Portable E-Nose Based on Polymer/CNT Sensor Array ... - IEEE Xplore

Portable E-Nose Based on Polymer/CNT Sensor Array for Protein-Based Detection 12 1 3 Panida Lorwongtragoo1 , , Thara Seesaard , Chadarpon Tongta , Teerakiat Kerdcharoen4*

i

Materials Science and Engineering Programme, Faculty of Science, Mahidol University, Bangkok, 10400 Thailand Faculty of Science and Technology, Rajamangala University of Technology Suvarnabhumi, Nonthaburi, 11000 Thailand 3 Department of Chemistry, Faculty of Science, Thaksin University, Phatthalung, 93110 Thailand 4 * NANOTEC Center of Excellence at Mahidol University, National Nanotechnology Center, Bangkok, 10400 Thailand

2

Abstract-

Portable

electronic

nose

(e-nose)

consisting

For instance, Rakow et al. [13], Tang et al. [14] and Sutarlie and Yang [15] were successful on the colorimetric responses to amine compounds in range of ppm. However, the sensors based on chemically responsive dyes were also reported about non-reproducibility of the colour response limited with very low concentration of volatile amine [14]. Quartz crystal microbalance (QCM) sensors have also been widely used for the detection of amines [16]. Although the QCM sensor can respond to the compounds and can be reusable after flushing with reference gas or hot air, it requires for a complex fabrication process and expensive equipments [17-18]. In this work, we have extended the development of chemiresistive sensor based on polymer/CNT nanocomposite for the detection of the amine compounds as proposed in the previous work [19-20], by developing more sensors and integrating the sensor array into a handheld e-nose system. The composite materials have been demonstrated for the selectivity and sensitivity to be improved depending on the polymers. The designed e-nose system takes into account the energy consumption and the cost as well as the weight. The sensing mechanism of the non-conductive polymer added with conductive filler can be simply understood by a fractional volume increase of the polymer matrix [21-22]. The kind of interaction between the analyte gas and the sensing material highly determines the sensitivity, selectivity and reversibility of the gas sensors. For example, the weak interaction of binding molecules on sensing surface will result in low sensing response but better reversibility in turn. In other words, the good response can be achieved in case of the strong binding but the sensor may not recover to the original states [23]. In this paper, the underlying principles of gas adsorption on the polymer have been explained by quantum chemistry calculations based on the density functional theory. In the real application, the e-nose based on eight elements of polymer/CNT sensors was employed to classify three kinds of seafood such as dried fish, dried squid and dried shrimp, which normally generate different level of total volatile ammes. II. EXPERIMENT

of

polymer/carbon nanotube (CNT) sensor array was developed to detect protein-based foods. Gas sensors were fabricated by spin­ coating functionalized CNT/polymer nanocomposite materials onto interdigitated electrodes.

The sensors were tested with

various types of volatile compounds such as ammonia, amine compounds, acetic acid, water and organic solvents in the range of ppm level. It was found that most sensors yield strong signals to ammonia, amine compounds and acetic acid as well, while they present quite low response to organic solvents and water. To understand the relation of the interaction of amine species related to the sensor response, we have performed molecular modelling based on the density functional theory (DFT) on one polymer

structure

providing

the

best

response

to

volatile

ammonia. Based on the principal component analysis (PCA), this portable e-nose was successfully applied for the classification of the seafood releasing different amount of amine compounds.

Keywords- Electronic nose; Amine sensor; Seafood quality assessment; PolymerlCNT sensor I.

