IEEE Transactions on Dielectrics and Electrical Insulation
Vol. 13, No. 5; October 2006
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Layer-by-layer Films of Poly(o-ethoxyaniline), Chitosan and Chitosan-poly(methacrylic acid) Nanoparticles and their Application in an Electronic Tongue Carlos E. Borato, Fábio L. Leite, Luiz H. C. Mattoso Embrapa Instrumentação Agropecuária, CP 741, 13 560-970, São Carlos, SP, Brazil
Rejane C. Goy, Sergio P. Campana Filho Instituto de Química de São Carlos USP, CP 780, 13 560-970 São Carlos, SP, Brazil
Cláudio L. de Vasconcelos, Cypriano G. da Trindade Neto, Márcia R. Pereira, José L. C. Fonseca Departamento de Química, Universidade Federal do Rio Grande do Norte, CP 1662, 59078-970 Natal, RN, Brazil and Osvaldo N. Oliveira Jr. Instituto de Física de São Carlos USP, CP 369, 13 560-970, São Carlos, SP, Brazil
ABSTRACT Layer-by-layer (LbL) films have been produced with poly(o-ethoxyaniline) (POEA), chitosan and chitosan-poly(methacrylic acid) (CS-PMAA) nanoparticles. Because the adsorption of LbL films depends on ionic interactions and H-bonding, optimized conditions had to be established for the growth of multilayer films. Unusually thick films were obtained for POEA and CS-PMAA, thus demonstrating the importance of using chitosan in the form of nanoparticles. These nanostructured films were deposited on chromium electrodes to form a sensor array (electronic tongue) based on impedance spectroscopy. This system was used to detect copper ions in aqueous solutions. Index Terms – Electronic tongue, chromium electrodes, films, chitosan nanoparticles, POEA, impedance spectroscopy.
1 INTRODUCTION NANOSTRUCTURED films of chitosan, a polysaccharide obtained from the desacetylation of chitin, have been fabricated in the last few years for a variety of applications [1,2]. Chitosan is soluble in acidic media and can be used to produce layer-by-layer (LbL) films, which have been employed as sensing units in taste sensors [3], and as templates for immobilization of enzymes used for biosensing [4]. The main interest in chitosan in the form of thin films is to exploit its biocompatibility and ability to complex heavy metal ions [2], in addition to its strong interaction with cholesterol [5] and other biomolecules [6]. Nanoparticles of chitosan, on the other hand, have been used as bactericide and antimicrobial [7,8] and in the controlled release of drugs, insulin and albumin [9-11]. In general, chitosan nanoparticles performed better in inhibiting growth of microorganisms than raw chitosan [8]. It is therefore important to verify whether LbL films made of chitosan nanoparticles behave differently from those of chitosan. In this paper we compare the behavior of chitosan and Manuscript received on 9 May 2006, in final form 9 August 2006.
chitosan nanoparticles in LbL films with alternated layers of poly(o-ethoxyaniline) (POEA), a polyaniline derivative. POEA is highly stable, easily processed and may have its conductivity varied widely by doping and dedoping upon protonation and deprotonation, respectively [12]. It has also been used extensively in the fabrication of LbL films, where it normally functions as the polycation for adsorption via ionic interactions, or even through H-bonding [13]. With the combination of distinct materials, one may envisage biospecific recognition in LbL films, which opens up a number of novel possibilities. Of particular relevance for this work is the deposition of LbL films that may be used in taste sensors. We use impedance spectroscopy [14] as the method of detection with sensing units made of LbL films deposited onto metallic substrates and immersed in the liquid samples to be analyzed. The aim is to exploit the high sensitivity provided by the combination of nanostructured films with an ac electrical characterization method, which has given excellent results in distinguishing complex liquids, e.g. wine, coffee, juices and milk, and in detecting pollutants such as pesticides, heavy metals and humic substances in waters [15-19]. We also compare the performance of these sensing units with an array made of bare chrome electrodes.
