Chronocoulometry Research Articles

Electrochemical investigation of a novel surfactant for sensitive detection of folic acid in pharmaceutical and biological samples by multivariate optimization

The present study is a report about of an electrochemical sensor for folic acid (FA) detection based on the adsorption of a cationic surfactant, n-dodecylpyridinium chloride (DPC), at the surface of a carbon paste electrode (CPE). The DPC performance compares with the cetyltrimethylammonium bromide (CTAB) to improve the electrochemical reaction and response of FA. It is notable for the first time, DPC is successfully utilized in electrochemical analysis. Determination of FA is performed by differential pulse voltammetry (DPV), cyclic voltammetry (CV) and chronocoulometry (CC) techniques. Response surface methodology (RSM) and central composite rotatable design (CCRD) is chosen for optimization of effective variables in the voltammetric peak current of FA. Another innovation in this study is the utilization of cubic terms in the experimental design. Under the optimized conditions, the FA oxidation peak current was linear to the FA concentration in the range of 0.01 µM–10.69 μM with the detection limit of 2.9 nM (3σ). After studying the influence of probable interferences, it was found that the offered method has excellent selectivity for FA. Finally, the offered procedure was successfully applied to the FA detection in tablet and urine samples with satisfactory results.

Correlation between redox species adsorption and electron transfer kinetics of mildly oxidized graphene: A chronocoulometry and SECM study

The influence of redox species adsorption on the heterogeneous electron transfer (HET) rate of graphene, as well as the methodology for the rational design of intermolecular interactions to optimize the performance of graphene as an electrode modifier, are not completely understood. We investigate the influence of redox species adsorption on the HET rate of a mildly oxidized graphene-modified electrode by chronocoulometry (CC) and cyclic voltammetry (CV) combined with scanning electrochemical microscopy (SECM), using outer-sphere redox species FcCH2OH1+/0 and inner redox species Fe(CN)64−/3–. The results demonstrate that adsorption of outer-sphere redox species on mildly oxidized graphene induces enhancement of HET, which bridges the differences regarding the reactivity of basal and edge plane sites of graphene in the recent literature.

Experimental and theoretical studies of a novel electrochemical sensor based on molecularly imprinted polymer and B, N, F-CQDs/AgNPs for enhanced specific identification and dual signal amplification in highly selective and ultra-trace bisphenol S determination in plastic products

As an ideal alternative to bisphenol A (BPA), bisphenol S (BPS) has similar biotoxicity, teratogenicity, carcinogenicity and mutagenicity as BPA. Nevertheless, to date, a fast, sensitive and portable method for meeting on-site measurement of BPS had not been established. Hence, it was particularly urged to develop a fast and highly sensitive method for tracing BPS. Currently, a novel molecularly imprinted polymer (MIP) electrochemical sensor had been successfully fabricated for the detection of BPS, wherein the composite of three-doped carbon quantum dots (B, N, F-CQDs) and silver nanoparticles (AgNPs) were utilized as an electron conducting layer, and MIP was applied as recognition element of target molecules. The step-by-step fabrication process and the adsorption capacity of the modified electrode were evaluated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronocoulometry (CC). The results indicated that the synergy between B, N, F-CQDs and AgNPs dramatically improved the sensitivity of the electrode and achieved the amplification of the electrical signal. Meanwhile, the electrochemical activities of BPS were explored by CV and differential pulse voltammetry (DPV). And, the various parameters relating to the electrochemical kinetic properties of BPS were calculated. To the best of our knowledge, this was rarely reported in peer journals. The MIP remarkably improved the selectivity of the sensor owing to the specific recognition of the imprinted cavities. The linear response range of the new sensor was 1 × 10−8 M to 5 × 10−5 M with a detection limit of 1.12 × 10−8 M and the electrode designed in this paper could meet the requirement of trace-level measurement of BPS in biological and environmental samples. Additionally, the sensor was used to determine BPS in plastic products with good anti-interference and acceptable recovery.

