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Development of a portable electronic nose for detection of pests and plant damage
Computers and Electronics in Agriculture 108 (2014) 87–94
Contents lists available at ScienceDirect
Computers and Electronics in Agriculture journal homepage: www.elsevier.com/locate/compag
Development of a portable electronic nose for detection of pests and plant damage B.D. Lampson a, Y.J. Han a,⇑, A. Khalilian b, J.K. Greene b, D.C. Degenhardt b, J.O. Hallstrom c a
School of Agricultural, Forest, and Environmental Sciences, Clemson University, 237 McAdams Hall, Clemson, SC 29634, USA School of Agricultural, Forest, and Environmental Sciences, Edisto Research and Education Center, 64 Research Drive, Blackville, SC 29817, USA c School of Computing, Clemson University, 212 McAdams Hall, Clemson, SC 29634, USA b
a r t i c l e
i n f o
Article history: Received 24 September 2013 Received in revised form 2 June 2014 Accepted 6 July 2014
Keywords: Volatile Electronic nose Pest control Portable sensors Carbon black–polymer composites Integrated pest management
a b s t r a c t Agricultural pests are responsible for millions of dollars of crop losses and control costs every year. To reduce these losses and minimize control costs, new methods to detect pests and/or pest damage must be investigated in order to optimize control measures. One such method evaluated in this study was to detect the chemicals released by pests or pest-damaged products. A portable device was developed to draw volatiles from pests or pest-damaged products over carbon black–polymer composite sensors and measure the change in resistance for each sensor. The device successfully sampled pest and plant volatiles and these volatiles were detected using carbon black–polymer composite sensors. These results indicated an electronic nose is a feasible approach to detect pests and/or pest damage. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction Integrated pest management is a practiced concept that involves a variety of chemical, biological, cultural, and physical pest control techniques designed to reduce pest status to tolerable levels, maximize profitability, and preserve the environment. Some of these management techniques involve proactive, preventative measures, but others are reactive strategies, such as chemical control, where fields are treated before substantial damage has occurred and only when a pest density and/or damage threshold has been met or exceeded. These techniques involve monitoring pest density and/or damage, and sampling methods are needed to accurately estimate levels of pest density/damage. One possible method of sampling involves detecting chemicals produced by pests or pest-damaged products. Carbon black–polymer composites have been used to detect natural and synthetic insect volatiles as well as damaged agricultural products, and therefore, several studies have previously worked toward the goal
Abbreviation: PAD, Pest and damage detector. ⇑ Corresponding author. Tel.: +1 864 656 4077; fax: +1 864 653 0338. E-mail addresses: [email protected] (B.D. Lampson), [email protected] (Y.J. Han), [email protected] (A. Khalilian), [email protected] (J.K. Greene), [email protected] (D.C. Degenhardt), [email protected] (J.O. Hallstrom). http://dx.doi.org/10.1016/j.compag.2014.07.002 0168-1699/Ó 2014 Elsevier B.V. All rights reserved.
of developing of using an electronic nose for pest detection (Henderson et al., 2010; Suh et al., 2011; Degenhardt et al., 2012). Carbon black–polymer composites have been shown to increase resistance in the presence of specific volatiles (Lonergan et al., 1996). Portable electronic noses that employ various types of carbon black–polymer composites and pattern recognition software are commercially available, such as the hand-held Cyranose 320 (Smith Detection, Pasadena, CA). The Cyranose 320 has been shown to detect natural and synthetic insect volatiles as well as damaged agricultural products (Henderson et al. 2006; Suh et al., 2011; Degenhardt et al., 2012). However, this electronic nose is expensive (>$10,000), requires trained personnel for analysis, lacks real-time software for ‘‘on-the-go’’ measurements of volatiles, and is not designed specifically for the purpose of detecting pests or the damage they cause.
2. Objectives The overall objective of this research was to develop an electronic nose using carbon black–polymer composite sensors for detecting pests and/or pest damage. This pest and damage (PAD) detector would be small, lightweight, inexpensive, easy to interpret, and able to provide rapid results for in-field decision making. The specific objectives of this paper are to document the
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development process and to report the current status of the latest generation of the detector. 3. Methods and materials 3.1. Fabrication of carbon black–polymer composites Composite solutions were made using 20 mg of suspended carbon black (BP2000, Cabot Co., Billerica, MA) and 80 mg of polymer in 10 ml of solvent. Polymers used were poly(vinyl butyral), poly(4-vinylphenol), poly(bisphenol A carbonate), poly(styreneco-allyl alcohol), poly(styrene-co-maleic anhydride), poly(vinyl acetate), poly(vinylidene chloride-co-acrylonitrile-co-methyl methacrylate), poly(vinylpyrrolidone), poly(ethylene glycol), and poly(ethylene oxide). These polymers were chosen based on their use in previous research (Lonergan et al., 1996). Tetrahydrofuran was used as the solvent for all sensors except benzene was used for the poly(ethylene oxide) sensor. All polymers and solvents were obtained from Sigma–Adrich (St. Louis, MO). Solutions were sonicated for one minute prior to coating the sensor boards to ensure carbon black suspension and then immediately coated and allowed to dry for an hour. This process was repeated until resistance was between 100 kX and 1 MX. 3.2. Development of PAD detector 3.2.1. First generation PAD detector Carbon black–polymer composite sensors were constructed by dip coating a universal electrode board (surfboard 6012, Capital Advanced Technologies, Carol Stream, IL) into a carbon black–polymer mixture. Dip coating involves submerging the electrode board into the carbon black–polymer mixture several times. Before dip coating, the electrode board was separated into 6 separate sensors with two electrodes, spaced 0.254 cm from center to center. To develop the PAD detector, the components were assembled into a fiberglass NEMA enclosure (Model NF-6610, Bud Industries Inc., Willoughby, IL) (Fig. 1). This enclosure had external dimensions of 19.7 cm 19.7 cm 12.2 cm and a weight of 2 kg. The microdiaphragm pump (Model NMS020L, KNF Neuberger Inc., Trenton, NJ) was connected by 0.318 cm OD, 0.159 cm ID polyethylene tubing to a polyethylene sensor box. This tubing also connected the pump to the subminiature solenoid valve (Model GH3115-C203, Gems Sensors & Controls, Plainville, CT). The pump had a weight of 0.029 kg, and the solenoid valve had a weight of 0.0718 kg. A variable power supply (Mini-Lab 200, Knight Electronics, Inc., Dallas, TX) was used to supply various voltages, and data acquisition hardware (miniLAB 1008, Measurement Computing Corporation, Norton, MA) was used to control the pump and valve
Fig. 1. Inside the first generation PAD detector.
