A Novel Electrochemical Sensor Based on Poly(1,5-diaminonaphthalene) and Poly(1,2-diaminoanthraquinone) Core-shell Composite Electrodes for Effective Voltammetric Determination of Nitrite

In this article, poly(1,2-diaminoanthraquinone) (pDAAQ) and poly(1,5-diaminonaphthalene) (pDAN) were electrochemically deposited layer by layer on a glassy carbon electrode (GCE) to generate pDAAQ/pDAN@GCE and pDAN/pDAAQ@GCE composite electrodes, respectively. The morphology and characteristics of the modified electrodes were investigated via electrochemical impedance spectroscopy)EIS), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy)SEM). The obtained results reveal the outstanding performance of the pDAN/pDAAQ@GCE electrode for electrochemical nitrite sensing where pDAAQ plays a vital role as the inner layer. Cyclic voltammetry (CV), linear sweep voltammetry (LSV), and differential pulse voltammetry (DPV) measurements revealed that the oxidation peak current of nitrite was proportional to its concentration. The best LSV results were obtained in a concentration range of 10–150 μM, with a limit of detection of 1.2 μM. Furthermore, the pDAN/pDAAQ@GCE composite electrode was used to determine nitrite ions in real water samples with good results.     

Construction of an electrochemical sensor based on the electrodeposition of Au-Pt nanoparticles mixtures on multi-walled carbon nanotubes film for voltammetric determination of cefotaxime

Mixtures of gold-platinum nanoparticles (Au-PtNPs) are fabricated consecutively on a multi-walled carbon nanotubes (MWNT) coated glassy carbon electrode (GCE) by the electrodeposition method. The surface morphology and nature of the hybrid film (Au-PtNPs/MWCNT) deposited on glassy carbon electrodes is characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques. The modified electrode is used as a new and sensitive electrochemical sensor for the voltammetric determination of cefotaxime (CFX). The electrochemical behavior of CFX is investigated on the surface of the modified electrode using linear sweep voltammetry (LSV). The results of voltammetric studies exhibited a considerable improvement in the oxidation peak current of CFX compared to glassy carbon electrodes individually coated with MWCNT or Au-PtNPs. Under the optimized conditions, the modified electrode showed a wide linear dynamic range of 0.004-10.0 μM with a detection limit of 1.0 nM for the voltammetric determination of CFX. The modified electrode was successfully applied for the accurate determination of trace amounts of CFX in pharmaceutical and clinical preparations.     

基于羧基化碳纳米管修饰电极伏安法同时测定痕量锢和铝

基于羧基化多壁碳纳米管(c-MWCNT),制备了可同时测定In3+和Al3+的新型碳材料修饰电极.利用循环伏安法(CV)和交流阻抗法(EIS)对此修饰电极进行了表征,用线性扫描伏安法(LSV)研究了In3+与Al3+共存于修饰电极上的电化学行为.与裸玻碳电极相比,新型碳材料修饰电极的电化学活性得到很大提高;In3+与A...     

Effect of Various Deposition Techniques,Electrode Materials and Posttreatment with Tetrabutylammonium and Tetrabutylphosphonium Salts on the Electrochemical Behavior and Stability of Various Prussian Blue Modified Electrodes

The effect of various deposition techniques, electrode materials and posttreatment with tetrabutylammonium and tetrabutylphosphonium salts on the electrochemical behavior and stability of various Prussian blue (PB) modified electrodes, namely PB modified glassy carbon electrodes, silicate‐film supported PB modified glassy carbon electrodes, PB‐doped silicate glassy carbon electrodes, PB modified carbon ceramic electrodes using electrochemical deposition and PB modified carbon ceramic electrodes using chemical deposition is reported. Cyclic voltammetry and amperometric measurements of hydrogen peroxide were performed in a flow injection system while the carrier phosphate buffer (pH 7.0) with a flow rate of 0.8 mL min^?1 was propelled into the electrochemical flow through cell housing the PB modified working electrode as well as an Ag|AgCl|0.1 M KCl reference and a Pt auxiliary electrode. The results showed that the deposition procedure, electrode material and posttreatment with additional chemicals can significantly alter the stability and electrochemical behavior of the PB film. Among the studied PB modified electrodes, those based on carbon ceramic electrodes modified with a film of electropolymerized PB showed the best electrochemical stability.     