An Ultrasensitive and Highly Selective Electrochemical Aptasensor for Environmental Endocrine Disrupter Bisphenol A Determination Using Gold Nanoparticles/Nitrogen, Sulfur, and Phosphorus Co-Doped Carbon Dots as Signal Enhancer and Its Electrochemical Kinetic Research

Electrochemistry will bring revolutionary detection methods for bisphenol A (BPA) which is a endocrine disrupter. Electrochemical aptasensor appears to be a promising approach to this end because of its brilliant specificity, high affinity, low cost and rapid response time. However, electrochemical aptasensor suffers from reducing signal when anti-BPA aptamers are modified on electrode surface. In response, we report an electrochemical aptasensor based on gold nanoparticles (AuNPs) and nitrogen, sulfur, and phosphorus co-doped carbon dots (N,S,P-CDs) modified glassy carbon electrode(GCE) for amplified signal detection of BPA. The thiol-gold (S-Au) bonds between the AuNPs and the thiol termini on anti-BPA aptamers anchor the anti-BPA aptamers to the GCE. N,S,P-CDs as electrode modifications are applied to expand the active area and enhance electron-transport ability. In this work, the presences of N,S,P-CDs and the AuNPs were assessed via Fourier transform infrared (FTIR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffractometer (XRD), etc. The sensing scheme and electrochemical response of the proposed sensor were investigated by chronocoulometry (CC), cyclic voltammetry (CV), electrochemical impedance spectra (EIS) and differential pulse voltammetry (DPV). Meanwhile, we focused on discussing the kinetic parameters of [Fe(CN)6]3−/4− on the composite electrode that had reacted with BPA, such as active surface areas (A), surface concentration (Г0), the standard rate constant (k) and electron transfer coefficient (α). Aptasensor revealed a high sensitivity and had a linear electrochemical response to BPA in the concentration range of 0.01 μM–120 μM, with a low detection limit of 5.273 × 10−10 M. Moreover, the proposed aptasensor could be applied for the detection of BPA in real samples with great precision, high sensitivity, excellent selectivity, brilliant reproducibility and satisfactory results. Therefore, this convenient and sensitive aptasensor is proved to a promising and reliable tool for detecting BPA in food and environmental pollution.

An ultra-sensitive label-free electrochemiluminescence CKMB immunosensor using a novel nanocomposite-modified printed electrode.

This study presents a novel and ultrasensitive electrochemiluminescence approach for the quantitative assessment of creatine kinase MB (CK-MB). Both carbon, carbon nano-onions (CNOs) and metal-based nanoparticles, such as gold nanoparticles (AuNPs) and iron oxide (Fe3O4), were combined to generate a unique nanocomposite for the detection of CKMB. The immunosensor construction involved the deposition of the nanocomposite on the working electrode, followed by the incubation of an antibody and a blocking agent. Tris(2,2′-bipyridyl)-ruthenium(ii) chloride ([Ru(bpy)3]2+Cl) was used as a luminophore, where tri-n-propylamine (TPrA) was selected as the co-reactant due to its aqueous immobility and luminescence properties. The analytical performance was demonstrated by cyclic voltammetry on ECL. The characterization of each absorbed layer was performed by cyclic voltammetry (CV) and chronocoulometry (CC) techniques in both EC and ECL. For further characterization of iron oxide, gold nanoparticles and carbon nano-onions, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) were performed. The proposed immunosensor showcases a wide linear range (10 ng mL−1 to 50 fg mL−1), with an extremely low limit of detection (5 fg mL−1). This CKMB immunosensor also exhibits remarkable selectivity, reproducibility, stability and resistance capability towards common interferences available in human serum. In addition, the immunosensor holds great potential to work with real serum samples for clinical diagnosis.