and to measure the voltage drops across the sensors as well as the valve status (Fig. 2). The sensors were inserted into a breadboard in the sensor box. With this system, an air stream was drawn across an array of four carbon black–polymer composite sensors. First, a 20-s purge cycle drew ambient air across the sensors. Then, a solenoid valve energized and redirected the air flow so it drew sample air across the sensors for a 20-s sampling cycle. Then, ambient air was drawn across the sensors for a 20-s post-sample purge cycle. These cycles were repeated an additional two times. Voltage drops across the sensors were recorded onto a laptop using data acquisition hardware, and these voltage drops were converted into resistances. The device was tested using volatiles from a damaged leaf. First, a leaf was extracted from a test plant. Then, the leaf was damaged by perforating it with a hole punch twenty times. The leaf was then placed in a nylon bag (Oven bags, Reynolds, Richmond, VA), a small hole was cut into the bag, and the sampling tube was inserted into the hole. Volatiles were then extracted by the PAD detector. 3.2.2. Second generation PAD detector In order to make the device more portable, improvements were made to the first generation PAD detector, including a smaller enclosure, an enclosed power source, and an enclosed microcontroller board. This enclosure (1050 Micro Case, Pelican Products, Inc., Torrance, CA) had exterior dimensions of 19 cm 12.8 cm 7.9 cm and a weight of 0.38 kg. The power source was a 12 V, 1.3 Ah AGM battery (WKA12–1.3F, Werker), and it had a weight of 0.621 kg and exterior dimensions of 9.7 cm 5.1 cm 4.3 cm, excluding leads. The microcontroller board was the MoteStack (Clemson University, Clemson, SC). The MoteStack consisted of 3 motes: the MoteStack I/O board (v2.4), the MoteStack storage board (v2.2), and the MoteStack base (v2.5). When combined, these motes had exterior dimensions of 5.6 cm 5.6 cm 4.6 cm and a weight of 0.076 kg. A temperature sensor (DS18S20, Dallas Semiconductor, San Jose, CA) was added in the second generation PAD detector. The control circuit was responsible for the digital outputs that controlled the pump and solenoid valve, and the sensor circuit was responsible for the analog inputs from the composite sensors. The control circuit and the sensor circuit were built using small breadboards (Fig. 3). The control circuit (Fig. 4) was constructed on the breadboard and secured with thermoplastic adhesive. In this circuit, the 12 V was supplied by the battery. The MoteStack was responsible for providing the digital output for controlling the pump and valve. The sensor circuit (Fig. 5) was constructed on a second breadboard and also secured with thermoplastic adhesive. In the sensor circuit, the MoteStack supplied the 5 V and recorded the voltage drop across the carbon black–polymer composite sensors R1–R4. In addition to the MoteStack, a portable datalogger (midi logger GL220, Graphtec Corporation, Yokohama, Japan) measured these voltage drops across the composite sensors via an 8-pin DIN connector. The datalogger was used during the development phase in order to instantly visualize the data. A voltage follower circuit was constructed using an LM324 operational amplifier to act as a high impedance bridge between the sensor circuit and the datalogger. The control circuit breadboard weighed 0.053 kg, and the sensor breadboard weighed 0.013 kg. 3.2.3. Third generation PAD detector To develop the third generation PAD detector, a number of features were added, including a smaller enclosure, smaller control circuit, and smaller sensor circuit. The components were assembled into an ABS enclosure (Model 100-42-NO-E, Box Enclosures and Assembly Services, Lake Bluff, IL) (Fig. 6). This enclosure had
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Fig. 2. Functional schematic of the first generation PAD detector.
Fig. 3. Inside the second generation PAD detector.
external dimensions of 19 cm 10. cm 4.8 cm and a weight of 0.2 kg. The new sensor boards were made by drop coating a carbon black–polymer mixture onto a custom printed circuit board (PCB) to make a sensor array (Fig. 7). Drop coating involved pipetting
Fig. 6. Components of the third generation PAD detector.
small volumes of the carbon black–polymer composite until the desired resistance was reached. The PCBs were designed in-house and fabricated by Pad2Pad (Mahwah, NJ). The PCBs were 29 mm 14 mm with 4 sets of 6 interdigitated electrodes. The electrodes were 200 lm wide, spaced 500 lm from center to center. Each sensor array weighed 1.72 g.