INTRODUCTION

In recent decades there are significantly increasing interest in the applications of e-nose for qualitative analysis of odors. This technology is non-destructive, rapid, reliable and inexpensive [1-2] as compared to the conventional techniques such as GC/MS [3] and most importantly the measurement can be performed at the point of use. For these reasons, numerous publications have been devoted to the development and improvement of the sensing materials, device system as well as methods of data analysis. The performance of e-nose relies on the combination of gas sensor array. It has been recommended to use broadly-cross reactive arrays of chemical sensors for generating a unique pattern for each odorant [4]. For the applications in fish and seafood industry, the research works on amine sensors are focused on improving sensitivity and selectivity as well as decreasing the manufacturing cost. Amines are well-known as common compounds released from bio-degradation process of protein­ based foods, as usually referred to Total Volatile Basic Nitrogen (TVB-N) [5-6]. Several research groups developing in the amine sensors have contributed on the electrochemical transducer [7-8], optical transducer [9-10] and gravimetric transducer [11-12] to employ in the e-nose system.

A. Sensor Fabrication

Fabrication method of the sensor based on CNT/polymer was given in the details as presented in the previous work [19].

978-1-4673-1124-3112/$31.00 ©2012 IEEE

NEMS 2012, Kyoto, JAPAN, March 5-8,2012

1

TABLE I. THE CHEMICAL COMPONENTS OF SENSING MATERIALS

Sensor ID SI S2

S3

Polymer Polyvinyl chloride (PVC) Cumene terminated polystyrene-co-maleic anhydride (Cumene-PSMA) Poly(styrene-co-maleic acid) partial isobutyl! methyl mixed ester (PSE)

S4

Polyvinylpyrrolidon (PVP)

S5

Polyvinyl chloride (PVC)

S6

S7 S8

Cumene terminated polystyrene-co-maleic anhydride (Cumene-PSMA) Poly(styrene-co-maleic acid) partial isobutyl! methyl mixed ester (PSE) Polyvinylpyrrolidon (PVP)

Carbon Nanotnbe

Solvent

SWNT-COOH

THF

SWNT-COOH

Acetone

SWNT-COOH

Acetone

SWNT-COOH

Ethanol

SWNT-OH

THF

SWNT-OH

Acetone

SWNT-OH

Acetone

SWNT-OH

Ethanol

(b)

(a)

Fig. lea) Handheld e-nose and (b) schematic of measurement circuit based on voltage divider method

The chemical compounds used as sensing materials are summarised in Table I. The polymers were varied as 4 types to introduce the difference of the physical and chemical properties for generating the specific patterns of activation across the sensor array, according to the principle of e-nose [24]. For the same reason, two types of the functionalized single-walled carbon nanotubes were used to disperse in each of the polymer matrix. The carboxylic-functionalized single-walled carbon nanotubes (SWNT-COOH) and the hydroxyl functionalized single­ walled carbon nanotubes (SWNT-OH) were purchased from Cheap Tube Inc containing 90wt% carbon with 1-2 nm in diameter and 0.5-2.0 !lm in length. The degree of functionalization on SWNT is 2.73% and 3.96% for SWNT­ COOH and SWNT-OH, respectively, according to the supplier. Briefly, each polymer was dissolved in the proper solvent to obtain the polymer solutions. CNT powder was loaded as 20 wt% of polymer matrix to obtain a high sensor response according to the recipe as proposed by Piromjitpong, et al [20]. Spin -coating method was used to form the sensing film onto the interdigitated gold electrode by setting the spinning rate around 1500-2000 rpm for 30 s. After film formation, it was heated at ISO °C for 3 h to obtain a stable sensor. B. Electrical response to the analyte gases

and 7 min to obtain the responsive resistance with injecting the volatile into the chamber. The last minute was represented as a steady-state condition of the response. The sensor exposed to the analyte gas was determined from the fractional method [24-25] to obtain a dimensionless response and provide a normalized response signal. The average of baseline resistance in the first period (Ro) is subtracted and then divided from the average of the signals in the steady-state condition (R,). % Sensor response

R -R

= _s __ 0

Ro

x 100

(I)