Electroreduction of Oxygen and Electrooxidation of Methanol at Carbon and Single Wall Carbon Nanotube Supported Platinum Electrodes

The present research aimed at investigating the electrocatalytic properties and the electrochemical deposition of Pt nanoparticles on carbon powder, carbon nanotube and preparation of carbon and single wall carbon nanotube supported platinum electrodes. The Pt nanoparticles were synthesized by electroreduction of hexachloroplatinic acid in aqueous solution at ?200 mV. Electrocatalytic properties of the modified electrodes for oxygen reduction were investigated by cyclic voltammetry in O₂ saturated solution containing 0.1 M HClO₄. Methanol electrooxidation at the modified surfaces in 0.5 M HCLO₄ was studied by cyclic voltammetry. The corresponding results showed that the Pt/SWCNT/GC electrode exhibits more improved catalytical activity than the Pt/C/GC electrode.     

Electrochemical,microscopic, and EQCM studies of cathodic electrodeposition of ZnO/FAD and anodic polymerization of FAD films modified electrodes and their electrocatalytic properties

Two kinds of chemically modified electrodes were prepared. In the first type of electrodes, zinc oxide (ZnO) and flavin adenine dinucleotide (FAD) molecules were deposited onto the glassy carbon-, gold-, and SnO₂-coated glass electrodes by using cyclic voltammetry from the bath solution containing aqueous 0.1 M zinc nitrate, 0.1 M sodium nitrate, and 1 × 10⁻⁴ M FAD. It was called as ZnO/FAD modified electrodes. The second type of modified electrode was prepared by the electropolymerization method. Electrochemical polymerization of FAD was carried out from the acidic solution containing 1 × 10⁻⁴ M FAD monomers onto electrode surfaces. This poly(FAD)-modified electrode yields a new redox couple in addition to the monomers redox couple. The influence of the concentrations, pH, and electrocatalytic properties of the ZnO/FAD- and poly(FAD)-modified electrodes are investigated by means of the in situ technique electrochemical quartz–crystal microgravimetry (EQCM) combined with cyclic voltammetry and the ex situ technique scanning electron microscopy. From these studies, it appears that the cathodic deposition of ZnO/FAD-modified electrodes gives only one redox couple, and the anodically polymerized FAD film-modified electrodes gives two reversible redox couples. The pH dependence of the redox responses were investigated and the kinetics of electron transfer was evaluated. In addition, the EQCM technique was employed to follow the deposition process of both kinds of modified electrodes in real time as well as the characteristics of the charge transfer associated with the surface-confined redox-active couples. The electrocatalytic activity of the poly(FAD)-modified electrode towards the reduction of hydrogen peroxide and the oxidation of dopamine and ascorbic acid was explored. The important electrocatalytic properties of poly(FAD)-modified electrode were observed for simultaneous separation of dopamine and ascorbic acid in neutral solution. This poly(FAD)-modified electrode has several advantages than the previously reported FAD-modified electrodes.     

Silica‐modified Electrodes for Electrochemical Detection of Malachite Green

New silica‐modified glassy carbon electrodes prepared with three different sorts of ordered mesoporous silica (OMS) were characterized and tested for the electrochemical detection of Malachite Green (MG). The electrodes were prepared by drop casting using silica suspensions and, for stability sake, a Nafion coating was deposited on the electrode top by the same technique. Square wave anodic stripping voltammetry was used to investigate the effect of various experimental parameters (deposition time, solution pH, silica type and concentration) on the performance of the modified electrodes. The best electrode (GC/MCM‐41‐NH₂/Nafion) with detection limit 0.36 μM, sensitivity 0.164±0.003 A/M; linear domain 1–6 μM was applied to detect MG in a commercial product commonly used as biocide in aquaria for ornamental fish.     