Fig. 4. Control circuit for controlling the pump and valve with the MoteStack.
Fig. 5. Sensor circuit for measuring voltage drop across the sensors. Resistors R1–R4 represent the carbon black–polymer composite sensors.
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Fig. 7. Printed circuit board for carbon black–polymer composite sensor arrays. Fig. 9. Control circuit printed circuit board with sensor board.
The control circuit PCB was designed in-house and fabricated by PCB (Pad2Pad, Mahwah, NJ) (Fig. 8). The headers of the sensor PCB were inserted through the stainless steel sensor box and inserted into a socket on the control circuit PCB (Fig. 9). The sensor box weighed 0.575 kg, and the control circuit PCB weighed 0.0219 kg. With this system, an air stream was drawn across the array of four carbon black–polymer composite sensors, and the change in resistance of the sensors was calculated. To test the functionality of the third generation PAD detector, 3 test insects were placed inside a 10 mL test tube. First, empty test tubes were sampled as controls to determine the initial volatiles within the tubes. Two small holes were placed in the top of the test tubes to prevent a vacuum. The insects were agitated for 20 s to stimulate volatile production, and then the sampling tubing was inserted into one of the holes in the test tube. The sampling tube was inserted until it was within 3 cm of the bottom of the test tube. First, a 25-s purge cycle drew ambient air across the sensors. Then, a solenoid valve energized and redirected the air flow from the test tubes across the sensor for a 700-ms sampling cycle. 3.2.4. Fourth generation PAD detector The fourth generation PAD Detector was further improved to be more suitable for field testing (Fig. 10). In this generation, a smaller battery and a smaller microcontroller board were used. A 12 V, 4.5
Ah lithium ion rechargeable battery (Model LBP-124500, MG Electronics, Hauppauge, NY) was used as a power supply, and the Arduino Uno R3 (Arduino LCC, Italy) was used as the microcontroller board. The dimensions of the battery were 5 cm 8 cm 2 cm, and the weight of the battery was 0.15 kg. Also, new relative humidity and temperature sensors were added to record environmental variables. The temperature sensor used was model LM35CH (National Semiconductor, Santa Clara, CA) and humidity sensor used was HIH-4000-003 (Honeywell, Morristown, NJ). In addition, a filter was added to the ambient air intake in order to reduce volatiles in the ambient air, and a sampler was added to the sample air intake in order to reduce volatile head space and reduce false negatives. With this system, an air stream was drawn across an array of four carbon black–polymer composite sensors, and the change in resistance of the sensors was calculated. First, the sampler was placed over a plant structure, such as a cotton boll. Second, a 2-s purge cycle drew ambient air across the sensors. Third, a solenoid valve energized and redirected the air flow so it drew sample volatiles across the sensors for a 2-s sampling cycle. Finally, ambient air was drawn across the sensors for a 2-s post-sample purge cycle. This procedure was repeated two additional times.
Fig. 8. Design schematics for the control board used in the third generation PAD detector. Red lines indicate traces on the top layer, and green lines indicate traces on the bottom layer. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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rolactone), poly(etylene glycol), poly(ethylene oxide) showed consistent resistance changes between repetition. These sensors also showed a return to the baseline resistance after being exposed to ambient air. 4.2. Second generation PAD detector results The second generation PAD detector was able to be completely contained within a portable enclosure by the addition of a power source and microcontroller board. Also, the new enclosure reduced the total volume of the device by 59% from the first generation PAD detector. The total weight of the second generation PAD detector was 1.24 kg. The performance of the second generation system was comparable to that of the first generation system. 4.3. Third generation PAD detector results Fig. 10. Components of the fourth generation pest and damage detector.
4. Results 4.1. First generation PAD detector results Responses from sensors made with poly(4-vinylphenol), poly(caprolactone), poly(etylene glycol), poly(ethylene oxide), poly(styrene-co-allyl alcohol), and poly(vinylpyrrolidone) showed an increase in resistance while exposed to damaged cotton leaf volatiles (Fig. 11). The blue dots represent 20-s purging cycles, and the red dots represent the resistance increase due to the damaged test leaf volatiles during the subsequent 20-s sampling cycles. Different polymers respond differently to the test volatiles. Three repetition showed that the sensors made from poly(4-vinylphenol), poly(cap-
The third generation PAD detector reduced the weight and volume of the previous generation PAD detector. The total weight of the third generation PAD detector was 1.1 kg, a reduction in weight of 14% from the second generation device. The new enclosure also reduced the total volume of the enclosure by 53% from the second generation PAD detector. The flow rate of the pump under testing conditions was measured to be 20 cm3/s. The total volume of the sampling tubing was calculated to be 1.2 cm3, and the total volume of the test tubes were 10 cm3. It was calculated that the entire volume of a test tube could be sampled in 700 ms. Composite sensors made from poly(4-vinylphenol), poly(styrene-co-allyl alcohol), poly(vinyl acetate), and poly(vinylpyrrolidone) showed an increased response when exposed to volatiles from test insects (Fig. 12). The blue dots show the tail end of a
Fig. 11. Response of first generation PAD detector sensors to damaged test leaf volatiles. (a) poly(4-vinylphenol) sensor; (b) poly(caprolactone) sensor; (c) poly(ethylene glycol) sensor; (d) poly(ethylene oxide) sensor; (e) poly(styrene-co-allyl alcohol) sensor; (f) poly(vinylpyrrolidone) sensor.