C. Handheld E-Nose System

The handheld e-nose was designed to support key requirements such as lightweight, low power consumption, easy to use, low cost and low maintenance. Fig.1 (a) shows the picture of the handheld e-nose and Fig. 1(b) shows a measurement circuit inside the case. The system consists of three main parts: (i) air flow unit, (ii) sensing unit and (iii) data acquisition unit [26-28]. All parts are packed in a small plastic case with a dimension of 8.3 cm x15.8 cm x 8cm. The total weight is only 170 g. A small electric fan is used for sucking the odors into the sensing unit. The SI-S8 sensors were placed in the prepared sockets of the sensing unit. For the data acquisition unit, a simple measurement circuit based on the voltage divider method was used and the data were acquired through a USB DAQ device as shown in Fig. 1(b). D. Seafood Discrimination

Eight fabricated sensors (S1-S8) were tested to the single volatile compounds: dimethylamine, dipropylamine, pyridine, and ammonium hydroxide, acetic acid, tetrahydrofuran, ethyl alcohol, acetone and water by varying the concentration in a closed chamber as 50, 200, 500 and 1000 ppm. The measurement circuit based on voltage divider method was used to obtain the resistances of each sensor. The data were acquired through a USB DAQ device (NI USB-6008). The resistances are recorded with 2 periods: 2 min to obtain baseline of reference resistance without injecting any volatile

In this work, we have illustrated the real-world application by classification of dried seafood which normally generate different amount of amine and ammonia compounds. Dried squid, dried fish and dried shrimp were obtained from a supermarket in Thailand. The closed packages indicating the same manufacturing date were used as the analyte samples. Measurement of each sample odor was performed by the handheld e-nose. 20 g of each sample was kept in a closed glass bottle at room temperature for 10 min to generate the odor into the headspace. The handheld e-nose was used to

2

measure the fresh air to obtain the reference baseline for 2 min. After that, the sample bottle was opened and the handheld e­ nose was directly pointed at the top of the bottle for 5 min. With help of the electric fan inside the e-nose, the sensor signal can quickly reach a steady state. The recorded data were determined in term of the percent sensor response as shown in Eq. (I). Principal component analysis (PCA) was employed to discriminate the states of various protein­ containing foods, using the advantage of non-specific chemical interactions in the sensor array. III. MOLECULAR MODEL To understand the interaction of the polymer and amme compounds, the PSE presenting the best response to amine and ammonia [19], as compared to other polymers according to the experimental results, was chosen to study by the first principles calculation. Thus, we shall consider only at the active site (carboxyl group of the PSE molecule) which can be adsorbed by base molecules such as ammonia and amine compounds via hydrogen bond interactions [29-32]. For the PSE structure, only the main part of poly(styrene-co-maleic acid) was considered by neglecting the partial part of the isobutyl/methyl mixed ester.

Full geometry optimization of the individual PSE and analyte molecules was carried out using density functional theory (DFT) [33] with Becke's three-parameter functional with the gradient-corrected correlation of Lee, Yang and Parr (B3LYP) [34] along with the 6-31 +G(d,p) basis set. The diffuse function was recommended to be included in the basis set to improve the long-range interaction and provide reliable prediction of the properties of hydrogen-bonded complexes [30]. Conformation and total energy of the complex molecule between the PSE and the base molecule was fully relaxed with the same calculation level. The adsorption energy (�Ead) is calculated by (2)

,d.,Ead = EPSE@llase-molecule - EpSE - Enase-molecule

Where

EPSC@Base-molecule

is the total energy of the complex

molecule between the PSE and the base molecule. total energy of isolated PSE molecule and

EpSE

Ellasc-mo!ccu]c

is the is the

total energy of isolated the base-molecule, i.e. ammonia, dimethylamine, pyridine and dipropylamine. Beside the adsorption energy, the intermolecular distance between the nitrogen heteromolecule and the donating proton, r(R··N) and the elongated distance of the covalent bond holding the proton, reO-H) were also considered.

