Rita de Cássia Silva Luz

Amperometric sensor for nitrite using a glassy carbon electrode modified with alternating layers of iron(III) tetra-(N-methyl-4-pyridyl)-porphyrin and cobalt(II) tetrasulfonated phthalocyanine.

The development of a highly sensitive amperometric sensor for nitrite using a glassy carbon electrode modified with alternated layers of iron(III) tetra-(N-methyl-4-pyridyl)-porphyrin (FeT4MPyP) and cobalt(II) tetrasulfonated phthalocyanine (CoTSPc) is described. The modified electrode showed an excellent catalytic activity and stability for the nitrite oxidation decreasing the peak potentials about 200mV toward less positive values and presenting much higher peak currents than those obtained on the bare GC electrode. A linear response range of 0.2-8.6mumoll(-1), with a sensitivity of 0.37muAlmumol(-1) and detection limit of 0.04mumoll(-1) were obtained with this sensor. The repeatability of the proposed sensor, evaluated in term of relative standard deviation, was verified to be 1.4% for 10 measurements of 0.2mumoll(-1) nitrite solution. Interference caused by common ions has been investigated in simulated mixtures containing high concentration level of interfering ions and the sensor was found to be tolerant against these ions. The developed sensor was applied for the nitrite determination in water samples and the results were in agreement with those obtained by a comparative method described in the literature. The average recovery for these samples was 100.1 (+/-0.7)%.

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 -0.7V versus SCE. The sensor presented better performance in 0.1moll(-1) acetate buffer at pH4.0. 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 23200nmoll(-1) was obtained with a sensitivity of 3.057nAlnmol(-1)cm(-2). The detection limit for 4-NP determination was 7.5nmoll(-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)%.

Amperometric sensor for nitrite based on copper tetrasulphonated phthalocyanine immobilized with poly-L-lysine film.

In this work, an amperometric sensor for nitrite detection based on a glassy carbon electrode modified with copper tetrasulphonated phthalocyanine immobilized by polycationic poly-L-lysine film is presented. The modified electrode showed an excellent catalytic activity toward nitrite oxidation. A linear response range from 0.12 up to 12.20 micromol L(-1) was obtained with a sensitivity of 0.83 microA L micromol(-1). The detection limit for nitrite was 36 nmol L(-1). The repeatability of the proposed sensor, evaluated in terms of relative standard deviation, was 1% for 10 measurements of 10 micromol L(-1) nitrite solution. Finally, the developed sensor was applied for nitrite determination in water samples and the results were in agreement to the comparative method. The average recovery for the samples was 101 (+/-4)%.

Dissolved oxygen amperometric sensor based on layer-by-layer assembly using host–guest supramolecular interactions

The development of a simple, efficient and sensitive sensor for dissolved oxygen is proposed using the host-guest binding of a supramolecular complex at a host surface by combining a self-assembled monolayer (SAM) of mono-(6-deoxy-6-mercapto)-beta-cyclodextrin (betaCDSH), iron (III) tetra-(N-methyl-4-pyridyl)-porphyrin (FeTMPyP) and cyclodextrin-functionalized gold nanoparticles (CDAuNP). The supramolecular modified electrode showed excellent catalytic activity for oxygen reduction. The reduction potential of oxygen was shifted about 200 mV toward less negative values with this modified electrode, presenting a peak current much higher than those observed on a bare gold electrode. Cyclic voltammetry and rotating disk electrode (RDE) experiments indicated that the oxygen reduction reaction involves probably 4-electrons with a rate constant (k(obs)) of 7 x 10(4) mol(-1) Ls(-1). A linear response range from 0.2 up to 6.5 mg L(-1), with a sensitivity of 5.5 microA L mg(-1) (or 77.5 microA cm(-2) L mg(-1)) and a detection limit of 0.02 mg L(-1) was obtained with this sensor. The repeatability of the proposed sensor, evaluated in terms of relative standard deviation was 3.0% for 10 measurements of a solution of 6.5 mg L(-1) oxygen.