Preparation of a Double‐step Modified Carbon Paste Electrode for Trace Quantification of Acyclovir Using TiO2 Nanoparticle and β‐Cyclodextrin

AbstractIn this work we reported, a simple and reproducible double‐step modified carbon paste electrode (CPE) for recognition and designation of Acyclovir (ACV). In the first stage, for acquiring the structure of TiO2 NPs‐CPE, 5 % TiO2 nanoparticles (NPs) doped into the electrode tissue. In the second stage, β‐Cyclodextrin (β‐CD) anchored on the TiO2 NPs‐CPE surface by electropolymerization which yields a β‐CD/TiO2 NPs‐CPE. Topography, characteristics and electrochemical response of the fabricated electrodes with such techniques as: the field emission scanning electron microscopy (FESEM), chronocoulometry (CC), cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were analyzed. Also the spent TiO2 NPs powders were characterized by X‐ray diffraction (XRD). The results illustrated that this sensor designed efficiently increases the surface area of composite electrode and the performance of the oxidation of ACV at the surface modified electrode compared to the bare electrode improved. Under the desirable situations, the proposed of analytical procedure was proved to be applicable in two linear calibration ranges betwixt 0.09 to 2.98 and 2.98 to 47.61 μM. The detection limit was estimated for low concentrations ACV 21 nM (S/N=3). Eventually, the fabricated composite electrode was successfully applied for the detection of trace amounts of the ACV in the blood serum samples.

An electrochemical biosensor for the detection of Pb2+ based on G-quadruplex DNA and gold nanoparticles

We present a novel simple strategy for the detection of Pb2+ based on G-quadruplex DNA and gold nanoparticles. First, gold nanoparticles were chemically adsorbed onto the surface of a thiol-modified gold electrode. Subsequently, the substrate DNA1 was adsorbed onto the surfaces of the gold nanoparticles via thiol-gold bonds, so that the complementary guanine-rich DNA2 could be hybridized to the gold electrode in sequence. [Ru(NH3)6]3+ (RuHex), which can be electrostatically adsorbed onto the anionic phosphate of DNA, served as an electrochemical probe. The presence of Pb2+ can induce DNA2 to form a stable G-quadruplex and fall off the gold electrode. The amount of RuHex remaining on the electrode surface was determined by electrochemical chronocoulometry (CC). The prepared biosensor showed high sensitivity for Pb2+ with a linear range with respect to ln(cPb2+) from 0.01 to 200nM and a low detection limit of 0.0042nM under optimal conditions. Because of the high selectivity of the Pb2+-specific DNA2, the designed biosensor also showed low false-positive signal rates with other metal ions in real-world examples. Therefore, this strategy has the potential for practical application in environmental monitoring. Graphical abstract ᅟ.

A yolk shell Fe3O4 @PA-Ni@Pd/Chitosan nanocomposite -modified carbon ionic liquid electrode as a new sensor for the sensitive determination of fluconazole in pharmaceutical preparations and biological fluids

In this study, a versatile method was used to synthesize Ni@Pd core–shell nanoparticles, immobilized on Fe3O4@polyaniline yolk–shell composites (Fe3O4@PA). The constructed Fe3O4@PA-Ni@Pd composite and Chitosan were utilized for the modification of carbon ionic liquid electrode (CILE) in high sensitive determination of fluconazole (FLU). A carbon ionic liquid electrode constructed using graphite powder mixed with 1-Butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) in place of paraffin as the binder showed strong electrocatalytic activity to the direct oxidation of Fluconazole. The properties of the electrode surface were characterized by scanning electron microscope (SEM), Transmission electron microscopy (TEM), X-ray diffraction (XRD), Thermal gravimetric analysis (TGA), X-Ray Photo-Emission Electron Microscopy (XPES), Electrochemical Impedance Spectroscopy (EIS), Chronocoulometry (CC) and chronoamperometery (CA) techniques. The recommended quadratic model obtained from the full factorial Box–Behnken design (BBD) was in accordance with the experimental data in an acceptable range. The response was studied in relation to such critical factors as pH, accumulation time, concentration of nanoparticles, and scan rate. The peak currents were proportional to fluconazole concentration in a linear range from 0.01 to 400μmolL−1, with a detection limit of 3.5nmolL−1. Then the constructed sensor was successfully used for the quantification of fluconazole in serum, urine, and tablets.