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2 EXPERIMENTAL DETAILS POEA was synthesized according to the procedures described by Mattoso et al [20]. Chitin extracted from the exoskeleton of crabs was submitted to desacetylation [21] resulting in chitosan with viscosity average molecular weight (Mv) of 170,000 g/mol and average degree of acetylation ( DA ) of 10%. The dispersion of chitosan nanoparticles (CSPMAA) was obtained from a 0.2% chitosan solution in methacrylic acid (0.5%) using potassium persulfate as initiator [22]. For the fabrication of LbL films of POEA (0.06%) and chitosan (0.15%) or chitosan nanoparticles (0.2%), the first step was to determine an optimized immersion time for the substrate in the aqueous solutions, which were 3 minutes for POEA and 8 minutes for chitosan and CS-PMAA, respectively. The substrates were made of glass cleaned with a solution of 7:3 H2SO4/H2O2 (v/v) (during 60 min.) and then with a solution of 5:1:1 H2O/NH4OH/H2O2 (v/v)) (during 40 min.). Film growth on the substrate was monitored by measuring the UV-VIS. absorption spectra of the substrate + film, with absorption in the visible region being basically due to POEA. Before proceeding to film fabrication, the interaction in solution was investigated by measuring the UVVIS. spectra of mixtures of POEA and chitosan or CS-PMAA. The materials used in the study were combined to generate 10 distinct films. LbL films with 10 bilayers were produced for POEA alternated with chitosan or with CS-PMAA, where the POEA solutions had pH 3 or 5. Films were also produced from mixed solutions of 1:1 POEA/chitosan or POEA/CSPMAA, and from a single component, namely POEA, chitosan and CS-PMAA. The 10-layer films from a single component could be built, with no alternating layers, because secondary interactions participated in the adsorption process, in addition to the ionic interactions. All films were characterized with a Topometrix 2010 Discoverer atomic force microscopy (AFM), operating in the contact mode. LbL films of POEA and chitosan or CS-PMAA were also deposited onto chrome electrodes for impedance spectroscopy measurements. The latter were measured with a Solartron 1260 Impedance Gain Phase Analyser at 200 Hz and bias voltage of 50 mV. These films were used as sensing units to detect copper ions in aqueous solution of CuSO4. The detection studies were made in two different steps, both using two arrangements referred to as A and B. Each arrangement comprised five sensing units with double face (i.e. two back-to-back units), resulting in ten sensing units. Measurements using units with no deposited films, i. e. bare metal electrodes, were also carried out. Table 1 shows a list of films deposited in each arrangement. The electrodes for the impedance measurements were either interdigitated bare chrome electrodes or interdigitated chrome electrodes coated with the films mentioned in Table 1. The measurements were taken with the electrodes immersed in the aqueous solutions. Two sets of experiments were performed. In the first, higher concentrations of CuSO4 were used, viz. 1, 5, 10, 20 and 50x10-3 mol/L. The sensing units were immersed in 50 mL of the solutions, with 20 min. elapsing for reaching equilibrium before the measurement was taken. Measurements with distilled water were performed before and after the
experiments with CuSO4 to check whether the electrodes had been contaminated. Three measurements were taken for each concentration and, more importantly, the concentration was chosen randomly for each measurement. That is to say, we did not obtain the measurements in a growing or decreasing concentration of CuSO4 to minimize systematic errors. In the second set of experiments, the aim was to check reproducibility of the measurements and attempt to determine whether even lower concentrations of copper could be detected. This was carried out by pouring 50mL of distilled water into an acrylic trough constructed especially for coupling the sensor array. After stabilization, measurements were taken in pure water at each 20 min. For the 31st measurement, pure water was added to the sample (i.e. copper ions were deliberately introduced, but the sample suffered manipulation). In addition, in some other experiments aliquots of varying concentrations of CuSO4 were added to pure water to be compared with the cases where only pure water was added.
