- Email: [email protected]
Line patterning of graphite and the fabrication of cheap, inexpensive, “throw-away” sensors
Available online at www.sciencedirect.com
Sensors and Actuators B 130 (2008) 723–729
Line patterning of graphite and the fabrication of cheap, inexpensive, “throw-away” sensors Everaldo Carlos Venancio a,b,∗ , Luiz Henrique Capparelli Mattoso b , Paulo S´ergio de Paula Herrmann J´unior b , Alan Graham MacDiarmid a,1 a b
Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, USA National Nanotechnology Laboratory for Agribuseness (LNNA), Embrapa Agricultural Instrumentation, C.P. 741, S˜ao Carlos, SP 13560-970, Brazil Received 18 July 2007; accepted 22 October 2007 Available online 11 December 2007
Abstract A new simple method (“line patterning technique”) using only standard office equipment is described whereby clearly defined, electrically conducting patterns of graphite can be deposited on polymer (plastic) or paper substrates. The properties of the conductive patterns have been characterized by electrical conductivity and SEM measurements. Sensors were constructed by using interdigitated patterns of graphite deposited on plastic and paper, and coated with a thin film of conducting electronic polymer, e.g. polyaniline emeraldine salt. © 2007 Elsevier B.V. All rights reserved. Keywords: Line patterning; Graphite; Electronic devices; Nanofibers; Conducting polymers
1. Introduction
2. Experimental procedure
The development of cheap and “throw-away” sensor technology is very important since it can be used for many different applications, such as in the development of biosensors [1], elctronic noses [2] and electronic tongues [3–5]. Electronic conducting polymers [6] have been used for sensor application [2–5] due to their chemical and physical properties, which can be tuned in order to achieve the desirable specificity and performance [7]. We have previously described a method [8–10] whereby conducting patterns of conducting polymer, and electroless [11–13], gold, nickel and silver are simply deposited on an overhead transparency (poly(ethylene therephthalate), PET) or paper. This method has been used to prepare simple devices [8–10]. The present study describes how the technique may be applied to the deposition of inexpensive, “throw-away” carbon patterns on plastic and paper substrates using common, inexpensive, commercially available aqueous dispersions of graphite.
2.1. Graphite dispersion
∗
Corresponding author at: LNNA, Embrapa Agricultural Instrumentation, C.P. 741, S˜ao Carlos, SP 13560-970, Brazil. Tel.: +55 16 33742477; fax: +55 16 33725958. E-mail address: [email protected] (E.C. Venancio). 1 In memoriam. 0925-4005/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2007.10.037
The graphite dispersions were prepared by using the commercial graphite aqueous dispersion (Aquadag E, Acheson Co., Ontario, CA, USA). Our graphite dispersion was prepared using Aquadag E and deionized water in the following proportions: 1:4 (1 part of Aquadag E:4 parts of water, w/w). The water was added to the Aquadag E with vigorous stirring. It was then stirred vigorously for 30 min before use. Aquadag E [14] consists essentially of an aqueous dispersion of, e.g., carbon, poly(vinyl pyrrolidone) (dispersing agent) and sodium silicate (binder). The crosslinking of the silicate ion during the mild heating treatment is presumably related to the inertness of the Aquadag E pattern to water after developing. 2.2. Computer procedure The desired pattern was prepared on a conventional computer and was then converted to a negative image on the computer screen by means of software (e.g. MS Paint or similar) as shown in Scheme 1 (1,2). This negative image was then printed on a 100-m thick poly(ethylene terephthalate) transparency film
724
E.C. Venancio et al. / Sensors and Actuators B 130 (2008) 723–729
Scheme 1. Summary of sequential steps used to obtain patterned lines of graphite on different types of substrates, i.e. plastic and paper.
(Nashua XF-20, Nashua) using a 1200 dpi office laser printer (Hewlett-Packard LaserJet 5000N) and Hewlett-Packard Laser Jet Toner Cartridge C4129X. The “backside” of the plastic film was next covered completely with strips of adhesive tape to prevent contact of the “backside” with the dispersion in the step described in Section 2.3. The same procedure was used for the negative image on paper. 2.3. Coating procedure
appropriate for the intended use of the interdigitated patterns. There is no apparent reason why the resolution should not be improved if desired. 2.4. Total electrical resistance After drying by the above procedure the total resistance (2probe) along the length of a single line of the patterns shown in Fig. 2 was measured by a FLUKA 77II multimeter. The variation in the resistance of each line of Fig. 2 (decreasing resistance of lines A–C) is probably related to a difference in the thickness of the graphite films. No attempt was made to obtain greater uniformity in resistance of the lines.
2.3.1. Plastic substrate The plastic film with the printed lines on one side was then twice immersed completely in our dispersion prepared as described in Section 2.2. The dispersion wetted both the toner films and the “white” lines, i.e. exposed portion of plastic substrate shown in Scheme 1 (2). Sonication in toluene for 1 min followed by sonication in methyl ethyl ketone removes both the printed toner (together was its adhering graphite film) and the adhesive tape on the backside of the substrate resulting in the object shown in Scheme 1 (4). This consists of an insulating plastic substrate with conducting lines of carbon. It should be noted that acetone cannot be used in the step when rinsing the PET film since PET dissolves in acetone.
2.6. Deposition of polyaniline on the interdigitated pattern
2.3.2. Paper substrate The negative image printed on commercial office copy paper (Business multipurpose 4200 Paper, 75 g/m2 , Xerox Co., USA), or parchment paper, i.e. “tracing paper” (9 in. × 12 in., 25 lb, 41 g/m2 , Strathmore Papers, Stanford, CT, USA) may be coated either by dipping or by a roller. For both methods of coating, the backside of each type of paper must first be covered by adhesive tape to prevent it coming in contact with the graphite dispersion. The toner substrate and adhesive tape are removed simultaneously by 30 s sonication in acetone. The film on any type of substrate, together with its attached substrate was dried by stream of air in fume hood for 10 min and then in an air oven at 145 ◦ C for 5 min. The unexpectedly good resolutions formed, for example, in the interdigitated patterns shown in Scheme 1 (4), are given at greater magnification in Fig. 1(a). The resolution obtained was
2.6.1. Coating using an aqueous dispersion (at pH ∼ 3) of nanofibers of AMPSA-doped polyaniline emeraldine salt The sensor based on nanofibers of polyaniline emeraldine·AMPSA (AMPSA stands for 2-acrylamido-2methyl-1-propane-sulfonic acid) salt [15] was prepared by dipping the 16-finger interdigitated electrode of graphite on plastic substrate into an aqueous dispersion (pH ∼ 3) of nanofibers of polyaniline emeraldine·AMPSA salt. The nanofibers of polyaniline were prepared by using interfacial polymerization method [16]. The pH of the aqueous dispersion of nanofibers of polyaniline was adjusted to pH ∼ 3 by using a diluted aqueous solution (pH ∼ 2) of AMPSA. After being prepared, the sensor was put inside a desiccator without desiccant and kept under dynamic vacuum at room temperature (22–25 ◦ C) for 3 h. Then the vacuum was broken and then the sensors were kept inside the desiccator without desiccant agent in the presence of static laboratory air.