15

Dimethylamine

Pyridine

Dipropylamine '1

.� .

o

Aceticarid

Fig. 2. Percent sensor response of 8 sensor elements (SI-S8) tested with 50 ppm-IOOO ppm of ammonia(NH3),dimethylamine, pyridine,dipropylamine, acetic acid (CH3COOH), tetrahydrofuran (THF),ethanol (EtOH), acetone and water (H20) and radar plot of the percent sensor response when tested with 1000 ppm of acid-base compounds

3

strength of ammonia or amines interaction on the carboxyl group of the PSE can be ranked as dipropylamine > dimethylamine > ammonia > pyridine. Moreover these calculated values also correspond to pKb values as presented in the literatures. In most cases, the sensor responses follow the same trend as the above-mentioned ranking of acid-base interactions, except for ammonia. Although dipropylamine and dimethylamine can form stronger interaction with PSE than ammonia, we thus found that ammonia with high mobility can easily diffuse into the sensing material resulting in superiority of the sensor response among other base molecules. As the results, the sensor responses of the PSE to the base-molecules is in the order as ammonia > dipropylamine > dimethylamine > pyridine [19].

IV. RESULTS AND D ISCUSSION Fifty to one thousand parts per million concentrations of analyte gases such as ammonium hydroxide, dimethylamine, pyridine, dipropylamine, acetic acid, tetrahydrofuran, ethanol, acetone and water were used to test the SI-S8 sensors at room temperature. The sensor resistance increases when the analyte gas was injected into the chamber. It is mainly related to the increased volume of the polymer matrix due to the swelling effect [21-22]; however the process of the charge transfer between CNT and the binding gas [35] is also possible [19, 36]. Fig. 2 shows percentage change of the resistance for all sensors as determined by Eq. (1). According to the experimental results as shown in Fig.2, all sensors show chemoselectivity in the range of the acid-base detection. The SI-S8 sensors can respond to ammonia and amine compounds as well as acetic acid whereas these sensors show low responses to organic solvents such as THF, ethanol acetone and water. The increasing of resistance with rising volatile concentration can be modelled by the Plateau­ Bretano-Stevens law [37-38] in accordance with the previous work [19]. The insets in Fig.3 demonstrate the radar plot of the percent sensor responses when the sensors were tested with 1000 ppm of ammonia, amines and acetic acid. The sensor responses show differences in their patterns when exposed with the different volatiles. Differences of the functional groups existing in the sensing materials can generate various patterns [39]. In this work, we found that varying of polymers has influence to the change of the patterns rather than varying the functionalized CNT. Therefore, the results can imply that the response of the sensor based on CNT/polymer composite is caused by the swelling effect rather than the charge transfer process. According to the experimental evidence in Fig. 2, we have focused on the PSE polymer (S3 and S7) which presents specific response to basic volatiles such as ammonia and amines, rather than the PVP polymer (S4 and S8) that provide good response to both acid and base molecules. Molecular modelling can give the information to understand the underlying principles of the sensors [40]. Moreover, the computer modelling approaches are possible to be used for obtaining affinity and selective sensors [41]. A carboxyl site on the PSE was chosen as an important target for forming interaction with the base molecule. In addition, the presence of carboxyl group allows the nitrogen heteroatom of ammonia or amines to form hydrogen bond [29-31]. Based on molecular calculation, the strength of intermolecular interaction can be indicated by the adsorption energy, the intermolecular distance r(Hoo·N) and the elongated distance reO-H) [29]. Table II summarizes the results of the first principles calculation of the PSE/base-molecule complex, pKb values from literatures and the percent responses of S3 and S7 from the experimental observation whereas the optimized geometries of complex forming are shown in Fig. 3. The calculated results show the strong correlation of three values, reO-H), r(Hoo·N) and �Ead. It was found that the

TABLE II. THE BOND DISTANCE R(O-H),R(H.. ·N) AND ADSORPTION ENERGY (t,E,,,) OF VOLATILE MOLECULE ON PSE POLYMER SHOWN IN FIG. 2 CALCULATED BY B3LYP/ 6-31+G(D,P)

