Dissolved oxygen sensor based on cobalt tetrasulphonated phthalocyanine immobilized in poly-L-lysine film onto glassy carbon electrode

A simple and efficient method for determining dissolved oxygen at pH 6.5 is proposed using differential pulse voltammetry (DPV) and chronoamperometry. The sensor was prepared by modifying a glassy carbon (GC) electrode surface with a cobalt tetrasulphonated phthalocyanine (CoTSPc) immobilized in a poly-L-lysine (PLL) film. This sensor showed excellent catalytic activity and stability for oxygen reduction. With this modified electrode the reduction potential of the oxygen was shifted about 200 mV toward less negative value, presenting a peak current much higher than those measured on a bare GC electrode. The linear response range, sensitivity and detection limit obtained were, respectively, 0.2-8.0 mg l(-1), 11.0 mu A l mg(-1) cm(-2) and 96 mu g l(-1) for chronoamperometry and 0.2-8.0 mg l(-1), 18.3 mu A l mg(-1) cm(-2) and 72 mu g l(-1) for DPV. The repeatability and reproductibility of the proposed sensor evaluated in term of relative standard deviation were, respectively, 4.5% and 4.8% for 10 measurements of a 8.0 mg l(-1) oxygen solution. The number of electrons involved in oxygen reduction, the heterogenous rate constant (k) and the diffusion coefficient (D.) value were evaluated by cyclic voltammetry and with a rotating disk electrode (RDE). These studies showed that two electrons are involved in the oxygen reduction. An average value of the heterogenous rate constant was found to be 4.25 x 10(4) mol(-1) l s(-1) and the diffusion coefficient was 2.0 x 10(-5) cm(2) s(-1). (c) 2005 Elsevier B.V. All rights reserved.11421019102

Investigations of nanometric films of doped polyaniline by using electrochemical surface plasmon resonance and electrochemical quartz crystal microbalance

In the present work, the ionic transport in copper tetrasulfonated phthalocyanine doped polyaniline (PANI/CuTsPc) film and its effects on the optical properties of the polymer is presented. The studies were performed in situ and in real time by using electrochemical surface plasmon resonance (ESPR) and electrochemical quartz crystal microbalance (EQCM). The electropolymerization was performed by potentiodynamic method and the EQCM experiments showed that the PANI/CuTsPc films behave rigidly validating the use of the Sauerbray equation. Both protonic and anionic participation in the charge compensation process were calculated and showed that the presence of the CuTsPc in the PANI film suppress the anionic transportation. Finally, the ESPR experiments showed that changes in the optical properties of the PANI/CuTsPc film were more expressive in the same potential range where the protonic transport was dominant. (c) 2006 Elsevier B.V. All rights reserved.5891708

Electrocatalytic activity of 2,3,5,6-tetrachloro-1,4-benzoquinone/multi-walled carbon nanotubes immobilized on edge plane pyrolytic graphite electrode for NADH oxidation

This work reports the electrocatalytic activity of 2,3,5,6-tetrachloro-1,4-benzoquinone (TCBQ)/multi-walled carbon nanotubes (MWCNT) immobilized on an edge plane pyrolytic graphite electrode for nicotinamide adenine dinucleotide (NADH) oxidation. Scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS) were used to confirms the presence of chloro after the nanotube modification with 2,3,5,6-tetrachloro-1,4-benzoqui none. The surface charge transfer constant, k(s), and the charge transfer coefficient for the modified electrode, alpha, were estimated as 98.5 (+/- 0.6) s(-1) and 0.5, respectively. With this modified electrode the oxidation potential of the NADH was shifted about 300 mV toward a less positive value, presenting a peak current much higher than those measured on an unmodified edge plane pyrolytic graphite electrode (EPPG). Cyclic voltammetry and rotating disk electrode (RDE) experiments indicated that the NADH oxidation reaction involves 2 electrons and a heterogenous rate constant (k(obs)) of 3.1 x 10(5) mol(-1) l s(-1). The detection limit, repeatability, long-term stability, time of response and linear response range were also investigated. (C) 2008 Elsevier Ltd. All rights reserved.53144706471

Voltammetric determination of 4-nitrophenol at a lithium tetracyanoethylenide (LiTCNE) modified glassy carbon electrode

