DNA Langmuir-Blodgett modified glassy carbon electrode as voltammetric sensor for determinate of methotrexate

A highly sensitive electrochemical biosensor for the detection of trace amounts of methotrexate has been designed. Double stranded (ds)DNA molecules are immobilized onto a pretreated glassy carbon electrode (GCE(ox)) surface with Langmuir-Blodgett (LB) technique. The adsorptive voltammetric behaviors of methotrexate on DNA-modified electrode were explored by means of cyclic voltammetry (CV) and square wave voltammetry (SWV). The oxidation mechanism was proposed and discussed in this work. In addition, the optimum experimental conditions for the detection of methotrexate were explored, and the currents measured by SWV presented a good linear property as a function of the concentrations of methotrexate in the range of 2.0 × 10⁻⁸ to 4.0 × 10⁻⁶ mol L⁻¹, with an LOD of 5.0 × 10⁻⁹ mol L⁻¹. The method proposed was applied for the determination of methotrexate in pharmaceutical dosage and diluted human urine with wonderful satisfactory successfully.     

Electrocatalytic oxidation of hydrazine at overoxidized polypyrrole film modified glassy carbon electrode

Electrocatalytic oxidation of hydrazine (HZ) was studied on an overoxidized polypyrrole (OPPy) modified glassy carbon electrode using cyclic voltammetry and chronoamperometry techniques. The OPPy-modified glassy carbon electrode has very high catalytic ability for electrooxidation of HZ, which appeared as a reduced overpotential in a wide operational pH range of 5-10. The overall numbers of electrons involved in the catalytic oxidation of HZ, the number of electrons involved in the rate-determining and diffusion coefficient of HZ were estimated using cyclic voltammetry and chronoamperometry. It has been shown that using the OPPy-modified electrode, HZ can be determined by cyclic voltammetry and amperometry with limit of detection 36 and 3.7 μM, respectively. The results of the analysis suggest that the proposed method promises accurate results and could be employed for the routine determination of HZ.     

Electrochemical behavior and voltammetric determination of 4-aminophenol based on graphene-chitosan composite film modified glassy carbon electrode

The graphene-chitosan composite film modified glassy carbon electrode (GCE) was fabricated and used to determine 4-aminophenol (4-AP). In 0.1 M pH 6.3 phosphate buffer solution, the redox peak currents of 4-AP increased significantly and the peak-to-peak separation decreased greatly at graphene-chitosan composite film modified GCE compared with bare GCE and chitosan modified GCE, indicating that graphene possessed electrocatalytic activity towards 4-AP. The experimental conditions were optimized and the kinetic parameters were investigated. The oxidation mechanism was discussed. Under the optimal experimental conditions, the oxidation peak current was proportional to 4-AP concentration in the range from 0.2 to 550 μM with the correlation coefficient of 0.9930. The detection limit was 0.057 μM (S/N = 3). Using the proposed method, 4-AP was successfully determined in water samples and paracetamol tablets with standard addition method, suggesting that this method can be applied to determine 4-AP in environments and pharmaceuticals.     

Simultaneous voltammetric determination of tramadol and acetaminophen using carbon nanoparticles modified glassy carbon electrode

A sensitive and selective electrochemical sensor was fabricated via the drop-casting of carbon nanoparticles (CNPs) suspension onto a glassy carbon electrode (GCE). The application of this sensor was investigated in simultaneous determination of acetaminophen (ACE) and tramadol (TRA) drugs in pharmaceutical dosage form and ACE determination in human plasma. In order to study the electrochemical behaviors of the drugs, cyclic and differential pulse voltammetric studies of ACE and TRA were carried out at the surfaces of the modified GCE (MGCE) and the bare GCE. The dependence of peak currents and potentials on pH, concentration and the potential scan rate were investigated for these compounds at the surface of MGCE. Atomic force microscopy (AFM) was used for the characterization of the film modifier and its morphology on the surface of GCE. The results of the electrochemical investigations showed that CNPs, via a thin layer model based on the diffusion within a porous layer, enhanced the electroactive surface area and caused a remarkable increase in the peak currents. The thin layer of the modifier showed a catalytic effect and accelerated the rate of the electron transfer process. Application of the MGCE resulted in a sensitivity enhancement and a considerable decrease in the anodic overpotential, leading to negative shifts in peak potentials. An optimum electrochemical response was obtained for the sensor in the buffered solution of pH 7.0 and using 2 μL CNPs suspension cast on the surface of GCE. Using differential pulse voltammetry, the prepared sensor showed good sensitivity and selectivity for the determination of ACE and TRA in wide linear ranges of 0.1-100 and 10-1000 μM, respectively. The resulted detection limits for ACE and TRA was 0.05 and 1 μM, respectively. The CNPs modified GCE was successfully applied for ACE and TRA determinations in pharmaceutical dosage forms and also for the determination of ACE in human plasma.     