Direct electrochemical conversion of bilirubin oxidase at carbon nanotube-modified glassy carbon electrodes

We report on direct electron transfer reactions of bilirubin oxidase at multi-walled carbon nanotube (MWCNT) modified glassy carbon electrodes (GCE). The bioelectrocatalytic oxygen reduction was recorded using linear sweep voltammetry (LSV) with BOD in solution, adsorbed and covalently linked to the nanotubes. The MWCNT modification of GC electrodes strongly enhances the oxygen reduction compared to the signals at unmodified GCE. Under anaerobic conditions with a high protein concentration in solution a pair of redox peaks with a formal potential of 450 ± 15 mV vs Ag/AgCl, 1 M KCl (pH 7.4) was found with cyclic voltammetry. The redox conversion is indicated to be surface-controlled and pH-dependent (54.5 mV/pH). The quasi-reversible redox reaction might be attributed to the trinuclear T2/T3 cluster of BOD.     

Permselectivity of neurotransmitters at overoxidized polypyrrole-film-coated glassy carbon electrodes

The permselectivity of neurotransmitters such as dopamine, epinephrine, and norepinephrine at overoxidized polypyrrole (OPPY)-film-coated glassy carbon electrodes has been investigated. The chemically-modified electrodes exhibit attractive permselectivity and antifouling properties of rejecting anionic species, e.g. ascorbate, etc. Compared with the response of neurotransmitters at modified electrodes overoxidized in phosphate buffer solution (pH 7.4), higher sensitivity and reversibility response can be obtained at modified electrodes overoxidized in sodium hydroxide solution. The effect of film thickness on the permselective response was tested. Rotating disk electrode experiments were used to determine the apparent diffusion coefficients of several electroactive solutes in the OPPY films. The influence of the hydrophobicity of the organic ions on the permeability within the polymer films was discussed. Dopamine and epinephrine were determined at the 1 x 10(-6)-1 x 10(-4) M level by means of voltammetry after an exposure period of 2 min in 0.1 M phosphate buffer (pH 7.4) with detection limits of 8 x 10(-7) M and 6 x 10(-7) M respectively.     

Electrochemical behavior of methyl viologen at graphite electrodes modified with Nafion sol–gel composite

Electrodes were prepared by spin-coating spectroscopic graphite rods with a Nafion doped sol. Coating solutions consisting of Nafion:TEOS (tetraethoxysilane) ratios of 3:1 and 4:1 gave smooth films on the electrode surface. These modified electrodes were evaluated and compared with Nafion modified and bare spectroscopic graphite electrodes using methyl viologen (MV²⁺) as a representative cationic electroactive probe. Substantial partitioning of MV²⁺ into the Nafion:sol–gel matrix to the electrode surface was observed by cyclic voltammetry and square wave voltammetry. Cyclic voltammograms of MV²⁺ in 0.1 M NaCl at Nafion:sol–gel 4:1 modified electrodes showed a reversible reduction to MV⁺ with E^0′=−0.695 V vs. Ag/AgCl. Results of scan rate variation showed the wave to be characterized by semi-infinite diffusion for scan rates in the range 50–500 mV/s. Slowing the scan rate below 50 mV/s resulted in a transition to thin-layer behavior. MV²⁺ partitioned much more quickly into the sol–gel-Nafion modified electrodes compared to pure Nafion modified electrodes. Reversibility of the MV²⁺-loaded modified Nafion-doped sol–gel coatings on electrodes was obtained by soaking in 1 M NaCl solution. Concentration calibration plots for MV²⁺ at the sol–gel-Nafion modified electrodes were nonlinear. Substantial enhancement of current signal at low concentrations was observed by square wave voltammetry.     

