of nitrite on glassy carbon electrodes modified with cobalt nanoparticles, poly(3,4-ethylenedioxythiophene) (PEDOT), and graphene. The modified electrode was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy. The results suggest that this new type of electrode combines the advantages of PEDOT-graphene films and cobalt nanoparticles and exhibits excellent electrocatalytic activity towards the oxidation of nitrite. There is a linear relationship between the peak current and the nitrite concentration in the range from 0.5?μM to 240?μM, and the detection limit is 0.15?μM. The modified electrodes also enable the determination of nitrite at low potentials where the noise level and interferences by other electro-oxidizable compounds are weak.

Electrodeposition of cobalt oxide nanoparticles on carbon nanotubes, and their electrocatalytic properties for nitrite electrooxidation

We describe a modified glassy carbon electrode (GCE) for the sensitive determination of nitrite in waste water samples. The GCE was modified by electrodeposition of cobalt oxide nanoparticles on multi-walled carbon nanotubes (MWCNTs) deposited on a conventional GCE. Scanning electron microscopy and electrochemical techniques were used for the characterization of the composite material which is very uniform and forms a kind of nanoporous structure. Electrochemical experiments showed that the modified electrode exhibited excellent electrocatalytic properties for nitrite. Amperometry revealed a good linear relationship between peak current and nitrate concentration in the 0.5 to 250???M range with a detection limit of 0.3???M (S/N?=?3). The method has been applied to the amperometric detection of nitrite. The modified electrode displays good storage stability, reproducibility, and selectivity for a promising practical application.

Electrochemical behavior and in-vitro antimicrobial screening of some thienylazoaryls dyes

Background

A series of recently reported phenolic azo dyes 7a–e were prepared by coupling the thienyl diazonium sulfate of 3-Amino-4H-benzo[f]thieno[3,4-c](2H)chromen-4-one with selected diversely substituted phenolic and naphtholic derivatives. These compounds were evaluated for their antibacterial and antifungal activities. Furthermore their voltammetric behavior was compared at a glassy carbon electrode.

Results

The voltammetric behavior of the five recently reported azo dyes has been compared at a glassy carbon electrode. It is shown that the azo dyes 7a–e with a hydroxyl group in the ortho position with respect to the azo bridge give rise to well defined, irreversible peaks for the oxidation and reduction process within a pH range of 2–7. The mechanisms of electrochemical oxidation of compound 7a–c and 7e are proposed. For the hydroxyl-substituted dyes, re-oxidation peaks were obtained in the subsequent scan. The antimicrobial activities of the reported compounds 7a–e along with the entire precursors 1–4 and 6a–e were performed against selected bacterial and fungal species and their activities compared to those of nystatin, griseofulvin and ciprofloxacin used as reference drugs.

Conclusions

The present study showed significant antimicrobial activity of compounds 6d, 7a and 7c,e against the tested microorganisms; this result confirms the antimicrobial potency of azo compounds and some of their precursors.

     

Preparation and characterization of methylene blue-SDS- multiwalled carbon nanotubes nanocomposite for the detection of hydrogen peroxide

A nanocomposite was prepared by physical adsorption of?(cationic) methylene blue (MB) on (anionic) sodium dodecylsulfate (SDS) that was wrapped on multiwalled carbon nanotubes (MWCNTs) on the surface of a glassy carbon electrode. This electrostatic interaction enables electrical communication between the electrode and analyte. Horseradish peroxidase was then immobilized in a film of gelatin on the nanocomposite to form a biosensor for hydrogen peroxide. Scanning electron microscopy, transmission electron microscopy, Fourier transform infrared and UV?Cvis spectrometry, and cyclic voltammetry were applied to characterize the electrode. The addition of both MWCNTs and MB causes a synergistic effect and leads to a large signal enhancement. The prepared nanocomposite material modified sensor shows better response in presence of several interferences. The biosensor has detection limit of 5 nM of hydrogen peroxide (at S/N?=?3) with a linear response between 0.2???M and 1.4?mM. Its lifetime is >4?months under dry conditions at 4?°C.

Glassy carbon electrode modified with poly-Neutral Red for photoelectrocatalytic oxidation of NADH

A new approach is described for the photoelectrocatalytic oxidation of Reduced ß-Nicotinamide Adenine Dinucleotide (NADH). It is based on a glassy carbon electrode (GCE) modified with a film of poly-Neutral Red (poly-NR) that is obtained by electropolymerization. Electrochemical measurements revealed that the modified electrode displays electrocatalytic and photo-electrocatalytic activity towards oxidation of NADH. If irradiated with a 250-W halogen lamp, the electrode yields a strongly increased electrocatalytic current compared to the current without irradiation. Amperometric and photo-amperometric detection of NADH was performed at +150 mV vs. Ag/AgCl/KCl_sat and the currents obtained are linearly related to the concentration of NADH. Linear calibration plots are obtained in the concentration range from 1.0 μM to 1.0 mM for both methods. However, the slope of the current-NADH concentration curve of the photo-electrocatalytic procedure was 2-times better than that obtained without irradiation.