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Fig. 12. Response of third generation PAD detector sensors to test insect volatiles. (a) poly(4-vinylphenol) sensor; (b) poly(styrene-co-allyl alcohol) sensor; (c) poly(vinyl acetate) sensor; (d) poly(vinylpyrrolidone) sensor.
Fig. 13. Response of fourth generation PAD detector sensors to undamaged cotton bolls. (a) poly(styrene-co-allyl alcohol) sensor; (b) poly(vinyl acetate) sensor; (c) poly(vinylpyrrolidone) sensor.
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alcohol) and poly(vinylpyrrolidone) showed an increase in resistance when exposed to volatiles from undamaged cotton bolls (Fig. 13). However, the sensor made from poly(vinyl acetate) did not show significant changes in resistance levels between purging and sampling cycles. Most promising was the sensor made from poly(vinylpyrrolidone), which showed very consistent resistance changes. 5. Discussion The PAD detector was a small, lightweight, and inexpensive device with carbon black–polymer composite sensors which changed resistance in the presence of certain volatiles. The final version of the PAD detector measured 19 cm 10. cm 4.8 cm, weighed 0.6 kg, and cost less than $400. The PAD detector showed increases in resistance in response to certain volatiles and returned to baseline resistance when purged with ambient air. This indicated that the sensors responded to the volatiles of interest and demonstrated it was feasible to use the PAD detector to detect pest and/or plant volatiles. Different polymers respond differently to various volatiles in response time and the amount of resistance change. Future testing should include examining sensor response to a particular volatile or group of volatiles and optimizing the sensor array for that particular application. In addition, further testing to optimize total sampling time may be performed. The sensor made from poly(vinylpyrrolidone) should be tested against damaged and undamaged cotton bolls to access the potential of the PAD detector in this regard. Future development for the PAD detector may involve the incorporation of an algorithm to automate the interpretation of the sensor readings into a binary decision about the presence or absence of the pest. This control scheme shown in Fig. 14 would detect and indicate the presence of the pest or pest damage and use a green or red LED to indicate the presence or absence of these pests. 6. Conclusions Fig. 14. Pest and damage detector control scheme flowchart.
25-s purging cycle, and the red dots represent the resistance change due to the insect volatiles during the subsequent 700 ms sampling cycles. The resistance change for control samples were similar among the sensor arrays for all sensors during the sampling period. These sensors showed increases in resistance up to 5%. 4.4. Fourth generation PAD detector results The fourth and final generation PAD detector was the lightest and most portable generation of the PAD detector. The new battery reduced the weight of the power supply by 76%. The total weight of the fourth generation PAD detector was 0.6 kg, a reduction of 48% over the third generation PAD detector. The addition of red and green LEDs made the device easy to interpret. Also, the addition of a SD Card Reader (Virtuabotix, Colorado Springs, CO) allowed storage of data while testing the PAD detector algorithms. Replacing the MoteStack with the Arduino Uno R3 also reduced the volume required for the microcontroller board by 58%. The fourth generation PAD detector was designed to sample volatiles around plant structures, such as cotton bolls. Three composite sensors made from poly(styrene-co-allyl alcohol), poly(vinyl acetate), and poly(vinylpyrrolidone) were tested for undamaged cotton bolls. Composite sensors made from poly(styrene-co-allyl
A small, lightweight, and inexpensive device was developed for detecting the presence of pest or plant volatiles. Because these composites were shown to increase in resistance when exposed to volatiles and decrease in resistance when exposed to ambient air, the PAD detector can be an effective tool in measuring sensor response to volatiles from pests and/or plants. More research should be conducted to automate the interpretation of the sensor readings into a binary decision about the present or absence of pest. Future testing may include examining sensor response to a particular volatile or group of volatiles and optimizing the sensor array for that particular application. In addition, future research should include determining if there are other volatiles to which the sensor array is sensitive that may result in a false positive. Acknowledgements The author would like to acknowledge Dr. Ya-ping Sun for the use of his lab, Dr. Monica Veca for her help fabricating the sensors, and Dr. Jason Hallstrom for graciously providing and programming the MoteStack. I would also like to acknowledge the support of Cotton Incorporated and the South Carolina Cotton Board. This material is based upon work supported by NIFA/USDA, under project number SC1700289 and SC-1700442. Technical Contribution No. 6182 of the Clemson University Experiment Station.
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References Degenhardt, D.C., Greene, J.K., Khalilian, A., 2012. Temporal dynamics and electronic nose detection of stink bug-induced volatile emissions from cotton bolls. Psyche 236762, 1–9. Henderson, W.G., Khalilian, A., Turnipseed, S., Han, Y.J., 2006. Innovative technology for detecting stink bug feeding in cotton. In: Proceedings of the Beltwide Cotton Conferences, January 2006, San Antonio, TX, National Cotton Council of America, Memphis, TN. pp. 487–490.
