Voltammetric Behavior of Antileukemia Drug Glivec. Part I – Electrochemical Study of Glivec

The electrochemical behavior of the antileukemia drug glivec was investigated at a glassy carbon electrode (GCE). The oxidation is a complex, pH‐dependent, irreversible electrode process involving the transfer of 2 electrons and 2 protons and the formation of an electroactive product, P_glivec, which strongly adsorbs on the GCE surface and undergoes reversible oxidation. The adsorption of P_glivec at the GCE surface yields a compact monolayer that inhibits further oxidation of glivec. The electrochemical reduction is a simple pH dependent irreversible process involving the transfer of 2 electrons and 2 protons and occurs with the formation of a nonelectroactive product. The diffusion coefficient of glivec was calculated to be D_O=7.35×10^?6 cm² s^?1 in pH 4.5 0.1 M acetate buffer.     

Electrochemical oxidation determination and voltammetric behaviour of 4-nitrophenol based on Cu2O nanoparticles modified glassy carbon electrode

Cu₂O nanoparticles (nano-Cu₂O) modified glassy carbon electrode (GCE) was fabricated and used to investigate the electrochemical behaviour of 4-nitrophenol (4-NP) by cyclic voltammetry (CV), chronoamperometry (CA), chronocoulometry (CC) and differential pulse voltammetry (DPV). Compared with GCE, a remarkable increase in oxidation peak current was observed. It indicates that nano-Cu₂O exhibits remarkable enhancement effect on the electrochemical oxidation of 4-NP. Under the optimised experimental conditions, the oxidation peak currents were propotional to 4-NP concentration in the range from 1.0?×?10^?6 to 4.0?×?10^?4?mol?L^?1 with a detection limit of 5.0?×?10^?7?mol?L^?1 (S/N?=?3). The fabricated electrode presented good repeatability, stability and anti-interference. Finally, the proposed method was applied to determine 4-NP in water samples. The recoveries for these samples were from 94.60% to 105.5%.     

Sensitive Determination of Terbutaline Using a Platform Based on Nanoparticles of Europium Oxide and Carbon Nanotubes

This study presents a sensitive voltammetric determination of terbutaline (TER) on a platform based on carbon nanotubes (CNTs) and europium oxide nanoparticles (Eu₂O₃NPs) coated glassy carbon electrodes (GCEs). An ultrasonic bath was performed for the preparation of composite material. The material was characterized by energy dispersive X‐ray spectroscopy (EDX), X‐ray diffraction method (XRD) and scanning electron microscopy (SEM). The Eu₂O₃NPs/CNTs/GCE system was assessed for the oxidation of terbutaline (TER). A broad oxidation peak was appeared at 0.71 V using a bare GCE. However, the voltammetry of TER has been improved at a GCE coated with CNTs and a well‐defined anodic peak exhibited at 0.61 V. Furthermore, the nanoparticles of Eu₂O₃ and CNTs coated GCE has greatly improved the electrochemical behaviour of TER and a sharp peak was appeared at 0.59 V. Cyclic voltammetry at Eu₂O₃NPs/CNTs/GCE also reveals a high catalytic effect for the oxidation of TER with an oxidation peak that is distinctly enhanced compared to GCE and CNTs/GCE. Eu₂O₃ nanoparticles were utilized to enhance the surface area of GCE and then improve the sensitivity of the procedure. The response of TER was linear over a concentration range of 2.0×10^?8 M ?9.5×10^?6 M with an LOD of 3.7×10^?9 M. Square wave voltammetric analysis of tablets by Eu₂O₃NPs/CNTs/GCE yielded a recovery of 99.2 % with an RSD% of 3.2. The modified electrode (EuO₂NPs/CNTs/GCE) provides accuracy and precision to the analysis of samples.     