Voltammetric sensors based on gel composites containing carbon nanotubes and an ionic liquid

Possibilities of using electrode coatings based on a gel of carboxylated multiwall carbon nanotubes (MWCNTs) in an ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate, [BMIm]PF₆) for the creation of a voltammetric sensor with electrocatalytic properties with respect to the pharmacological group of catecholamines—levodopa, methyldopa, and carbidopa—are considered. Using cyclic voltammetry, it was found that a glassy carbon electrode coated with a thin layer of an MWCNT–[BMIm]PF₆ gel or an MWCNT–[BMIm]PF₆–Nafion gel-composite induced a decrease in overvoltage (~60 mV), improved the reversibility of the redox reaction, and increased oxidation currents of the studied substances in comparison with an unmodified glassy carbon electrode. The concentration dependence of the analytical signal was linear in the ranges of 1–250, 2–350, and 5–400 mM for carbidopa, levodopa, and methyldopa, respectively. In the determination of the specified substances in diluted urine samples and tableted drugs, the accuracy index was 98–102% and the relative standard deviation, 0.3–5% (n = 5, P = 0.95).     

A uric acid sensor based on electrodeposition of nickel hexacyanoferrate nanoparticles on an electrode modified with multi-walled carbon nanotubes

An electrode sensitive to uric acid was prepared by electrodeposition of nickel(II) hexacyanoferrate(III) on the surface of a glassy carbon electrode modified with multi-walled carbon nanotubes. The morphology of the material was characterized by scanning electron microscopy and Fourier transform infrared spectrometry. The modified electrode were characterized via cyclic voltammetry and amperometry (i - t). It exhibited efficient electron transfer ability and a strong and fast (< 3?s) response towards uric acid which is linear in the range from 0.1???M to 18???M, with a lower detection limit of 50 nM (at an S/N ratio of 3). In addition, the electrode exhibited good reproducibility and long-term stability.

Copper polydopamine complex/multiwalled carbon nanotubes as novel modifier for simultaneous electrochemical determination of ascorbic acid,dopamine, acetaminophen,nitrite and xanthine

In this study, a novel modified glassy carbon electrode with copper polydopamine complex/multiwalled carbon nanotubes (GCE/Cu²⁺@PDA-MWCNTs) was fabricated and used for voltammetric determination of ascorbic acid (AA), dopamine (DA), acetaminophen (AC), nitrite (Nit), and xanthine (XN). Different techniques such as field emission electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, and electrochemical impedance spectroscopy were performed for characterization of the GCE/Cu²⁺@PDA-MWCNTs. Different electrochemical methods such as cyclic voltammetry, electrochemical impedance spectroscopy and differential pulse voltammetry (DPV) methods were employed to study the behavior of AA, DA, AC, Nit, and XN on this proposed modified electrode. The proposed modified electrode displays intense and indelible electrooxidation response for simultaneous determination of AA, DA, AC, Nit, and XN to five well-separated peaks in the potential range from 0.1 to 1.1 V using CV and DPV methods in phosphate buffer solution with pH 2.0. Under the optimum conditions, the calibration curves were liner up to 175, 125, 75, 150, and 115 μM with detection limits of 0.82, 0.45, 0.87, 0.92, and 0.67 μM for AA, DA, AC, Nit, and XN, respectively. This sensor was used to successfully determine these compounds in human urine and serum samples.

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Electrocatalytic determination of penicillamine using multiwall carbon nanotubes paste electrode and chlorpromazine as a mediator

In this study, we describe the application of carbon paste electrode modified with multiwall carbon nanotubes as a voltammetric sensor for determination of penicillamine (PA) in the presence of chlorpromazine as a mediator. This modified electrode showed very efficient electrocatalytic activity for the anodic oxidation of PA. The peak current of linear sweep voltammograms of PA increased linearly with it’s concentration in the range of 0.5–500 μM PA. The detection limit for PA was 0.2 μM. The RSDs for 1.0 and 10.0 μM PA were 1.1 and 1.7%, respectively. The proposed sensor was successfully applied for the determination of PA in human urine and tablet.     

Micropatterning of biomolecules on a glass substrate in fused silica microchannels by using photolabile linker-based surface activation

Platinum nanoparticles were electrodeposited onto a film of dihexadecyl hydrogen phosphate deposited on a glassy carbon electrode (GCE) and modified with dispersed acetylene black. Scanning electron microscopy and electrochemical impedance spectroscopy revealed that this nanocomposite has a uniform nanostructure and a large surface area that enables fast electron-transfer kinetics. The modified GCE showed high electrocatalytic activity for the oxidation of nitric oxide (NO). Under optimal conditions, the oxidation peak current of nitric oxide is linearly related to the concentration of NO in the concentration range between 0.18 and 120?μM, and the detection limit is as low as 50?nM (at an S/N of 3). The modified electrode was successfully applied to sensing of NO as released from rat liver.