An Electrochemical Sensor for Sensitive Determination of L-cysteine and Its Electrochemical Kinetics on AgNPs/GQDs/GCE Composite Modified Electrode

L-cysteine plays an essential role in protecting liver cells from toxic damage and regulating phospholipids in the liver. However, some of the methods used to detect L-cysteine suffer from low sensitivity and multiple steps. Herein, we developed a high-sensitivity electrochemical sensor which was manufactured by electrodepositing silver nanoparticles (AgNPs) on a glassy carbon electrode (GCE) modified with graphene quantum dots (GQDs) for detecting L-cysteine. GQDs and AgNPs as electrode modifications were applied to amplify the active area and enhance electron-transport ability for magnifying the sensor signal. Fourier transform infrared (FTIR), X-ray diffraction (XRD) and Raman spectra were used for characterization of GQDs. Field emission scanning electron microscopy (FESEM) was applied to characterize AgNPs. Cyclic voltammetry (CV), differential pulse voltammetry (DPV), chronocoulometry (CC), electrochemical impedance spectra (EIS) were employed to investigate the electrochemical and kinetic behaviors of L-cysteine on composite modified electrode, we focused on discussing the kinetic parameters, such as active areas (A), diffusion coefficient (D), proton transfer number (m), standard rate constant (k) and electron transfer coefficient (α). These experimental conditions such as pH and detection rate had been optimized. Under the optimized conditions, the DPV response of the composite electrode to L-cysteine was obtained in the concentration from 2 × 10−4 to 1 × 10−7 mol/L with a lower detection limit of 1 × 10−8 mol/L. Moreover, composite electrode displayed brilliant specific recognition ability to L-cysteine, which prevented the interference from other compounds (e.g., L-tryptophan, ascorbic acid, aneurine hydrochloride), and common ions (K+, NH4+, Cl−, NO3−). In addition, the sensor has some unique advantages, such as excellent reproducibility, good stability, high sensitivity and could become a promising strategy of detecting L-cysteine.

Electrochemical Identification of DNA Single Nucleotide Polymorphisms (SNPs) Based on Different Redox Probes

In this article we investigated the effect of different redox probes (Ru(NH3)63+, Fe(CN)63−/4−, methylene blue(MB)) on electrochemical identification of DNA single nucleotide polymorphisms (SNPs) by chronocoulometry (CC), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). Thiol-modified probe DNA (p-DNA) and mercaptohexanol (MCH) were co-assembled on Au surface to form p-DNA/MCH mixed self-assembled monolayers (SAMs). The surface coverage of p-DNA (Гp-DNA) on Au was adjusted by changing the concentration ratio of p-DNA and MCH (Cp-DNA/CMCH = 1:100 or 1:1) for mixed assembly. The p-DNA/MCH SAMs on Au were hybridized with complementary DNA (c-DNA) or mutant DNA (m-DNA) in solution, and the SNPs sites of mutant DNA were located at up, middle and down positions of hybridized DNA duplex. Experimental results showed that DNA SNPs could be identified using Fe(CN)63−/4− or MB as the probes but using Ru(NH3)63+. Furthermore, the identification effect of DNA SNPs was closely related to Гp-DNA. DNA SNPs could be identified more easily by Fe(CN)63−/4− at lower Гp-DNA and by MB at higher Гp-DNA. However, the SNPs positions (up, middle or down) could not be identified obviously using Ru(NH3)63+, Fe(CN)63−/4− or MB.

SYNTHESIS OF ACETIC ACID FROM ETHANOL BY ELECTROOXIDATION TECHNIQUE USING Ni-Cu-PVC ELECTRODE

A usage of Ni-Cu-PVC electrode for the oxidation of ethanol by electrochemical technique will be reported in this paper. In this work, the effect of electrodes on the yields of acetic acid was determined. Electrode used was made of the mixtures of Ni powder, Cu powder and of polyvinyl chloride (PVC) with various percentages. Electrooxidation of 0.20 M ethanol in 0.16 M KOH (24 mL) were carried out using chrono coulometry (CC) at a potential of 1050 mV for 6 hours with continious stirring. Electrooxdation result obtained was analyzed using High Performance Liquid Chromatography (HPLC). The test result shows that the composition of Ni:Cu:PVC at 75:20:5 have higher efficiency in the electrooxidation of ethanol to acetic acid.