Henderson, W.G., Khalilian, A., Han, Y.J., Greene, J.K., Degenhardt, D.C., 2010. Detecting stink bugs/damage in cotton utilizing a portable electronic nose. Comput. Electron. Agr. 70, 157–162. Lonergan, M.C., Severin, E.J., Doleman, B.J., Beaber, S.A., Grubbs, R.H., Lewis, N.S., 1996. Array-based vapor sensing using chemically sensitive, carbon black polymer resistors. Chem. Mater. 8, 2298–2312. Suh, C.P., Ding, N., Lan, Y., 2011. Using an electronic nose to rapidly assess grandlure content in boll weevil pheromone lures. J. Bionic Eng. 8, 449–454.
Contents lists available at ScienceDirect
Computers and Electronics in Agriculture journal homepage: www.elsevier.com/locate/compag
Development of a portable electronic nose for detection of pests and plant damage B.D. Lampson a, Y.J. Han a,⇑, A. Khalilian b, J.K. Greene b, D.C. Degenhardt b, J.O. Hallstrom c a
School of Agricultural, Forest, and Environmental Sciences, Clemson University, 237 McAdams Hall, Clemson, SC 29634, USA School of Agricultural, Forest, and Environmental Sciences, Edisto Research and Education Center, 64 Research Drive, Blackville, SC 29817, USA c School of Computing, Clemson University, 212 McAdams Hall, Clemson, SC 29634, USA b
a r t i c l e
i n f o
Article history: Received 24 September 2013 Received in revised form 2 June 2014 Accepted 6 July 2014
Keywords: Volatile Electronic nose Pest control Portable sensors Carbon black–polymer composites Integrated pest management
a b s t r a c t Agricultural pests are responsible for millions of dollars of crop losses and control costs every year. To reduce these losses and minimize control costs, new methods to detect pests and/or pest damage must be investigated in order to optimize control measures. One such method evaluated in this study was to detect the chemicals released by pests or pest-damaged products. A portable device was developed to draw volatiles from pests or pest-damaged products over carbon black–polymer composite sensors and measure the change in resistance for each sensor. The device successfully sampled pest and plant volatiles and these volatiles were detected using carbon black–polymer composite sensors. These results indicated an electronic nose is a feasible approach to detect pests and/or pest damage. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction Integrated pest management is a practiced concept that involves a variety of chemical, biological, cultural, and physical pest control techniques designed to reduce pest status to tolerable levels, maximize profitability, and preserve the environment. Some of these management techniques involve proactive, preventative measures, but others are reactive strategies, such as chemical control, where fields are treated before substantial damage has occurred and only when a pest density and/or damage threshold has been met or exceeded. These techniques involve monitoring pest density and/or damage, and sampling methods are needed to accurately estimate levels of pest density/damage. One possible method of sampling involves detecting chemicals produced by pests or pest-damaged products. Carbon black–polymer composites have been used to detect natural and synthetic insect volatiles as well as damaged agricultural products, and therefore, several studies have previously worked toward the goal
Abbreviation: PAD, Pest and damage detector. ⇑ Corresponding author. Tel.: +1 864 656 4077; fax: +1 864 653 0338. E-mail addresses: [email protected] (B.D. Lampson), [email protected] (Y.J. Han), [email protected] (A. Khalilian), [email protected] (J.K. Greene), [email protected] (D.C. Degenhardt), [email protected] (J.O. Hallstrom). http://dx.doi.org/10.1016/j.compag.2014.07.002 0168-1699/Ó 2014 Elsevier B.V. All rights reserved.
of developing of using an electronic nose for pest detection (Henderson et al., 2010; Suh et al., 2011; Degenhardt et al., 2012). Carbon black–polymer composites have been shown to increase resistance in the presence of specific volatiles (Lonergan et al., 1996). Portable electronic noses that employ various types of carbon black–polymer composites and pattern recognition software are commercially available, such as the hand-held Cyranose 320 (Smith Detection, Pasadena, CA). The Cyranose 320 has been shown to detect natural and synthetic insect volatiles as well as damaged agricultural products (Henderson et al. 2006; Suh et al., 2011; Degenhardt et al., 2012). However, this electronic nose is expensive (>$10,000), requires trained personnel for analysis, lacks real-time software for ‘‘on-the-go’’ measurements of volatiles, and is not designed specifically for the purpose of detecting pests or the damage they cause.