2.5. SEM studies Scanning electron microscopy studies were carried out by using a field-emission scanning electron microscope JEOL 6300-FV HRSEM. An energy level of 5 keV was used. The SEM of portion of a digital line on plastic substrate is given in Fig. 3.
E.C. Venancio et al. / Sensors and Actuators B 130 (2008) 723–729
725
Fig. 1. 16-Finger interdigitated electrode of graphite on (a) overhead transparency; (b) paper (xerox business multipurpose 4200 paper, Model 3R2047); (c) tracing paper.
2.6.2. Coating using in situ deposition of HCl-doped polyaniline emeraldine salt The sensor based on an in situ deposited thin film of polyaniline was prepared by using an 1.0 mol dm−3 hydrochloric acid aqueous solution containing a 0.014 mol dm−3 aniline and 0.014 mol dm−3 ammonium peroxydisulfate. The procedure consisted of the immersion of the graphite interdigitated electrode, i.e. the interdigitated portion only, into a 50 mL glass
beaker containing 20 mL 0.028 mol dm−3 aniline dissolved in 1.0 mol dm−3 hydrochloric acid aqueous solution under vigorous magnetic stirring using a magnetic stir bar. The interdigitated electrode was positioned in the center of the beaker. Then, 20 mL of 0.028 mol dm−3 ammonium peroxydisulfate dissolved in 1.0 mol dm−3 hydrochloric acid aqueous solution was added to the beaker. The chemical reaction was monitored by measuring the open circuit potential using a saturated calomel electrode
726
E.C. Venancio et al. / Sensors and Actuators B 130 (2008) 723–729
Fig. 2. 2-Probe electrical resistance measurements: (a) along the graphite lines that were obtained by using the line patterning technique. () Plastic (overhead transparency); () xerox paper; () tracing paper. (b) Effect of the number of dippings into the 1:4 graphite aqueous dispersion for plastic (overhead transparency) substrate.
(SCE) as a reference electrode and a platinum wire as a working elctrode. The chemical reaction was stopped at the position “A” in Fig. 4(a), after 80 min (OCP ∼ 0.46 V vs. SCE), where the thin film of polyaniline is obtained in the emeraldine oxidation state. The color pattern indicated in Fig. 4(a) is related to the pathway of the aqueous oxidative polymerization of aniline [17] in acidic
Fig. 3. SEM image of graphite line deposited on the overhead transparency. It was obtained using the line patterning technique. Magnification: 5000×.
Fig. 4. (a) Open circuit potential (OCP) vs. SCE for the in situ polymerization of aniline described in Section 2.6.2. (b) UV/VIS/NIR spectrum of the solid thin film of polyaniline emeraldine·HCl salt in situ deposited on plastic (PET) as described in Section 2.6.2.
medium (pH ∼ 0). The interdigitated electrode coated with the thin film of emeraldine·HCl salt was then removed from the reaction medium and it was then rinsed with excess of 1.0 mol dm−3 hydrochloric acid aqueous solution using a wash bottle. A clear and transparent thin film of emeraldine·HCl was obtained. A piece of plastic (PET) was used as a blank and it was then used for further spectroscopic characterization in the ultraviolet, visible and near infrared (UV/VIS/NIR) region. Fig. 4(b) shows the UV/VIS/NIR spectrum for the thin film of emeraldine·HCl salt in situ deposited on plastic (PET). This UV/VIS/NIR spectrum shows the characteristic absorption peaks of polyaniline emeraldine·HCl salt [16(b)]. 2.6.3. Sensing moisture from laboratory air at room temperature The gas chamber setup was made using glassware (125 mL filter flask, glass tube, and glass valve), tubing and flow meter (GILMONT no. 12). The flow rate of dry nitrogen gas (Grade 4.9, BOC Gases) was 1500 mL min−1 and the temperature of the nitrogen gas in the gas chamber was measured by using a thermometer. After pumping with dynamic vacuum, the resistance was measured in static laboratory air. The resistance was then constantly measured while the sensor was exposed to the stream
E.C. Venancio et al. / Sensors and Actuators B 130 (2008) 723–729
of dry nitrogen at room temperature (22–25 ◦ C). After dried in the presence of nitrogen stream, the sensor was then exposed to the moisture from the static laboratory air. The temperature and the relative humidity of the static laboratory air were recorded. The sensor was again exposed to stream of nitrogen for 10 min followed by exposure to the moisture from the static laboratory air for 10 min. The sensitivity to the moisture was calculated as described in Eq. (1), where R is the maximum resistance of the sensor in the presence of stream of dry nitrogen and R0 is the minimum resistance in the presence of static laboratory air: R (%) =
R − R0 × 100 R0
(1)
3. Results and discussion
727
The graphite pattern, which was obtained using plastic, was put in the presence of 1 mol dm−3 hydrochloric acid aqueous solution (pH ∼ 0) at room temperature (22–25 ◦ C) under vigorous magnetic stir for 1 h. It was surprising that the graphite lines were not removed and its electrical resistance did not change. This result showed that, once developed, the graphite lines are acid and water resistant. The explanation for this result is that the graphite dispersion contains silicates, which can form a network after the thermal treatment at 145 ◦ C [14]. During the thermal treatment (at 145 ◦ C) the alkali metal carboxylic acid salt contained in the graphite dispersion decomposes and assists the crystallization of the polymer (polyvinylpyrrolidone, PVP)–alkali silicates–graphite system. After the crystallization, it cannot be dissolved by simple exposure to water or an acid aqueous solution.
3.1. Line patterning of graphite on plastic (poly(ethylene terephthalate))
3.2. Line patterning of graphite on paper
The most important phenomena in the use of the line patterning technique are the difference in interaction between the dispersion, in this case the graphite dispersion and the printed and non-printed lines present in the pattern. Therefore, the use of dipping process resulted in the successful line patterning of graphite. The method described in this study depends primarily on the relatively strong adhesion of the carbon dispersion to an exposed substrate and the process of removal of the toner lines (together with the carbon film deposited on it) by the organic solvents employed in the washing process. In principle, it is not necessary to cover the backside of the substrate with adhesive tape but it is desirable simply to prevent the graphite dispersion to contact the backside. The adhesive tape covering the backside is removed after coating and drying the entire system with the carbon film. Fig. 1(a) presents the pattern of graphite on plastic (overhead transparency). As it can be seen it has presented a very good resolution. The toner lines were completely removed leaving only the graphite lines. This process is really easy to be carried out without any other complication or modification of commercially available office supplies (LaserPrinter, toner, overhead transparency). de Rossi [18] have shown the fabrication of patterns of graphite on transparency using inkjet printer. As pointed out by them, their graphite patterns on transparency have shown relatively high resistance. To improve the conductive in such patterns, it was printed more than 30 times. However, this procedure has implied in loss of resolution on obtaining the graphite pattern due to the need of printing the same graphite lines several times in order to achieve relatively low electrical resistance. Therefore, the advantage of the line patterning of carbon (graphite) on plastic (overhead transparency) is clear (Fig. 2). In addition, the line patterning technique did not imply in any modification of the printer. Fig. 3 shows the SEM image of the graphite-patterned line on plastic. The topography of the graphite films as depicted by the SEM studies shows no unexpected features. It should be also noted that the films show good uniformity.
