Polymethylthiophene/Nafion-modified glassy carbon electrode for selective detection of dopamine in the presence of ascorbic acid

The possible use of an electrode modified with electroactive conductive poly(3-methylthiophene) (PMeT)/Nafion as a chemical sensor was investigated for the voltammetric analysis of Dopamine (DA). The electrochemical behavior of dopamine was examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. By using a PMeT-modified glassy carbon (GC/PMeT) electrode, DA and Ascorbic Acid (AA) signals could be separated but the AA at high concentrations still caused significant interference by overlapping the DA peak. In comparison to the GC/PMeT electrode, the glassy carbon (GC/Nafion/PMeT) electrode modified with hybrid film Nafion/PMeT was found to permit a superior separation by shifting the oxidation of AA peak toward the less positive potential. The DPV curves for a mixture of DA and AA at an GC/Nafion/PMeT electrode in a 0.1 M H₂SO₄ solution showed peaks of DA and AA, at 0.45 and 0.21 V, respectively, indicating that the difference in the oxidation potential was 240 mV. In the 0.1 M H₂SO₄ solution, the oxidation peak current on the differential pulse voltammograms for the GC/PMeT electrode increased linearly with the concentration of DA in the range 1 × 10⁻⁶ to 1 × 10⁻³ M, and the oxidation peak current on the differential pulse voltammograms for the GC/Nafion/PMeT electrode in the range 5 × 10⁻⁷ to 2 × 10⁻⁴ M. The DA detection sensitivity of the GC/Nafion/PMeT electrode (26.7 μA μM⁻¹ cm⁻²) was 22 times higher than that of the GC/PMeT electrode (1.21 μA μM⁻¹ cm⁻²).     

Electrochemical determination diethylstilbestrol by a single-walled carbon nanotube/platinum nanoparticle composite film electrode

Platinum nanoparticles (Pt_nano) were prepared and used in combination with single-wall carbon nanotube (SWNT) for fabricating electrochemical sensors with remarkably improved sensitivity toward diethylstilbestrol (DES). The glassy carbon (GC) electrode modified with SWNT/Pt_nano composite film exhibited excellent electrochemical behaviors toward the redox of DES. Compared with the bare GC electrode and SWNTs film modified GC electrode, the redox peak currents at the SWNTs/Pt_nano composite film modified GC electrode was enhanced greatly. The experimental parameters, which influence the peak current of DES, were optimized. Under optimal conditions, a linear response of DES was obtained in the range from 1.0 × 10⁻⁷ to 2.0 × 10⁻⁵ mol L⁻¹ (R = 0.997) and with a limit of detect (LOD) of 1.5 × 10⁻⁸ mol L⁻¹. The proposed procedure was successfully applied to determine the active ingredient in the DES tablet with satisfactory results.     

Green synthesized Au–Ag bimetallic nanoparticles modified electrodes for the amperometric detection of hydrogen peroxide

Simple and eco-friendly electro deposition method was employed for the fabrication of Au–Ag bimetallic nanoparticles modified glassy carbon electrode. Nano Au–Ag film modified glassy carbon electrode surface morphology has been examined using atomic force microscopy. Electrodeposited Au–Ag bimetallic nanoparticles were found in the average size range of 15–50 nm. The electrochemical investigations of nano Au–Ag/1-butyl-3-methylimidazolium tetrafluoroborate-nafion film have been carried out using cyclic voltammetry and electrochemical impedance spectroscopy. The nano Au–Ag/1-butyl-3-methylimidazolium tetrafluoroborate-nafion film modified glassy carbon electrode holds the good electrochemical behavior and stability in pH 7.0 phosphate buffer solutions. The nano Au–Ag/1-butyl-3-methylimidazolium tetrafluoroborate-nafion modified glassy carbon electrode was successfully employed for the detection of H₂O₂ in the linear range of 1–250 μM in lab samples, and 1 × 10⁻³–2 × 10⁻² M in real samples, respectively.     