2. Objectives The overall objective of this research was to develop an electronic nose using carbon black–polymer composite sensors for detecting pests and/or pest damage. This pest and damage (PAD) detector would be small, lightweight, inexpensive, easy to interpret, and able to provide rapid results for in-field decision making. The specific objectives of this paper are to document the
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development process and to report the current status of the latest generation of the detector. 3. Methods and materials 3.1. Fabrication of carbon black–polymer composites Composite solutions were made using 20 mg of suspended carbon black (BP2000, Cabot Co., Billerica, MA) and 80 mg of polymer in 10 ml of solvent. Polymers used were poly(vinyl butyral), poly(4-vinylphenol), poly(bisphenol A carbonate), poly(styreneco-allyl alcohol), poly(styrene-co-maleic anhydride), poly(vinyl acetate), poly(vinylidene chloride-co-acrylonitrile-co-methyl methacrylate), poly(vinylpyrrolidone), poly(ethylene glycol), and poly(ethylene oxide). These polymers were chosen based on their use in previous research (Lonergan et al., 1996). Tetrahydrofuran was used as the solvent for all sensors except benzene was used for the poly(ethylene oxide) sensor. All polymers and solvents were obtained from Sigma–Adrich (St. Louis, MO). Solutions were sonicated for one minute prior to coating the sensor boards to ensure carbon black suspension and then immediately coated and allowed to dry for an hour. This process was repeated until resistance was between 100 kX and 1 MX. 3.2. Development of PAD detector 3.2.1. First generation PAD detector Carbon black–polymer composite sensors were constructed by dip coating a universal electrode board (surfboard 6012, Capital Advanced Technologies, Carol Stream, IL) into a carbon black–polymer mixture. Dip coating involves submerging the electrode board into the carbon black–polymer mixture several times. Before dip coating, the electrode board was separated into 6 separate sensors with two electrodes, spaced 0.254 cm from center to center. To develop the PAD detector, the components were assembled into a fiberglass NEMA enclosure (Model NF-6610, Bud Industries Inc., Willoughby, IL) (Fig. 1). This enclosure had external dimensions of 19.7 cm 19.7 cm 12.2 cm and a weight of 2 kg. The microdiaphragm pump (Model NMS020L, KNF Neuberger Inc., Trenton, NJ) was connected by 0.318 cm OD, 0.159 cm ID polyethylene tubing to a polyethylene sensor box. This tubing also connected the pump to the subminiature solenoid valve (Model GH3115-C203, Gems Sensors & Controls, Plainville, CT). The pump had a weight of 0.029 kg, and the solenoid valve had a weight of 0.0718 kg. A variable power supply (Mini-Lab 200, Knight Electronics, Inc., Dallas, TX) was used to supply various voltages, and data acquisition hardware (miniLAB 1008, Measurement Computing Corporation, Norton, MA) was used to control the pump and valve
Fig. 1. Inside the first generation PAD detector.
and to measure the voltage drops across the sensors as well as the valve status (Fig. 2). The sensors were inserted into a breadboard in the sensor box. With this system, an air stream was drawn across an array of four carbon black–polymer composite sensors. First, a 20-s purge cycle drew ambient air across the sensors. Then, a solenoid valve energized and redirected the air flow so it drew sample air across the sensors for a 20-s sampling cycle. Then, ambient air was drawn across the sensors for a 20-s post-sample purge cycle. These cycles were repeated an additional two times. Voltage drops across the sensors were recorded onto a laptop using data acquisition hardware, and these voltage drops were converted into resistances. The device was tested using volatiles from a damaged leaf. First, a leaf was extracted from a test plant. Then, the leaf was damaged by perforating it with a hole punch twenty times. The leaf was then placed in a nylon bag (Oven bags, Reynolds, Richmond, VA), a small hole was cut into the bag, and the sampling tube was inserted into the hole. Volatiles were then extracted by the PAD detector. 3.2.2. Second generation PAD detector In order to make the device more portable, improvements were made to the first generation PAD detector, including a smaller enclosure, an enclosed power source, and an enclosed microcontroller board. This enclosure (1050 Micro Case, Pelican Products, Inc., Torrance, CA) had exterior dimensions of 19 cm 12.8 cm 7.9 cm and a weight of 0.38 kg. The power source was a 12 V, 1.3 Ah AGM battery (WKA12–1.3F, Werker), and it had a weight of 0.621 kg and exterior dimensions of 9.7 cm 5.1 cm 4.3 cm, excluding leads. The microcontroller board was the MoteStack (Clemson University, Clemson, SC). The MoteStack consisted of 3 motes: the MoteStack I/O board (v2.4), the MoteStack storage board (v2.2), and the MoteStack base (v2.5). When combined, these motes had exterior dimensions of 5.6 cm 5.6 cm 4.6 cm and a weight of 0.076 kg. A temperature sensor (DS18S20, Dallas Semiconductor, San Jose, CA) was added in the second generation PAD detector. The control circuit was responsible for the digital outputs that controlled the pump and solenoid valve, and the sensor circuit was responsible for the analog inputs from the composite sensors. The control circuit and the sensor circuit were built using small breadboards (Fig. 3). The control circuit (Fig. 4) was constructed on the breadboard and secured with thermoplastic adhesive. In this circuit, the 12 V was supplied by the battery. The MoteStack was responsible for providing the digital output for controlling the pump and valve. The sensor circuit (Fig. 5) was constructed on a second breadboard and also secured with thermoplastic adhesive. In the sensor circuit, the MoteStack supplied the 5 V and recorded the voltage drop across the carbon black–polymer composite sensors R1–R4. In addition to the MoteStack, a portable datalogger (midi logger GL220, Graphtec Corporation, Yokohama, Japan) measured these voltage drops across the composite sensors via an 8-pin DIN connector. The datalogger was used during the development phase in order to instantly visualize the data. A voltage follower circuit was constructed using an LM324 operational amplifier to act as a high impedance bridge between the sensor circuit and the datalogger. The control circuit breadboard weighed 0.053 kg, and the sensor breadboard weighed 0.013 kg. 3.2.3. Third generation PAD detector To develop the third generation PAD detector, a number of features were added, including a smaller enclosure, smaller control circuit, and smaller sensor circuit. The components were assembled into an ABS enclosure (Model 100-42-NO-E, Box Enclosures and Assembly Services, Lake Bluff, IL) (Fig. 6). This enclosure had
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Fig. 2. Functional schematic of the first generation PAD detector.
Fig. 3. Inside the second generation PAD detector.
external dimensions of 19 cm 10. cm 4.8 cm and a weight of 0.2 kg. The new sensor boards were made by drop coating a carbon black–polymer mixture onto a custom printed circuit board (PCB) to make a sensor array (Fig. 7). Drop coating involved pipetting
Fig. 6. Components of the third generation PAD detector.
small volumes of the carbon black–polymer composite until the desired resistance was reached. The PCBs were designed in-house and fabricated by Pad2Pad (Mahwah, NJ). The PCBs were 29 mm 14 mm with 4 sets of 6 interdigitated electrodes. The electrodes were 200 lm wide, spaced 500 lm from center to center. Each sensor array weighed 1.72 g.
Fig. 4. Control circuit for controlling the pump and valve with the MoteStack.
Fig. 5. Sensor circuit for measuring voltage drop across the sensors. Resistors R1–R4 represent the carbon black–polymer composite sensors.
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Fig. 7. Printed circuit board for carbon black–polymer composite sensor arrays. Fig. 9. Control circuit printed circuit board with sensor board.
The control circuit PCB was designed in-house and fabricated by PCB (Pad2Pad, Mahwah, NJ) (Fig. 8). The headers of the sensor PCB were inserted through the stainless steel sensor box and inserted into a socket on the control circuit PCB (Fig. 9). The sensor box weighed 0.575 kg, and the control circuit PCB weighed 0.0219 kg. With this system, an air stream was drawn across the array of four carbon black–polymer composite sensors, and the change in resistance of the sensors was calculated. To test the functionality of the third generation PAD detector, 3 test insects were placed inside a 10 mL test tube. First, empty test tubes were sampled as controls to determine the initial volatiles within the tubes. Two small holes were placed in the top of the test tubes to prevent a vacuum. The insects were agitated for 20 s to stimulate volatile production, and then the sampling tubing was inserted into one of the holes in the test tube. The sampling tube was inserted until it was within 3 cm of the bottom of the test tube. First, a 25-s purge cycle drew ambient air across the sensors. Then, a solenoid valve energized and redirected the air flow from the test tubes across the sensor for a 700-ms sampling cycle. 3.2.4. Fourth generation PAD detector The fourth generation PAD Detector was further improved to be more suitable for field testing (Fig. 10). In this generation, a smaller battery and a smaller microcontroller board were used. A 12 V, 4.5
Ah lithium ion rechargeable battery (Model LBP-124500, MG Electronics, Hauppauge, NY) was used as a power supply, and the Arduino Uno R3 (Arduino LCC, Italy) was used as the microcontroller board. The dimensions of the battery were 5 cm 8 cm 2 cm, and the weight of the battery was 0.15 kg. Also, new relative humidity and temperature sensors were added to record environmental variables. The temperature sensor used was model LM35CH (National Semiconductor, Santa Clara, CA) and humidity sensor used was HIH-4000-003 (Honeywell, Morristown, NJ). In addition, a filter was added to the ambient air intake in order to reduce volatiles in the ambient air, and a sampler was added to the sample air intake in order to reduce volatile head space and reduce false negatives. With this system, an air stream was drawn across an array of four carbon black–polymer composite sensors, and the change in resistance of the sensors was calculated. First, the sampler was placed over a plant structure, such as a cotton boll. Second, a 2-s purge cycle drew ambient air across the sensors. Third, a solenoid valve energized and redirected the air flow so it drew sample volatiles across the sensors for a 2-s sampling cycle. Finally, ambient air was drawn across the sensors for a 2-s post-sample purge cycle. This procedure was repeated two additional times.
Fig. 8. Design schematics for the control board used in the third generation PAD detector. Red lines indicate traces on the top layer, and green lines indicate traces on the bottom layer. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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rolactone), poly(etylene glycol), poly(ethylene oxide) showed consistent resistance changes between repetition. These sensors also showed a return to the baseline resistance after being exposed to ambient air. 4.2. Second generation PAD detector results The second generation PAD detector was able to be completely contained within a portable enclosure by the addition of a power source and microcontroller board. Also, the new enclosure reduced the total volume of the device by 59% from the first generation PAD detector. The total weight of the second generation PAD detector was 1.24 kg. The performance of the second generation system was comparable to that of the first generation system. 4.3. Third generation PAD detector results Fig. 10. Components of the fourth generation pest and damage detector.