A highly sensitive amperometric sensor for oxygen based on iron(II) tetrasulfonated phthalocyanine and iron(III) tetra-(N-methyl-pyridyl)-porphyrin multilayers

The development of a highly sensitive sensor for oxygen is proposed using a glassy carbon (GC) electrode modified with alternated layers of iron(II) tetrasulfonated phthalocyanine (FeTsPc) and iron(III) tetra-(N-methyl-pyridyl)-porphyrin (FeT4MPyP). The modified electrode showed excellent catalytic activity for the oxygen reduction. The reduction potential of the oxygen was shifted about 330 mV toward less negative values with this modified electrode, presenting a peak current much higher than those observed on a bare GC electrode. Cyclic voltammetry and rotating disk electrode (RDE) experiments indicated that the oxygen reduction reaction involves 4 electrons with a heterogenous rate constant (k(obs)) of 3x10(5) mol(-1) L s(-1). A linear response range from 0.2 up to 6.4 mg L(-1), with a sensitivity of 4.12 microA L mg(-1) (or 20.65 microA cm(-2) L mg(-1)) and a detection limit of 0.06 mg L(-1) were obtained with this sensor. The repeatability of the proposed sensor, evaluated in terms of relative standard deviation (R.S.D.) was 2.0% for 10 measurements of a solution of 6.4 mg L(-1) oxygen. The sensor was applied to determine oxygen in pond and tap water samples showing to be a promising tool for this purpose.

Development of a sensor for L-Dopa based on Co(DMG)2ClPy/multi-walled carbon nanotubes composite immobilized on basal plane pyrolytic graphite electrode

L-Dopa is the immediate precursor of the neurotransmitter dopamine, being the most widely prescribed drug in the treatment of Parkinsons disease. A sensitive and selective method is presented for the voltammetric determination of L-Dopa in pharmaceutical formulations using a basal plane pyrolytic graphite (BPPG) electrode modified with chloro(pyridine)bis(dimethylglyoximato)cobalt(III) (Co(DMG)(2)ClPy) absorbed in a multi-walled carbon nanotube (MWCNT). Scanning Electron Microscopy and Fourier Transform Infrared Spectroscopy were used to characterize the materials. The electrocatalytical oxidation of L-Dopa using the Co(DMG)(2)ClPy/MWCNT/BPPG electrode was investigated by cyclic voltammetry and square wave voltammetry. The parameters that influence the electrode response (the amount of Co(DMG)(2)ClPy and of MWCNT, buffer solution, buffer concentration, buffer pH, frequency and potential pulse amplitude) were investigated. Voltammetric peak currents showed a linear response for L-Dopa concentration in the range of 3 to 100 μM, with a sensitivity of 4.43 μAcm(-2)/μM and a detection limit of 0.86 μM. The related standard deviation for 10 determinations of 50 μM L-Dopa was 1.6%. The results obtained for L-Dopa determination in pharmaceutical formulations (tablets) were in agreement with the compared official method. The sensor was successfully applied for L-Dopa selective determination in pharmaceutical formulations.

Electrocatalysis of reduced L-glutathione oxidation by iron (III) tetra-(N-methyl-4-pyridyl)-porphyrin (FeT4MPyP) adsorbed on multi-walled carbon nanotubes

The development of a highly sensitive voltammetric sensor for reduced l-glutathione (GSH) using a basal plane pyrolytic graphite (BPPG) electrode modified with iron(III) tetra-(N-methyl-4-pyridyl)-porphyrin (FeT4MPyP) adsorbed on multi-walled carbon nanotubes (MWCNT) is described. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were used to verify the morphologies and composition of the MWCNT after modification with the FeT4MPyP complex. The modified electrode showed very efficient electrocatalytic activity for l-glutathione oxidation, substantially decreasing the oxidation peak to -0.025V vs Ag/AgCl. A linear response range from 5 micromolL(-1) to 5 mmolL(-1) was obtained with a sensitivity of 703.41 microALmmol(-1). The detection limit for GSH determination was 0.5 micromolL(-1) and the relative standard deviation (R.S.D.) for 10 determinations of 250 micromolL(-1) GSH was 1.4%. The modified electrode was applied for GSH determination in erythrocyte samples and the results were in agreement to those obtained by a comparative method described in the literature.

