Browsing by Author "Oliveira, O. N."
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- Detection of chloroform with a sensor array consisting of electrochemically deposited polythiophenes films: Processes governing the electrical responsePublication . Carvalho, E. R.; Correa, A. A.; Consolin Filho, N.; Oliveira, O. N.; Gomes, Henrique L.; Mattoso, L. H. C.; Neto, L. MartinA sensor array made up with electrodeposited polythiophene films onto interdigitated gold electrodes has been used to detect small concentrations of chloroform in water, down to 0.1 mg L-1. An analysis of the impedance data revealed two relaxation processes, one attributed to the polymer coating and associated with the double layer and the other ascribed to the electrolyte. Because these processes depended on the type of polythiophene derivative and on doping, the sensitivity of the electrodes varied. The most sensitive to chloroform was the poly(methyl thiophene) oxidized at 5 mC. Also, doped layers were more sensitive, from which one may infer that a plausible mechanism for detection is the removal of dopant ions by the solvent. Surprisingly, a bare gold metal electrode was more sensitive than some electropolymerized samples, probably because the relaxation processes in the latter were not strongly affected by chloroform.
- Strategies to optimize biosensors based on impedance spectroscopy to detect phytic acid using layer-by-layer filmsPublication . Moraes, M. L.; Maki, R. M.; Paulovich, F. V.; Rodrigues Filho, U. P.; De Oliveira, M. C. F.; Riul, A.; De Souza, N. C.; Ferreira, M.; Gomes, Henrique L.; Oliveira, O. N.Impedance spectroscopy has been proven a powerful tool for reaching high sensitivity in sensor arrays made with nanostructured films in the so-called electronic tongue systems, whose distinguishing ability may be enhanced with sensing units capable of molecular recognition. In this study we show that for optimized sensors and biosensors the dielectric relaxation processes involved in impedance measurements should also be considered, in addition to an adequate choice of sensing materials. We used sensing units made from layer-by-layer (LbL) films with alternating layers of the polyeletrolytes, poly(allylamine) hydrochloride (PAH) and poly(vinyl sulfonate) (PVS), or LbL films of PAH alternated with layers of the enzyme phytase, all adsorbed on gold interdigitate electrodes. Surprisingly, the detection of phytic acid was as effective in the PVS/PAH sensing system as with the PAH/phytase system, in spite of the specific interactions of the latter. This was attributed to the dependence of the relaxation processes on nonspecific interactions such as electrostatic cross-linking and possibly on the distinct film architecture as the phytase layers were found to grow as columns on the LbL film, in contrast to the molecularly thin PAH/PVS films. Using projection techniques, we were able to detect phytic acid at the micromolar level with either of the sensing units in a data analysis procedure that allows for further optimization.