Electrochemical behavior of tartaric acid at CuGeO3 nanowire modified glassy carbon electrode

The electrochemical behavior of tartaric acid at the CuGeO₃ nanowire modified glassy carbon electrode has been investigated by cyclic voltammetry (CV). The results show that two pairs of semireversible electrochemical peaks are observed and can be assigned to the process of oxidation–reduction and adsorption–desorption of tartaric acid at the modified glassy carbon electrode, respectively. The intensity of the CV peaks increases linearly with the increase of the content of tartaric acid in the range of 0.01–5 mM and scan rate ranging from 25–200 mV s^?1. CuGeO₃ nanowire modified glassy carbon electrode exhibits good detection ability for tartaric acid in neutral solution with the detection limit of 8.9 and 7.7 μM for cvp1 and cvp2, respectively, at a signal-to-noise ratio of 3. The CuGeO₃ nanowire modified glassy carbon electrode has good reproducibility and stability.     

Electrochemical Determination of Dopamine Using a Poly(3,4-Ethylenedioxythiophene)-Reduced Graphene Oxide-Modified Glassy Carbon Electrode

Poly(3,4-ethylenedioxythiophene) was deposited on a reduced graphene oxide-decorated glassy carbon electrode through an electrochemical polymerization. The resulting glassy carbon electrode-reduced graphene oxide-poly(3,4-ethylenedioxythiophene) electrode was applied as an electrochemical biosensor for the determination of dopamine in the presence of ascorbic acid and uric acid. The material deposited on glassy carbon electrode was investigated in terms of morphology and structural analysis. The comparison of electrochemical behavior of the glassy carbon electrode-reduced graphene oxide-poly(3,4-ethylenedioxythiophene) electrode with the glassy carbon electrode-graphene oxide, glassy carbon electrode-reduced graphene oxide, and glassy carbon electrode-poly(3,4-ethylenedioxythiophene) electrodes exhibited high electrocatalytic activity for dopamine detection. Electrochemical kinetic parameters of glassy carbon electrode-reduced graphene oxide-poly(3,4-ethylenedioxythiophene), including the charge transfer coefficient α (0.49) and electron transfer rate constant k_s (1.04), were determined and discussed. The glassy carbon electrode-reduced graphene oxide-poly(3,4-ethylenedioxythiophene) electrode was studied for the determination of dopamine by differential pulse voltammetry and exhibited a linear range from 19.6 to 122.8?µM with a sensitivity of 3.27?µA?µM^?1?cm^?2 and a detection limit of 1.92?µM. The developed biosensor exhibited good selectivity toward dopamine with high reproducibility and stability.     

CeO<Subscript>2</Subscript> nanoparticle-modified electrode as a novel electrochemical interface in the quantification of Zn<Superscript>2+ </Superscript>ions at trace level: application to real sample analysis

A simple strategy has been proposed to quantify Zn²⁺ ions using CeO₂ nanoparticle-modified glassy carbon electrode. The CeO₂ nanoparticles were prepared by sucrose-nitrate decomposition method, and it was characterized by X-ray diffraction (XRD), FT-IR, TEM, and surface area analyzer. The synthesized CeO₂ nanoparticles were used as modifier molecules as a thin film on glassy carbon electrode (GCE) in the trace level quantification of Zn²⁺ by using cyclic voltammetry (CV) and differential pulse anodic stripping voltammetry (DPASV) techniques. The fabricated sensor exhibited a good analytical response towards Zn²⁺ ions. The modified electrode showed a wide linearity in the concentration range 20–380 μg L^?1 with a limit of detection 0.36 μg L^?1. The proposed electrochemical sensor was successfully applied to trace level Zn²⁺ quantification from real sample matrices.     