3 RESULTS AND DISCUSSION The first clear difference between chitosan and the dispersion of chitosan nanoparticles (CS-PMAA) is observed in the interaction with POEA in aqueous solutions, as demonstrated in the spectra of Figure 1. The incorporation of CS-PMAA causes the absorption of POEA to shift considerably to lower wavelengths owing to dedoping of POEA. Indeed, for a pH 3 POEA solution an absorption peak appears at ca. 780 nm, but as chitosan nanoparticles are added the peak shifts to ca. 530 nm, which is characteristic of dedoped POEA. POEA dedoping can be associated with the “competition” for its positive charges – as POEA was protonated - with the nanoparticles. Further dedoping or changes in the oxidation state were also observed for a pH 5 solution of POEA and CS-PMAA, which also shifted to lower wavelengths. On the other hand, Figure 1b shows that addition of chitosan solution (not in the form of nanoparticles) into a pH 3 solution of POEA does not cause any shift. The absorbance merely decreases as a result of a smaller relative quantity of POEA in the mixed solution due to a dilution effect as the amount of chitosan is increased. The adsorption of POEA in LbL films of chitosan and CSPMAA was also markedly different, as a much higher amount of POEA was adsorbed for CS-PMAA. This effect was particularly strong for POEA at pH 5 and CS-PMAA at pH 3, as indicated in Figure 2 and Table 2. For instance, a 10-bilayer LbL film of POEA/CS-PMAA produced under the conditions just mentioned was ten times thicker than a similar film with pH 3 for POEA. Even more surprising was the observation that LbL films of POEA/chitosan were much thinner, as also indicated in Figure 2 and Table 2. A visual inspection of LbL films of POEA/CS-PMAA confirmed the fabrication of very thick films, which is also consistent with AFM images in Figure 3 where an unusually large scale appears for the Z-axis (height). The LbL film for POEA/CS-PMAA is ca. 5 μm thick, which is atypical for a LbL film. In fact, films obtained with CS-PMAA – with no alternating layers - are already thick, which clearly points to the importance of the nanoparticles for a strong adsorption.
IEEE Transactions on Dielectrics and Electrical Insulation 1.2
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The roughness is extremely high, almost two orders of magnitude larger than for a chitosan film (Table 2). The films with CS-PMAA are also thicker and rougher than POEA films alternated with any other polyanion reported in the literature. Also presented in Table 2 are the values for POEA films in
which POEA layers have been deposited on top of already formed POEA layers, with no alternating material. Such deposition is possible because – in addition to ionic interactions – H-bonding plays an important role in the adsorption of polyanilines [23]. Thicker films are deposited
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for solutions of POEA pH 5 since there is little repulsion as POEA is dedoped. The latter film is also less rough than those obtained with POEA pH 3. Interestingly, the film for POEA pH 3 alternated with CS-PMMA is much thicker (30 times) than the film obtained with the mixture between POEA and CS-PMMA. It seems therefore that strong adsorption leading to thick films only takes place if CS-PMMA nanoparticles form a layer on their own, either in a film with a single component or alternated with POEA. The growth of a layer containing CS-PMMA mixed with POEA is constrained, which inevitably has to do with the interaction with POEA. Since POEA forms much thinner layers, apparently the number of embedded CS-PMMA nanoparticles is limited by the conformation of POEA. Nevertheless, a precise understanding of such interaction will require further studies. We also deposited 10-bilayer LbL films onto double-faced chrome electrodes to form sensor arrays as depicted in Table 1. Impedance measurements were taken at 200 Hz and bias voltage of 50mV, and the data were treated with an equivalent circuit analysis. The figure of merit used was the capacitance
of the system. Two sets of experiments were performed, the first involving higher concentrations of CuSO4, namely (1, 5, 10, 20 and 50x10-3mol/L). In a second set, to be discussed later, we checked the reproducibility of the sensing units with smaller concentrations of CuSO4. With the concentrations mentioned, each sensing unit could detect and distinguish between these concentrations. By way of illustration, Figure 4 shows the data for the sensing units of arrangements A and B, which were taken before and after the films were deposited. Therefore, sensing units 1 through 4 correspond to bare chrome electrodes while the other sensing units are labeled according to the material used in the LbL film. It is seen that all sensing units are capable of detecting the presence of varied amounts of copper in the aqueous solutions. Moreover, identical results were obtained in the measurements with pure water, before and after a series of experiments, which indicates that the sensing units can be reused if properly washed, an important feature for an electronic tongue. Note also the lower capacitance values for the units with LbL films, though the ability to detect copper was not affected.