Nitrogen-doped carbon nanotubes decorated poly (L-Cysteine) as a novel, ultrasensitive electrochemical sensor for simultaneous determination of theophylline and caffeine

In present study, a novel and facile electrochemical sensor based on glassy carbon electrode (GCE) modified with nitrogen-doped carbon nanotubes (N-CNT) decorated with poly (L-Cysteine) (PLCY) were fabricated and applied for the simultaneous voltammetric determination of theophylline (THEO) and caffeine (CAF). The morphology and structure of multilayer film modified on the surface of glassy carbon electrode were investigated successfully by Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) and Raman Spectroscopy. And the properties of the modified electrode were investigated by Chronocoulometry (CC), Cyclic Voltammetry (CV) and Differential Pulse Voltammetry (DPV) were utilized to investigate the electrochemical behavior of THEO and CAF on the composite film modified electrode. The results showed that the determination towards THEO and CAF can be operated at the same potential window with the oxidation current peak separated and non-interfering respectively. Compared to the bare GCE, the PLCY/N-CNT/GCE can signally meliorate the electrocatalytic activity towards the oxidation of THEO and CAF with a remarkably increase in the anodic peak currents of 495.94% and 465.48%. Under the optimal conditions, the fabrication multilayer film sensor had excellent performances in determination towards THEO and CAF with a wide linear dynamic range from 0.10 to 70.0μM and 0.40–140.0μM, low detection limit (S/N = 3) of 0.033μM and 0.20μM, respectively. The PLCY/N-CNT/GCE sensor also had advantages as easy-made, high-sensitivity, stability and reproducibility. Moreover, it was successfully used to analyze the THEO and CAF in green tee, oral theophylline sustained release tablets and energy drink sample with a satisfactory result.

Estimation of Energetic and Charge Transfer Properties of Iridium(III) Bis(2-phenylpyridinato-<italic>N,C</italic>2’)acetylacetonate by Electrochemical Methods

Iridium(III) bis(2-phenylpyridinato-N,C2’)acetylacetonate ((ppy)2Ir(acac)), a green dopant used in organic light-emitting devices (OLEDs), was subjected to electrochemical characterization to estimate its formal oxidation potential (Eo’), HOMO energy level (EHOMO), electron transfer rate constant (ko’), and diffusion coefficient (Do). The employed combination of voltammetric methods, i.e., cyclic voltammetry (CV), chronocoulometry (CC), and the Nicholson method, provided meaningful insights into the electron transfer kinetics of (ppy)2Ir(acac), allowing the determination of ko’ and Do. The quasireversible oxidation of (ppy)2Ir(acac) furnished information on Eo’ and EHOMO, allowing the latter parameter to be easily estimated by electrochemical methods without relying on expensive and complex ultraviolet photoemission spectroscopic (UPS) measurements. Keywords: Iridium(III) bis(2-phenylpyridinato-N,C2’)acetylacetonate, (ppy)2Ir(acac), HOMO, Cyclic voltammetry, Chronocoulometry

Pt/graphene aerogel deposited in Cu foam as a 3D binder-free cathode for CO2 reduction into liquid chemicals in a TiO2 photoanode-driven photoelectrochemical cell

A nanostructured Pt/graphene aerogel directly deposited in Cu foam (Pt/GA/CF) was used as a 3D binder-free cathode to convert CO2 into liquid chemicals in a TiO2 photoanode-driven photoelectrochemical cell. The surface morphology, microstructure, mineralogical and elemental compositions, and electrochemical performance of the Pt/GA/CF electrode were characterized via SEM/EDX, TEM, X-ray diffraction, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy (EIS), and chronocoulometry (CC). EIS analysis revealed that Pt/GA/CF with reduced impedance possessed a better electron transfer capacity than the electrode that combines Pt-modified reduced graphene oxide with CF through polymer binders (Pt/RGO/CF). SEM and CC analyses confirmed that the uniform dispersion of 3D nanoporous Pt/GA in CF scaffold effectively prevented its self-agglomeration and increased the electrochemical adsorption surface area of Pt/GA/CF to 15 times higher than that of Pt/RGO/CF. The efficient charge transportation and high reactant adsorptivity of the Pt/GA/CF electrode significantly improved CO2 reduction and facilitated the conversion of C1 products to high-order products. Formic acid, acetic acid, propionic acid, methanol, and ethanol were detected as the liquid products of CO2 reduction. The carbon atom conversion rate of CO2 reduction on Pt/GA/CF markedly increased to 5040nmol/(hcm2).