Electrochemical sensor based on a poly(para-aminobenzoic acid) film modified glassy carbon electrode for the determination of melamine in milk

A novel and simple sensor is developed in this paper for melamine detection, which is based on an electropolymerized molecularly imprinted polymer (MIP) of para-aminobenzoic acid (pABA). The poly(para-aminobenzoic acid) (P-pABA) film was deposited in a pABA solution by potentiodynamic cycling of potential with and without the template (melamine) on a glassy carbon electrode. The surface feature of the modified electrode was characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The molecular imprinted sensor was tested by differential pulse voltammetry (DPV) to verify the changes in redox peak currents of hexacyanoferrate. Several important parameters controlling the performance of the P-pABA were investigated and optimized. In the optimal conditions, the relative redox peak currents of hexacyanoferrate were linear. The concentration of melamine ranged from 4.0 μM to 0.45 mM, with a linear correlation coefficient of 0.9992. The detection limit was 0.36 μM (S/N = 3). The MIP sensor was successfully applied to the determination of melamine in milk products and showed high selectivity, sensitivity, and reproducibility. The results of this research demonstrate that it is feasible to use the molecular imprinting methodology when preparing sensing devices for analytes that are electrochemically inactive.     

Simultaneous determination of dopamine and uric acid on nafion/sodium dodecylbenzenesulfonate composite film modified glassy carbon electrode

A novel electrochemical sensor has been constructed by using a glassy carbon electrode (GCE) coated with nafion/sodium dodecylbenzenesulfonate (SDBS). Differential pulse voltammetry (DPV) was used to study the electrochemical behaviors of dopamine (DA) and uric acid (UA). An optimum of 5 mM SDBS together with 0.05 wt% of nafion was used to improve the resolution and the determination sensitivity successfully. In 0.1 M phosphate buffer solution (pH 6.5), the modified electrode exhibited high electrocatalytical activity toward the oxidation of DA and UA with obvious reduction of overpotential. Compared with bare GCE, the modified electrode resolved the voltammetric response of DA and UA into two well-defined voltammetric peaks by DPV, which can be used for simultaneous determination of these species in mixture. The peak currents obtained from DPV were linearly related to the concentrations of DA and UA in the ranges of 4.0 × 10⁻⁷–8.0 × 10⁻⁵ M and 4.0 × 10⁻⁶–8.0 × 10⁻⁴ M, respectively. The detection limit of DA and UA (signal-to-noise ration was 3) were 5.0 × 10⁻⁸ and 4.0 × 10⁻⁷ M, respectively.     

Electrocatalytic oxidation of deoxyguanosine on a glassy carbon electrode modified with a ruthenium oxide hexacyanoferrate film

The electrocatalytic oxidation of deoxyguanosine on a ruthenium hexacyanoferrate (RuOHCF) glassy carbon (GC) modified electrode was investigated in acid medium by using rotating disc electrode (RDE) voltammetry. Chronoamperometric experiments allowed information on the charge transport rate through the RuOHCF film and at a very short time window a diffusion-like behavior was observed with a D_ct value of 2.7 × 10⁻¹¹ cm² s⁻¹ for a film with Γ = 4.47 × 10⁻⁹ mol cm⁻². The influence of systematic variation of rotation rate, film thickness and the electrode potential indicates that the rate of cross-chemical reaction between Ru(IV) centers immobilized into the film and deoxyguanosine controls the overall electrodic process and the value of the rate constant was found to be 3.2 × 10⁶ mol⁻¹ L¹ s⁻¹. The relatively high rate constant of the cross-reaction, the facile penetration of the substrate through the film and the fast transport of electrons suggest that the electrocatalytic process occurs throughout the film layer.     