Volatile Molecule Ammonia

Dirnethyiamine Pyridine

Dipropylamine

reO-H)

r(Hoo·V)

Mod

A

A

kcal/mol

1.010 1.020 1.000 1.030

1.711 1.679 1.754 1.660

-17.09 -17.46 -15.26 -18.60

0

0

pKb

0/0 Sensor response S3/S7

4.74[42[ 3.29 [43] 8.75[42] 3.09 [44[

11.7110.2 3.9/6.7 2.0/3.0 5.3/6. 5

ta)

(el

Hydrogen

Carbon

•

•

Nitrogen

Oxygen

Fig. 3. Optimized conformation of (a) ammonia, (b) dimethylamine, (c) pyridine and (d) dipropylarnine interacting on a carboxyl group of PSE polymer by B3LYP/6-31+G(d,p)

4

To compare the differences of the functionalized CNT in the same polymer matrix, it was observed that most sensors produced from the SWNT-OH exhibit significantly larger sensor response than the sensor produced from the SWNT­ COOH. This can be attributed to the degree of functionalization of SWNT that the hydroxyl function was presented on the SWNT 31% more than the carboxyl function. For the real application, we have used all sensors (SI-S8) installed in the sensing unit of the handheld e-nose. Decomposition of nitrogen-containing compounds such as amino acid in protein based food can form ammonia and amine compounds [45-46] due to microbial spoilage, enzymatic spoilage, chemical spoilage and physical spoilage [47]. According the experimental observation of the static testing, these sensors have been demonstrated that they can respond to ammonia, amines or acid and can generate the specific patterns as shown by the radar plots in Fig. 2. In Fig. 4, we illustrate the application of the fabricated sensors to classify the differences of three dried seafood, i.e. dried fish, dried squid and dried shrimp. We applied PCA to the data set extracted from the sensor responses after exposed with the headspace of each samples. The PCA plot can discriminate three samples. Three clusters of PCA plot indicate that there are differences of volatiles generated from the different dried seafood. V.

2

� 0 N

,...: :=. N

U Q.

0

0

�

-1

-2

-3

• a

Dried fish

A

Dried squid

•

Dried shrimp

-3

·2

·1

0 PC1

1

2

3

4

(66.6%)

Fig. 4. 2D PCA plot in PC1 and PC2 components for classification of three kinds of seafood: dried fish,dried squid and dried shrimp

REFERENCES [I]

A. Pacquit,K. T. Lau,H. McLaughlin,1. Frisby,B. Quilty,D. Diamond, "Development of a volatile amine sensor for the monitoring of fish spoilage," Talanta, 69,p. 515-520, 2006.

[2]

1.K. Heising, M. Dekker, P.V. Bartels, M. A.l. S. van Boekel, "A non­ destructive ammonium detection method as indicator for freshness for packed tish: Application on cod," Journal of Food Engineering, in press.

[3]

A. D. Wilson, M. Baietto, "Applications and Advances in Electronic­ Nose Technologies," Sensors, ,9,5099-5148,2009.

[4]

B. 1. Doleman, N. S. Lewis, "Comparison of odor detection thresholds and odor discriminablities of a conducting polymer composite electronic nose versus mammalian olfaction," Sensors and Actuators E, 72, p. 4150,2001.

[5]

A. K. Anderson, "Biogenic and volatile amine-related qualities of three popular fish species sold at Kuwait fish markets " Food Chemistry, 107, p.761-767,2008.

[6]

C. R.-Capillas, C. M. Gillyon, W. F.A. Homer, "Determination of volatile basic nitrogen and trimethylamine nitrogen in fish sauce by flow injection analysis," Eur Food Res Technol, 210, p.434-436, 2000.