Selective determination of dopamine in the presence of ascorbic acid using ferrocenyl-tethered PAMAM dendrimers modified glassy carbon electrode

Determination of dopamine (DA) in the absence and presence of ascorbic acid (AA) by ferrocenyl-tethered PAMAM G3 dendrimers (Fc-D) modified glassy carbon electrode (GCE) was reported. The modified electrode was characterized with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Factors influencing the detection processes were optimized and kinetic parameters were calculated. The sensor exhibited excellent catalytic activities for the oxidation–reduction reactions of DA and eliminated the interference of AA. Under optimal condition, the linear range of 1 × 10⁻⁵–1.5 × 10⁻³ mol L⁻¹ and the detection limit of 4.7 × 10⁻⁶ mol L⁻¹ was obtained. This study provides a new idea for the determination of DA in the presence of AA.     

Selective determination of uric acid in the presence of ascorbic acid at poly(<Emphasis Type="Italic">p</Emphasis>-aminobenzene sulfonic acid)-modified glassy carbon electrode

The electrocatalytic behavior of uric acid has been investigated with a glassy carbon electrode modified with p-aminobenzene sulfonic acid through electrochemical polymerization. This resulting electrode shows an excellent electrocatalytic response to uric acid and ascorbic acid, with a peak-to-peak separation of 0.267 V in a 0.1 mol L⁻¹ phosphate buffer solution (PBS) at pH 7.0. These results indicate that the proposed electrode can eliminate the serious interference of ascorbic acid, which coexists with uric acid in body fluids. Differential pulse voltammetry (DPV) was used for detecting uric acid with selectivity and sensitivity. The anodic peak current of uric acid was proportional to its concentration in the range of 1.2 × 10⁻⁷–8.0 × 10⁻⁴ mol L⁻¹, with a detection limit of 4.0 × 10⁻⁸ mol L⁻¹. The proposed method has been applied with satisfactory results to the determination of uric acid in human urine without any pretreatment.     

A New PVC Membrane Ion Selective Electrode for Determination of Cationic Surfactant in Mouthwash

A new membrane electrode was prepared, using cetylpyridinium chloride based Sn(IV) phosphate (CPC-SnP) as the electroactive material. The electrode exhibits a linear response for the surfactant cetylpyridinium chloride (CPC) in the concentration range 5.0 × 10⁻³–5.0 × 10⁻⁶ mol dm⁻³ with a slope as a 29.1 mV/decade change in the concentration. The working pH range and the response time for the electrode are 2–6 and 30 s respectively. Selectivity coefficients for several cations were determined. The determination of CPC in mouth wash gave results that compare favorably with those obtained by the two phase titration method. This electrode has been utilized as an indicator electrode in the potentiometric titration of cationic surfactant CPC as well as in direct determination of CPC.     

High-performance supercapacitor of manganese oxide/reduced graphene oxide nanocomposite coated on flexible carbon fiber paper

Although supercapacitors have higher power density than batteries, they are still limited by low energy density and low capacity retention. Here we report a high-performance supercapacitor electrode of manganese oxide/reduced graphene oxide nanocomposite coated on flexible carbon fiber paper (MnO₂–rGO/CFP). MnO₂–rGO nanocomposite was produced using a colloidal mixing of rGO nanosheets and 1.8 ± 0.2 nm MnO₂ nanoparticles. MnO₂–rGO nanocomposite was coated on CFP using a spray-coating technique. MnO₂–rGO/CFP exhibited ultrahigh specific capacitance and stability. The specific capacitance of MnO₂–rGO/CFP determined by a galvanostatic charge–discharge method at 0.1 A g⁻¹ is about 393 F g⁻¹, which is 1.6-, 2.2-, 2.5-, and 7.4-fold higher than those of MnO₂–GO/CFP, MnO₂/CFP, rGO/CFP, and GO/CFP, respectively. The capacity retention of MnO₂–rGO/CFP is over 98.5% of the original capacitance after 2000 cycles. This electrode has comparatively 6%, 11%, 13%, and 18% higher stability than MnO₂–GO/CFP, MnO₂/CFP, rGO/CFP, and GO/CFP, respectively. It is believed that the ultrahigh performance of MnO₂–rGO/CFP is possibly due to high conductivity of rGO, high active surface area of tiny MnO₂, and high porosity between each MnO₂–rGO nanosheet coated on porous CFP. An as-fabricated all-solid-state prototype MnO₂–rGO/CFP supercapacitor (2 × 14 cm) can spin up a 3 V motor for about 6 min.     

