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.

A lead(II) sensor based on a glassy carbon electrode modified with Fe3O4 nanospheres and carbon nanotubes

We have developed a highly sensitive and selective sensor for lead(II) ions. A glassy carbon electrode was modified with Fe₃O₄ nanospheres and multi-walled carbon nanotubes, and this material was characterized by scanning electron microscopy and X-ray diffraction. The electrode displays good electrochemical activity toward Pb(II) and gives anodic and cathodic peaks with potentials at ?496 mV and ?638 mV (vs. Ag/AgCl) in pH?6.0 solution. The sensor exhibits a sensitive and fairly selective response to Pb(II) ion, with a linear range between 20 pM and 1.6 nM, and a detection limit as low as 6.0 pM (at a signal-to noise ratio of 3). The sensor was successfully applied to monitor Pb(II) in spiked water samples.

Amperometric determination of sulfide ion by glassy carbon electrode modified with multiwall carbon nanotubes and copper (II) phenanthroline complex

Electrocatalytic oxidation of sulfide ion on a glassy carbon electrode (GCE) modified with multiwall carbon nanotubes (MWCNTs) and a copper (II) complex was investigated. The Cu(II) complex was used due to the reversibility of the Cu(II)/Cu(III) redox couple. The MWCNTs are evaluated as a transducer, stabilizer and immobilization matrix for the construction of amperometric sensor based on Cu(II) complex adsorbed on MWCNTs immobilized on the surface of GCE. The modified GCE was applied to the selective amperometric detection of sulfide at a potential of 0.47 V (vs. Ag/AgCl) at pH 8.0. The calibration graph was linear in the concentration range of 5 µM–400 µM; while the limit of detection was 1.2 µM, the sensitivity was 34 nA µM^?1. The interference effects of SO₃ ^2?, SO₄ ^2?, S₂O₃ ^2?, S₄O₆ ^2?, Cysteine, and Cystein were negligible at the concentration ratios more than 40 times. The modified electrode is more stable with time and more easily restorable than unmodified electrode surface. Also, modified electrode permits detection of sulfide ion by its oxidation at lower anodic potentials.      

Anodic stripping voltammetric determination of silver ion at a carbon paste electrode modified with carbon nanotubes

A carbon paste electrode (CPE) was modified with multi-wall carbon nanotubes and successfully applied to the determination of silver ion by differential pulse anodic stripping voltammetry. Compared to a conventional CPE, a remarkably improved peak current response and sensitivity is observed. The analytical procedure consisted of an open circuit accumulation step for 2?min in ?0.4?V, this followed by an anodic potential scan between +0.2 and?+?0.6?V to obtain the voltammetric peak. The oxidation peak current is proportional to the concentration of silver ion in the range from 1.0?×?10^?8 to 1.0?×?10^?5?mol?L^?1, with a detection limit of 1.8?×?10^?9?mol?L^?1 after an accumulation time of 120?s. The relative standard deviation for 7 successive determinations of Ag(I) at 0.1???M concentration is 1.99%. The procedure was validated by determining Ag(I) in natural waters.

Amperometric sensing of NADH and ethanol using a hybrid film electrode modified with electrochemically fabricated zirconia nanotubes and poly (acid fuchsin)

We report on a glassy carbon electrode (GCE) modified with a film of chitosin containing acid fuchsin (AF) adsorbed onto zirconia nanotubes. The mixture was polymerized by cyclic voltammetric scannings in the potential range from - 0.8?V to +1.3?V in buffer solution to produce a hybrid film electrode (nano-ZrO₂/PAF/GCE). The morphology of the hybrid film electrode surface was characterized by scanning electron microscopy. Its electrochemical properties were studied via electrochemical impedance spectroscopy. The electrochemical response of nicotinamide adenine dinucleotide (NADH) was investigated by differential pulse voltammetry and amperometry. The results indicated that the nano-ZrO₂/PAF/GCE possesses well synergistic catalytic activity towards NADH. Compared to an unmodified GCE, the oxidation overpotential is negatively shifted by 224?mV, and the oxidation current is significantly increased. Under optimal conditions, the amperometric response is linearly proportional to the concentration of NADH in the 1.0 – 100.0?μM concentration range. Ethanol also can be determined by amperometry if alcohol dehydrogenase and NADH are added to the sample. Two linear relationships between current and alcohol concentration were obtained. They cover the range from 0.03 to 1.0?mM, and from 1.0 to 12.0?mM.

Non-enzymatic analysis of glucose on printed films based on multi-walled carbon nanotubes

We report on the fabrication of an enzyme–free electrochemical sensor for glucose based on a printed film consisting of multi–walled carbon nanotubes (MWCNTs). The MWCNT–based film can be produced by means of a flexographic printing process on a polycarbonate (PC) substrate. The electrochemical response of the MWCNT–based film (referred to as MWCNT–PC) towards the oxidation of glucose at pH 7 was studied by means of cyclic voltammetry and electrochemical impedance spectroscopy. The MWCNT–PC film exhibits substantial electrocatalytic activity towards the oxidation of glucose at an anodic potential of 0.30?V (vs. Ag/AgCl). The findings reveal that the MWCNT–PC film enables non–enzymatic sensing of glucose with a detection limit as low as 2.16?μM and a sensitivity of 1045?μA?mM^?1?cm^?2.

Carbon fiber microelectrodes modified with carbon nanotubes as a new support for immobilization of glucose oxidase

Carboxylated carbon nanotubes were coated onto carbon microfiber electrodes to create a micron-scale bioelectrode. This material has a high surface area and can serve as a support for immobilization of enzymes such as glucose oxidase. A typical carbon nanotube loading of 13???g?cm^?1 yields a coating thickness of 17???m and a 2000-fold increase in surface capacitance. The modified electrode was further coated with a biocatalytic hydrogel composed of a conductive redox polymer, glucose oxidase, and a crosslinker to create a glucose bioelectrode. The current density on oxidation of glucose is 16.6?mA?cm^?2 at 0.5?V (vs. Ag/AgCl) in oxygen-free glucose solution. We consider this approach to be useful for designing and characterizing surface treatments for carbon mats and papers by mimicking their local microenvironment.

Square wave anodic stripping voltammetric determination of lead(II) using a glassy carbon electrode modified with a lead ionophore and multiwalled carbon nanotubes

We report on a glassy carbon electrode (GCE) modified with a lead ionophore and multiwalled carbon nanotubes. It can be applied to square wave anodic stripping voltammetric determination of Pb(II) ion after preconcentration of Pb(II) at ?1.0?V (vs. SCE) for 300?s in pH?4.5 acetate buffer containing 400?μg?L^?1 of Bi(III). The ionophore-MWCNTs film on the GCE possesses strong and highly selective affinity for Pb(II) as confirmed by quartz crystal microbalance experiments. Under the optimum conditions, a linear response was observed for Pb(II) ion in the range from 0.3 to 50?μg?L^?1. The limit of detection (at S/N?=?3) is 0.1?μg?L^?1. The method was applied to the determination of Pb(II) in water samples with acceptable recovery.

Iodide-induced adsorption of lead(II) ion on a glassy carbon electrode modified with ferroferric oxide nanoparticles

Spherical Fe₃O₄ nanoparticles (NPs) were prepared by hydrothermal synthesis and characterized by scanning electron microscopy and X-ray diffraction. A glassy carbon electrode was modified with such NPs to result in a sensor for Pb(II) that is based on the strong inducing adsorption ability of iodide. The electrode gives a pair of well-defined redox peaks for Pb(II) in pH 5.0 buffer containing 10 mM concentrations of potassium iodide, with anodic and cathodic peak potentials at ?487 mV and ?622 mV (vs. Ag/AgCl), respectively. The amperometric response to Pb(II) is linear in the range from 0.10 to 44 nM, and the detection limit is 40 pM at an SNR of 3. The sensor exhibits high selectivity and reproducibility.

Voltammetric determination of bisphenol A in food package by a glassy carbon electrode modified with carboxylated multi-walled carbon nanotubes

A highly sensitive and mercury-free method for determination of bisphenol A (BPA) was established using a glassy carbon electrode that was modified with carboxylated multi-walled carbon nanotubes. A sensitive oxidation peak is found at 550?mV in linear sweep voltammograms at pH?7. Based on this finding, trace levels of bisphenol A can be determined over a concentration range that is linear from 10?nM to 10⁴?nM, the correlation coefficient being 0.9983, and the detection limit (S/N?=?3) being 5.0?nM. The method was successfully applied to the determination of BPA in food package.

Selective and low potential electrocatalytic oxidation of NADH using a 2,2-diphenyl-1-picrylhydrazyl immobilized graphene oxide-modified glassy carbon electrode

DPPH (2,2-diphenyl-1-picrylhydrazil), a free radical-containing organic compound, is used widely to evaluate the antioxidant properties of plant constituents. Here, we report an efficient electroactive DPPH molecular system with excellent electrocatalytic sensor properties, which is clearly distinct from the traditional free radical-based quenching mechanism. This unusual molecular status was achieved by the electrochemical immobilization of graphene oxide (GO)-stabilized DPPH on a glassy carbon electrode (GCE). Potential cycling of the DPPH adsorbed-GCE/GO between ??1 and 1 V (Ag/AgCl) in a pH 7 solution revealed a stable and well-defined pair of redox peaks with a standard electrode potential, E⁰′?=?0?±?0.01 V (Ag/AgCl). Several electrochemical characterization studies as well as surface analysis of the GCE/GO@DPPH-modified electrode by transmission electron microscopy, Raman, and infrared spectroscopy collectively identified the imine/amine groups as the redox centers of the electroactive DPPH on GO. The use of different carbon-supports showed that only oxygen-functionalized GO and MWCNTs could provide major electroactivity for DPPH. This highlights the importance of a strong hydrogen-bonded network structure assisted by the concomitant π-π interactions between the organic moiety and oxygen function groups of carbon for the high electroactivity and stability of the GCE/GO@DPPH-NH/NH₂-modified electrode. The developed electrode exhibited remarkable performance towards the electrocatalytic oxidation of NADH at 0 V (Ag/AgCl). The amperometric i-t sensing of NADH showed high sensitivity (488 nA μM^?1 cm^?2) and an extended linear range (50 to 450 μM) with complete freedom from several common biochemical/chemical interferents, such as ascorbic acid, hydrazine, glucose, cysteine, citric acid, nitrate, and uric acid.     

Ultrasensitive determination of hydrazine using a glassy carbon electrode modified with Pyrocatechol Violet electrodeposited on single walled carbon nanotubes

A glassy carbon electrode (GCE) was modified with pyrocatechol violet (PCV) that was electrodeposited on single walled carbon nanotubes (SWCNTs) via continuous cycling between 0 and 0.9 V (vs. SCE). The resulting electrode exhibits excellent electrocatalytic activity towards the oxidation of hydrazine at 0.3 V. The apparent surface coverage of the electrode is at least 24 times higher (2.7?×?10^?10 mol cm^?2) than that obtained with a bare GCE (1.1?×?10^?11 mol cm^?2). This is attributed to a remarkably strong synergistic effect between the acid-pretreated SWCNTs and the electrodeposited PCV coating. Response is fast (2 s) and sensitive (281 mA M^?1 cm^?2). Other features include a wide linear range (150 nM to 0.4 mM) and a low detection limit (150 nM at an SNR of 3). The sensor has been successfully applied to the determination of hydrazine in water and cigarette samples with good accuracy and precision. In addition, the morphology and the wetting properties of the coating were studied by scanning electromicroscopy and contact angle measurements.

Anodic stripping voltammetry of silver(I) using a carbon paste electrode modified with multi-walled carbon nanotubes

We describe a silver(I)-selective carbon paste electrode modified with multi-walled carbon nanotubes and a silver-chelating Schiff base, and its electrochemical response to Ag(I). Effects of reduction potential and time, accumulation time, pH of the solution and the stripping medium were studied by differential pulse anodic stripping voltammetry and optimized. The findings resulted in a method for the determination of silver over a linear response range (from 0.5 to 235 ng?mL^?1) and with a detection limit as low as 0.08 ng?mL^?1. The sensor displays good repeatability (with the RSD of ±?2.75 % for 7 replicates) and was applied to the determination of Ag(I) in water samples and X-ray photographic films.

A novel non-enzyme hydrogen peroxide sensor based on an electrode modified with carbon nanotube-wired CuO nanoflowers

We have prepared a novel sensor for hydrogen peroxide that is based on a glassy carbon electrode modified with a film containing multi-walled carbon nanotubes wired to CuO nanoflowers. The nanoflowers were characterized by X-ray powder diffraction, and the electrode was characterized by cyclic voltammetry (CV) and scanning electron microscopy. The response of the modified electrode towards hydrogen peroxide was investigated by CV and chronoamperometry and showed it to exhibit high electrocatalytic activity, with a linear range from 0.5?μM to 82?μM and a detection limit of 0.16?μM. The sensor also displays excellent selectivity and stability.

Highly sensitive carbon paste electrode with silver-filled carbon nanotubes as a sensing element for determination of free cyanide ion in aqueous solutions

We report on newly synthesized Ag(I)-filled multiwall carbon nanotubes as a potential sensing element in ion-selective carbon paste electrodes for the determination of free cyanide in aqueous solution. The electrode was obtained by entrapping the silver-filled nanotubes into a carbon paste and displays a Nernstian response with a slope of 59.8?±?0.3?mV decade^?1, a very wide linear range (from 21.0?nM to 0.1?M of cyanide), a lower detection limit of 13.0?nM, and a response time of <2?min. The operational lifetime is up to 3?months without significant deviation in normal function.