[7]

N. Guemion,RJ. Ewen, K. Pihlainen, N.M. Ratcliffe,G.c. Teare,"The fabrication and characterisation of a highly sensitive polypyrrole sensor and its electrical responses to amines of differing basicity at high humidities," Synthetic Metals, Volume, 126,P. 301-310, 2002.

[8]

C. Zamani, O. Casals, T. Andreu, J. R.Morante, A. R.-Rodriguez, "Detection of amines with chromium-doped W03 mesoporous material," Sensors and Actuators B, 140,p. 557-562,2009.

[9]

A. Grafe, K. Haupt, G. J. Mohr, "Optical sensor materials for the detection of amines in organic solvents," Analytica Chimica Acta, 565, p. 42-47, 2006.

CONCLUSIONS

The sensor array based on polymer/CNT nanocomposite has been developed to generate the specific patterns by using differences of the polymer matrix and functionalized CNT. The fabricated sensors have been demonstrated to show good responses to specific volatiles such as ammonia, amines and acid whereas they present very low response to organic solvents. The first principles calculation based on B3LYP/631 +G(d,p) approach could provide the understanding involving the interaction of the base molecule with the PSE polymer. It was found that the ammonia or amines can form hydrogen bond with the carboxyl group on the PSE molecule with adsorption energy -15.26-18.60 kcal/mol corresponding to the values of pKb of the binding molecules. Based on the theoretical calculation and the experimental sensor testing, the mechanism underlying the sensor response were concluded to be the outcome of the counterbalance between basicity and mobility of the volatiles. In the last part, the handheld e-nose containing these eight sensor elements can be used to discriminate the different dried seafood.

[10] G.l. Mohr, U.-W. Grummt, "Photochemistry of the amine-sensor dye 4N,N-dioctylamino-4'-trifluoroacetylazobenzene," Journal oj' Photochemistry and Photobiology A: Chemistry, 163,p.341-345,2004.

ACKNOWLEDGMENT

[II] K. Aoki, L. C. Brousseau and T. E. Mallouk,"Metal phosphonate-based quartz crystal microbalance sensors for amines and ammonia," Sensors and Actuators E, 13-14, p.703-704, 1993.

This work was supported by Mahidol University and the National Science and Technology Agency. A research career development grant from the Thailand Research Fund to TK and a CHE-Ph.D.-SW-NEU. scholarship from the Commission of Higher Education to PL are acknowledged.

[12] H.c. Hao, K.T. Tang, P.H. Ku, 1.S. Chao, c.H. Li, C.M. Yang, D.l. Yao, "Development of a portable electronic nose based on chemical surface acoustic wave array with multiplexed oscillator and readout electronics," Sensors and Actuators B, 146,p. 545-553,2010.

5

[13] N. A. Rakow, A. Sen, M.C. Janzen, J. B. Ponder, K S. Suslick, "Molecular Recognition and Discrimination of Amines with a Colorimetric Array," Angew. Chem. Tnt. Ed. 44,p. 4528 -4532,2005.

[33] A. D. Becke, "Density-functional thermochemistry. III. The role of exact exchange," J. Chern. Phys. 98 (7), p.5648-5652, 1993.

[14] Z. Tang,J.Yang, J.n Yu, B.Cui, " A Colorimetric Sensor for Qualitative Discrimination and Quantitative Detection of Volatile Amines," Sensors, 10,6463-6476,2010.

[34] P. J. Stephens,F J. Devlin, C. F. Chabalowski, M. 1. Frisch, "Ab Initio Calculation of Vibrational Absorption and Circular Dichroism Spectra Using Density Functional Force Fields," J. Phys. Chem., 98 (45), p. 11623-11627,1994.

[15] L. Sutarlie, K-L. Yang, "Colorimetric responses of transparent polymers doped with metal phthalocyanine for detecting vaporous amines," Sensors and Actuators B, 134,p. 1000--1004. 2008.