<Emphasis Type="Italic">Meso</Emphasis>-Tetra-(3,5-Dibromo-4-Hydroxydroxyphenyl) Porphyrin Copper (II) Self-Assembled Modified Gold Electrode Through <Emphasis Type="SmallCaps">l</Emphasis>-Cysteine: The Preparation,Electrochemical Behavior and its Application

In this study, a sensor for the sensitive determination of ascorbic acid (AA) has been fabricated based on meso-tetra-(3,5-dibromo-4-hydroxydroxyphenyl) porphyrin copper (II) (T(DBHP)P-Cu) modified Au electrode through l-cysteine (l-cys). Firstly, l-cys modified Au electrode was prepared through self-assembled technology. Then T(DBHP)P-Cu was adsorbed on l-cys/Au through covalent binding. The fabrication process and electrochemical behavior of T(DBHP)P-Cu/l-cys/Au were studied by cyclic voltammetry and differential pulse voltammetry. The results showed that AA exhibited good electrochemical activity at T(DBHP)P-Cu/l-cys/Au. The oxidation peak current increased linearly with AA concentration in the range of 1.00 × 10⁻³–1.02 × 10⁻⁵ mol L⁻¹ with a detection limit of 5.41 × 10⁻⁷ mol L⁻¹. Additionally, the modified electrode could be applied to the detect AA in practical samples.     

Electrochemical properties and simultaneous determination of dihydroxybenzene isomers at ordered mesoporous carbon-modified electrode

The voltammetric behaviors of dihydroxybenzene isomers were studied at an ordered mesoporous carbon-modified glassy carbon (OMC/GC) electrode. Compared to the bare electrode, the electrocatalytic activity of the modified electrode toward dihydroxybenzenes is evidenced by the increase of the peak current and the decrease of the peak separation (ΔE _p) in 0.1 M pH 5.0 phosphate buffer solution (PBS). Furthermore, at the OMC/GC-modified electrode, the three isomers could be separated entirely. The oxidation peak potential difference between hydroquinone and catechol is 154 mV, whereas that difference between catechol, and resorcinol is 370 mV. In the amperometric detection, the peak currents of dihydroxybenzene increased linearly with increasing dihydroxybenzene contents. The detection limits were 7.6 × 10⁻⁸ M, 1.0 × 10⁻⁷ M, 9.0 × 10⁻⁸ M for hydroquinone, catechol and resorcinol, respectively, which are the lowest values ever reported for dihydroxybenzene isomers. These make OMC/GC electrode a promising candidate for the simultaneous determination of isomers.     

Study of electrochemical properties and the charge/discharge mechanism for Li<Subscript>4</Subscript>Mn<Subscript>5</Subscript>O<Subscript>12</Subscript>/MnO<Subscript>2</Subscript>-AC hybrid supercapacitor