The reduction of 4-nitrophenol (4-NP) has been carried out on a modified glassy carbon electrode using cyclic and differential pulse voltammetry (DPV). The sensor was prepared by modifying the electrode with lithium tetracyanoethylenide (LiTCNE) and poly-L-lysine (PLL) film. With this modified electrode 4-NP was reduced at -0.7 V versus SCE. The sensor presented better performance in 0.1 mol l(-1) acetate buffer at pH 4.0. The other experimental parameters, such as concentration of LiTCNE and PLL, pulse amplitude and scan rate were optimized. Under optimized operational conditions, a linear response range from 27 up to 23200 nmol l(-1) was obtained with a sensitivity of 3.057 nA l nmol(-1) cm(-2). The detection limit for 4-NP determination was 7.5 nmol l(-1). The proposed sensor presented good repeatability, evaluated in term of relative standard deviation (R.S.D. = 4.4%) for n = 10 and was applied for 4-NP determination in water samples. The average recovery for these samples was 103.0 (+/-0.7)%. (C) 2004 Elsevier B.V. All rights reserved.64493594

Cobalt tetrasulphonated phthalocyanine immobilized on poly-L-lysine film onto glassy carbon electrode as amperometric sensor for cysteine

The present work describes the development of a simple and efficient method for the amperometric determination of cysteine (CySH) in wild medium at an applied potential of 0.150 V versus Ag/AgCl. In this sense, the electrocatalytic oxidation of cysteine (CySH) was carried out on a glassy carbon electrode modified with cobalt tetrasulphonated phthalocyanine (CoTSPc) and poly-L-lysine (PLL) film. The immobilization of CoTSPc in PLL film was performed by a simple evaporation of the solvent. The CoTSPc/PLL film, formed on the GC electrode showed an electrocatalytic activity to the CySH oxidation. The sensor presented its best performance in 0.1 mol l(-1) Pipes at pH 7.5. Under optimized operational conditions, the sensor provided a wide linear response range for CySH from 0.50 up to 216.0 mu mol l(-1) with a sensitivity and detection limit of 157 nA cm(-2) l mu mol(-1) and 150 nmol l(-1), respectively. The proposed sensor presented higher sensitivity when compared to the other modified electrodes described in the literature and showed a stable response for at least 200 successive determinations. The repeatability of the measurements with the same sensor and different sensors, evaluated in term of relative standard deviation, were 4.1 and 5.2%, respectively, for n = 10. The developed sensor was applied for the CySH determination in food supplement samples and the results were statistically the same to those obtained by a comparative method described in the literature at a confidence level of 95%. (c) 2006 Elsevier B.V. All rights reserved.42218419

Highly Sensitive and Selective Basal Plane Pyrolytic Graphite Electrode Modified with 1,4-Naphthoquinone/MWCNT for Simultaneous Determination of Dopamine, Ascorbate and Urate

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)The present work describes the development of a highly selective and sensitive voltammetric sensor for dopamine (DA), ascorbic acid (AA) and uric acid (UA) using a basal plane pyrolytic graphite (BPPG) electrode modified with 1,4-naphthoquinone (NQ) adsorbed on multiwalled carbon nanotubes (MWCNT). The modified electrode showed an excellent electrochemical activity towards the oxidations of DA, AA and UA. Three well-defined voltammetric peaks, in a buffered solution at pH7.5, were obtained by differential pulse voltammetry (DPV) at 0.050, 0.145 and 0.270Vvs. Ag/AgCl for AA, DA and UA, respectively. Linear calibration plots were obtained in the range of 1070nmolL1 for DA, 40280 mu molL1 for AA and 214 mu molL1 for UA, with detection limits of 3nmolL1, 1.9 mu molL1 and 0.1 mu molL1, respectively. The sensor was successfully applied in human urine samples and the results showed that the modified electrode has no interferences from urine sample.253SI723731Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

A Novel Sensor Based on Manganese azo-Macrocycle/Carbon Nanotubes to Perform the Oxidation and Reduction Processes of Two Diphenol Isomers

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)The present work describes the development of a selective and sensitive voltammetric sensor for simultaneous determination of catechol (CC) and hydroquinone (HQ), based on a glassy carbon (GC) electrode modified with manganese phthalocyanine azo-macrocycle (MnPc) adsorbed on multiwalled carbon nanotubes (MWCNT). Scanning electron microscopy and scanning electrochemical microscopy were used to characterize the composite material (MnPc/MWCNT) on the glassy carbon electrode surface. The modified electrode showed excellent electrochemical activity towards the simultaneous oxidation and reduction of CC and HQ. On the MnPc/MWCNT/GC electrode, both CC and HQ can generate a pair of quasi-reversible and well-defined redox peaks. Under optimized experimental and operational conditions, the cathodic peak currents were linear over the range 1-600 mu molL(-1) for both CC and HQ, with limits of detection of 0.095 and 0.041 mu molL(-1), respectively. The anodic peak currents were also linear over the range 1-600 mu molL(-1) for both CC and HQ, with limits of detection of 0.096 and 0.048 mu molL(-1), respectively. The proposed method was effectively applied for the simultaneous detection of hydroquinone and catechol in water samples and the results were in agreement with those obtained by a comparative method described in the literature.263602611Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG)Rede Mineira de QuimicaInstituto Nacional de Ciencia e Tecnologia (INCT) de BioanaliticaConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