Polymer/Iron Oxide Nanoparticle Modified Glassy Carbon Electrodes for the Enhanced Detection of Epinephrine

Novel electrochemical sensors for epinephrine (EP) based on a glassy carbon electrode (GCE) modified with a redox polymer film and iron (III) oxide nanoparticles (Fe₂O₃NP) have been developed. Two redox polymers‐poly(brilliant cresyl blue) (PBCB) and poly(Nile blue) (PNB), and two different architectures‐polymer/Fe₂O₃/GCE and Fe₂O₃/polymer/GCE were investigated. The electrochemical oxidation of epinephrine at the modified electrodes was performed by differential pulse voltammetry (DPV), in pH 7 electrolyte, and the analytical parameters were determined. The results show enhanced performance, more sensitive responses and lower detection limits at the modified electrodes, compared to other electrochemical epinephrine sensors reported in the literature. The best voltammetric response with the lowest detection limit was obtained for the determination of epinephrine at PBCB/Fe₂O₃/GCE. The novel sensors are reusable, with good reproducibility and stability, and were successfully applied to the determination of epinephrine in commercial injectable adrenaline samples.     

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.     

Ni0.1Co0.9Fe2O4-based electrochemical sensor for the detection of paracetamol

A novel electrochemical sensor based on nickel-doped cobalt ferrite nanoparticles (Ni_0.1Co_0.9Fe₂O₄)-modified glassy carbon electrode (NCF/GCE) was presented for the sensitive detection of paracetamol. Experimental conditions such as pH, applied potentials and concentration were investigated using cyclic voltammetric and chronoamperometric techniques. The modified electrode exhibited excellent catalytic response towards the oxidation of paracetamol with good reproducibility. The overpotential for oxidation of paracetamol is decreased, and the current response enhanced significantly on the modified electrode in comparison with that of bare electrode. Linear calibration curve is obtained over the range 2 μM to 8,000 μM having a detection limit of 11 nM. The modified electrode facilitated the simultaneous detection of paracetamol, ascorbic acid, and dopamine with good reproducibility.     

Simultaneous sensing of L-tyrosine and epinephrine using a glassy carbon electrode modified with nafion and CeO2 nanoparticles

An electrochemical sensor was developed and tested for detection of L-tyrosine in the presence of epinephrine by surface modification of a glassy carbon electrode (GCE) with Nafion and cerium dioxide nanoparticles. Fabrication parameters of a surfactant-assisted precipitation method were optimized to produce 2–3 nm CeO₂ nanoparticles with very high surface-to-volume ratio. The resulting nanocrystals were characterized structurally and morphologically by X-ray diffractometery (XRD), scanning and high resolution transmission electron microscopy (SEM and HR-TEM). The nanopowder is sonochemically dispersed in a Nafion solution which is then used to modify the surface of a GCE electrode. The electrochemical activity of L-tyrosine and epinephrine was investigated using both a Nafion-CeO₂ coated and a bare GCE. The modified electrode exhibits a significant electrochemical oxidation effect of L-tyrosine in a 0.2 M Britton-Robinson (B-R) buffer solution of pH 2. The electro-oxidation peak current increases linearly with the L-tyrosine concentration in the molar concentration range of 2 to 160 μM. By employing differential pulse voltammetry (DPV) for simultaneous measurements, we detected two reproducible peaks for L-tyrosine and epinephrine in the same solution with a peak separation of about 443 mV. The detection limit of the sensor (signal to noise ratio of 3) for L-tyrosine is ~90 nM and the sensitivity is 0.20 μA μM⁻¹, while for epinephrine these values are ~60 nM and 0.19 μA μM⁻¹. The sensor exhibited excellent selectivity, sensitivity, reproducibility and stability as well as a very good recovery time in real human blood serum samples.

Simultaneous electrochemical determination of L-tyrosine and epinephrine in blood plasma with Nafion-CeO₂/GCE modified electrode showing a 443 mV peak-to-peak potential difference between species oxidation peak currents.