Table 2. Average height (Z) and roughness for 10-bilayer LbL films. Films Z (nm) Roughness (nm)
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IEEE Transactions on Dielectrics and Electrical Insulation
Vol. 13, No. 5; October 2006
When the responses of the sensing units of a given array were combined in a Principal Component Analysis (PCA), clusters are formed for the different copper concentrations, as shown in Figure 5. PCA is a statistical technique largely used for feature extraction and is based on the reduction of input data dimension [24]. It works by processing data variance with a set of principal components, the first of which presents the highest variance and provides most of the information to discriminate the input data. Notably, the first component corresponds to more than 98% of the variance in three of the plots, which not only denotes good reproducibility but also indicates that this component could be taken on its own to distinguish between the various samples. Indeed, data points for samples with higher concentrations are progressively located to the right hand side of the plot, which means that the first principal component is highly correlated with the ion concentration in the aqueous solutions. A comparison between Figures 5a, 5c with 5b, 5d indicates that the distinguishing ability was practically the same for the arrays before and after film deposition. We shall discuss this point later on. Having sensor unit 1
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confirmed that the sensing units could easily detect copper ions in aqueous solutions at the mM level, we examined the possibility of going further down in concentration. It is known that electrical properties are very sensitive to any impurities in the water, especially when interfaces are analyzed [25], which is actually the reason for the high sensitivity of the electronic tongues based on nanostructured films and using impedance spectroscopy. However, this high sensitivity may lead to artifacts with nominally identical samples being distinguished from each other by mere manipulation of the samples. With these concerns in mind, we conceived experiments with copper ion concentrations down to the nM level, in addition to control experiments in which water was added into water. Figure 6 illustrates some of these results for a bare chrome sensing unit, from which one can see that for 1 μM of CuSO4 or higher the electrical response is distinguished from that of water being added into pure water (control experiment). For concentrations below 1 μM, an effect could also be seen if the scale for the capacitance was expanded, but then the changes were within the range of changes in the control experiments.
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Figure 4. Electric response, taking the film capacitance as figure of merit, for several sensing units immersed into solutions containing copper: (a) arrangement A without films, (b) arrangement A with films, (c) arrangement B without films and (d) arrangement B with films.
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The ability to detect μM concentrations was demonstrated for sensing units with or without a film deposited, as shown in Figure 7. Though these results again indicate that bare metal electrodes may be used for taste sensors, which reduces the cost considerably, an optimized response may be obtained when interactions between analyte and film material are strong. This appears to be the case in Figure 7, for the sensitivity of the electrode coated with a 10-bilayer LbL film of dedoped POEA and chitosan was higher than for the bare electrode. Figure 8 shows the distinguishing ability of the sensor arrangement A in PCA plots, again before (bare electrodes) and after depositing the LbL films. Similar results were obtained with arrangement B, whose data are therefore omitted. Consistent with the conclusions drawn from the results for separate sensing units, samples with 1 μM of CuSO4 concentrations or above could be distinguished in all cases, but those with lower concentrations were lamped together with the data points for pure water. With regard to the surprising results for the sensing units made of bare chrome electrodes, two points should be emphasized: i) the
response from nominally identical electrodes varied considerably, which was actually exploited in obtaining a sensor array with the same (nominally) electrode materials. In another paper [26], this has been shown to arise from the morphological differences among chrome electrodes that were produced by electrodeposition. The differences appear because the electrical response basically depends on the interface phenomena. ii) by the same token, with the interface with the liquid under study governing the response, the performance of a sensor array made of bare metal electrodes may equal that of an array produced with nanostructured films, as indicated here in Figures 4, 5 and 8. There are nevertheless cases in which strong interactions with the analyte become important, as illustrated in Figure 7 for LbL films of dedoped POEA alternated with chitosan. Therefore, the challenge in searching for new materials for electronic tongues is twofold: one has not only to seek various materials that respond differently to analytes but also identify materials with some degree of specificity in their interaction with the analytes.