The use of paper as a substrate to obtain patterns of graphite opens a new possibility for the fabrication of cheap and throwaway electronic devices. In this work we present the use of multipurpose office paper (xerox paper) and tracing paper as a substrate. Fig. 1(b) presents a pattern of graphite on multipurpose office paper (xerox paper) which was obtained by a dipping process. The patterns have presented good resolution as well as relatively low total electrical resistance when it is compared with patterns of conducting polymers [8,10]. Fig. 1(c) presents the 16-finger interdigitated electrode of graphite on tracing paper. The size of the pattern is the same as described in Fig. 1(a) and (b). As it can be seen, the graphite pattern presents a good resolution. The results (Fig. 1(b) and (c)) showed that a wide variety of paper can be used in the line patterning process. It is really surprising that the toner can be removed and leaves only the graphite lines. It is important to point out that only the method using glass roller works for tracing paper. In all other substrates dipping and glass roller methods presented approximately similar quality. In addition, the patterns of graphite on paper, xerox paper and tracing paper, were put in the presence of 1 mol dm−3 hydrochloric acid aqueous solution (pH ∼ 0) at room temperature (22–25 ◦ C) under vigorous magnetic stirring for 1 h. It was surprising that the graphite lines were not removed and its electrical resistance did not change. Therefore, as in the example using pattern of graphite on transparency, these results showed that, once developed, the graphite lines are acid and water resistant. The total electrical resistance of the graphite patterned lines (Fig. 2) can be minimized by increasing the thickness of the patterned lines, i.e. increasing the number of coatings of graphite dispersion during the line patterning process (Fig. 2(b)). However, there is a relationship between the number of coatings and the resolution of the patterned lines. Therefore, the conditions described in Section 2 of this report are suitable for the fabrication of electronic devices for sensor applications.
728
E.C. Venancio et al. / Sensors and Actuators B 130 (2008) 723–729
Fig. 5. Sensitivity to the presence of moisture of 16-finger interdigitated electrode of graphite coated with a thin film of polyaniline emeraldine·HCl (PANI·HCl) salt, obtained by in situ deposition, and with nanofibers of polyaniline emeraldine·AMPSA (PANI·AMPSA) salt. The measurements were done at room temperature (∼25 ◦ C) and atmospheric pressure.
3.3. Sensor application Fig. 5 shows the electrical response of two sensors prepared using the 16-finger interdigitated electrode of graphite on overhead transparency. The sensors were fabricated using two different types of polyaniline, i.e. nanofibers of AMPSA-doped polyaniline emeraldine salt and a film of in situ deposited HCldoped polyaniline emeraldine salt, respectively. The sensitivity given by the sensor prepared using nanofibers of AMPSA-doped polyaniline emeraldine salt (R = 93.3 ± 19%) is much higher than the one obtained with the film of in situ deposited HCldoped polyaniline emeraldine salt (R = 5.05 ± 0.79%). These results can be explained based on the differences in surface area of the two types of polyaniline emeraldine salt. Nanofibers of polyaniline emeraldine salt are expected to have higher active surface area when compared with the in situ deposited HCldoped polyaniline emeraldine salt film. Thus, the interaction between the molecules of water vapor and the sensor is enhanced by using nanofibers of polyaniline. Since the outermost surface of the film is expected to strongly interact with the water vapor, it suggests that the in situ deposited polyaniline emeraldine salt film might have more inactive materials that do not contribute for the sensor performance. In addition, this type of limitation could not be expected for the nanofiber-based sensor since it presents high surface area. Therefore, it might explain the differences in performance that were observed between the two sensors. 4. Conclusions The resolution of the graphite conducting patterns obtained by the procedure described is sufficient for our intended uses of the pattern. It could undoubtedly be improved if desired for a given use. We have demonstrated that the graphite lines can be conveniently coated with, e.g., the conducting electronic polymer,
polyaniline if desired, because of certain characteristic properties of polyaniline on graphite substrate as compared to carbon sensors devices, as it is described in this paper. The line patterning of carbon (graphite) can be used to produce graphite patterns on plastic (overhead transparency) and on paper substrates. It did not require any modification on the equipments which were used (laser printer, commercial overhead transparency, commercial multipurpose office paper, tracing paper). It can be carried out just by using available commercial office supplies. The results have shown a good resolution and suitable resistance values for electronic device fabrication. The line patterning of carbon (graphite) has the advantage over conventional methods of printing conducting phase using regular ink-jet printer, which needs to be carried out by doing modifications on the printer. Using just two coatings it was obtained graphite patterns with relatively low total electrical resistance. Another important result was that these patterns of graphite, once developed, are acid (pH ∼ 0) and water resistant. Nanofibers of polyaniline showed the best results for sensing moisture (humidity) from air. Since the sensing process occurs at the surface of the polyaniline, nanofibers of polyaniline are expected to enhance the sensing process due to its higher active surface area. This result opens up a new possibility for the construction of sensing devices at low-cost and high-sensitivity. In conclusion, we believe the simplicity and cheapness of the techniques and concepts given in this report can be refined and extended in a variety of direction depending on the ultimate purpose for which the patterns are desired. Acknowledgements The authors wish to thank the Office of Naval Research (grant no. N00014-01-1-0933), the Nanotechnology Institute of Pennsylvania (NTI, Benjamin Franklin Technology Partners, Southern Pennsylvania, USA), the Fundac¸a˜ o de Amparo a` Pesquisa do Estado de S˜ao Paulo (FAPESP, E.C. Venancio, 01/10415-6), CNPq and Embrapa/CNPDIA (E.C. Venancio, P.S.P. Herrmann J´unior and L.H.C. Mattoso, Brazil) for support of this work. References [1] B.D. Malhotra, A. Chaubey, S.P. Singh, Prospects of conducting polymers in biosensors, Anal. Chim. Acta 578 (2006) 59–74. [2] (a) A. Guadarrama, M.L. Rodr´ıguez-M´endez, J.A. de Saja, Influence of electrochemical deposition parameters on the performance of poly3-methyl thiophene and polyaniline sensors for virgin olive oils, Sens. Actuator B: Chem. 100 (2004) 60–64; (b) R. Stella, J.N. Barisci, G. Serra, G.G. Wallace, D. de Rossi, Characterisation of olive oil by an electronic nose based on conducting polymer sensors, Sens. Actuator B: Chem. 63 (2000) 1–9; (c) T.C. Pearce, S.S. Schiffman, H.T. Nagle, J.W. Gardner, Handbook of Machine Olfaction: Electronic Nose Technology, Wiley–VCH, 2003. [3] E.C. Venancio, N. Consolin Filho, C.J.L. Constantino, L. Martin-Neto, L.H.C. Mattoso, Studies on the interaction between humic substances and conducting polymers for sensor application, J. Braz. Chem. Soc. 16 (2005) 24–30. [4] K. Toko, Electronic tongue, Biosens. Bioelectron. 13 (1998) 701–709.