4. Results 4.1. First generation PAD detector results Responses from sensors made with poly(4-vinylphenol), poly(caprolactone), poly(etylene glycol), poly(ethylene oxide), poly(styrene-co-allyl alcohol), and poly(vinylpyrrolidone) showed an increase in resistance while exposed to damaged cotton leaf volatiles (Fig. 11). The blue dots represent 20-s purging cycles, and the red dots represent the resistance increase due to the damaged test leaf volatiles during the subsequent 20-s sampling cycles. Different polymers respond differently to the test volatiles. Three repetition showed that the sensors made from poly(4-vinylphenol), poly(cap-
The third generation PAD detector reduced the weight and volume of the previous generation PAD detector. The total weight of the third generation PAD detector was 1.1 kg, a reduction in weight of 14% from the second generation device. The new enclosure also reduced the total volume of the enclosure by 53% from the second generation PAD detector. The flow rate of the pump under testing conditions was measured to be 20 cm3/s. The total volume of the sampling tubing was calculated to be 1.2 cm3, and the total volume of the test tubes were 10 cm3. It was calculated that the entire volume of a test tube could be sampled in 700 ms. Composite sensors made from poly(4-vinylphenol), poly(styrene-co-allyl alcohol), poly(vinyl acetate), and poly(vinylpyrrolidone) showed an increased response when exposed to volatiles from test insects (Fig. 12). The blue dots show the tail end of a
Fig. 11. Response of first generation PAD detector sensors to damaged test leaf volatiles. (a) poly(4-vinylphenol) sensor; (b) poly(caprolactone) sensor; (c) poly(ethylene glycol) sensor; (d) poly(ethylene oxide) sensor; (e) poly(styrene-co-allyl alcohol) sensor; (f) poly(vinylpyrrolidone) sensor.
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Fig. 12. Response of third generation PAD detector sensors to test insect volatiles. (a) poly(4-vinylphenol) sensor; (b) poly(styrene-co-allyl alcohol) sensor; (c) poly(vinyl acetate) sensor; (d) poly(vinylpyrrolidone) sensor.
Fig. 13. Response of fourth generation PAD detector sensors to undamaged cotton bolls. (a) poly(styrene-co-allyl alcohol) sensor; (b) poly(vinyl acetate) sensor; (c) poly(vinylpyrrolidone) sensor.
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alcohol) and poly(vinylpyrrolidone) showed an increase in resistance when exposed to volatiles from undamaged cotton bolls (Fig. 13). However, the sensor made from poly(vinyl acetate) did not show significant changes in resistance levels between purging and sampling cycles. Most promising was the sensor made from poly(vinylpyrrolidone), which showed very consistent resistance changes. 5. Discussion The PAD detector was a small, lightweight, and inexpensive device with carbon black–polymer composite sensors which changed resistance in the presence of certain volatiles. The final version of the PAD detector measured 19 cm 10. cm 4.8 cm, weighed 0.6 kg, and cost less than $400. The PAD detector showed increases in resistance in response to certain volatiles and returned to baseline resistance when purged with ambient air. This indicated that the sensors responded to the volatiles of interest and demonstrated it was feasible to use the PAD detector to detect pest and/or plant volatiles. Different polymers respond differently to various volatiles in response time and the amount of resistance change. Future testing should include examining sensor response to a particular volatile or group of volatiles and optimizing the sensor array for that particular application. In addition, further testing to optimize total sampling time may be performed. The sensor made from poly(vinylpyrrolidone) should be tested against damaged and undamaged cotton bolls to access the potential of the PAD detector in this regard. Future development for the PAD detector may involve the incorporation of an algorithm to automate the interpretation of the sensor readings into a binary decision about the presence or absence of the pest. This control scheme shown in Fig. 14 would detect and indicate the presence of the pest or pest damage and use a green or red LED to indicate the presence or absence of these pests. 6. Conclusions Fig. 14. Pest and damage detector control scheme flowchart.
25-s purging cycle, and the red dots represent the resistance change due to the insect volatiles during the subsequent 700 ms sampling cycles. The resistance change for control samples were similar among the sensor arrays for all sensors during the sampling period. These sensors showed increases in resistance up to 5%. 4.4. Fourth generation PAD detector results The fourth and final generation PAD detector was the lightest and most portable generation of the PAD detector. The new battery reduced the weight of the power supply by 76%. The total weight of the fourth generation PAD detector was 0.6 kg, a reduction of 48% over the third generation PAD detector. The addition of red and green LEDs made the device easy to interpret. Also, the addition of a SD Card Reader (Virtuabotix, Colorado Springs, CO) allowed storage of data while testing the PAD detector algorithms. Replacing the MoteStack with the Arduino Uno R3 also reduced the volume required for the microcontroller board by 58%. The fourth generation PAD detector was designed to sample volatiles around plant structures, such as cotton bolls. Three composite sensors made from poly(styrene-co-allyl alcohol), poly(vinyl acetate), and poly(vinylpyrrolidone) were tested for undamaged cotton bolls. Composite sensors made from poly(styrene-co-allyl
A small, lightweight, and inexpensive device was developed for detecting the presence of pest or plant volatiles. Because these composites were shown to increase in resistance when exposed to volatiles and decrease in resistance when exposed to ambient air, the PAD detector can be an effective tool in measuring sensor response to volatiles from pests and/or plants. More research should be conducted to automate the interpretation of the sensor readings into a binary decision about the present or absence of pest. Future testing may include examining sensor response to a particular volatile or group of volatiles and optimizing the sensor array for that particular application. In addition, future research should include determining if there are other volatiles to which the sensor array is sensitive that may result in a false positive. Acknowledgements The author would like to acknowledge Dr. Ya-ping Sun for the use of his lab, Dr. Monica Veca for her help fabricating the sensors, and Dr. Jason Hallstrom for graciously providing and programming the MoteStack. I would also like to acknowledge the support of Cotton Incorporated and the South Carolina Cotton Board. This material is based upon work supported by NIFA/USDA, under project number SC1700289 and SC-1700442. Technical Contribution No. 6182 of the Clemson University Experiment Station.
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