Electrochemical Behavior and Determination of L‐Tyrosine at Single‐walled Carbon Nanotubes Modified Glassy Carbon Electrode

Based on single‐walled carbon nanotubes (SWCNTs) modified glassy carbon electrode (GCE/SWCNTs), a novel method was presented for the determination of L ‐tyrosine. The GCE/SWCNTs exhibited remarkable catalytic and enhanced effects on the oxidation of L ‐tyrosine. In 0.10 mol/L citric acid‐sodium citrate buffer solution, the oxidation potential of L ‐tyrosine shifted negatively from +1.23 V at bare GCE to +0.76 V at GCE/SWCNTs. Under the optimized experimental conditions, the linear range of the modified electrode to the concentration of L ‐tyrosine was 5.0×10^?6–2.0×10^?5 mol/L (R₁=0.9952) and 2.7×10^?5–2.6×10^?4 mol/L (R₂=0.9998) with a detection limit of 9.3×10^?8 mol/L. The kinetic parameters such as α (charge transfer coefficient) and D (diffusion coefficient) were evaluated to be 0.66, 9.82×10^?5 cm² s^?1, respectively. And the electrochemical mechanism of L ‐tyrosine was also discussed.     

Enhanced electron transfer by bovine serum albumin covalently attached to glassy carbon electrode and its application to determination of hydroquinone

Bovine serum albumin (BSA) was covalently attached to glassy carbon electrode (GCE) surface by the electrochemical method. An enhancement for the redox of hydroquinone (HQ) on BSA/GCE was confirmed by cyclic voltammetry and electrochemical impedance spectroscopy measurement. The electron transfer rate constant (k _s) on the BSA/GCE electrode is almost three orders of magnitude higher than that on bare GCE. The enhancing effect can be attributed to the electrostatic force between the positively charged HQ and negatively charged BSA. It is found that the enhanced redox process of HQ can be used to determine HQ sensitively. The oxidation current can reach 95% of its steady-state value within 30 s. The linear range for HQ determination is from 2.5 × 10^?8 M to 1.325 × 10^?6 M with a detection limit of 8.6 × 10^?9 M at a signal-to-noise ratio of 3. The study may provide a simple, rapid and sensitive method for determination of HQ which is present in the natural environment and in chemical industry effluent.     

Electrochemical determination of ascorbic acid using the poly-cysteine film-modified electrode

A poly(L-cysteine) thin film was prepared onto electrode surface via electropolymerization. In pH 7.0 phosphate buffer, L-cysteine was oxidized during the cyclic potential sweep between −0.60 and 2.00 V, forming a thin film at the glassy carbon electrode (GCE) surface. The electrochemical behaviors of ascorbic acid at the bare GCE and the poly(L-cysteine) film-coated GCE were investigated. The oxidation peak potential of ascorbic acid shifts to more negative potential at the poly(L-cysteine) film-modified GCE. Moreover, the oxidation peak current significantly increases at the poly(L-cysteine) film-modified GCE. These phenomena indicate that poly(L-cysteine) film shows highly-efficient catalytic activity to the oxidation of ascorbic acid. Based on this, a sensitive and simple electrochemical method was proposed for the determination of ascorbic acid. The oxidation peak current of ascorbic acid is proportional to its concentration over the range from 1.0 × 10⁻⁶ to 5.0 × 10⁻⁴ mol l⁻¹. The limit of detection is evaluated to be 4.0 × 10⁻⁷ mol l⁻¹.     

A method based on electrodeposition of reduced graphene oxide on glassy carbon electrode for sensitive detection of theophylline

Graphene nanosheets were directly electrodeposited onto a glassy carbon electrode (GCE) from the electrolyte solution containing graphene oxide (GO); the resulting electrode (ED-GO/GCE) was characterized with scanning electron microscopy. A simple and rapid electrochemical method was developed for the determination of theophylline (TP), based on the excellent properties of ED-GO film. The result indicated that ED-GO film-modified GCE exhibited efficient electrocatalytic oxidation for TP with relatively high sensitivity and stability. The electrochemical behavior of TP at ED-GO/GCE was investigated in detail. Under the optimized conditions, the oxidation peak current was proportional to the TP concentration in the range of 8.0?×?10^?7 to 6.0?×?10^?5 mol?L^?1 with the detection limit of 1.0?×?10^?7 mol?L^?1 (S/N?=?3). The proposed method was successfully applied to green tea samples with satisfactory results.     