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Figure 5. PCA plots for the measurements using arrangements A and B with and without films, in detecting various amounts of copper in water. The copper concentrations are indicated by differing symbols as given in the inset. PC1 and PC2 in the axes refer to the first and second principal components.
IEEE Transactions on Dielectrics and Electrical Insulation
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Measurements number Figure 7. Capacitance monitored as increasing amounts of copper solution were added to the water, for two sensing units: with no film and another with a 10-bilayer LbL film of dedoped POEA (pH 5) alternated with chitosan film
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Figure 8. PCAs plot for the measurements with arrangement A, including those taken with very small amounts of copper: (a) without film and (b) with deposited films. The different symbols refer to various concentrations of CuSO4 employed and samples of water, as indicated in the insert. PC1 and PC2 in the axes refer to the first and second principal components.
4 CONCLUSIONS We have shown that entirely different LbL films are obtained when chitosan is used in the form of nanoparticles (CS-PMAA), for the films are much thicker than when raw chitosan is employed. In a particular case, where the POEA solution had pH 5 and CS-PMAA had pH 3, a 10-bilayer film reached ca. 5μm of thickness, which is unusual for an LbL film. Interaction between the chitosan nanoparticles in the dispersion and POEA was proven to be much stronger than for chitosan, being sufficient to alter the doping state of POEA. UV-VIS. absorption measurements with mixed solutions of POEA and CS-PMAA indicated that the latter cause POEA to be dedoped. The LbL films could also be used in sensing units to detect copper ions in solution down to the μM level. Furthermore, we showed that high-performance electronic tongues could also be obtained with an array of bare chrome
electrodes, which may have important implications in lowering the costs of such devices.
ACKNOWLEDGMENTS This work was supported by FAPESP, CNPq, Capes, Nanobiotec, IMMP/MCT, Embrapa/Labex Program and CTHidro (Brazil).
REFERENCES [1] [2]
[3]
G. A. F. Roberts, Chitin chemistry, London, UK, Macmillan Press, pp. 349, 1992. K. Kurita, Y. Koyama and A. Tanaguchi, “Studies on chitin. IX. Crosslinking of water-soluble chitin and evaluation of the products as adsorbents for cupric ion”, J. Appl. Polym. Sci., Vol. 31, pp. 1169-1176, 1986. R. A. A. Muzzarelli, “Human enzymatic activities related to the therapeutical administration of chitin derivatives”, Cell. Mol. Biol. Life Sci., Vol. 53, pp. 131-140, 1997.