Determination of Sildenafil Citrate (Viagra ® ) in Various Pharmaceutical Formulations by Flow Injection Analysis with Multiple Pulse Amperometric Detection

O presente trabalho apresenta uma metodologia simples, rapida e de baixo custo para a determinacao de citrato de sildenafila (SC) em formulacoes farmaceuticas de referencia (Viagra®) e em produtos similares, genericos e manipulados, por amperometria de multiplos pulsos em sistema FIA (analise por injecao em fluxo). O metodo consiste na aplicacao de tres pulsos de potencial (sequenciais) em funcao do tempo sobre um eletrodo de trabalho de diamante dopado com boro. SC foi detectado em 1,6 e 1,9 V por meio de dois diferentes processos irreversiveis de oxidacao. Um terceiro pulso de potencial (1,0 V) foi aplicado para regeneracao da superficie do eletrodo. Foram obtidos limites de deteccao na ordem de 10 nmol L-1 e desvio padrao relativo menor que 0,2% (n = 10) para SC 4,5 X 10-5 mol L-1, permitindo 86 injecoes por hora. Estudos de adicao e recuperacao nas amostras ficaram proximos de 100% e os resultados foram validados por cromatografia.

Ultrasensitive Determination of Malathion Using Acetylcholinesterase Immobilized on Chitosan-Functionalized Magnetic Iron Nanoparticles

A renewable, disposable, low cost, and sensitive sensor for the detection of organophosphorus pesticides was constructed by immobilizing the acetylcholinesterase enzyme (AChE), via glutaraldehyde, on magnetic iron nanoparticles (Fe3O4) previously synthesized and functionalized with chitosan (CS). The sensor was denoted AChE/CS/Fe3O4. The magnetic nanoparticles were characterized by Fourier transform infrared spectroscopy and transmission electron microscopy. Acetylthiocholine (ATCh) was incubated with AChE/CS/Fe3O4 and attached to a screen-printed electrode using a magnet. The oxidation of thiocholine (from ATCh hydrolysis) was monitored at an applied potential of +0.5 V vs. Ag/AgCl(KClsat) in 0.1 mol L−1 phosphate buffer solution (pH 7.5) as the supporting electrolyte. A mixture of the pesticide malathion and ATCh was investigated using the same procedure, and the results were compared and expressed as inhibition percentages. For determination of malathion, the proposed sensor presented a linear response in the range from 0.5 to 20 nmol L−1 (R = 0.9942). The limits of detection (LOD) and quantification (LOQ) were 0.3 and 0.8 nmol L−1, respectively. Real samples were also investigated, with recovery values of 96.0% and 108.3% obtained for tomato and pond water samples, respectively. The proposed sensor is a feasible option for malathion detection, offering a linear response, good sensitivity, and a low detection limit.

SPR analysis of the interaction between a recombinant protein of unknown function in Leishmania infantum immobilised on dendrimers and antibodies of the visceral leishmaniasis: A potential use in immunodiagnosis.

In this work, an SPR immunosensor was developed to elucidate the reaction kinetics between a protein of unknown function in Leishmania infantum (hypothetical C1 protein) and specific antibodies of the visceral leishmaniasis (VL). A platform, which is based on layer-by-layer assembly was formed by cysteamine in combination with a fourth-generation poly(amidoamine) dendrimer (PAMAM(G4)) on gold surface for the immobilisation of the protein. This film resulted in amplification of the signal of SPR. Then, a kinetic model based on a bivalent ligation suggested that the reaction between the C1 protein and the anti-C1 antibody occurs in two steps. The value of the equilibrium dissociation constant (KD1×KD2=1.64×10(-7) mol L(-1)) demonstrated high binding affinity between the biomolecules. Furthermore, low limits of detection (LOD=7.37 nmol L(-1)) and quantification (LOQ=7.83 nmol L(-1)) were presented with the proposed SPR immunosensor. Afterwards, the addition of real samples consisting of positive and negative canine sera for VL was accompanied by high sensitivity and selectivity by SPR immunosensor. Therefore, this study quantitatively demonstrated the strong antigenic character of a hypothetical protein and consequently its potential use in the immunodiagnosis of the VL.