Mediatorless amperometric bienzyme glucose biosensor based on horseradish peroxidase and glucose oxidase cross-linked to multiwall carbon nanotubes

We report on a bienzyme-channeling sensor for sensing glucose without the aid of mediator. It was fabricated by cross-linking horseradish peroxidase (HRP) and glucose oxidase (GOx) on a glassy carbon electrode modified with multiwalled carbon nanotubes (MWNTs). The bienzyme was cross-linked with the MWNTs by glutaraldehyde and bovine serum albumin. The MWNTs were employed to accelerate the electron transfer between immobilized HRP and electrode. Glucose was sensed by amperometric reduction of enzymatically generated H₂O₂ at an applied voltage of ?50 mV (vs. Ag/AgCl). Factors influencing the preparation and performance of the bienzyme electrode were investigated in detail. The biosensor exhibited a fast and linear response to glucose in the concentration range from 0.4 to 15 mM, with a detection limit of 0.4 mM. The sensor exhibited good selectivity and durability, with a long-term relative standard deviation of <5 %. Analysis of glucose-spiked human serum samples yielded recoveries between 96 and 101 %.

Determination of zearalenone with a glassy carbon electrode modified with nanocomposite consisting of palladium nanoparticles and a conductive polymeric ionic liquid

A glassy carbon electrode (GCE) modified with polymeric nanocomposite consisting of palladium nanoparticles and a conductive polymeric ionic liquid was prepared. The modified GCE was applied to sensitive and fairly selective electrochemical determination of the mycotoxin zearalenone. Electrocatalytic oxidation is performed in a solution containing 20 % (V/V) acetonitrile and 80 % (V/V) of 1 M perchloric acid. Cyclic voltammetry and square wave voltammetry revealed a well-defined electrocatalytic peak current at overpotential of +0.69 V versus Ag/AgCl. Under optimized experimental conditions, there is a linear relationship between anodic peak current and zearalenone concentration in the range from 0.03 to 35 ng?mL￣¹, and the detection limit is 0.01 ng?mL￣¹. The method was successfully applied to the analysis of zearalenone in spiked food samples and gave recoveries between 95.6 and 104.0 %.

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Graphical abstract The nanocomposite (PdVC-PIL) was prepared by polymerization of ionic liquid monomer (PIL) in presence of Pd nanoparticles on Vulcan XC-72R carbon (PdVC). The solution containing nanocomposite was placed on the glassy carbon electrode (GCE). The voltammetry activity of modified electrode (PdVC-PIL/GCE) was compared to a bare GCE for zearalenone determination.

     

Electrochemical oxidation and nanomolar detection of acetaminophen at a carbon-ceramic electrode modified by carbon nanotubes: a comparison between multi walled and single walled carbon nanotubes

Carbon-ceramic electrodes (CCE) modified with carbon nanotubes were prepared, and the electrochemical behavior towards acetaminophen (ACOP) was investigated using both a bare CCE and electrodes modified with either single walled carbon nanotubes (SWCNT) or multi walled carbon nanotubes (MWCNT) in an effort to understand which of them is the better choice in terms of electrocatalyzing the oxidation of ACOP, and thus for sensing it. The SWCNT are found to be the better material in significantly enhancing the oxidation peak current and improving the reversibility of the oxidation. Under optimal conditions, linearity between the oxidation peak current and the concentration of ACOP is obtained for the concentration range from 40?nM to 85???M, with a detection limit of 25?nM. Finally, ACOP was successfully determined with the SWCNT modified electrode in pharmaceutical samples.

Electrochemical determination of NADH using a glassy carbon electrode modified with Fe3O4 nanoparticles and poly-2,6-pyridinedicarboxylic acid, and its application to the determination of antioxidant capacity

We have prepared a glassy carbon electrode modified with poly-2,6-pyridinedicarboxylic acid and with magnetic Fe₃O₄ nanoparticles. This modification enhances the effective surface area and the electrocatalytic oxidation of nicotinamide adenine dinucleotide (NADH) in addition to providing positively charged groups for electrostatic assembly of the phosphate group of NADH. The modified electrode responds linearly to NADH in the range from 5?×?10^?8 to 2.5?×?10^?5?M and gives a lower detection limit of 1?×?10^?8?M. It displays satisfactory selectivity and reproducibility. The sensor was applied to rapid screening of plant extracts for their antioxidant properties.

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.