RESUMEN
A nanocomposite formed from molybdenum disulphide (MoS2) and graphene quantum dots (GQDs) was proposed as a novel and suitable support for enzyme immobilisation displaying interesting electrochemical properties. The conductivity of the carbon based screen-printed electrodes was highly improved after modification with MoS2 nanoflakes and GQDs, the nanocomposite also providing compatible matrix for laccase immobilisation. The influence of different modification steps on the final electroanalytical performances of the modified electrode were evaluated by UV-vis absorption and fluorescence spectroscopy, scanning electron microscopy, transmission electron microscopy, X ray diffraction, electrochemical impedance spectroscopy and cyclic voltammetry. The developed laccase biosensor has responded efficiently to caffeic acid over a concentration range of 0.38-100µM, had a detection limit of 0.32µM and a sensitivity of 17.92nAµM(-1). The proposed analytical tool was successfully applied for the determination of total polyphenolic content from red wine samples.
Asunto(s)
Técnicas Biosensibles , Lacasa/química , Polifenoles/aislamiento & purificación , Puntos Cuánticos/química , Carbono/química , Espectroscopía Dieléctrica , Enzimas Inmovilizadas/química , Grafito/química , Límite de Detección , Molibdeno/química , VinoRESUMEN
The present work describes the development of an electrochemical method based on the use of 2,2'-diphenyl-1-picrylhidrazyl free radical (DPPH) for the determination of the antiradical properties of several olive oils. Differential pulse voltammetry was used as measuring technique while the electrochemical process was recorded at a platinum screen-printed working electrode. The decrease in 2,2'-diphenyl-1-picrylhidrazyl peak current intensity was measured at a specific potential value of +160 mV vs. screen-printed pseudo-reference electrode, in the presence of α-, δ- and γ-tocopherol and olive oil samples, respectively. The obtained results using differential pulse voltammetry, as detection technique for real samples analysis, showed a satisfactory agreement with those obtained by high-performance liquid chromatography coupled with fluorescence detection. The reported electrochemical method is rapid and easy to use, feasible and accessible to be used as an alternative to 2,2'-diphenyl-1-picrylhidrazyl spectrophotometric based method.
Asunto(s)
Cromatografía Líquida de Alta Presión/métodos , Aceite de Oliva/química , Aceites de Plantas/química , Tocoferoles/química , Vitamina E/química , Radicales LibresRESUMEN
A disposable amperometric biosensor was developed for the detection of total polyphenolic compounds from tea infusions. The biosensor was designed by modifying the surface of a carbon screen-printed electrode with platinum nanoparticles and reduced graphene oxide, followed by the laccase drop-casting and stabilization in neutralised 1% Nafion solution. The obtained biosensor was investigated by scanning electron microscopy and electrochemical techniques. It was observed that platinum nanoparticles-reduced graphene oxide composite had synergistic effects on the electron transfer and increased the electroactive surface area of the carbon screen-printed electrode. The constructed analytical tool showed a good linearity in the range 0.2-2 µM for caffeic acid and a limit of detection of 0.09 µM. The value of Michaelis-Menten apparent constant was calculated from the electrochemical version of Lineweaver-Burk equation to be 2.75 µM. This disposable laccase biosensor could be a valuable tool for the estimation of total polyphenolic content from tea infusions.
Asunto(s)
Materiales Biocompatibles , Técnicas Biosensibles , Grafito/química , Lacasa/química , Nanopartículas del Metal , Platino (Metal)/química , Polifenoles/análisis , Microscopía Electrónica de Rastreo , Óxidos/química , Reproducibilidad de los ResultadosRESUMEN
Four previously documented ligand design strategies for achieving Ag(I) discrimination have been applied to the design of a new N-benzylated N2S3-donor macrocycle; the latter shows high selectivity for Ag(I) over Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) in log K and bulk membrane transport studies.