An amperometric sensor based on electrochemically triggered reaction: Redox-active Ar-NO/Ar-NHOH from 4-nitrophthalonitrile-modified electrode for the low voltage cysteine detection

The present work describes the development of a highly sensitive amperometric sensor based on a simple and efficient carbon paste electrode modified with a new redox "mediator", 4-nitrophthalonitrile, toward detection of cysteine (CySH) in neutral medium at an applied potential of 0.33 V vs. Ag/AgCl. The sensor showed its best performance in 0.1 mol L-1 phosphate buffer solution, at pH 7.0. After optimizing the operational conditions, the sensor provided a linear response range for CySH from 0.8 up to 13.2 mu mol L-1 with sensitivity, detection and quantification limits of 37 nA L mu mol(-1), 0.25 mu mol L-1 and 0.80 mu mol L-1, respectively. The sensitivity of the proposed sensor was much higher when compared to other sensors described in the literature and showed a stable response for at least 80 successive determinations. The repeatability of the measurements with the sensor and the preparation of a series of electrodes, evaluated in terms of relative standard deviation, were 4.1 and 5.0%, respectively, for n = 10. The developed sensor was applied for cysteine determination in food supplement samples and the results were statistically the same with those obtained by the comparative method described in the literature at a confidence level of 95%. (c) 2007 Elsevier B.V. All rights reserved.6121879

Development of a voltammetric sensor for diospyrin determination in nanomolar concentrations

A sensor based on glassy carbon (GC) electrode modified with cobalt tetrasulfonated phthalocyanine, (CoTSPc) and a poly-L-lysine (PLL) film is proposed for diospyrin determination in nanomolar concentrations with differential pulse voltammetry (DPV) technique. The modified electrode showed excellent catalytic activity presenting much higher peak currents than those measured on a bare GC electrode. Linear response range, sensitivity and limit of detection (LOD) were of 1-120 nmol l(-1), 220.46 nA 1 nmol(-1) cm(-2) and 0.3 nmol l(-1), respectively. The repeatability of the proposed sensor, evaluated in term of relative standard deviation (R.S.D.), was measured as 4.4% for 10 experiments in 50 mu mol l(-1) diospyrin samples. The developed sensor was applied for the determination of diospyrin in the crude extracts of the stem-bark of Diospyros montana Roxb. and the average recovery for these samples was 101.9 (+/- 3.1)%. (c) 2005 Elsevier B.V. All rights reserved.6841378138

DNA and graphene as a new efficient platform for entrapment of methylene blue (MB): Studies of the electrocatalytic oxidation of beta-nicotinamide adenine dinucleotide

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)The modification of glassy carbon (GC) electrode with deoxyribonucleic acid (DNA) and graphene is utilized as a new efficient platform for entrapment of methylene blue (MB). Electrochemical and electroanalytical properties of the modified electrode (DNA/graphene/MB) were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and amperometry techniques. Cyclic voltammetric results indicated the excellent electrocatalytic activity of the resulting electrode toward oxidation of beta-nicotinamide adenine dinucleotide (NADH) at reduced overpotential (0.1 V vs. Ag/AgCl). It has been found that the DNA/graphene/MB modification has significantly enhanced the effective electrode response toward NADH oxidation. Cyclic voltammety and rotating disk electrode (RDE) experiments indicated that the NADH oxidation reaction involves two electrons and an electrocatalytic rate constant (k(obs)) of 1.75 x 10(6) mol(-1) L s(-1). The electrochemical sensor presented better performance in 0.1 mol L-1 phosphate buffer at pH 7.0. Other experimental parameters, such as the DNA, graphene, MB concentrations and the applied potential were optimized. Under optimized conditions, a linear response range from 10 mu mol L-1 to 1.50 mmol L-1 was obtained with a sensitivity of 12.75 mu A L mu mol(-1). The detection and quantification limits for NADH determination were 1.0 mu mol L-1 and 3.3 mu mol L-1, respectively. (C) 2013 Elsevier Ltd. All rights reserved.111543551Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Rede Mineira de QuimicaFundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG)Instituto Nacional de Ciencia e Tecnologia em BioanaliticaConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq