Detecting Insect Infestation: A Novel Application of Carbon/Polyethylene-co-vinyl Acetate Sensors
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Detecting Insect Infestation: A Novel Application of Carbon/Polyethylene-co-vinyl acetate Sensors Kanchana A. Weerakoon1 and Bryan A. Chin1 1 Materiels Engineering Department, Auburn University, Auburn, AL 36849, U.S.A. ABSTRACT Plants, when attacked by herbivores emit plant volatile compounds as a defensive mechanism to protect themselves from herbivores and parasites. Secreting these volatiles is not only toxic towards these insects but also aids enemies of the herbivores to recognize infested plants to locate their prey. A low mass fraction carbon black/polyethylene-co-vinylacetate composite sensor was designed and fabricated to detect insect infestation. This sensor was cost efficient, easy to fabricate and was highly stable in air. When an organic vapor is present, the carbon/polymer active layer swells creating a discontinuity in the conducting pathway between adjacent carbon particles, increasing the resistance of the film. When the analyte is no longer present, the polymer will return to its original state, showing a decrease in resistance. A variety of carbon/black polymer sensors with varying chemical characteristics could be created by using different polymer matrices. Polyethylene-co-vinyl acetate was chosen as the best polymer for this particular application based on its swelling ability in the presence of plant volatiles compared to other polymers. When the carbon concentration of the active layer was low enough to be near the percolation threshold, the sensor can be used as a “chemical switch”. The resistance of the sensor increased significantly mimicking a “switch off” response when exposed to the analyte vapor. When the analyte vapor was no longer present the sensor returned back to its original condition, showing a “switch on” response. The percolation point was obtained when the carbon concentration of the carbon/polymer composite was kept at 1.25 wt%. The sensor was tested and found to be sensitive to a variety of volatile organic compounds emitted during insect infestation including γ-terpinene, α-pinene, p-cymene, farnesene, and limonene and cis-hexenyl acetate. INTRODUCTION Insect infestation results in huge losses in the agricultural industry in the United States. Much of this loss is a direct result of inefficient and time consuming conventional methods that are being used to detect insect infestation including leaf analysis, pheromone traps, acoustic devices such as the Finger Printing Insect Detector and gas chromatography. On the other hand, a small sensor is ideal for field applications because it is suitable to be attached to plant bodies which could be used to check the presence of insect infestation at early stages. When attacked by herbivores, plants emit volatile compounds known as phytochemicals as a defensive mechanism to protect themselves from herbivores and parasites, which are not only toxic towards these insects but also aids enemies of the herbivores to recognize infested plants to locate their prey [13]. Corn, cotton, pine and Brussels sprouts when attacked by
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