     

Simultaneous determination of dopamine, uric acid and ascorbic acid with LaFeO3 nanoparticles modified electrode

LaFeO₃ nanoparticles of approximately 22 nm in size were synthesized and characterized by XRD and TEM. A novel glassy carbon electrode modified with LaFeO₃ nanoparticles was constructed and characterized by electrochemical impedance spectroscopy and cyclic voltammetry. The modified electrode exhibited strong promoting effect and high stability toward the electrochemical oxidation of dopamine (DA), which gave reversible redox peaks with a formal potential of 0.145 V (vs. Ag/AgCl) in pH 7.0 phosphate buffer solution. The anodic peak current (measured by constant potential amperometry) increased linearly with the concentration of dopamine in the range from 1.5?×?10^?7 to 8.0?×?10^?4 M. The detection limit was 3.0?×?10^?8 M. The relative standard deviation of eight successive scans was 3.47% for 1.0?×?10^?6 M DA. The interference by ascorbic acid was eliminated efficiently. The method was used to determine DA in dopamine hydrochloride injections and showed excellent sensitivity and recovery.     

Direct electrochemical behavior of hemoglobin at surface of Au@Fe3O4 magnetic nanoparticles

Nanoparticles (NPs) consisting of an Fe₃O₄ core and a thin gold shell (referred to as Au@Fe₃O₄ NPs) were self-assembled on the surface of a glassy carbon electrode modified with ethylenediamine. Following adsorption of hemoglobin, its interaction with the NPs was studied by UV–Vis spectroscopy, electrochemical impedance spectroscopy, and cyclic voltammetry. Stable and well-defined redox peaks were observed at about ?350 mV and ?130 mV in pH 6.0 buffer. The modified electrode was used as a mediator-free sensor for hydrogen peroxide (H₂O₂), with a linear range from 3.4 µM to 4.0 mM of H₂O₂, and with a 0.67 µM detection limit (at an S/N of 3). The apparent Michaelis-Menten constant is 2.3 mM.     

Simultaneous sensing of L-tyrosine and epinephrine using a glassy carbon electrode modified with nafion and CeO2 nanoparticles

An electrochemical sensor was developed and tested for detection of L-tyrosine in the presence of epinephrine by surface modification of a glassy carbon electrode (GCE) with Nafion and cerium dioxide nanoparticles. Fabrication parameters of a surfactant-assisted precipitation method were optimized to produce 2–3 nm CeO₂ nanoparticles with very high surface-to-volume ratio. The resulting nanocrystals were characterized structurally and morphologically by X-ray diffractometery (XRD), scanning and high resolution transmission electron microscopy (SEM and HR-TEM). The nanopowder is sonochemically dispersed in a Nafion solution which is then used to modify the surface of a GCE electrode. The electrochemical activity of L-tyrosine and epinephrine was investigated using both a Nafion-CeO₂ coated and a bare GCE. The modified electrode exhibits a significant electrochemical oxidation effect of L-tyrosine in a 0.2 M Britton-Robinson (B-R) buffer solution of pH 2. The electro-oxidation peak current increases linearly with the L-tyrosine concentration in the molar concentration range of 2 to 160 μM. By employing differential pulse voltammetry (DPV) for simultaneous measurements, we detected two reproducible peaks for L-tyrosine and epinephrine in the same solution with a peak separation of about 443 mV. The detection limit of the sensor (signal to noise ratio of 3) for L-tyrosine is ~90 nM and the sensitivity is 0.20 μA μM^?1, while for epinephrine these values are ~60 nM and 0.19 μA μM^?1. The sensor exhibited excellent selectivity, sensitivity, reproducibility and stability as well as a very good recovery time in real human blood serum samples.

Simultaneous electrochemical determination of L-tyrosine and epinephrine in blood plasma with Nafion-CeO₂/GCE modified electrode showing a 443 mV peak-to-peak potential difference between species oxidation peak currents.     