E.C. Venancio et al. / Sensors and Actuators B 130 (2008) 723–729 [5] (a) A. Riul Jr., R.R. Malmegrim, F.J. Fonseca, L.H.C. Mattoso, An artificial taste sensor based on conducting polymers, Biosens. Bioelectron. 18 (2003) 1365–1369; (b) L. Lvova, A. Legin, Y. Vlasov, G.S. Cha, H. Nam, Multicomponent analysis of Korean green tea by means of disposable all-solid-state potentiometric electronic tongue microsystem, Sens. Actuator B: Chem. 95 (2003) 391–399. [6] (a) E.C. Venancio, P.-C. Wang, A.G. MacDiarmid, The azanes: a class of material incorporating nano/micro-self-assembled hollow spheres obtained by aqueous oxidative polymerization of aniline, Synth. Met. 156 (2006) 357–369; (b) W.-S. Huang, B.D. Humphrey, A.G. MacDiarmid, Polyaniline a novel conducting polymer, J. Chem. Soc., Faraday Trans. 82 (1986) 2385–2400. [7] (a) J. Janata, M. Josowicz, Conducting polymers in electronic chemical sensors, Nat. Mater. 2 (2003) 19–24; (b) T.A. Skhoteim, J. Reynolds, Handbook of Conducting Polymers, 3rd ed., CRC, 2007. [8] D. Hohnholz, A.G. MacDiarmid, Line patterning of conducting polymers: new horizons for inexpensive, disposable electronic devices, Synth. Met. 121 (2001) 1327–1328. [9] A.G. MacDiarmid, “Synthetic metals”: a novel role for organic polymers (nobel lecture), Angew. Chem. Int. Ed. 40 (2001) 2581–2590. [10] D. Hohnholz, A.G. MacDiarmid, Plastic electronic devices through line patterning of conducting polymers, Adv. Funct. Mater. 15 (2005) 51–56. [11] N.J. Pinto, P. Carri´on, J.X. Qui˜nones, Electroless deposition of nickel on electrospun fibers of 2-acrylamido-2-methyl-1-propanesulfonic aciddoped polyaniline, Mater. Sci. Eng. A 366 (2004) 1–5. [12] J.P. Marton, Process for the selective formation of coatings by electroless deposition, US Patent 3,676,213 (1972). [13] S.S. Tzeng, F.Y. Chang, EMI shielding effectiveness of metal-coated carbon fiber-reinforced ABS composites, Mater. Sci. Eng. A 302 (2001) 258–267. [14] A.J. Stock, F.M. Hunter, Compositions and methods for producing electrically conductive coatings, US Patent 3,518,116 (1970). [15] (a) X. Zhang, R. Chan-Yu-King, A. Jose, S.K. Manohar, Nanofibers of polyaniline synthesized by interfacial polymerization, Synth. Met. 145 (2004) 23–29; (b) M.F. Hundley, P.N. Adams, R.B. Mattes, The influence of 2-acrylamido2-methyl-1-propanesulfonic acid (AMPSA) additive concentration and stretch orientation on electronic transport in AMPSA-modified polyaniline films prepared from an acid solvent mixture, Synth. Met. 129 (2002) 291–297. [16] (a) J.C. Michaelson, A.J. McEvoy, Interfacial polymerization of aniline, J. Chem. Soc. Chem. Commun. 1 (1994) 79–80;
729
(b) J. Huang, S. Virji, B.H. Weiller, R.B. Kaner, Polyaniline nanofibers: facile synthesis and chemical sensors, J. Am. Chem. Soc. 125 (2003) 314–315. [17] S.K. Manohar, A.G. MacDiarmid, A.J. Epstein, Polyaniline: pernigranile, an isolable intermediate in the conventional chemical synthesis of emeraldine, Synth. Met. 41 (1991) 711–714. [18] D. de Rossi, Ink-jet printed and high sensitivity conducting polymer odour sensors for olive oil olfactory assessment. Electronic noses and sensor array-based systems: design and applications, in: W.J. Hurst (Ed.), Proceedings of the 5th International Symposium on Olfaction and the Electronic Nose, CRC Press, 1999.
Biographies Everaldo Carlos Venancio received his PhD in science (physical chemistry) in 2000 from the Institute of Chemistry of S˜ao Carlos (IQSC) at University of S˜ao Paulo (USP), Brazil. He worked with Prof. Alan G. MacDiarmid for the period of 2002–2007 at the Department of Chemistry of the University of Pennsylvania, USA. He is currently working as a visiting research scientist at Embrapa Agricultural Instrumentation (Embrapa/CNPDIA), Brazil. His research interests are mainly related to nanoscience and nanotechnology directed towards the development of controllable methods of synthesis of nanostructures of conducting electronic polymers for application in energy storage, cell growth and differentiation, and sensors. Luiz Henrique Capparelli Mattoso received his PhD in materials science and engineering in 1993 from Materials Engineering Department at Federal University of S˜ao Carlos (DEMa-UFSCar), Brazil. He is currently a full researcher at Embrapa Agricultural Instrumentation Center in Brazil. His field of interests includes conducting polymers, chemical and biological sensors, nanostructured materials, polymeric blends and nanocomposites. ´ Paulo S´ergio de Paula Herrmann Junior received his PhD in science (physical chemistry) in 1999 from the Institute of Chemistry of S˜ao Carlos (IQSC) at University of S˜ao Paulo (USP), Brazil. He is currently a full researcher at Embrapa Agricultural Instrumentation Center in Brazil. His field of interests includes scanning probe microscopy and nanotechnology. Alan Graham MacDiarmid (1927–2007) received the Nobel Prize in Chemistry, 2000. He received his PhD in chemistry at the University of Wisconsin at Madison (1953) and the University of Cambridge (1955). He was blanchard professor of chemistry at the Department of Chemistry at the University of Pennsylvania, USA. He was the chemist responsible in 1977 for the chemical and electrochemical doping of polyacetylene, (CH)x , the “prototype” conducting polymer, and the “rediscovery” of polyaniline.