Ruthenium porphyrin functionalized single-walled carbon nanotube arrays--a step toward light harvesting antenna and multibit information storage

Ruthenium porphyrin functionalized single-walled carbon nanotube arrays have been prepared using coordination of the axial position of the metal ion onto 4-aminopyridine preassembled single-walled carbon nanotubes directly anchored to a silicon(100) surface (SWCNTs-Si). The formation of these ruthenium porphyrin functionalized single-walled carbon nanotube array electrodes (RuTPP-SWCNTs-Si) has been monitored using infrared spectroscopy (IR), differential pulse voltammetry (DPV), atomic force microscopy (AFM), laser desorption time-of-flight mass spectroscopy (LDI-TOF-MS), UV-vis spectroscopy, fluorescence spectroscopy, and cyclic voltammetry. Electrochemical results show two successive one-electron reversible redox waves. The surface concentration of the ruthenium porphyrin molecules is 3.44 x 10 (-8) mol cm (-2). Optical results indicate that the immobilization of ruthenium porphyrin enhances the light absorption of SWCNTs-Si surfaces in the visible light region. Moreover mixed assembly of ferrocene/porphyrin onto carbon nanotube arrays has been achieved by altering the ratio of two redox-active species in the deposition solution. These results suggest the ruthenium porphyrin modified electrodes are excellent candidates for molecular memory devices and light harvesting antennae.     

Voltammetric Reduction of a 4‐Nitroimidazole Derivative on a Multiwalled Carbon Nanotubes Modified Glassy Carbon Electrode

We report the electrochemical behavior of a 4‐nitroimidazole derivative, 1‐methyl‐4‐nitro‐2‐hydroxymethylimidazole (4‐NImMeOH), on glassy carbon electrode (GCE) modified with multiwalled carbon nanotubes (MWCNT). As dispersing agents, dimethylformamide (DMF) and water were used. The electrochemical response of the resulting electrodes was evaluated using linear sweep, cyclic and square‐wave voltammetry (LSV, CV and SWV). Several parameters such as medium pH, nature and concentration of the CNTs dispersion and accumulation time were tested. The optimal conditions determined for obtain better response were: pH 2, dispersion concentration=4 mg/mL of CNT in water, accumulation time=7 min. The MWCNT‐modified GCE exhibited attractive electrochemical properties producing enhanced currents with a significant reduction in the overpotential and good signal‐to‐noise characteristics, in comparison with the bare GCE. The modified electrode is highly repeatable for consecutive measurements, reaching a variation coefficient of 2.9% for ten consecutive runs.     

A novel nitrite sensor based on graphene/polypyrrole/chitosan nanocomposite modified glassy carbon electrode

A novel nitrite sensor was fabricated based on a graphene/polypyrrole/chitosan nanocomposite film modified glassy carbon electrode. The nanocomposite film was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and Raman spectroscopy. The electron transfer behaviour of the modified electrodes was investigated in [Fe(CN)(6)](3-)/(4-) redox probe using cyclic voltammetry and electrochemical impedance spectroscopy. Differential pulse voltammetry and amperometry were used to study the electrochemical properties of the proposed sensor. Under optimum conditions, the sensor exhibited good reproducibility and stability for nitrite determination. Linear response was obtained in the range of 0.5-722 μM with a detection limit of 0.1 μM (S/N = 3) for nitrite determination.     

Investigation of electrochemical behavior of lipid lowering agent atorvastatin calcium in aqueous media and its determination from pharmaceutical dosage forms and biological fluids using boron-doped diamond and glassy carbon electrodes

The electrochemical behavior of atorvastatin calcium at glassy carbon and boron-doped diamond electrodes has been studied using voltammetric techniques. The possible mechanism of oxidation was discussed with model compounds. The dependence of the peak current and potentials on pH, concentration, scan rate and nature of the buffer were investigated for both electrodes. The oxidation of atorvastatin was irreversible and exhibited a diffusion-controlled fashion on the diamond electrode. A linear response was obtained within the range of 9.65 x 10(-7) - 3.86 x 10(-5) M in 0.1 M H(2)SO(4) solution for both electrodes. The detection limits of a standard solution are estimated to be 2.11 x 10(-7) M with differential pulse voltammetry (DPV) and 2.05 x 10(-7)M with square wave voltammetry (SWV) for glassy carbon electrode, and 2.27 x 10(-7) M with DPV and 1.31 x 10(-7)M with SWV for diamond electrodes in 0.1 M H(2)SO(4) solution. The repeatability of the methods was found good for both electrodes. The methods were fully validated and successfully applied to the high-throughput determination of the drug in tablets, human serum and human urine with good recoveries.     