Preparation of chitosan/N-doped graphene natively grown on hierarchical porous carbon nanocomposite as a sensor platform for determination of tartrazine

In this work, the chitosan and N-doped graphene natively grown on hierarchical porous carbon (N-PC-G/CS) nanocomposite was obtained by ultrasonic method, as a novel sensor platform for determination of tartrazine (TT). The nanocomposite as prepared had well dispersivity in water and excellent conductivity. The N-PC-G/CS nanocomposite was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption-desorption, fourier transform infrared (FTIR) and electrochemical impedance spectroscopy (EIS). The application of N-PC-G/CS for determination of tartrazine (TT) was investigated by chronocoulometry (CC), cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Under optimized conditions, the sensor displayed a sensitive response to TT within a wide concentration range of 0.05–15.0μmol/L, the detection limits is 0.036μmol/L (S/N=3). Furthermore, this nanocomposite could be efficiently applied for determination of TT in soft drink samples.

Anodic Behavior of the Aluminum Current Collector in Imide-Based Electrolytes: Influence of Solvent, Operating Temperature, and Native Oxide-Layer Thickness.

The inability of imide salts to form a sufficiently effective passivation layer on aluminum current collectors is one of the main obstacles that limit their broad application in electrochemical energy-storage systems. However, under certain circumstances, the use of electrolytes with imide electrolyte salts in combination with the aluminum current collector is possible. In this contribution, the stability of the aluminum current collector in electrolytes containing either lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) or lithium fluorosulfonyl-(trifluoromethanesulfonyl) imide (LiFTFSI) as conductive salt was investigated by electrochemical techniques, that is, cyclic voltammetry (CV) and chronocoulometry (CC) in either room-temperature ionic liquids or in ethyl methyl sulfone. In particular, the influence of the solvent, operating temperature, and thickness of the native oxide layer of aluminum on the pit formation at the aluminum current collector surface was studied by means of scanning electron microscopy. In general, a more pronounced aluminum dissolution and pit formation was found at elevated temperatures as well as in solvents with a high dielectric constant. An enhanced thickness of the native aluminum oxide layer increases the oxidative stability versus dissolution. Furthermore, we found a different reaction rate depending on dwell time at the upper cut-off potential for aluminum dissolution in TFSI- and FTFSI-based electrolytes during the CC measurements; the use of LiFTFSI facilitated the dissolution of aluminum compared to LiTFSI. Overall, the mechanism of anodic aluminum dissolution is based on: i) the attack of the Al2 O3 surface by acidic species and ii) the dissolution of bare aluminum into the electrolyte, which, in turn, is influenced by the electrolyte's dielectric constant.

Electrochemical Biosensors Combined with Isothermal Amplification for Quantitative Detection of Nucleic Acids.

In recent years, various isothermal amplification techniques have been developed as alternatives to polymerase chain reaction (PCR). The integration of isothermal amplification with electrical or electrochemical devices has enabled high-throughput nucleic acid-based assays with high sensitivity. We performed solid-phase rolling circle amplification (RCA) on the surface of a Au electrode, and detected RCA products in situ using chronocoulometry (CC) with [Ru (NH3)6]3+ as the signaling molecule. Detection sensitivity for DNA and a microRNA (miR-143) was 100 fM and 1 pM, respectively. Furthermore, we conducted potentiometric DNA detection using an ethidium ion (Et+)-selective electrode (Et+ISE) for real-time monitoring of isothermal DNA amplification by primer-generation RCA (PG-RCA). The Et+ISE potential enabled real-time monitoring of the PG-RCA reaction in the range of 10 nM–1 μM of initial target DNA. Devices based on these electrochemical techniques represent a new strategy for replacing conventional PCR for on-site detection of nucleic acids of viruses or microorganisms.