Carbon nanotube-modified glassy carbon electrode for anodic stripping voltammetric detection of Uranyle

A multi-wall carbon nanotube (MWNT) modified glassy carbon electrode (GCE) is described for the measurement of trace levels of uranium by anodic stripping voltammetry. In a pH 4.4 NaAc-Hac buffer containing 0.010 mol L⁻¹ Mg(NO₃)₂, UO₂ ²⁺ was adsorbed onto the surface of a MWNT film coated glassy carbon electrode and then reduced at −0.40 V vs. Ag/AgCl. During the positive potential sweep the reduced uranium was oxidized and a well-defined stripping peak appeared at +0.20 V vs. Ag/AgCl. Low concentrations of Mg²⁺ significantly enhanced the stripping peak currents since they induced UO₂ ²⁺ to adsorb at the electrode surface. The response was linear up to 1.2 × 10⁻⁷ mol L⁻¹ and the relative standard deviation at 2.0 × 10⁻⁸ mol L⁻¹ uranium was 5.2%. Potential interferences were examined. The attractive behavior of the new “mercury-free” uranium sensor holds promise for on-site environmental and industrial monitoring of uranium.     

Modified glassy carbon electrode with Nafion/MWNTs as a sensitive voltammetric sensor for the determination of paeonol in pharmaceutical and biological samples

A simple, highly sensitive method was reported for directly voltammetric determination of paeonol in drug samples and human biological samples. Nafion/multi-wall carbon nanotubes’ (MWNTs) composite film was coated on the glassy carbon electrode. The adsorptive voltammetric behavior of paeonol on the Nafion/MWNTs-modified electrode was investigated using cyclic voltammetry (CV) and differential pulse anodic stripping voltammetry (DPASV). The results indicated that the Nafion/MWNTs-modified electrode could remarkably enhance electrocatalytic activity toward the oxidation of paeonol, and showed an excellent resistance capability toward the electrode passivation. A highly sensitive voltammetric sensor was developed for the detection of paeonol in pharmaceutical and biological samples. Under the optimum conditions, the anodic peak current was proportional to paeonol concentration in the range of 6.0 × 10⁻⁷–6.0 × 10⁻⁵ M with a detection limit of 4.0 × 10⁻⁷ M. Some kinetic parameters were determined, and multi-step mechanism for oxidation of paeonol was proposed.     

Electrochemical detection of copper ion using a modified copolythiophene electrode

This paper studies the detection of copper ions by using an iminodiacetatic acid (IDA) modified conducting copolymer electrode. The copolymer film comprising 3-methyl thiophene (3MT) and 3-thiophene acetic acid (3TA) was chosen as the selective metal cation sensing electrode. The carboxylic group of the copolymer was modified to produce IDA group for metal ion capture. The modified electrode was used for the electrochemical analysis of trace copper ions by square wave voltammetry (SWV) technique. The electrode was found to be highly selective to Cu²⁺ in the range of 0.1-10 μM. The modified electrode offered an excellent way, with a high stability and reusability, for selective determination of Cu²⁺ in a solution of mixed metal ions.     

Electrochemiluminescent behavior of luminol on the glassy carbon electrode modified with CoTPP/MWNT composite film

A glassy carbon electrode (GCE) modified with cobalt(II) meso-tetraphenylporphrine/multiwall-carbon nanotube (CoTPP/MWNT) was applied to investigate the electrochemiluminescent (ECL) behavior of luminol. The ECL intensity of luminol was found to be increased greatly on this modified electrode. The presence of cobalt(II) meso-tetraphenylporphrine (CoTPP) can catalyze the reduction of oxygen on the electrode surface to produce HOO⁻, which can increase the ECL intensity of luminol. Moreover, MWNT can provide the more effective area of the electrode, and can act as a promoter to enhance the electrochemical reaction. The proposed method enables a detection limit for luminol of 1.0 × 10⁻⁸ mol/L in the neutral solution. Under the optimum condition, the enhanced ECL intensity of luminol by H₂O₂ had a linear relationship with the concentration of H₂O₂ in the range of 1.0 × 10⁻⁷ to 8.0 × 10⁻⁸ mol/L with the detection limit of 5.0 × 10⁻⁹ mol/L.     

Electrodeposition of Pt-Fe(III) nanoparticle on glassy carbon electrode for electrochemical nitric oxide sensor

An electrochemical sensor for the detection of nitric oxide (NO) was developed by electrodeposition of Pt-Fe(III) nanoparticle on a glassy carbon electrode. This sensor exhibits excellent electrocatalytic activity for the oxidation of NO. A Nafion membrane coating was used to avoid the interference of nitrite and other potential interferences which may co-exist with NO in the biological systems. The effect of scan number in the electrodeposition process and the behavior of the sensor with respect to bulk pH have been studied. The catalytic peak current is found to be linear with the NO concentration over a wider range of 8.4 × 10⁻⁸ to 7.8 × 10⁻⁴ M, with a detection limit of 1.8 × 10⁻⁸ M (s/n = 3). In addition, the sensor has also good stability and anti-interference ability.     

