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A Chemiresistor Sensor Array for Insect Infestation Detection By A Chemiresistor Sensor Array for Insect Infestation Detection by Kanchana Anuruddika Kumari Weerakoon A dissertation submitted to the Graduate Faculty of Auburn University in partial fulfillment of the requirements for the Degree of Doctor of Philosophy Auburn, Alabama May 7th , 2012 Key words: Polythiophene sensor Polyaniline sensor, Polymer/carbon composite sensor, Sensor array, insect infestation, Thin film sensor array Copyright 2012 by Kanchana Anuruddika Kumari Weerakoon Approved by Bryan A. Chin, Chair, Professor of Materials Engineering Minseo Park, Associate Professor of Physics Dong Joo (Daniel) Kim, Associate Professor of Materials Engineering Zhong Yang Cheng, Associate Professor of Materials Engineering 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 ii 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. iii Acknowledgments I would like to thank my advisor Dr. Bryan A. Chin for his guidance in doing this research, helping me to develop and complete my dissertation and funding my education at Auburn University. I would also like to thank Dr. Dong-Joo Kim, Dr. Zhong-Yang Cheng and Dr. Minseo Park for agreeing to be a part of my dissertation committee. I would also like to thank Dr. Maria Auad for agreeing to be my university reader. I would like to thank my lab mates for all their support. I would like to thank past members of our group Dr. Helen Yang for helping me start this research work and guiding me in the right direction. I would also like to thank Dr. John Shu for all his help with test cell design, data acquisition setup and testing methodology. I would like to thank Yating Chai for all her help. I would also like to thank Shin Horikawa for all the help and useful discussions. I would also like to thank Tom Carrington in the chemistry department for helping me with Gas Chromatography and Dr Maria Auad for helping me with Atomic Force Microscopy. Last but not least I would like to thank my family. My husband Pathum Mendis for helping me and being there for me always. My daughter Saneli Mendis for being a good baby specially while writing my dissertation. My Parents and Parents in laws Menik Weerakoon, Gamini Weerakoon, Premila Mendis and Pemsiri Mendis for all their help, love and encouragement. I would also like to thank my brothers, brother in law and sisters in laws for all their love and support. iv Table of Contents Abstract ......................................................................................................................................... ii Acknowledgments........................................................................................................................ iv List of Tables ................................................................................................................................ x List of Figures .............................................................................................................................. xi 1. Introduction ............................................................................................................................ 1 1.1. Back Ground ............................................................................................................. 1 1.1.1. Insect Infestation and Global Economy ............................................................... 1 1.1.2. Current Methods of Detection ............................................................................... 1 1.1.2.1. Conventinal Methods .......................................................................................... 4 1.1.2.1.1. Regular Inspection ........................................................................................... 4 1.1.2.1.2. Traps ................................................................................................................ 4 1.1.2.1.3. Barriers ............................................................................................................. 5 1.1.2.1.4. Physical Disturbances ...................................................................................... 6 1.1.2.2. Modern Methods ................................................................................................. 6 1.1.2.2.1. Irradiation ......................................................................................................... 6 1.1.2.2.2. Temperature Control ........................................................................................ 7 1.1.2.2.3. Gas chromatography Analysis ......................................................................... 7 1.1.2.2.4. Acoustic Wave Sensor Control ........................................................................ 8 1.1.3. A Plant Defense Mechanism: Phytochemical Emmision ...................................... 8 v 1.1.4. Using Defense Mechanisms of Plants to Detect Insect Infestation ..................... 17 1.2 Sensors for Volatile Organic Compound Detection ................................................ 19 1.2.1. Metal Oxide Sensors ............................................................................................ 19 1.2.2. Acoustic Gas Sensors ........................................................................................... 25 1.2.3. Optical Sensors .................................................................................................... 30 1.2.4. Conductive Electroactive Polymer Sensors ......................................................... 32 1.2.4.1. Intrinsically Conductive Polymer Sensors ........................................................ 32 1.2.4.2. Polymer/Carbon Composite for Sensing Volatiles ........................................... 45 1.3. Research Objectives ................................................................................................ 51 1.4. References ............................................................................................................... 53 2. Sensor Design and Gas Exposure Test Setup ........................................................................ 56 2.1 Sensor Substrate ....................................................................................................... 56 2.2 Electrode Pattern ...................................................................................................... 56 2.3. Microfabrication Procedure ................................................................................................ 57 2.3.1. Wafer Cleaning Procedure ............................................................................................... 57 2.3.2. Thermal Oxidation ........................................................................................................... 61 2.3.3. Photoresist Deposition ..................................................................................................... 61 2.3.4. Photoresist Exposure and Pattern Development .............................................................. 64 2.3.5. Electrode Deposition ........................................................................................................ 66 2.3.6. Lift off Procedure ............................................................................................................. 66 2.3.7. Wafer Dicing Process ...................................................................................................... 68 2.4. Polymer Film Deposition .................................................................................................... 68 2.4.1.
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