Sensors and Actuators B 130 (2008) 723–729
Line patterning of graphite and the fabrication of cheap, inexpensive, “throw-away” sensors Everaldo Carlos Venancio a,b,∗ , Luiz Henrique Capparelli Mattoso b , Paulo S´ergio de Paula Herrmann J´unior b , Alan Graham MacDiarmid a,1 a b
Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, USA National Nanotechnology Laboratory for Agribuseness (LNNA), Embrapa Agricultural Instrumentation, C.P. 741, S˜ao Carlos, SP 13560-970, Brazil Received 18 July 2007; accepted 22 October 2007 Available online 11 December 2007
Abstract A new simple method (“line patterning technique”) using only standard office equipment is described whereby clearly defined, electrically conducting patterns of graphite can be deposited on polymer (plastic) or paper substrates. The properties of the conductive patterns have been characterized by electrical conductivity and SEM measurements. Sensors were constructed by using interdigitated patterns of graphite deposited on plastic and paper, and coated with a thin film of conducting electronic polymer, e.g. polyaniline emeraldine salt. © 2007 Elsevier B.V. All rights reserved. Keywords: Line patterning; Graphite; Electronic devices; Nanofibers; Conducting polymers
1. Introduction
2. Experimental procedure
The development of cheap and “throw-away” sensor technology is very important since it can be used for many different applications, such as in the development of biosensors [1], elctronic noses [2] and electronic tongues [3–5]. Electronic conducting polymers [6] have been used for sensor application [2–5] due to their chemical and physical properties, which can be tuned in order to achieve the desirable specificity and performance [7]. We have previously described a method [8–10] whereby conducting patterns of conducting polymer, and electroless [11–13], gold, nickel and silver are simply deposited on an overhead transparency (poly(ethylene therephthalate), PET) or paper. This method has been used to prepare simple devices [8–10]. The present study describes how the technique may be applied to the deposition of inexpensive, “throw-away” carbon patterns on plastic and paper substrates using common, inexpensive, commercially available aqueous dispersions of graphite.
2.1. Graphite dispersion
∗
Corresponding author at: LNNA, Embrapa Agricultural Instrumentation, C.P. 741, S˜ao Carlos, SP 13560-970, Brazil. Tel.: +55 16 33742477; fax: +55 16 33725958. E-mail address: [email protected] (E.C. Venancio). 1 In memoriam. 0925-4005/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2007.10.037
The graphite dispersions were prepared by using the commercial graphite aqueous dispersion (Aquadag E, Acheson Co., Ontario, CA, USA). Our graphite dispersion was prepared using Aquadag E and deionized water in the following proportions: 1:4 (1 part of Aquadag E:4 parts of water, w/w). The water was added to the Aquadag E with vigorous stirring. It was then stirred vigorously for 30 min before use. Aquadag E [14] consists essentially of an aqueous dispersion of, e.g., carbon, poly(vinyl pyrrolidone) (dispersing agent) and sodium silicate (binder). The crosslinking of the silicate ion during the mild heating treatment is presumably related to the inertness of the Aquadag E pattern to water after developing. 2.2. Computer procedure The desired pattern was prepared on a conventional computer and was then converted to a negative image on the computer screen by means of software (e.g. MS Paint or similar) as shown in Scheme 1 (1,2). This negative image was then printed on a 100-m thick poly(ethylene terephthalate) transparency film
724
E.C. Venancio et al. / Sensors and Actuators B 130 (2008) 723–729
Scheme 1. Summary of sequential steps used to obtain patterned lines of graphite on different types of substrates, i.e. plastic and paper.
(Nashua XF-20, Nashua) using a 1200 dpi office laser printer (Hewlett-Packard LaserJet 5000N) and Hewlett-Packard Laser Jet Toner Cartridge C4129X. The “backside” of the plastic film was next covered completely with strips of adhesive tape to prevent contact of the “backside” with the dispersion in the step described in Section 2.3. The same procedure was used for the negative image on paper. 2.3. Coating procedure
appropriate for the intended use of the interdigitated patterns. There is no apparent reason why the resolution should not be improved if desired. 2.4. Total electrical resistance After drying by the above procedure the total resistance (2probe) along the length of a single line of the patterns shown in Fig. 2 was measured by a FLUKA 77II multimeter. The variation in the resistance of each line of Fig. 2 (decreasing resistance of lines A–C) is probably related to a difference in the thickness of the graphite films. No attempt was made to obtain greater uniformity in resistance of the lines.
2.3.1. Plastic substrate The plastic film with the printed lines on one side was then twice immersed completely in our dispersion prepared as described in Section 2.2. The dispersion wetted both the toner films and the “white” lines, i.e. exposed portion of plastic substrate shown in Scheme 1 (2). Sonication in toluene for 1 min followed by sonication in methyl ethyl ketone removes both the printed toner (together was its adhering graphite film) and the adhesive tape on the backside of the substrate resulting in the object shown in Scheme 1 (4). This consists of an insulating plastic substrate with conducting lines of carbon. It should be noted that acetone cannot be used in the step when rinsing the PET film since PET dissolves in acetone.
2.6. Deposition of polyaniline on the interdigitated pattern
2.3.2. Paper substrate The negative image printed on commercial office copy paper (Business multipurpose 4200 Paper, 75 g/m2 , Xerox Co., USA), or parchment paper, i.e. “tracing paper” (9 in. × 12 in., 25 lb, 41 g/m2 , Strathmore Papers, Stanford, CT, USA) may be coated either by dipping or by a roller. For both methods of coating, the backside of each type of paper must first be covered by adhesive tape to prevent it coming in contact with the graphite dispersion. The toner substrate and adhesive tape are removed simultaneously by 30 s sonication in acetone. The film on any type of substrate, together with its attached substrate was dried by stream of air in fume hood for 10 min and then in an air oven at 145 ◦ C for 5 min. The unexpectedly good resolutions formed, for example, in the interdigitated patterns shown in Scheme 1 (4), are given at greater magnification in Fig. 1(a). The resolution obtained was
2.6.1. Coating using an aqueous dispersion (at pH ∼ 3) of nanofibers of AMPSA-doped polyaniline emeraldine salt The sensor based on nanofibers of polyaniline emeraldine·AMPSA (AMPSA stands for 2-acrylamido-2methyl-1-propane-sulfonic acid) salt [15] was prepared by dipping the 16-finger interdigitated electrode of graphite on plastic substrate into an aqueous dispersion (pH ∼ 3) of nanofibers of polyaniline emeraldine·AMPSA salt. The nanofibers of polyaniline were prepared by using interfacial polymerization method [16]. The pH of the aqueous dispersion of nanofibers of polyaniline was adjusted to pH ∼ 3 by using a diluted aqueous solution (pH ∼ 2) of AMPSA. After being prepared, the sensor was put inside a desiccator without desiccant and kept under dynamic vacuum at room temperature (22–25 ◦ C) for 3 h. Then the vacuum was broken and then the sensors were kept inside the desiccator without desiccant agent in the presence of static laboratory air.
2.5. SEM studies Scanning electron microscopy studies were carried out by using a field-emission scanning electron microscope JEOL 6300-FV HRSEM. An energy level of 5 keV was used. The SEM of portion of a digital line on plastic substrate is given in Fig. 3.
E.C. Venancio et al. / Sensors and Actuators B 130 (2008) 723–729
725
Fig. 1. 16-Finger interdigitated electrode of graphite on (a) overhead transparency; (b) paper (xerox business multipurpose 4200 paper, Model 3R2047); (c) tracing paper.
2.6.2. Coating using in situ deposition of HCl-doped polyaniline emeraldine salt The sensor based on an in situ deposited thin film of polyaniline was prepared by using an 1.0 mol dm−3 hydrochloric acid aqueous solution containing a 0.014 mol dm−3 aniline and 0.014 mol dm−3 ammonium peroxydisulfate. The procedure consisted of the immersion of the graphite interdigitated electrode, i.e. the interdigitated portion only, into a 50 mL glass
beaker containing 20 mL 0.028 mol dm−3 aniline dissolved in 1.0 mol dm−3 hydrochloric acid aqueous solution under vigorous magnetic stirring using a magnetic stir bar. The interdigitated electrode was positioned in the center of the beaker. Then, 20 mL of 0.028 mol dm−3 ammonium peroxydisulfate dissolved in 1.0 mol dm−3 hydrochloric acid aqueous solution was added to the beaker. The chemical reaction was monitored by measuring the open circuit potential using a saturated calomel electrode
726
E.C. Venancio et al. / Sensors and Actuators B 130 (2008) 723–729
Fig. 2. 2-Probe electrical resistance measurements: (a) along the graphite lines that were obtained by using the line patterning technique. () Plastic (overhead transparency); () xerox paper; () tracing paper. (b) Effect of the number of dippings into the 1:4 graphite aqueous dispersion for plastic (overhead transparency) substrate.
(SCE) as a reference electrode and a platinum wire as a working elctrode. The chemical reaction was stopped at the position “A” in Fig. 4(a), after 80 min (OCP ∼ 0.46 V vs. SCE), where the thin film of polyaniline is obtained in the emeraldine oxidation state. The color pattern indicated in Fig. 4(a) is related to the pathway of the aqueous oxidative polymerization of aniline [17] in acidic
Fig. 3. SEM image of graphite line deposited on the overhead transparency. It was obtained using the line patterning technique. Magnification: 5000×.
Fig. 4. (a) Open circuit potential (OCP) vs. SCE for the in situ polymerization of aniline described in Section 2.6.2. (b) UV/VIS/NIR spectrum of the solid thin film of polyaniline emeraldine·HCl salt in situ deposited on plastic (PET) as described in Section 2.6.2.
medium (pH ∼ 0). The interdigitated electrode coated with the thin film of emeraldine·HCl salt was then removed from the reaction medium and it was then rinsed with excess of 1.0 mol dm−3 hydrochloric acid aqueous solution using a wash bottle. A clear and transparent thin film of emeraldine·HCl was obtained. A piece of plastic (PET) was used as a blank and it was then used for further spectroscopic characterization in the ultraviolet, visible and near infrared (UV/VIS/NIR) region. Fig. 4(b) shows the UV/VIS/NIR spectrum for the thin film of emeraldine·HCl salt in situ deposited on plastic (PET). This UV/VIS/NIR spectrum shows the characteristic absorption peaks of polyaniline emeraldine·HCl salt [16(b)]. 2.6.3. Sensing moisture from laboratory air at room temperature The gas chamber setup was made using glassware (125 mL filter flask, glass tube, and glass valve), tubing and flow meter (GILMONT no. 12). The flow rate of dry nitrogen gas (Grade 4.9, BOC Gases) was 1500 mL min−1 and the temperature of the nitrogen gas in the gas chamber was measured by using a thermometer. After pumping with dynamic vacuum, the resistance was measured in static laboratory air. The resistance was then constantly measured while the sensor was exposed to the stream
E.C. Venancio et al. / Sensors and Actuators B 130 (2008) 723–729
of dry nitrogen at room temperature (22–25 ◦ C). After dried in the presence of nitrogen stream, the sensor was then exposed to the moisture from the static laboratory air. The temperature and the relative humidity of the static laboratory air were recorded. The sensor was again exposed to stream of nitrogen for 10 min followed by exposure to the moisture from the static laboratory air for 10 min. The sensitivity to the moisture was calculated as described in Eq. (1), where R is the maximum resistance of the sensor in the presence of stream of dry nitrogen and R0 is the minimum resistance in the presence of static laboratory air: R (%) =
R − R0 × 100 R0
(1)
3. Results and discussion
727
The graphite pattern, which was obtained using plastic, was put in the presence of 1 mol dm−3 hydrochloric acid aqueous solution (pH ∼ 0) at room temperature (22–25 ◦ C) under vigorous magnetic stir for 1 h. It was surprising that the graphite lines were not removed and its electrical resistance did not change. This result showed that, once developed, the graphite lines are acid and water resistant. The explanation for this result is that the graphite dispersion contains silicates, which can form a network after the thermal treatment at 145 ◦ C [14]. During the thermal treatment (at 145 ◦ C) the alkali metal carboxylic acid salt contained in the graphite dispersion decomposes and assists the crystallization of the polymer (polyvinylpyrrolidone, PVP)–alkali silicates–graphite system. After the crystallization, it cannot be dissolved by simple exposure to water or an acid aqueous solution.
3.1. Line patterning of graphite on plastic (poly(ethylene terephthalate))
3.2. Line patterning of graphite on paper
The most important phenomena in the use of the line patterning technique are the difference in interaction between the dispersion, in this case the graphite dispersion and the printed and non-printed lines present in the pattern. Therefore, the use of dipping process resulted in the successful line patterning of graphite. The method described in this study depends primarily on the relatively strong adhesion of the carbon dispersion to an exposed substrate and the process of removal of the toner lines (together with the carbon film deposited on it) by the organic solvents employed in the washing process. In principle, it is not necessary to cover the backside of the substrate with adhesive tape but it is desirable simply to prevent the graphite dispersion to contact the backside. The adhesive tape covering the backside is removed after coating and drying the entire system with the carbon film. Fig. 1(a) presents the pattern of graphite on plastic (overhead transparency). As it can be seen it has presented a very good resolution. The toner lines were completely removed leaving only the graphite lines. This process is really easy to be carried out without any other complication or modification of commercially available office supplies (LaserPrinter, toner, overhead transparency). de Rossi [18] have shown the fabrication of patterns of graphite on transparency using inkjet printer. As pointed out by them, their graphite patterns on transparency have shown relatively high resistance. To improve the conductive in such patterns, it was printed more than 30 times. However, this procedure has implied in loss of resolution on obtaining the graphite pattern due to the need of printing the same graphite lines several times in order to achieve relatively low electrical resistance. Therefore, the advantage of the line patterning of carbon (graphite) on plastic (overhead transparency) is clear (Fig. 2). In addition, the line patterning technique did not imply in any modification of the printer. Fig. 3 shows the SEM image of the graphite-patterned line on plastic. The topography of the graphite films as depicted by the SEM studies shows no unexpected features. It should be also noted that the films show good uniformity.