Electrocatalytic oxidation of sulfite by acetylferrocene at glassy carbon electrode

The electrochemical oxidation of sulfite catalyzed by acetylferrocene (AFc) at a glassy carbon electrode (GCE) in 0.2 M NaClO₄ aqueous solution has been studied by cyclic voltammetry. Although sulfite itself showed a sluggish electrochemical response at the GCE, the response could be enhanced greatly by using AFc as a mediator, which enables a sensitive determination of the substrate (sulfite). The reaction rate constant for catalytic oxidation was evaluated as (7.02 ± 0.05) × 10⁴ M ^?1 s^?1 by chronoamperometry. Experimental conditions that maximize the current efficiency of the electrocatalytic oxidation, such as the pH and both the catalyst (AFc) and substrate (sulfite) concentrations, were also investigated. The electrochemical kinetics of electrocatalytic oxidation of sulfite by AFc has been studied by cyclic voltammetry. In the presence of 5 × 10^?4 M AFc, the oxidation current is proportional to the sulfite concentration and the calibration plot was linear over the concentration range 2 × 10^?4–2.4 × 10^?3 M . This result can be applied in the determination of real samples. Copyright © 2005 John Wiley & Sons, Ltd.     

Electrochemical Behavior of Caffeic Acid Assayed with Gold Nanoparticles/Graphene Nanosheets Modified Glassy Carbon Electrode

A gold nanoparticle (AuNP) and graphene nanosheet (GN) modified glassy carbon electrode (GCE) is proposed as voltammetric sensor for caffeic acid assay. The sensor exhibits a surface‐confined and reversible process for oxidation of caffeic acid revealed by cyclic voltammetry. The results show more favorable electron transfer kinetics than the bare GCE. The linear response of the sensor is from 5×10^?7 to 5×10^?5 M with a detection limit of 5×10^?8 M (S/N=3). The AuNP/GN nanocomposite shows more favorable electrochemical activity and should be a kind of more robust and advanced functional material, which provides a promising platform for electrochemical sensors and biosensors. The method was successfully applied to detect caffeic acid in pharmaceutical tablets with satisfactory results.     

Voltammetric determination of trace doxorubicin at a nano-titania/nafion composite film modified electrode in the presence of cetyltrimethylammonium bromide

A sensitive electrochemical method was developed for the determination of doxorubicin at a glassy carbon electrode (GCE) modified with a nano-titania (nano-TiO₂)/nafion composite film. Nano-TiO₂ was dispersed into nafion to give a homogeneous suspension. After solvent evaporation, a uniform film of nano-TiO₂/nafion composite was obtained on the GCE surface. The nano-TiO₂/nafion composite film modified GCE exhibited excellent electrochemical behavior toward the reduction of doxorubicin. Compared to the reduction of doxorubicin at the bare GCE, the reduction current of doxorubicin at the nano-TiO₂/nafion composite film modified GCE was greatly enhanced. Based on this, a novel voltammetric method was applied to the determination of doxorubicin. The experimental parameters that influence the reduction current of doxorubicin, were optimized. Under optimal conditions, a linear response of doxorubicin was obtained in the range from 5.0?×?10^?9 to 2.0?×?10^?6 mol L^?1 (R?=?0.998) and with a limit of detection (LOD) of 1.0?×?10^?9 mol L^?1(S/N?=?3). The RSD of the measurement is 4.7%, and the RSD of the inter-electrode is of 5.1% which indicate the reproducibility of this method. The current response decreased only by around 3.8% of its initial response after 2 weeks exposing the electrode in air. The procedure was applied to assay doxorubicin in human plasma samples with the recoveries of 94.9–104.4%.     