Spinel Li₄Mn₅O₁₂ was prepared by a sol–gel method. The manganese oxide and activated carbon composite (MnO₂-AC) were prepared by a method in which KMnO₄ was reduced by activated carbon (AC). The products were characterized by XRD and FTIR. The hybrid supercapacitor was fabricated with Li₄Mn₅O₁₂ and MnO₂-AC, which were used as materials of the two electrodes. The pseudocapacitance performance of the Li₄Mn₅O₁₂/MnO₂-AC hybrid supercapacitor was studied in various aqueous electrolytes. Electrochemical properties of the Li₄Mn₅O₁₂/MnO₂-AC hybrid supercapacitor were studied by using cyclic voltammetry, electrochemical impedance measurement, and galvanostatic charge/discharge tests. The results show that the hybrid supercapacitor has electrochemical capacitance performance. The charge/discharge test showed that the specific capacitance of 51.3 F g⁻¹ was obtained within potential range of 0–1.3 V at a charge/discharge current density of 100 mA g⁻¹ in 1 mol L⁻¹ Li₂SO₄ solution. The charge/discharge mechanism of Li₄Mn₅O₁₂ and MnO₂-AC was discussed.     

Development of a new biosensor for mediatorless voltammetric determination of hydrogen peroxide and its application in milk samples

A new biosensor for the voltammetric detection of hydrogen peroxide was developed based on immobilization of catalase on a clinoptilolite modified carbon paste electrode using bovine serum albumin and glutaraldehyde. The biosensor response was evaluated according to electrode composition, reaction time, solution pH and temperature. The voltammetric signals were linearly in proportion to H₂O₂ concentration in the range 5.0 × 10⁻⁶–1.0 × 10⁻³ M with a correlation coefficient of 0.9975. The detection limit is 8.0 × 10⁻⁷ M and the relative standard deviation for 4.0 × 10⁻⁴ M hydrogen peroxide was 1.83% (n = 6). The biosensor exhibited high sensitivity, and it was determined that it could be used for more than 2 months. In addition, the biosensor was successfully applied for the determination of hydrogen peroxide in milk samples.     

A novel zeolite-multiwalled carbon nanotube composite for the electroanalysis of copper(II) ion

The application of zeolite Y-multiwalled carbon nanotube (MWCNT) nanocomposite modified glassy carbon electrode (zeolite Y-MWCNT/GCE) in the electroanalysis of Cu²⁺ ion is presented. In order to bring out the unique advantage of the zeolite Y-MWCNT/GCE, experiments were carried out also at graphite/GCE, MWCNT/GCE and zeolite Y-graphite/GCE. For the same surface area, the performance of zeolite Y-MWCNT/GCE was superior to the other modified electrodes in terms of current sensitivity for Cu²⁺ ion. The combination of zeolite Y and MWCNT as a nanocomposite resulted in a good synergetic effect. The Cu⁺² ion sensor exhibited a linear calibration range between 5 × 10⁻⁸ and 1 × 10⁻⁵ mol L⁻¹ with a detection limit of 1.12 × 10⁻⁸ mol L⁻¹ (0.72 ppb).     

Electrocatalytic oxidation of ascorbic acid at a 2,2′-(1,8-octanediylbisnitriloethylidine)-bis-hydroquinone modified carbon paste electrode

Cyclic voltammetry and chronoamperometry were used to investigate the electrochemical behavior of ascorbic acid at a carbon paste electrode modified with 2,2′-(1,8-octanediylbisnitriloethylidine)-bis-hydroquinone (1,8-OBNEBHQ). The modified carbon paste electrode showed high electrocatalytic activity toward ascorbic acid; the current was enhanced significantly relative to the situation prevailing when an unmodified carbon paste electrode was used. The electrocatalytic process was highly dependent on the pH of the supporting electrolyte. The apparent charge transfer rate constant, k_s, and transfer coefficient, α, for electron transfer between 1,8-OBNEBHQ and carbon paste electrode were calculated as 20.2 ± 0.5 s⁻¹ and 0.47, respectively. Using differential pulse voltammetry, the calibration curves for AA were obtained over the range of 5–30 and 40–1,500 μM, respectively. The detection limit (kσ, k = 2) was 0.6 μM. With good selectivity and sensitivity, the present method provides a simple method for selective detection of ascorbic acid in biological samples.     