Study on the Electrochemical Behaviour of Apigenin and Its Interaction with Dna

The electrochemical behavior of the antitumor herbal drug apigenin was studied in 0.1 M B-R buffer solution (50% ethanol, pH 9.0) by cyclic voltammetry (CV), normal pulse voltammetry (NPV), chronoamperometry (CA) and chronocoulometry (CC) at glassy carbon electrode. In CV, only one irreversible anodic peak with Ep = 0.580V was appeared at scan rate of 50 mV/s and a new electroanalytical method for this herbal drug was established according to this anodic peak. The peak currents are linearly relationship with apigeninconcentrations in a range from 5.0×10-6 M to 9.0×10-5 M. Using the established method without pre-separation,apigenin in herbal drug was determined with satisfactory results. Moreover, the electrode process dynamics parameters were also investigated by electrochemical techniques and the possible electrode reaction mechanism was deduced. We also study the interaction of apigenin with DNA by DPV and Ultraviolet –Visible (UV) spectra. The results show apigenin doesn’t interact with DNA under the conditions.

Electropolymerization of β-cyclodextrin onto multi-walled carbon nanotube composite films for enhanced selective detection of uric acid

An amperometric uric acid (UA) sensor incorporating a multi-walled carbon nanotubes (MWCNT) network in Nafion and electropolymerized β-cyclodextrin (β-CD) layer is investigated. The electrochemical sensor is comprised of a glassy carbon electrode modified with Nafion-MWCNT nanocomposite film, a β-CD polymer inner selective layer, and a Hydrothane polyurethane (HPU) outer selective coating. The surface morphology and electronic structure of the electrode material are characterized using transmission electron microscopy (TEM), scanning electron microscope (SEM), and Fourier transform infrared (FTIR) spectroscopy. The electrocatalytic activity of the sensor is studied using cyclic voltammetry (CV), chronocoulometry (CC) and differential pulse voltammetry (DPV). Analytical performance of the electrochemical sensor scheme with and without MWCNT and/or β-CD polymer is determined from direct UA injection during an amperometric analysis. The effective surface area is notably higher for Nafion-MWCNT coated glassy carbon electrodes, which in turn enhanced the sensitivity when coated with β-CD polymer. The results indicated an excellent electrocatalytic property of Nafion-MWCNT/β-CD film for UA detection with enhanced sensitivity (2.11μA·mM−1), wide linear responses over physiologically relevant concentrations, and fast response times. Enhancement is attributed to MWCNT offering increased electroactive surface area and the ability of β-CD to selectively sequester UA.

The investigation of electrodeposited Cu2O/ITO layers by chronocoulometry process: effect of electrical potential**Project supported the PNR (Nos. 8/U311/R77, U311/R81), the “Agencethematique de rechercheen science ettechnologie” (ATRST), the National Administration of Scientific Research, the CNEPRU of Oran University of Sciences and Technology (No. B00L02UN310220130011), and the Scientific Research Projects Coordination (Nos. 2012-01-01-KAP05, 2012-01-01-KAP06) Yildiz Technical University.

The thin films of Cu2O are deposited by electrodeposition technique onto indium tin oxide (ITO)-coated glass substrate at different potentials. The precursor is an aqueous solution which contains respectively 0.05 M of CuSO4 and citric acid at kept temperature of 60 °C and the applied potential varies within the {−0.4 V, −0.7 V} SCE range. Based on the chronocoulometry (CC) process, the electrochemical, structural and optical parameters are determined. We measured the current as function of potential within the {−0.4 V, −0.7 V} range and the higher current is found to be within the {−0.7V, −0.3 V} band. The grain sizes are of 12.12 nm and 35.47 nm according to (110) and (221) orientations respectively. The hightextural coefficient of 0.943 is recorded for the potential −0.7 V The transmittance of 72.25 %, within the visible band, is obtained for the as-grown layer at −0.4 V and the band gap is found to be 2.2 eV for the electrodeposition potential of −0.7 V