The use of paper as a substrate to obtain patterns of graphite opens a new possibility for the fabrication of cheap and throwaway electronic devices. In this work we present the use of multipurpose office paper (xerox paper) and tracing paper as a substrate. Fig. 1(b) presents a pattern of graphite on multipurpose office paper (xerox paper) which was obtained by a dipping process. The patterns have presented good resolution as well as relatively low total electrical resistance when it is compared with patterns of conducting polymers [8,10]. Fig. 1(c) presents the 16-finger interdigitated electrode of graphite on tracing paper. The size of the pattern is the same as described in Fig. 1(a) and (b). As it can be seen, the graphite pattern presents a good resolution. The results (Fig. 1(b) and (c)) showed that a wide variety of paper can be used in the line patterning process. It is really surprising that the toner can be removed and leaves only the graphite lines. It is important to point out that only the method using glass roller works for tracing paper. In all other substrates dipping and glass roller methods presented approximately similar quality. In addition, the patterns of graphite on paper, xerox paper and tracing paper, were put in the presence of 1 mol dm−3 hydrochloric acid aqueous solution (pH ∼ 0) at room temperature (22–25 ◦ C) under vigorous magnetic stirring for 1 h. It was surprising that the graphite lines were not removed and its electrical resistance did not change. Therefore, as in the example using pattern of graphite on transparency, these results showed that, once developed, the graphite lines are acid and water resistant. The total electrical resistance of the graphite patterned lines (Fig. 2) can be minimized by increasing the thickness of the patterned lines, i.e. increasing the number of coatings of graphite dispersion during the line patterning process (Fig. 2(b)). However, there is a relationship between the number of coatings and the resolution of the patterned lines. Therefore, the conditions described in Section 2 of this report are suitable for the fabrication of electronic devices for sensor applications.
728
E.C. Venancio et al. / Sensors and Actuators B 130 (2008) 723–729
Fig. 5. Sensitivity to the presence of moisture of 16-finger interdigitated electrode of graphite coated with a thin film of polyaniline emeraldine·HCl (PANI·HCl) salt, obtained by in situ deposition, and with nanofibers of polyaniline emeraldine·AMPSA (PANI·AMPSA) salt. The measurements were done at room temperature (∼25 ◦ C) and atmospheric pressure.
3.3. Sensor application Fig. 5 shows the electrical response of two sensors prepared using the 16-finger interdigitated electrode of graphite on overhead transparency. The sensors were fabricated using two different types of polyaniline, i.e. nanofibers of AMPSA-doped polyaniline emeraldine salt and a film of in situ deposited HCldoped polyaniline emeraldine salt, respectively. The sensitivity given by the sensor prepared using nanofibers of AMPSA-doped polyaniline emeraldine salt (R = 93.3 ± 19%) is much higher than the one obtained with the film of in situ deposited HCldoped polyaniline emeraldine salt (R = 5.05 ± 0.79%). These results can be explained based on the differences in surface area of the two types of polyaniline emeraldine salt. Nanofibers of polyaniline emeraldine salt are expected to have higher active surface area when compared with the in situ deposited HCldoped polyaniline emeraldine salt film. Thus, the interaction between the molecules of water vapor and the sensor is enhanced by using nanofibers of polyaniline. Since the outermost surface of the film is expected to strongly interact with the water vapor, it suggests that the in situ deposited polyaniline emeraldine salt film might have more inactive materials that do not contribute for the sensor performance. In addition, this type of limitation could not be expected for the nanofiber-based sensor since it presents high surface area. Therefore, it might explain the differences in performance that were observed between the two sensors. 4. Conclusions The resolution of the graphite conducting patterns obtained by the procedure described is sufficient for our intended uses of the pattern. It could undoubtedly be improved if desired for a given use. We have demonstrated that the graphite lines can be conveniently coated with, e.g., the conducting electronic polymer,
polyaniline if desired, because of certain characteristic properties of polyaniline on graphite substrate as compared to carbon sensors devices, as it is described in this paper. The line patterning of carbon (graphite) can be used to produce graphite patterns on plastic (overhead transparency) and on paper substrates. It did not require any modification on the equipments which were used (laser printer, commercial overhead transparency, commercial multipurpose office paper, tracing paper). It can be carried out just by using available commercial office supplies. The results have shown a good resolution and suitable resistance values for electronic device fabrication. The line patterning of carbon (graphite) has the advantage over conventional methods of printing conducting phase using regular ink-jet printer, which needs to be carried out by doing modifications on the printer. Using just two coatings it was obtained graphite patterns with relatively low total electrical resistance. Another important result was that these patterns of graphite, once developed, are acid (pH ∼ 0) and water resistant. Nanofibers of polyaniline showed the best results for sensing moisture (humidity) from air. Since the sensing process occurs at the surface of the polyaniline, nanofibers of polyaniline are expected to enhance the sensing process due to its higher active surface area. This result opens up a new possibility for the construction of sensing devices at low-cost and high-sensitivity. In conclusion, we believe the simplicity and cheapness of the techniques and concepts given in this report can be refined and extended in a variety of direction depending on the ultimate purpose for which the patterns are desired. Acknowledgements The authors wish to thank the Office of Naval Research (grant no. N00014-01-1-0933), the Nanotechnology Institute of Pennsylvania (NTI, Benjamin Franklin Technology Partners, Southern Pennsylvania, USA), the Fundac¸a˜ o de Amparo a` Pesquisa do Estado de S˜ao Paulo (FAPESP, E.C. Venancio, 01/10415-6), CNPq and Embrapa/CNPDIA (E.C. Venancio, P.S.P. Herrmann J´unior and L.H.C. Mattoso, Brazil) for support of this work. References [1] B.D. Malhotra, A. Chaubey, S.P. Singh, Prospects of conducting polymers in biosensors, Anal. Chim. Acta 578 (2006) 59–74. [2] (a) A. Guadarrama, M.L. Rodr´ıguez-M´endez, J.A. de Saja, Influence of electrochemical deposition parameters on the performance of poly3-methyl thiophene and polyaniline sensors for virgin olive oils, Sens. Actuator B: Chem. 100 (2004) 60–64; (b) R. Stella, J.N. Barisci, G. Serra, G.G. Wallace, D. de Rossi, Characterisation of olive oil by an electronic nose based on conducting polymer sensors, Sens. Actuator B: Chem. 63 (2000) 1–9; (c) T.C. Pearce, S.S. Schiffman, H.T. Nagle, J.W. Gardner, Handbook of Machine Olfaction: Electronic Nose Technology, Wiley–VCH, 2003. [3] E.C. Venancio, N. Consolin Filho, C.J.L. Constantino, L. Martin-Neto, L.H.C. Mattoso, Studies on the interaction between humic substances and conducting polymers for sensor application, J. Braz. Chem. Soc. 16 (2005) 24–30. [4] K. Toko, Electronic tongue, Biosens. Bioelectron. 13 (1998) 701–709.