Simultaneous determination of dopamine and serotonin by use of covalent modification of 5-hydroxytryptophan on glassy carbon electrode

An electrochemical biosensor was fabricated by covalent modification of 5-hydroxytryptophan (5-HTP) on the surface of glassy carbon electrode (GCE). The electrode, denoted as 5-HTP/GCE, was characterized by X-ray photoelectron spectroscopy, cyclic voltammetry and differential pulse voltammetry. For comparison, tryptophan modified GCE (TRP/GCE) and serotonin modified GCE (5-HT/GCE) were prepared by the same method. It was found that electrocatalytic ability of these electrodes was in the order of 5-HTP/GCE?>?TRP/GCE?>?5-HT/GCE for the oxidation of dopamine (DA) and 5-HT. The sensor was effective to simultaneously determine DA and 5-HT in a mixture. It can resolve the overlapping anodic peaks into two well-defined voltammetric peaks at 0.24 and 0.39 V (versus SCE). The linear response is in the range of 5.0?×?10^?7–3.5?×?10^?5 mol L^?1 with a detection limit of 3.1?×?10^?7 mol L^?1 for DA, and in the range of 5.0?×?10^?6–3.5?×?10^?5 mol L^?1 with a detection limit of 1.7?×?10^?6 mol L^?1 for 5-HT (s/n?=?3), respectively.     

Electrocatalysis Oxidation of GMP Based on Layered Double Hydroxide Functionalized with Anionic Surfactant and Room Temperature Ionic Liquid Modified Glassy Carbon Electrode

The electrocatalysis oxidation of guanosine‐5′‐monophosphate (GMP) was investigated on Mg‐Al layered double hydroxide (LDH) functionalized with sodium dodecyl sulfate (SDS) and room temperature ionic liquid (RTIL) modified glass carbon electrode (GCE). The cyclic voltammogram of GMP on the modified electrode (RTIL/ LDH‐SDS/GCE) exhibited a well defined anodic peak at 1.091 V in 0.2 mol·L^?1 pH 4.4 acetate buffer solution. The GMP oxidation was enhanced in the presence of anionic surfactant in the ?lms. The results suggest that the surfactant molecules intercalate the LDH layers to preconcentrate GMP molecules and the RTIL showed good ionic conductivity. The experimental parameters were optimized, the kinetic parameters were investigated and the probable oxidation mechanism was proposed. Under the optimized conditions, the oxidation peak current was proportional to GMP concentration in the range from 5.0×10^?7 to 1.0×10^?4 mol·L^?1 with the correlation coefficient of 0.9987 and the detection limit was 1.0×10^?7 mol·L^?1. The RTIL/LDH‐SDS/GCE showed a good electrochemical response to the oxidation of GMP and would be developed into a new biosensor.     

Determination of 1‐Naphthol with Denatured DNA–Modified Pretreated Glassy Carbon Electrode

Abstract

A highly sensitive electrochemical biosensor for the detection of trace amount of 1‐naphthol was designed. Acid‐denatured DNA were immobilized onto the pretreated glassy carbon electrode (GCE(ox)) surface. Two well‐defined oxidation peaks were observed on the denatured DNA‐modified GCE(ox) at about +0.80 V and +1.10 V (vs. Ag/AgCl) in 0.10‐M acetate buffer (pH 5.0). The peak current of the guanine residue decreased with increasing concentration of 1‐naphthol. The optimum experimental conditions for the detection of 1‐naphthol were explored, and the calibration was linear for 1‐naphthol in the range of 1.0×10^?8?1.1×10^?6 M, with a correlation coefficient of 0.998. The limit of detection (LOD) was 5.0×10^?9 M (S/N=3).     

Electrochemical Behaviors of Adenosine‐5′‐triphosphate on Molecular Wire Modified Carbon Paste Electrode and Its Sensitive Detection

A new electrochemical method was proposed for the determination of adenosine‐5′‐triphosphate (ATP) based on the electrooxidation at a molecular wire (MW) modified carbon paste electrode (CPE), which was fabricated with diphenylacetylene (DPA) as the binder. A single well‐defined irreversible oxidation peak of ATP appeared on MW‐CPE with adsorption‐controlled process and enhanced electrochemical response in a pH 3.0 Britton‐Robinson buffer solution, which was due to the presence of high conductive DPA in the electrode. The electrochemical parameters of ATP were calculated with the electron transfer coefficient (α) as 0.54, the electron transfer number (n) as 1.9, the apparent heterogeneous electron transfer rate constant (k_s) as 2.67 × 10^?5 s^?1 and the surface coverage (Γ_T) as 4.15 × 10^?10 mol cm^?2. Under the selected conditions the oxidation peak current was proportional to ATP concentration in the range from 1.0 × 10^?7 mol L^?1 to 2.0 × 10^?3 mol L^?1 with the detection limit as 1.28 × 10^?8 mol L^?1 (3σ) by sensitive differential pulse voltammetry. The proposed method showed good selectivity without the interferences of coexisting substances and was successful applied to the ATP injection samples detection.     