Langmuir-Blodgett film based biosensor for estimation of galactose in milk

A mono-enzyme amperometric biosensor has been developed for the estimation of galactose in milk and milk products. Galactose oxidase was immobilized with poly(3-hexyl thiophene)/stearic acid (P3HT/SA) on to indium tin-oxide (ITO) coated glass plates using Langmuir-Blodgett (LB) film deposition technique. The immobilized galactose oxidase in P3HT/SA LB films was characterized using Fourier-transform infrared (FTIR) spectroscopy and scanning electron microscopy. This P3HT/SA/GaO LB film on ITO-coated glass plate was used as working electrode with platinum as reference electrode for development of galactose biosensor. The biosensor shows the linearity 1-4 g/dl galactose. The effect of galactose concentration, pH, temperature, detection limit, response time and stability of the immobilized galactose oxidase in LB films were also studied. The electrode was found stable upto 45 °C and has a shelf life of more than 90 days.     

Electrochemical sensor for sulfite determination based on a nanostructured copper-salen film modified electrode

The electrochemical preparation described herein involved the electrocatalytic oxidation of sulfite on a platinum electrode modified with nanostructured copper salen (salen = N,N′-ethylenebis(salicylideneiminato)) polymer films. The complex was prepared and electropolymerized at a platinum electrode in a 0.1 mol L⁻¹ solution of tetrabutylammonium perchlorate in acetonitrile by cyclic voltammetry between 0 and 1.4 V vs. SCE. After cycling the modified electrode in a 0.50 mol L⁻¹ KCl solution, the estimated surface concentration was found to be equal to 2.2 × 10⁻⁹ mol cm⁻². This is a typical behavior of an electrode surface immobilized with a redox couple that can usually be considered as a reversible single-electron reduction/oxidation of the copper(II)/copper(III) couple. The potential peaks of the modified electrode in the electrolyte solution (aqueous) containing the different anions increase with the decrease of the ionic radius, demonstrating that the counter-ions influence the voltammetric behavior of the sensor. The potential peak was found to be linearly dependent upon the ratio [ionic charge]/[ionic radius]. The oxidation of the sulfite anion was performed at the platinum electrode at +0.9 V vs. SCE. However, a significant decrease in the overpotential (+0.45 V) was obtained while using the sensor, which minimized the effect of oxidizable interferences. A plot of the anodic current vs. the sulfite concentration for chronoamperometry (potential fixed = +0.45 V) at the sensor was linear in the 4.0 × 10⁻⁶ to 6.9 × 10⁻⁵ mol L⁻¹ concentration range and the concentration limit was 1.2 × 10⁻⁶ mol L⁻¹. The reaction order with respect to sulfite was determined by the slope of the logarithm of the current vs. the logarithm of the sulfite concentration.     

Cost-effective disposable thiourea film modified copper electrode for capacitive immunosensor

Cost-effective disposable electrodes were fabricated from copper clad laminate, usually used for printed circuit board (PCB) in electronic industries, by using dry film photoresist. Electro-oxidation (anodisation) was employed to obtain a good formation of thiourea film on the electrode surface. The affinity binding pair of carcinoembryonic antigen (CEA) and anti-carcinoembryonic antigen (anti-CEA) was used as a model system. Anti-CEA was immobilized on thiourea film via covalent coupling. This modified electrode was incorporated with a capacitive system for CEA analysis. This capacitive immunosensor provided a linear range between 0.01 and 10 ng ml⁻¹ with a detection limit of 10 pg ml⁻¹. When applied to analyze CEA in serum samples, the results agreed well with the enzyme linked fluorescent assay (ELFA) technique (P > 0.05). The proposed strategy for the preparation of disposable modified copper electrode is very cost effective and simple. Moreover, it provides good reproducibility. This technique can easily be applied to immobilize other biological sensing elements for biosensors development.     