Cathodic reaction kinetics and its implication on flow-assisted corrosion of aluminum alloy in aqueous ethylene glycol solution

The cathodic reaction kinetics and anodic behavior of Al alloy 3003 in aerated ethylene glycol–water solution, under well-controlled hydrodynamic conditions, were investigated by various measurements using a rotating disk electrode (RDE). The transport and electrochemical parameters for cathodic oxygen reduction were fitted and determined. The results demonstrate that the cathodic reaction is a purely diffusion-controlled process within a certain potential region. The experimentally fitted value of diffusion coefficient of oxygen is 3.0 × 10⁻⁸ cm² s⁻¹. The dependence of cathodic current on rotation speed was in quantitative agreement with Levich equation. At potentials more positive than the diffusion controlled region, the cathodic process was controlled by both diffusion and electrochemical kinetics. The electrochemical reaction rate constant, k ₀, was determined to be 1.1 × 10⁻⁹ cm s⁻¹. There is little effect of electrode rotation on anodic behavior of Al alloy during stable pitting. However, fluid hydrodynamics play a significant role in formation of the oxide film and the Al alloy passivity. An enhanced electrode rotation would increase the mass-transfer rate of solution, and thus the oxygen diffusion towards the electrode surface for reduction reaction. The generated hydroxide ions are favorable to the formation of Al oxide film on electrode surface.     

An Effective Amperometric Biosensor Based on Gold Nanoelectrode Arrays

A sensitive amperometric biosensor based on gold nanoelectrode array (NEA) was investigated. The gold nanoelectrode array was fabricated by template-assisted electrodeposition on general electrodes, which shows an ordered well-defined 3D structure of nanowires. The sensitivity of the gold NEA to hydrogen peroxide is 37 times higher than that of the conventional electrode. The linear range of the platinum NEA toward H₂O₂ is from 1 × 10⁻⁶ to 1 × 10⁻² M, covering four orders of magnitudes with detection limit of 1 × 10⁻⁷ M and a single noise ratio (S/N) of four. The enzyme electrode exhibits an excellent response performance to glucose with linear range from 1 × 10⁻⁵ to 1 × 10⁻² M and a fast response time within 8 s. The Michaelis–Menten constant km and the maximum current density i _max of the enzyme electrode were 4.97 mM and 84.60 μA cm⁻², respectively. This special nanoelectrode may find potential application in other biosensors based on amperometric signals.     

Voltammetric studies of titanium (IV) phosphate modified with copper hexacyanoferrate and electroanalytical determination of <Emphasis Type="Italic">N</Emphasis>-acetylcysteine

Titanium (IV) Phosphate copper hexacyanoferrate composite (TiPhCuHCF) was prepared using a new methodology for the synthesis. A preliminary characterization of the precursor and resulting materials was defined using spectroscopic and chemical techniques. The cyclic voltammogram of the modified electrode containing TiPhCuHCF exhibited two redox couples. The first and second redox couples present a formal potential (E ^θ′) of 0.18 and 0.76 V and were ascribed to the Cu^+/Cu²⁺ (E ^θ′)₁ and Fe²⁺(CN)₆/Fe³⁺(CN)₆ (E ^θ′)₂ processes, respectively. In a preliminary study, the peak located at 0.76 V displays a sensitive response to N-acetylcysteine. The modified graphite paste electrode showed a linear range from 1.0 × 10⁻⁵ to 7.0 × 10⁻⁴ mol L⁻¹ for the determination of N-acetylcysteine with a limit detection of 6.96 × 10⁻⁵ mol L⁻¹ and relative standard deviation of ± 5% (n = 3) and amperometric sensitivity of 24.79 × 10⁻³ A mol L⁻¹. The modified electrode was electrochemically stable and showed good reproducibility.     