Voltammetric Determination of Bisphenol A Using an Acetylene Black‐Dihexadecyl Hydrogen Phosphate Composite Film‐Modified Electrode

Abstract

Herein, acetylene black (AB) was easily dispersed into water in the presence of dihexadecyl hydrogen phosphate (DHP), resulting in a stable and homogeneous AB‐DHP suspension. Then, an AB‐DHP composite film coated glassy carbon electrode (GCE) was constructed after evaporation of water. The electrochemical behavior of bisphenol A was investigated using cyclic voltammetry (CV), linear sweep voltammetry (LSV), and differential pulse voltammetry (DPV). Compared with the unmodified GCE, the AB‐DHP film‐modified GCE not only significantly enhances the oxidation peak current of bisphenol A but also lowers the oxidation overpotential, suggesting that AB‐DHP film‐modified GCE has great potential in sensitive determination of bisphenol A. Based on this, a sensitive and simple electrochemical method was developed after optimization of the experimental parameters such as supporting electrolyte, the amount of AB‐DHP, scan rate, and accumulation time. The linearity is over the range form 2.0×10^?8 to 5.0×10^?6 mol l^?1, and the detection limit is 6.0×10^?9 mol l^?1. Finally, this method was successfully employed to determine bisphenol A in waste water samples.     

Amperometric Sensor for Detection of the Reduced Form of Nicotinamide Adenine Dinucleotide Using a Poly(pyronin B) Film Modified Electrode

An electrochemical method for the preparation of poly(pyronin B) film was proposed in this paper. A poly(pyronin B) (poly(PyB)) film modified glassy carbon electrode (GCE) has been fabricated via an electrochemical oxidation procedure and applied to the electrocatalytic oxidation of reduced form of nicotinamide adenine dinucleotide (NADH). The poly(PyB) film modified electrode surface has been characterized by atomic force microscope (AFM), scanning electron microscope (SEM), electrochemical impedance spectroscopy (EIS), UV‐visible absorption spectrophotometry (UV‐vis) and cyclic voltammetry (CV). These studies have been used to investigate the poly(PyB) film, which demonstrates the formation of the polymer film and the excellent electroactivity of poly(PyB) in neutral and even in alkaline media. Due to its potent catalytic effects towards the electrooxidation of NADH at lower potential (0.0 V), poly(PyB) film modified electrode can be used for the selective determination of NADH in real samples because of dopamine, ascorbic acid and uric acid oxidation can be avoided at this potential. The catalytic peak currents are linearly dependent on the concentrations of NADH in the range of 1.0×10^?6 to 5.0×10^?4 mol/L with correlation coefficients of 0.999. The detection limits for NADH is 0.5×10^?6 mol/L. Poly(PyB) modified electrode also shows good stability and reproducibility due to the irreversible attachment of polymer film at GCE surface.     

Sensitive amperometric pyridoxine sensor based on self‐assembled Prussian blue nanoparticle‐modified poly(o‐phenylenediamine)/glassy carbon electrode