Voltammetric studies of a novel bicopper complex modified glassy carbon electrode for the simultaneous determination of dopamine and ascorbic acid

A novel modified glassy carbon electrode (GCE) with a binuclear copper complex was fabricated using a cyclic voltammetric method in phosphate buffer solution. This modified electrode shows very efficient electrocatalytic activity for anodic oxidation of both dopamine (DA) and ascorbic acid (AA) via substantial decrease in anodic overpotentials for both compounds. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) using this modified electrode show two well-resolved anodic waves for the oxidation of DA and AA in mixed solution, which makes it possible for simultaneous determination of both compounds. Linear analytical curves were obtained in the ranges 2.0–120.0 μM and 5.0–160.0 μM for DA and AA concentrations by using DPV methods, respectively. The detection limits were 1.4 × 10⁻⁶ M of DA and 2.8 × 10⁻⁶ M of AA. This electrode was used for AA and DA determinations in medicine and foodstuff samples with satisfactory results.     

Preparation,optimization, and voltammetric characteristics of poly(o‐phenylenediamine) film as a dopamine‐selective polymeric membrane

Poly(o‐phenylenediamine) films were electrochemically prepared on gold electrodes from the corresponding monomer in an aqueous solution at a constant potential. The polymeric films prepared in this one‐step procedure were found to be thin and insoluble in the aqueous solution. Cyclic and differential pulse voltammetric techniques were used to examine the permeation properties of ascorbic acid and dopamine at the resultant polymeric film electrode. Then, the effects of the chemical and electrochemical variables (e.g., film thickness, polymerization potential, concentrations of monomer and electrolyte) on the permselectivity characteristics of the polymeric film were systematically investigated and the optimal values for each parameter were determined. Furthermore, it was found that the optimized polymer electrode was found to be stable for the successive runs. As a result, it is claimed that poly(o‐phenylenediamine) film can be used as a dopamine‐selective polymeric membrane. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 327–332, 2001     

Electrochemical characterization of poly(eriochrome black T) modified glassy carbon electrode and its application to simultaneous determination of dopamine, ascorbic acid and uric acid

A polymerized film of eriochrome black T (EBT) was prepared on the surface of a glassy carbon (GC) electrode in alkaline solution by cyclic voltammetry (CV). The redox response of the poly(EBT) film at the GC electrode appeared in a couple of redox peak in 0.1 M hydrochloride and the pH dependent peak potential was −55.1 mV/pH which was close to the Nernst behavior. The poly(EBT) film-coated GC electrode exhibited excellent electrocatalytic activity towards the oxidations of dopamine (DA), ascorbic acid (AA) and uric acid (UA) in 0.05 mM phosphate buffer solution (pH 4.0) and lowered the overpotential for oxidation of DA. The polymer film modified GC electrode conspicuously enhanced the redox currents of DA, AA and UA, and could sensitively and separately determine DA at its low concentration (0.1 μM) in the presence of 4000 and 700 times higher concentrations of AA and UA, respectively. The separations of anodic peak potentials of DA-AA and UA-DA reached 210 mV and 170 mV, respectively, by cyclic voltammetry. Using differential pulse voltammetry, the calibration curves for DA, AA and UA were obtained over the range of 0.1-200 μM, 0.15-1 mM and 10-130 μM, respectively. With good selectivity and sensitivity, the present method provides a simple method for selective detection of DA, AA and UA in biological samples.     

Electrocatalytic oxidation of thioglycolic acid at carbon paste electrode modified with cobalt phthalocyanine: application as a potentiometric sensor

The voltammetric behavior of thioglycolic acid (TGA) was studied at a carbon paste electrode modified with cobalt phthalocyanine (CoPc). The CoPc-modified electrode shows high electrocatalytic activity toward oxidation of TGA, lowering substantially the overpotential of anodic reaction. Results of the cyclic voltammetry show that TGA undergoes a two-step oxidation (each step with one electron) resulting the dimer of thiol. Enhancement of the rate of electron transfer results in a near-Nernstian behavior of modified electrode to the concentration of TGA and makes it as a suitable potentiometric sensor for the detection of this compound. This electrode shows a near-Nernstian response in a wide linear range of the concentration TGA (4 orders of magnitude). The modified electrode was used successfully for the determination of TGA and its salts in hair-treatment products and also in culture media. The modified electrode exhibited a fast response time (<10 s), very good stability, and had an extended lifetime.     

Nafion修饰玻碳电极伏安法测定痕量锡

报道了一种用Nafion修饰玻碳电极测定痕量锡的新方法。研究了Nafion膜的有关特性和测定的优化条件,当富集时间为3min时,峰电流与Sn(Ⅳ)浓度在1×10-9~1×10-7mol/L的范围呈良好的线性关系,检测限为2.46×10-10mol/L。该法用于实际水样中痕量锡的测定,平均回收率为97.24%。