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C.A. Constantine, S.V. Mello, A. Dupont, X. Cao, D. S. Dos Santos Jr., O. N. Oliveira Jr., F. T. Strixino, E. C. Pereira, T. Cheng, J. J. Defrank and R. M. Leblanc, “Layer-by-layer self-assembled chitosan/poly(thiophene-3-acetic acid) and organophosphorus hydrolase multilayers”, J. Am. Chem. Soc., Vol. 125, pp. 1805-1809, 2003. [5] N. K. Mathura and C. K. Narang, “Chitin and chitosan: versatile polysaccharides from marine animals”, J. Chem. Education, Vol. 67, pp. 938-942, 1990. [6] M. N. V. R. Kumar, “A review of chitin and chitosan applications”, Reactive and Functional Polym., Vol. 46, pp. 1-27, 2000. [7] S. A. Agnihotri, M. N. Mallikarjuna and T. M. Aminabhavi, “Recent advances on chitosan-based micro- and nanoparticles in drug delivery”, J. Controlled Release, Vol. 100, pp. 5-28, 2004. [8] L. Qi, Z. Xu, X. Q. Jiang and X Hu, “Preparation and antibacterial activity of chitosan nanoparticles,” Carbohydrate Research, Vol. 339, pp. 2693-2700, 2004. [9] T. Banerjee, S. Mitra, A. K. Singh, R. K. Sharma and A. Maitra., “Preparation, characterization and biodistribution of ultrafine chitosan nanoparticles”, Intern. J. Pharmaceutics, Vol. 243, pp. 93-105, 2002. [10] T. López-León, E. L. S. Carvalho, B. Seijo, J. L. Ortega-Vinuesa and D. Bastos-González, “Physicochemical characterization of chitosan nanoparticles: eletrokinetic and stability behavior”, J. Coll. and Interface Sci., Vol. 283, pp. 344-351, 2005. [11] S. Schaffazick, “Caracterização e Estabilidade Físico-Química de Sistemas Poliméricos Nanoparticulados para Administração de Fármacos”, Química Nova, Vol. 26, pp. 726-737, 2003. [12] P. N. Adams, P. J. Laughlin, A. P. Monkman and N. Bernhoeft, “A further step towards stable organic metals. Oriented films of polyaniline with high electrical conductivity and anisotropy”, Solid State Comm., Vol. 91, pp. 875-878, 1994. [13] L. G. Paterno, C. J. L. Constantino, O. N. Oliveira Jr. and L. H. C. Mattoso, “Self-assembled films of poly(o-ethoxyaniline) complexed with sulfonated lignin”, Coll. & Surf. B. Biointerfaces, 23, 257-262, 2002. [14] S. das Neves, C. N. P. da Fonseca and M. A. De Paoli, “A. Photoelectrochemical characterization of electrodeposited polyaniline”, Synth. Metals, Vol. 89, pp. 167-169, 1997. [15] A Riul Jr, R. R. Malmegrim, F. J. Fonseca and L. H. C. Mattoso, “An artificial taste sensor based on conducting polymers,” Biosensors and Bioelectron, Vol. 18, pp. 1365-1369, 2003. [16] B. Lawton and R. Pethig, “Determining the fat-content of milk and cream using ac conductivity measurements”, Measurement Sci. Technol. Vol. 4, pp. 38-41, 1993. [17] A. Riul Jr., H. C. Souza, R. R. Malmegrim, D. S. dos Santos Jr., A. C. P. L. F. Carvalho, F. J. Fonseca, O. N. Oliveira Jr. and L. H. C. Mattoso, “Wine classification by taste sensors made from ultra-thin films and using neural networks”, Sens. & Actuators B, Vol. 98, pp. 77-82, 2004. [18] C. E. Borato, A. Riul Jr., M. Ferreira, O. N. Oliveira Jr. and L. H. C. Mattoso, “Exploiting the versatility of taste sensors based on impedance spectroscopy”, Instrum. Sci. Tech. Vol. 32, pp. 21-30, 2004. [19] A. Legin, A. Rudnitskaya, Y. Vlasov, C. Di Natale, F. Davide and A. D’Amico, “Tasting of beverages using an electronic tongue,” Sens. & Actuators, B, Vol. 44, pp. 291-296, 1997. [20] L. H. C. Mattoso, S. K. Manohar, A. G. Macdiarmid