Electrochemical determination of ascorbic acid at the surface of a graphite electrode modified with multi-walled carbon nanotubes/tetradecyltrimethylammonium bromide

A multi-walled carbon nanotubes (MWCNTs)–tetradecyltrimethylammonium bromide (TTAB) film-coated graphite electrode (GE) was fabricated, and the electrochemical oxidation of ascorbic acid (AA) was studied in Britton–Robinson (B–R) buffer (pH 7.0) using cyclic, square wave, and differential pulse voltammetry (CV, SWV, and DPV). An electroanalytical study of AA and acetaminophen (ACOP) and of several mixtures of these compounds in different ratios was made. A sensitive linear voltammetric response for AA was obtained for the concentration range of 5 × 10⁻⁷ to 1.7 × 10⁻⁴ mol L⁻¹, with a correlation coefficient of 0.992, and the detection limit for AA was found to be 1.1 × 10⁻⁷ mol L⁻¹ using DPV. The relative standard deviation (RSD) was 2.7%, suggesting that the film electrode has excellent day-to-day reproducibility. The proposed voltammetric approach was also applied to the determination of the AA concentration in commercial tablets.     

Pulse anodic stripping voltammetric determination of copper with an amoxicillin–nafion modified glassy carbon electrode

The analysis of Cu²⁺ by pulse anodic stripping voltammetry using a Nafion-modified glassy Carbon electrode incorporated with Amoxicillin is described. A significant increase in the voltammetric response was achieved at the modified electrode compared to a bare glassy carbon electrode. Cu²⁺ was accumulated in HAc–NaAc buffer (pH 3.6) at a potential of −0.7 V (vs. Ag/AgCl) for a certain time and then determined by pulse anodic stripping voltammetry. Parameters and conditions, such as the mass of Nafion, the concentration of Amoxicillin, the pH of medium, the accumulation potential, and the accumulation time were optimized. Under the optimum conditions, the calibration curve was linear in the range 8 × 10⁻¹⁰–2 × 10⁻⁸ M with a correlation coefficient of 0.9998 and relative standard deviation 4.87% (n = 5). The detection limit was 1.3 × 10⁻¹⁰ M. A study of interfering substances was also performed and the analytical utility of the method was demonstrated by applying to various pharmaceutical products.     

Electrogenerated chemiluminescence of ruthenium (II) bipyridyl complex directly immobilized on glassy carbon electrodes

Ru(bpy)₃Cl₂ was used to modify the glass carbon electrodes (GCE) by oxidation and co-deposition on the electrode surface. The modified electrodes were characterized by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). About 2.2 × 10⁻⁹ mol Ru(bpy)₃ ²⁺ was immobilized on the GCE surface (ϕ = 4 mm). The modified GC electrodes showed stable electrochemiluminescence with tripropylamine (TPrA) as the co-reactant with a linear range from 10 to 500 μM (R ² = 0.999). Among the 10 amino acids tested, the modified electrode system showed selective response to arginine and lysine, indicating that the molecular structure played an important role as co-reactant. This simple and sensitive electrode modifying method when combined with flow-injection or liquid chromatography systems has the potential for amino acid analyses.     

Preparation and characterization of manganese oxide/CNT composites as supercapacitive materials

Manganese oxide was synthesized and dispersed on carbon nanotube (CNT) matrix by thermally decomposing manganese nitrates. CNTs used in this paper were grown directly on graphite disk by chemical vapor deposition technique. The capacitive behavior of manganese oxide/CNT composites was investigated by cyclic voltammetry and galvanostatic charge–discharge method in 1 M Na₂SO₄ aqueous solutions. When the loading mass of MnO₂ is 36.9 μg cm^− 2, the specific capacitance of manganese oxide/CNT composite (based on MnO₂) at the charge–discharge current density of 1 mA cm^− 2 equals 568 F g^− 1. Additionally, excellent charge–discharge cycle stability (ca. 88% value of specific capacitance remained after 2500 charge–discharge cycles) and power characteristics of the manganese oxide/CNT composite electrode can be observed. The effect of loading mass of MnO₂ on specific capacitance of the electrode has also been investigated.