An electrochemical biosensor for direct detection of DNA using polystyrene-g-soya oil-g-imidazole graft copolymer

A label-free electrochemical DNA biosensor was developed through the attachment of polystyrene-g-soya oil-g-imidazole graft copolymer (PS-PSyIm) onto modified graphene oxide (GO) electrodeposited on glassy carbon electrode (GC). GC/GO electrode was initially functionalised via electrochemical reduction of 4-nitrobenzene diazonium salt, followed by the electrochemical reduction of NO₂ to NH₂. Subsequent to the electrochemical deposition of gold nanoparticles on modified surface, the attachment of the PS-PSyIm graft copolymer on the resulting electrode was achieved. The interaction of PS-PSyIm with DNA at the bare glassy carbon electrode was studied by cyclic voltammetry technique, and it was found that interaction predominantly takes place through intercalation mode. The selectivity of developed DNA biosensor was also explored by DPV on the basis of considering hybridisation event with non-complementary, one-base mismatched DNA and complementary target DNA sequence. Large decrease in the peak current was found upon the addition of complementary target DNA. The sensitivity of the developed DNA biosensor was also investigated, and detection limit was found to be 1.20 nmol L^?1.     

Exfoliated graphite nanoplatelets and gold nanoparticles based electrochemical sensor for determination of levodopa

This paper describes a rapid, accurate, and sensitive method for the determination of levodopa in a pharmaceutical sample using a glassy carbon electrode modified with a hybrid nanocomposite constituted of exfoliated graphite nanoplatelets dispersed in a suspension of gold nanoparticles in carboxymethylcelullose (AuNP-CMC-xGnP/GCE). The nanocomposite was characterized by scanning electron microscopy, transmission electron microscopy, UV-Vis spectroscopy, and zeta potential. Electrochemical characterization of the proposed sensor by cyclic voltammetry and electrochemical impedance spectroscopy indicated that the nanocomposite used for the electrode modification facilitated electron transfer. Using square-wave voltammetry (SWV) under optimized conditions (0.50% (m/v) of AuNP-CMC-xGnP, 0.1 mol L^?1 sulfuric acid, frequency 30 Hz, pulse amplitude 50 mV, and scan increment 6.0 mV), the calibration curve showed a linear range for levodopa from 5 to 50 μmol L^?1, with a limit of detection of 0.5 μmol L^?1. The sensor demonstrated good repeatability and electrode-to-electrode repeatability, with relative standard deviations of 2 and 4%, respectively. The proposed method was successfully applied to quantify levodopa in a pharmaceutical sample by SWV, showing good accuracy. Recoveries of 98 to 107% demonstrated that the method is suitable for practical applications. Therefore, the proposed sensor represents a useful tool for rapid and accurate determination of levodopa.     

Nonenzymatic sensor for glucose based on a glassy carbon electrode modified with Ni(OH)2 nanoparticles grown on a film of molybdenum sulfide

A glassy carbon electrode (GCE) was modified with nickel(II) hydroxide nanoparticles and a film of molybdenum sulfide. The nanocomposite was prepared by two-step electrodeposition. Scanning electron microscopy reveals that the nanoparticles are uniformly deposited on the film. Cyclic voltammetry and chronoamperometry indicate that this modified GCE displays a remarkable electrocatalytic activity towards nonenzymatic oxidation of glucose. Response is linear in the 10–1,300 μM concentration range (R ² ?=?0.9987), the detection limit is very low (5.8 μM), response is rapid (< 2 s), and selectivity over ascorbic acid, dopamine, uric acid, fructose and galactose is very good.