and A. J. Epstein, “Studies of the chemical syntheses and on the characteristics of polyaniline derivatives”, J. Polym. Sci. Part A: Polym. Chem., Vol. 33, pp. 1227-1234, 1995. [21] S. P. Campana-Filho and J. Desbrières, “Chitin, chitosan and derivatives,” Natural Polymers and Agrofibers Composites, E. Frollini; A. L Leão; L. H. C. Mattoso, eds. USP; UNESP; EMBRAPA, pp. 41-71, 2000. [22] Y. Hu, X. Q. Jiang, Y. Ding, H. X. Ge, Y. Y. Yuan and C. Z. Yang, “Synthesis and characterization of chitosan-poly(acrylic acid) nanoparticles”, Biomaterials, Vol. 23, pp. 3193-3201, 2002. [23] L. G. Paterno and L. H. C. Mattoso, “Influence of different dopants on the adsorption, morphology and properties of self-assembled films of poly(o-ethoxyaniline)”, J. Appl. Polym. Sci., Vol. 83, pp. 1309-1316, 2001. [24] J. E. A. Jackson, A Users’ Guide to Principal Components; Wiley: New York, 1991. [25] D. M. Taylor, O. N. Oliveira Jr. and H. Morgan, “The effect of water quality on the electrical characteristics of Langmuir monolayers”, Thin Solid Films, Vol. 173, pp. L141-L147, 1989.
[26] C. E. Borato, F. L. Leite, O. N. Oliveira Jr. and L. H. C. Mattoso, “Efficient taste sensors made of bare metal electrodes”, Sensor Letters, Vol. 4 , pp. 210-214, 2006. Carlos Eduardo Borato was born in São Carlos, Brazil, in 1975. He received the B. Sc. degree in physics in 2000, and the M.Sc. degree in materials science and engineering, in 2002, both from the University of São Paulo. He is completing a Ph.D. Project at the University of São Paulo on novel materials and electrode systems for taste sensors.
Rejane Celi Goy was born in Tupã, Brazil, in 1974. She received the B.Sc. degree in chemistry in 1999, and the M.Sc. degree in materials science and engineering at the University of São Paulo (USP), in 2002. She is currently completing her Ph.D. degree, also at USP, on studies involving chitosan-based materials (spheres, microspheres and thin films) for detection and removal of cooper ions from aqueous solutions.
Fabio de Lima Leite was born in Itanhaém, Brazil, in 1975. He obtained the B.Sc. degree in physics from the São Paulo State University (UNESP), in 2000 and the M.Sc. degree in materials science and engineering from the University of São Paulo, in 2002. Currently, he is a Ph.D. student in the University of São Paulo, in São Carlos, and doing research on conducting polymers and atomic force microscopy at the Agricultural Instrumentation Unit of Embrapa. Cláudio Lopes de Vasconcelos was born in São Paulo, Brazil, in 1978. He received the B.Sc. degree in pharmacy in 2000, and the M.Sc. degree in 2003, both at the Federal University of Rio Grande do Norte. He has been working in polymer chemistry and colloids. At the moment, he is enrolled in a Ph.D. program at the Federal University of Rio Grande do Norte, with the research focusing on the study of polyelectrolytes in solution, stabilization of colloids and adsorption process of biomacromolecules. Cypriano Galvão da Trindade Neto was born in João Pessoa, Brazil, in 1977. He received the B.Sc. degree in pharmacy in 2000, and the M.Sc. degree in chemistry in 2004, both at the Federal University of Rio Grande do Norte (UFRN). He is completing a Ph.D. project at the Chemistry Department of UFRN focused on the study of permeability and diffusion in membranes of chitosan and its blends.