E.C. Venancio et al. / Sensors and Actuators B 130 (2008) 723–729 [5] (a) A. Riul Jr., R.R. Malmegrim, F.J. Fonseca, L.H.C. Mattoso, An artificial taste sensor based on conducting polymers, Biosens. Bioelectron. 18 (2003) 1365–1369; (b) L. Lvova, A. Legin, Y. Vlasov, G.S. Cha, H. Nam, Multicomponent analysis of Korean green tea by means of disposable all-solid-state potentiometric electronic tongue microsystem, Sens. Actuator B: Chem. 95 (2003) 391–399. [6] (a) E.C. Venancio, P.-C. Wang, A.G. MacDiarmid, The azanes: a class of material incorporating nano/micro-self-assembled hollow spheres obtained by aqueous oxidative polymerization of aniline, Synth. Met. 156 (2006) 357–369; (b) W.-S. Huang, B.D. Humphrey, A.G. MacDiarmid, Polyaniline a novel conducting polymer, J. Chem. Soc., Faraday Trans. 82 (1986) 2385–2400. [7] (a) J. Janata, M. Josowicz, Conducting polymers in electronic chemical sensors, Nat. Mater. 2 (2003) 19–24; (b) T.A. Skhoteim, J. Reynolds, Handbook of Conducting Polymers, 3rd ed., CRC, 2007. [8] D. Hohnholz, A.G. MacDiarmid, Line patterning of conducting polymers: new horizons for inexpensive, disposable electronic devices, Synth. Met. 121 (2001) 1327–1328. [9] A.G. MacDiarmid, “Synthetic metals”: a novel role for organic polymers (nobel lecture), Angew. Chem. Int. Ed. 40 (2001) 2581–2590. [10] D. Hohnholz, A.G. MacDiarmid, Plastic electronic devices through line patterning of conducting polymers, Adv. Funct. Mater. 15 (2005) 51–56. [11] N.J. Pinto, P. Carri´on, J.X. Qui˜nones, Electroless deposition of nickel on electrospun fibers of 2-acrylamido-2-methyl-1-propanesulfonic aciddoped polyaniline, Mater. Sci. Eng. A 366 (2004) 1–5. [12] J.P. Marton, Process for the selective formation of coatings by electroless deposition, US Patent 3,676,213 (1972). [13] S.S. Tzeng, F.Y. Chang, EMI shielding effectiveness of metal-coated carbon fiber-reinforced ABS composites, Mater. Sci. Eng. A 302 (2001) 258–267. [14] A.J. Stock, F.M. Hunter, Compositions and methods for producing electrically conductive coatings, US Patent 3,518,116 (1970). [15] (a) X. Zhang, R. Chan-Yu-King, A. Jose, S.K. Manohar, Nanofibers of polyaniline synthesized by interfacial polymerization, Synth. Met. 145 (2004) 23–29; (b) M.F. Hundley, P.N. Adams, R.B. Mattes, The influence of 2-acrylamido2-methyl-1-propanesulfonic acid (AMPSA) additive concentration and stretch orientation on electronic transport in AMPSA-modified polyaniline films prepared from an acid solvent mixture, Synth. Met. 129 (2002) 291–297. [16] (a) J.C. Michaelson, A.J. McEvoy, Interfacial polymerization of aniline, J. Chem. Soc. Chem. Commun. 1 (1994) 79–80;
729
(b) J. Huang, S. Virji, B.H. Weiller, R.B. Kaner, Polyaniline nanofibers: facile synthesis and chemical sensors, J. Am. Chem. Soc. 125 (2003) 314–315. [17] S.K. Manohar, A.G. MacDiarmid, A.J. Epstein, Polyaniline: pernigranile, an isolable intermediate in the conventional chemical synthesis of emeraldine, Synth. Met. 41 (1991) 711–714. [18] D. de Rossi, Ink-jet printed and high sensitivity conducting polymer odour sensors for olive oil olfactory assessment. Electronic noses and sensor array-based systems: design and applications, in: W.J. Hurst (Ed.), Proceedings of the 5th International Symposium on Olfaction and the Electronic Nose, CRC Press, 1999.
Biographies Everaldo Carlos Venancio received his PhD in science (physical chemistry) in 2000 from the Institute of Chemistry of S˜ao Carlos (IQSC) at University of S˜ao Paulo (USP), Brazil. He worked with Prof. Alan G. MacDiarmid for the period of 2002–2007 at the Department of Chemistry of the University of Pennsylvania, USA. He is currently working as a visiting research scientist at Embrapa Agricultural Instrumentation (Embrapa/CNPDIA), Brazil. His research interests are mainly related to nanoscience and nanotechnology directed towards the development of controllable methods of synthesis of nanostructures of conducting electronic polymers for application in energy storage, cell growth and differentiation, and sensors. Luiz Henrique Capparelli Mattoso received his PhD in materials science and engineering in 1993 from Materials Engineering Department at Federal University of S˜ao Carlos (DEMa-UFSCar), Brazil. He is currently a full researcher at Embrapa Agricultural Instrumentation Center in Brazil. His field of interests includes conducting polymers, chemical and biological sensors, nanostructured materials, polymeric blends and nanocomposites. ´ Paulo S´ergio de Paula Herrmann Junior received his PhD in science (physical chemistry) in 1999 from the Institute of Chemistry of S˜ao Carlos (IQSC) at University of S˜ao Paulo (USP), Brazil. He is currently a full researcher at Embrapa Agricultural Instrumentation Center in Brazil. His field of interests includes scanning probe microscopy and nanotechnology. Alan Graham MacDiarmid (1927–2007) received the Nobel Prize in Chemistry, 2000. He received his PhD in chemistry at the University of Wisconsin at Madison (1953) and the University of Cambridge (1955). He was blanchard professor of chemistry at the Department of Chemistry at the University of Pennsylvania, USA. He was the chemist responsible in 1977 for the chemical and electrochemical doping of polyacetylene, (CH)x , the “prototype” conducting polymer, and the “rediscovery” of polyaniline.