A Chemiresistor Sensor Array for Insect Infestation Detection

Abstract

Plants emit volatile organic compounds as a defensive mechanism to protect themselves from insects and pathogens. These volatile organic chemicals, also known as phytochemicals, are given off during the early stages of insect infestation and may be detected using a chemical sensor array. The chemiresistor sensor array, investigated in this study, consists of a silicon substrate, electroactive polymer based active layer and microelectronically fabricated interdigitated electrodes. The sensor array is inexpensive, easy to fabricate, and could be used for onsite detection of insect infestation. Compared to traditional methods of detecting insect infestation such as leaf inspection and insect traps, this method is quick, inexpensive and would not require trained personal. The sensor array investigated in this dissertation uses three types of polymers as active sensing layers; polythiophene, carbon/polymer and polyaniline. The polymer coatings were deposited onto the sensor platforms via drop casting and spin coating methods. The sensor array was exposed and found to be sensitive to a variety of phytochemicals including γ-terpinene, α-pinene, p-cymene, farnesene, limonene, and cis-hexenyl acetate. The sensor array created a unique fingerprint pattern for each of the different volatile gases. These fingerprints were further analyzed using principle component analysis. To optimize the uniqueness of the fingerprint, sensors that operated with different mechanisms were used. Incorporating sensors with multiple mechanisms into a single array system can be difficult, especially if different film responses are measured. Therefore, the same film response, relative resistance, was measured as a function of exposure time to the specific volatile gases. Polythiophene sensors in this study had a sensor detection mechanism that involved physical interactions between the volatile organic vapor and the sensor. The polyaniline sensor had a sensor mechanism which was redox reactions based. The polymer/carbon composite sensors, which consisted of a polymer matrix and carbon particles, operated through a mechanism involving the percolation point.