Sergio P. Campana-Filho was born in Jau, Brazil, in 1957. He obtained the B.Sc. and M.Sc. degrees in chemistry from the University of São Paulo, in 1979 and 1985, respectively, and the Ph.D. degree from the University of São Paulo (USP) in 1990. He is a lecturer at the Instituto de Química de São Carlos, USP, being an expert on the chemistry and physical chemistry of polysaccharides from microbial, vegetable and animal sources. For the last 16 years, he has been working on bacterial polysaccharides, cellulose, chitin and chitosan. His work is focused on the extraction processes, chemical derivatization, characterization and properties/applications of these polysaccharides and derivatives.
IEEE Transactions on Dielectrics and Electrical Insulation
Vol. 13, No. 5; October 2006
Márcia Rodrigues Pereira was born in Rio de Janeiro, Brazil, in 1963. She graduated in chemical engineering in 1986 at the State University of Rio de Janeiro. She got the M.Sc. degree in polymer science and technology at the Federal University of Rio de Janeiro on the subject of reinforcing of polyurethane elastomers (1991). In 1994 she obtained a PhD degree in chemistry at Durham University (UK) on the subject of permeability of polymeric membranes. Since 1997 she has been a lecturer at the Chemistry Department of the Federal University of Rio Grande do Norte and has been working with polymer membranes, solutions, colloids, and polyelectrolyte complexes. José Luís Cardozo Fonseca was born in Angra dos Reis, Brazil, in 1961. He graduated in chemical engineering in 1985 at the Federal University of Rio de Janeiro. At the same university he got the M.Sc. degree in polymer science and technology on the subject of viscoelastic behavior of polyurethanes (1990). In 1994 he obtained the Ph.D. degree at Durham University (UK) on the subject of glow-discharge plasma treatment of polymer films. Since 1996 he has been a lecturer at the Chemistry Department of the Federal University of Rio Grande do Norte and has been working with polymer solutions, colloids, polyelectrolyte complexes, and membranes.
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Osvaldo N. Oliveira Jr. was born in Barretos, Brazil, in 1960. He obtained the B.Sc. and M.Sc. degrees in physics from the University of São Paulo, in 1982 and 1984, respectively, and the Ph.D. degree from the University of Wales, Bangor, in 1990. Currently he is an associate professor at the University of São Paulo, in São Carlos, Dr. Oliveira has led research into the fabrication of novel materials in the form of ultrathin films obtained with the Langmuir-Blodgett and self-assembly techniques. Most of this work has been associated with fundamental properties of ultrathin films with molecular control, but technological aspects have also been addressed in specific projects. This is the case of an electronic tongue, whose response to a number of tastants is considerably more sensitive than the human gustatory system. Prof. Oliveira Jr. has helped establish the Núcleo Interinstitucional de Linguística Computacional (NILC), which is a leading institute for natural language processing of Portuguese. Research and development activities at NILC include the development of a grammar checker for Brazilian Portuguese, now available worldwide through Microsoft Word, and participation in the Universal Networking Language (UNL) Project, sponsored by the United Nations University. Luiz Henrique Capparelli Mattoso was born in São Carlos, Brazil, in 1961. He obtained the B.Sc., M.Sc. and Ph.D. degrees in materials science from the Federal University of São Carlos, São Paulo, in 1986, 1988 and 1993, respectively. Within this period he was a visiting researcher at the Universitè des Sciences et Tecnologies du Languedoc, Montpellier, and Domaine Universitaire Saint Martin d´Hères, Grenoble, in France, and University of Pennsylvania, USA. He was head of the Research and Development Department of the Instrumentation Research Center of the Brazilian Corporation for Research in Agriculture – Embrapa. He is currently a lead scientist on nanotechnology and polymer science at Embrapa, working in an international cooperation program between Brazil and the Agricultural Research Service (ARS) of the USDA, in Albany, CA, USA. He leads several R&D projects funded by government and companies on new uses of agricultural products in plastics and composites, conducting polymers and taste sensors, technological applications of natural rubber, the most recent being a nanotechnology network involving several universities and research institutes in Brazil in cooperation with USA, France and India.