Comparison of Voltammetric Techniques for Ammonia Sensing in Ionic Liquids

In electroanalytical chemistry, it is often observed that square wave voltammetry (SWV) and differential pulse voltammetry (DPV) are more sensitive techniques compared to linear sweep voltammetry (LSV), due to their method of sampling which minimises the charging current (non‐faradaic processes). In this work, a comparison of the three techniques (LSV, DPV and SWV) is performed for ammonia (NH₃) gas oxidation (a chemically and electrochemically irreversible redox process) in an ionic liquid over a concentration range of 10–100 ppm. Four different platinum electrodes are employed: a screen‐printed electrode (SPE), a thin‐film electrode (TFE), a microarray thin‐film electrode (MATFE) and a Pt microdisk electrode (μ‐disk). Calibration plots (current vs concentration) for all three different electrochemical techniques on all four surfaces showed excellent linearity with increased concentrations of NH₃ gas and relatively low limits of detection (LODs). On the larger mm‐sized surfaces (SPE and TFE), the current responses for LSV and SWV were quite similar, but DPV gave the lowest currents. Whereas for the smaller micron sized electrodes (MATFE and μ‐disk), currents were of the order LSV>SWV>DPV, with LSV being far superior to the pulse techniques. These findings suggest that the pulse techniques of SWV and DPV may not be the optimum methods, particularly on microelectrodes, for the detection of analytes such as ammonia in RTILs.     

Detection of As(III) via oxidation to As(V) using platinum nanoparticle modified glassy carbon electrodes: arsenic detection without interference from copper

The electrochemical detection of As(III) was investigated on a platinum nanoparticle modified glassy carbon electrode in 1 M aqueous HClO4. Platinum nanoparticle modified glassy carbon electrodes were prepared by potential cycling in 0.1 M aqueous KCl containing 1 mM K2PtCl6. In each potential cycle, the potential was held at + 0.5 V for 0.01 s and at -0.7 V for 10 s. 25 cycles were optimally used to prepare the electrodes. The resulting electrode surfaces were characterized with AFM. The response to arsenic(III) on the modified electrode was examined using cyclic voltammetry and linear sweep voltammetry. By using the As(III) oxidation peak for the analytical determination, there is no interference from Cu(II) if present in contrast to the other metal surfaces (especially gold) typically used for the detection of arsenic; Cu(II) precludes the use of the As(0) to As(III) peak for quantitative anodic stripping voltammetry measurements due to the formation of Cu3As2 and an overlapping interference peak from the stripping of Cu(0). After optimization, a LOD of 2.1 +/- 0.05 ppb was obtained using the direct oxidation of As(III) to As(V), while the World Health Organization's guideline value of arsenic for drinking water is 10 ppb, suggesting the method may have practical utility.     

Voltammetric determination of 4-nitrophenol at a sodium montmorillonite-anthraquinone chemically modified glassy carbon electrode

A new method for the determination of 4-nitrophenol(4-NP) by differential pulse voltammetry (DPV) based on adsorptive stripping technique was described. Cyclic voltammetry (CV) and linear scan voltammetry (LSV) were used in a comparative investigation into the electrochemical reduction of 4-NP at a Na-montmorillonite(SWy-2) and anthraquione (AQ) modified glassy carbon electrode. With this chemically modified electrode, 4-NP was first irreversibly reduced from phiNO(2) to phiNHOH at -0.78 V. A couple of well-defined redox peaks at +0.22 V (vs. SCE) were responsible for a two-electron redox peak between phiNHOH and phiNO. Studies on the effect of pH on the peak height and peak potential were carried out over the pH range 2.0-9.0 with the phosphate buffer solution. A pH of 3.4 was chosen as the optimum pH. The other experimental parameters, such as film thickness, accumulation time and potential etc. were optimized. Anodic peak currents were found to be linearly related to concentration of 4-NP over the range 0.3-45 mg l(-1), with a detection limit of 0.02 mg l(-1). The interference of organic and inorganic species on the voltammetric response have been studied. This modified electrode can be used to the determination of 4-NP in water samples.     