Electrochemical deposition of platinum nanoparticles in multiwalled carbon nanotube–Nafion composite for methanol electrooxidation

Platinum nanoparticles were successfully deposited within a multiwalled carbon nanotube (MWCNT)–Nafion matrix by a cyclic voltammetry method. A Pt(IV) complex was reduced to platinum nanoparticles on the surface of MWCNTs. The resulting Pt nanoparticles were characterized by scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The Pt–MWCNT–Nafion nanocomposite film-modified glassy carbon electrode had a sharp hydrogen desorption peak at about −0.2 V vs. Ag/AgCl (3 M) in a solution of 0.5 M H₂SO₄, which is directly related to the electrochemical activity of the Pt nanoparticles presented on the surface of MWCNTs. The electrocatalytic properties of the Pt–MWCNT–Nafion nanocomposite-modified glassy carbon electrode for methanol electrooxidation were investigated by cyclic voltammetry in a 2 M CH₃OH + 1 M H₂SO₄ solution. In comparison with the Pt-coated glassy carbon electrode and the Pt–Nafion modified glassy carbon electrode, the Pt–MWCNT–Nafion-modified electrode had excellent electrocatalytic activity toward methanol electrooxidation. The stability of the Pt–MWCNT–Nafion nanocomposite-modified electrode had also been evaluated.     

Electrochemical sensor using graphene/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanosheets functionalized with garlic extract for the detection of lead ion

Based on the modulated electronic properties of Fe₃O₄-graphene (Fe₃O₄/GN composite) as well as the outstanding complexation between Pb²⁺ and natural substances garlic extract (GE), a novel electrochemical sensor for the determination of Pb²⁺ in wastewater was prepared by immobilization of Fe₃O₄/GN composite integrated with GE onto the surface of glassy carbon electrode (GCE). Fe₃O₄/GN composite was employed as an electrochemical active probe for enhancing electrical response by facilitating charge transfer while GE was used to improve the selectivity and sensitivity of the proposed sensor to Pb²⁺ assay. The electrochemical sensing performance toward Pb²⁺ was appraised by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and square wave voltammetry (SWV). Under the optimized condition, the sensor exhibited two dynamic linear ranges (LDR) including 0.001 to 0.5 nM and 0.5 to 1000 nM with excellent low detection limit (LOD) of 0.0123 pM (S/N =?3) and quantification limit (LOQ) of 0.41 pM (S/N =?10). Meanwhile, it displayed remarkable stability, reproducibility (RSD of 3.61%, n =?3), and selectivity toward the assay for the 100-fold higher concentration of other heavy metal ions. Furthermore, the novel sensor has been successfully employed to detect Pb²⁺ from real water samples with satisfactory results.     

Synthesis and characterisation of Ag-nanoparticles immobilised on ordered mesoporous carbon as an efficient sensing platform: application to electrocatalytic determination of hydrazine

In this study, a new strategy for the preparation of a modified glassy carbon electrode (GCE) based on a novel nano-sensing layer for the electrocatalytic oxidation of hydrazine was suggested. The suggested nano-sensing layer was prepared with the immobilisation of silver nanoparticles (AgNPs) on ordered mesoporous carbon. The morphology and properties of the prepared nanocomposite on the surface of GCE were characterised by scanning electron microscopy, transmission electron microscopy, N₂ adsorption-desorption, X-ray powder diffraction and electrochemical impedance spectroscopy. The electrochemical response characteristics of the modified electrode towards the target analyte were investigated by cyclic voltammetry. Under optimal experimental conditions, the suggested modified GCE showed excellent catalytic activity towards the electro-oxidation of hydrazine (pH = 7.5) with a significant increase in anodic peak currents in comparison with the unmodified GCE. By differential pulse voltammetry and amperometric methods, the suggested sensor demonstrated wide dynamic concentration ranges of 0.08–33.8 µM and 0.01–128 µM with the detection limit (S/N = 3) of 0.027 and 0.003 µM for hydrazine, respectively. The suggested hydrazine sensor was successfully applied for the highly sensitive determination of hydrazine in different real samples with satisfactory results.     