Prussian blue nanoparticles (PBNPs) were prepared by a self‐assembly process on a glassy carbon electrode (GCE) modified with poly(o‐phenylenediamine) (PoPD) film. The stepwise fabrication process of PBNP‐modified PoPD/GCE was characterized using scanning electron microscopy and electrochemical impedance spectroscopy. The prepared PBNPs showed an average size of 70 nm and a homogeneous distribution on the surface of the modified electrode. The PBNPs/PoPD/GCE showed electrocatalytic activity towards the oxidation of pyridoxine (PN) and was used as an amperometric sensor. The modified electrode exhibited a linear response for PN oxidation over the concentration range 3–38.5 μM with a detection limit of ca 6.10 × 10^?7 M (S/N = 3) and sensitivity of 2.79936 × 10³ mA M^?1 cm^?2 using an amperometric method. The mechanism and kinetics of the catalytic oxidation reaction of PN were investigated using cyclic voltammetry and chronoamperometry. The values of α, k_cat and D were estimated as 0.36, 1.089 × 10² M^?1 s^?1 and 8.9 × 10^?5 cm² s^?1, respectively. This sensor also exhibited good anti‐interference and selectivity. Copyright © 2016 John Wiley & Sons, Ltd.     

Electrochemical Behavior of Apigenin at a Glassy Carbon Electrode and its Analytical Application

The electrochemical behavior of the antitumor herbal drug apigenin was studied in 0.1 mol L^?1 B‐R buffer solutions (50% ethanol, pH 3.0) by cyclic voltammetry (CV) at a glassy carbon electrode. In CV, two oxidation peaks (P₁ and P₂) with E_p1 = 1.03V and E_p2 = 1.23 V appeared at a scan rate of 0.05 V s^?1, and a new electroanalytical method for this herbal drug was established according to the oxidation peak P2. The peak currents have a linear relationship with apigenin concentration in a range from 9.0 × 10^?7 to 2.0 × 10^?5 mol L^?1. Using the established method, apigenin in a herbal drug was determined without pre‐separation with satisfactory results. Moreover, the electrode dynamics parameters were also investigated by electrochemical techniques and the possible electrode reaction mechanism was deduced.     

Nucleic Acid Biosensor for Detection of Human Immunodeficiency Virus Using Aquabis(1,10‐phenanthroline)copper(II) Perchlorate as Electrochemical Indicator

The electrochemical behavior of aquabis(1,10‐phenanthroline)copper(II) perchlorate [Cu(H₂O)(phen)₂]·2ClO₄, where phen=1,10‐phenanthroline, on binding to DNA at a glassy carbon electrode (GCE) and in solution, was described. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) results showed that [Cu(H₂O)(phen)₂]²⁺ had excellent electrochemical activity on the GCE with a couple of quasi‐reversible redox peaks. The interaction mode between [Cu(H₂O)(phen)₂]²⁺ and double‐strand DNA (dsDNA) was identified to be intercalative binding. An electrochemical DNA biosensor was developed with covalent immobilization of human immunodeficiency virus (HIV) probe for single‐strand DNA (ssDNA) on the modified GCE. Numerous factors affecting the probe immobilization, target hybridization, and indicator binding reactions were optimized to maximize the sensitivity and speed of the assay. With this approach, a sequence of the HIV could be quantified over the range from 7.8×10^?9 to 3.1×10^?7 mol·L^?1 with a linear correlation of γ=0.9987 and a detection limit of 1.3×10^?9 mol·L^?1.     

L‐Cysteine Voltammetry at a Carbon Paste Electrode Bulk‐Modified with Ferrocenedicarboxylic Acid

The electrochemical behavior of L ‐cysteine studied at the surface of ferrocenedicarboxylic acid modified carbon paste electrode (FDCMCPE) in aqueous media using cyclic voltammetry, differential pulse voltammetry and double potential step chronoamperometry. It has been found that under optimum condition (pH 8.00) in cyclic voltammetry, the oxidation of L ‐cysteine occurs at a potential about 200 mV less positive than that of an unmodified carbon paste electrode. The kinetic parameters such as electron transfer coefficient, α, and catalytic reaction rate constant, k_h were also determined using electrochemical approaches. The electrocatalytic oxidation peak current of L ‐cysteine showed a linear dependent on the L ‐cysteine concentration and linear analytical curves were obtained in the ranges of 3.0×10^?5 M–2.2×10^?3 M and 1.5×10^?5 M–3.2×10^?3 M of L ‐cysteine concentration with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods respectively. The detection limits (3σ) were determined as 2.6×10^?5 M and 1.4×10^?6 M by CV and DPV methods.