Nickel oxide nanoparticles prepared by gelatin and their application toward the oxygen evolution reaction

Green synthesis of pure nickel oxide nanoparticles (nano-NiO) in aqueous medium has been carried out using gelatin. The particles have been characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray (EDAX). Gelatin plays an important role in the formation of the nano-NiO. TEM image shows the formation of nano-NiO with average particle size 16 nm, which agrees well with the XRD data. Moreover, efficient and stable nano-NiO-based anodes were fabricated by casting of the nano-NiO and multi-walled carbon nanotube solution (NiO-MWNT) on glassy carbon (NiO-MWNT/GC), platine (NiO-MWNT/Pt), and carbon paste (NiO-MWNT/CP) electrodes. The electrocatalysis of oxygen evolution reaction (OER) at modified electrodes has been examined using linear scanning voltammetry (LSV). The OER is significantly enhanced upon modification of the electrodes with NiO-MWNT, as demonstrated by a negative shift in the LSV curves at the NiO-MWNT-modified electrodes compared to that obtained at the unmodified ones. The maximum electrocatalytic activity toward the OER was obtained in alkaline media. The values of energy saving of oxygen gas at a current density of 5 mA cm^?2 Pt, CP, and GC electrodes are 14.1, 16.0, and 21.6 kW h kg^?1, respectively. The low cost as well as the marked stability of the modified electrodes makes them promising candidates in industrial water electrolysis process.     

Anodic Stripping Voltammetric Detection of Arsenic(III) at Gold Nanoparticle‐Modified Glassy Carbon Electrodes Prepared by Electrodeposition in the Presence of Various Additives

The simple, fast and highly sensitive anodic stripping voltammetric detection of As(III) at a gold (Au) nanoparticle‐modified glassy carbon (GC) (nano‐Au/GC) electrode in HCl solution was extensively studied. The Au nanoparticles were electrodeposited onto GC electrode using chronocoulometric technique via a potential step from 1.1 to 0 V vs. Ag|AgCl|NaCl (sat.) in 0.5 M H₂SO₄ containing Na[AuCl₄] in the presence of KI, KBr, Na₂S and cysteine additives. Surfaces of the resulting nano‐Au/GC electrodes were characterized with cyclic voltammetry. The performances of the nano‐Au/GC electrodes, which were prepared using different concentrations of Na[AuCl₄] (0.05–0.5 mM) and KI additive (0.01–1.0 mM) at various deposition times (10–30 s), for the voltammetric detection of As(III) were examined. After the optimization, a high sensitivity of 0.32 mA cm^?2 μM^?1 and detection limit of 0.024 μM (1.8 ppb) were obtained using linear sweep voltammetry.     

阿奇霉素在多壁碳纳米管修饰电极上的电化学行为及其测定

运用循环伏安法与线性扫描伏安法研究了阿奇霉素在多壁碳纳米管修饰玻碳电极上的电化学行为,建立了一种直接测定阿奇霉素的电化学分析方法。结果表明,与裸玻碳电极相比,多壁碳纳米管修饰电极能显著提高阿奇霉素的氧化峰电流,阿奇霉素的电极过程完全不可逆,存在典型的吸附特性。在优化的实验条件下,氧化峰电流与阿奇霉素浓度在3.0×10-7～2.5×10-5 mol/L和2.5×10-5～5.0×10-4 mol/L范围内呈现良好的线性关系,检出限为1.0×10-7 mol/L。