[35] J. A. Robinson,E. S. Snow, S.c. Badescu,T. L. Reinecke,F. K Perkins, "Role of Defects in Single-Walled Carbon Nanotube Chemical Sensors," Nano Lett., 6,p. 1747-1751,2006.

[16] M.M. Ayad, N. L. Torad, "Quartz crystal microbalance sensor for detection of aliphatic amines vapours," Sensors and Actuators B, 147,p. 481-487,2010.

[36] B. Safadi, R. Andrews, E.A. Grulke, Multiwalled carbon nanotube polymer composites: synthesis and characterization of thin films, J. App!. Polym. Sci. 84 (2002) 2660-2669.

[17] H.T. Nagle, R. Gutierrez-Osuna, S.S. Schiffman,"The how and why of electronic noses," TEEE Spectrum, 35 (9),p. 22-34,1998.

[37] A. Szczurek, M. Maciejewska, "Relationship between odour intensity assessed by human assessor and TGS sensor array response, " Sensors and Actuators B, 106,p. 13-19,2005.

[18] A. J. Lilienthal, A. Loutfi,T. Duckett,"Airborne Chemical Sensing with Mobile Robots," Sensors, 6,p. 1616 - 1678,2006.

[38] V. V. Kamadia, Y. Yoon, M. W. Schilling, D. L. Marshall, Relationships between Odorant Concentration and Aroma Intensity,"J. Food Sci. 71,p. SI93-S197,2006.

[19] P. Lorwongtragool, A. Wisitsoraat, T. Kerdcharoen, "An Electronic Nose for Amine Detection Based on PolymerISWNT-COOH Nanocomposite," J. Nanosci. Nanotechnology, II,2011,inpress. [20] T. Piromjitpong, P. Lorwongtragool, P. Piromjitpong, T. Kerdcharoen, 'The Development in an Effective of Ammonia-Odor Sensor Based on PSE-PolymerISWNT Nanocomposite," in Proceedings oj" Chiang Mai Tnternational Conference on Biomaterials & Applications (CMTCBA 2 (11), Chiang Mai,Thailand,August 2011. [21] N. K Kang, T. S. Jun, D.-D. La, J. H. Oh, Y. W.Cho, Y. S. Kim, "Evaluation of the limit-of-detection capability of carbon black-polymer composite sensors for volatile breath biomarkers," Sensors and Actuators B, 147,p.55-60, 2010. [22] S. Maldonado, E. G.-Berrios, M. D. Woodka, B. S. Brunschwig, N.S. Lewis,"Detection of organic vapors and NH3(g) using thin-film carbon black-metallophthalocyanine composite chemiresistors," Sensors and Actuators B, 134,p.521-531, 2008.

[39] S. Ampuero, J.O. Bosset, 'The electronic nose applied to dairy products: a review," Sensors and Actuators B, 94 p.I-12, 2003. [40] H. Chang, .J. D.Lee, S. M.Lee, Y. H. Lee, "Adsorption of NH3 and N02 molecules on carbon nanotubes," App!. Phys. Lett., 79, p.38633865,2001. [41] M. A. Ryan,A. V. Shevade,C. J. Taylor, M. L. Homer, M. Blanco,J. R. Stetter,Computational Methods/or Sensor Material Selection, Springer; I" ed. ,2009. [42] T. Morimoto, J.Imai, M.Nagao, "Infrared Spectra of n-Butylamine Adsorbed on Silica-Alumina," The Journalof Physical Chemistry, 78, p.704-708, 1974. [43] K Kandori, N. Ohkoshi, A. Yasukawa, T. Ishikawa, "Morphology control and texture of hematite particles by dimethylformaminde in forced hydrolysis reaction," J. Mater. Res., 13,p. 1698-1706, 1998.

[23] D. James, S. M. Scott, Z. Ali, W.T. O'Hare, "Chemical Sensors for Electronic Nose Systems," Microchim. Acta, 149, p.I-17, 2005.

[44] D. H. Feldman, J. C. Cavagnol, "Estimation of I-Butanol and Ethyl Cellosolve in Waste Streams with Sudan III Reagent," Anal. Chem., 28 (II),p. 1746-1748,1956.

[24] T.C. Pearce, S.S. Schiffman, H.T. Nagle, and J.W. Gardner, Handbook oj"Machine Olfaction; Electronic Nose Technology, Wiley-VCH,2002.

[45] M. Y.Ali, M. 1. Sharif, R. K Adhikari, O. Faruque, "Post mortem variation in Total Volatile Base Nitrogen and Trimethylamine Nitrogen between Galda (Macrobrachium rosenbergii) and Bagda (Penaeus monodon)," Univ. j. zoo!. Rajshahi. Univ. 28, p.7-1O, 2010.

[25] K Arshak, E. Moore, G.M. Lyons, J. Harris and S. Clifford, "A review of gas sensors employed in electronic nose applications," Sensor Review, 24 (2),pp. 181-198,2004 [26] C. Wongchoosuk, S. Choopun, A. Tuantranont and T. Kerdcharoen, "Au-doped Zinc Oxide Nanostructure Sensors for Detection and Discrimination of Volatile Organic Compounds," Materials Research Tnnovation, Vol. 13,pp. 185-188,2009. [27] C. Wongchoosuk, A. Wisitsoraat, A. Tuantranont and T. Kerdcharoen, "Portable Electronic Nose Based on Carbon Nanotube-Sn02 Gas Sensors: Feature Extraction Techniques and Its Application for Detection of Methanol Contamination in Whiskeys," Sensors and Actuators B: Chemical, Vol. 147,pp. 392-399,2010. [28] P. Lorwongtragool, C. Wongchoosuk, T. Kerdcharoen, "Portable artificial nose system for assessing air quality in swine buildings," Proceedings of ECTl-CON2010 7th Tnternational Conference of

Electrical Engineering/Electronics, Computer, Telecommunications and Tnformation Technology Association, pp. 532 - 535,ISBN 978-1-42445606-2,Chaing Mai,THAILAND,19-21,2010. [29] L. Tao, J. Han, F-M.Tao, "Correlations and Predictions of Carboxylic Acid pKa Values Using Intermolecular Structure and Properties of Hydrogen-Bonded Complexes," J. Phys. Chem. A, 112, 775-782,2008. [30] D. Singh, P. K Bhattacharyya, J. B. Baruah, "Structural Studies on Solvates of Cyclic Imide Tethered Carboxylic Acids with Pyridine and Quinoline," Crystal Growth & Design, 10, p.348-359, 2010. [31] V. Dimitrova,S. Ilieva,B.Galabov,"Electrostatic potential at nuclei as a reactivity index in hydrogen bond formation. Complexes of ammonia with C-H, N-H and O-H proton donor molecules," Journal oj" Molecular Structure (Theochem), 637 , p.73-80, 2003. [32] R. S. Miller, D. Y. Curtin, I. C. Paul, "Reactions of Molecular Crystals with Gases. I. Reactions of Solid Aromatic Carboxylic Acids and Related Compounds with Ammonia and Amines," J. Amer. Chem. Soc.96, p.6340-6349, 1974.

6

[46] P. Howgate, "A Critical Review of Total Volatile Bases and Trimethylamine as Indices of Freshness of Fish. Part I. Determination," EJEAFChe, 9 (1), p.29-57, 2010. [47] C.

Wongchoosuk, P. Lorwongtragool, T. Kerdcharoen. Malodor Detection Based on Electronic Nose, Air Quality Monitoring, Assessment and Management, Nicolas A. Mazzeo (Ed.), ISBN: 978953-307-317-0,InTech, 2011. Available from: http:// www. Intechopen. com/articles/show/title/malodor-detection-based-on-electronic-nose.