A Simple and Sensitive Square Wave Stripping Pathway for the Analysis of Desmedipham Herbicide by Modified Carbon Paste Electrode Based on Hematite (α‐Fe2O3 Nanoparticles)

In the present study, desmedipham, used as an herbicide to control broad leaf weed in commonly sugar beet crops, was analyzed at the first time by cyclic voltammetry (CV) and square wave stripping voltammetry (SWSV) with the modified carbon paste electrode based on hematite nanoparticles (α‐Fe₂O₃?CPE). The modified α‐Fe₂O₃?CPE prepared by hematite (α‐Fe₂O₃ nanoparticles), which is very sensitive to carbon paste electrode (CPE) and glassy carbon electrode (GCE). Morphology of electrode surface detailed by scanning electron microscopy (SEM) and energy dispersive X‐ray analysis (EDX). The oxidation of desmedipham created irreversible well‐done two peaks at nearly +1.1 and +1.3 V. In order to obtain the best calibration graph, various important parameters such as pH, accumulation time, puls amplitude and frequency etc. were investigated. Under the optimum conditions, electrochemical behavior of desmedipham presented two linear working ranges at 0.15–1.20 mg/L and 1.20–4.50 mg/L. The limits of detection (LOD) for the desmedipham were calculated as 41.00 and 50.00 μg/L for the peak I and II, respectively. Furthermore, desmedipham was analyzed at high recovery in the presence of rizolex, fluometuron, teflubenzuron and some heavy metal ions. Consequently, the developed SWSV was successfully applied to evaluate desmedipham in spiked commercial strawberry juices at recoveries of 96.00–104.00 % with satisfactory relative standard deviations.     

MCM/ZrO2 nanoparticles modified electrode for simultaneous and selective voltammetric determination of epinephrine and acetaminophen

A novel MCM/ZrO₂ nanoparticles modified carbon paste electrode (MZ-CPE) was fabricated and used to study the electro oxidation of epinephrine (EP) and acetaminophen (AC) and their mixtures by electrochemical methods. The modified electrode showed electrocatalytic activity toward EP and AC oxidation with a decrease of the overpotential by 173 mV to a less positive potential for EP at the surface of the MZ-CPE and an increase in peak current at pH 7.0. Differential pulse voltammetry peak currents of EP and AC increased linearly with their concentrations in the ranges of 1.0 × 10^?6–2.5 × 10^?3 and 1.0 × 10^?6–2.0 × 10^?3 M, respectively, and the detection limits for EP and AC were 5.0 × 10^?7 and 4.5 × 10^?7 M, respectively.     

Fabrication of CeO2 Nanoparticle Modified Glassy Carbon Electrode for Ultrasensitive Determination of Trace Amounts of Uric Acid in Urine

The preparation of a glassy carbon electrode modified by CeO2 nanoparticles was described, which was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. In pH 6.0 buffer, the CeO2 nanoparticle modified electrode （CeO2 NP/GC） gave an excellent electrocatalytic activity for the oxidation of uric acid （UA）. The catalytic current of UA versus its concentration had a good linear relation in the range of 2.0 × 10^-7-5.0 × 10^- 4 mol/L, with the correlation coefficient of 0.9986 and detection limit of 1.0 ×10^-7 mol/L. The modified electrode can be used for the determination of UA in urine, which can tolerate the interference of ascorbic acid up to 1000-fold. The method was simple, quick and sensitive.     

Electrochemical Detection of Pb(II) by Glassy Carbon Electrode Modified with Amine-Functionalized Magnetite Nanoparticles

An amine-Fe₃O₄ modified glassy carbon (GC) electrode was constructed for detecting Pb(II) ions in wastewater. The electrode was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Square wave anodic stripping voltammetry (SWASV) was used to detect the Pb(II), and the detection limit of Pb(II) was 0.15 µM. The sensitivity of the electrode to detect Pb(II) was about 10.07 µA/µM, with a correlation coefficient of 0.991, which was approximately 10 times bigger than that of a pure Fe₃O₄ modified electrode. The electrode also showed good selectivity and stability. This results indicated that the amine-magnetite material could have some potential applications in heavy metal ions detection in wastewater.