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Chemically Diverse Sensor Arrays Based on Conducting Polymers in Sensing Characterization and Application

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Chemically Diverse Sensor Arrays Based on Conducting Polymers in Sensing Characterization and Application Chemically Diverse Sensor Arrays Based on Conducting Polymers in Sensing Characterization and Application by Akin Augustine Iyogun A thesis submitted to the Faculty of Graduate Studies of the University of Manitoba in partial fulfillment of the requirements of the degree of Doctor of Philosophy Department of Chemistry University of Manitoba Winnipeg Copyright © 2016 by Akin Augustine Iyogun Abstract There has been a growing need to develop an artificial mimic of mammalian olfaction in a manner analogous to the charged coupled device (CCD) chip in machine vision. This need is motivated by the existence of devices to mimic all five senses except the sense of smell and taste. One major challenge is the limited number of chemically different sensing surfaces that are be useful as multi-sensor array comparable with olfaction in its capacity to engage ≈1000 unique olfactory receptors to discriminate odorants. To be technically viable, such a device will involve the development and incorporation of several chemically distinct sensors to perform similar functions as its natural counterpart. A typical array of artificial sensors would be composed of easily tunable, chemically diverse sensing elements. An approach to create such a multi-sensor array was explored in this research involving electrosynthesis of homopolymers and copolymers sensors. The resulting array consists of 81 (eighty-one) chemically unique sensors, which were used to discriminate analytes such as homologues of alcohols and fuels. Electro-copolymerization offers unique means of creating new sensor materials different from their homopolymer counterparts, where conducting and non-conducting components of the eventual sensors offered complementary means to improve the number of chemically different sensors generated from them and also impact their electrical characteristics. Modification of both homopolymers and copolymer sensors was performed through growth of sensors at varied oxidation (growth) potential, or holding individual ‘as-grown’ sensor films to different redox potential after growth. These modifications altered the physiochemical properties of resulting films such as the electrical conductivity and film thickness, which influence analyte sorption II characteristics and performance behavior. Therefore, chemically (compositionally) different sensor films were generated. Additionally, changing dopant-type during electrodeposition served to further modify resulting sensors. This simple fabrication method was designed to construct a large array of inexpensive sensors, electrochemically deposited to discriminate and classify different analytes. While variable signature resistance responses were generated from sensors interacting with analytes, differential response patterns were created to discriminate amongst them. The task of identifying unique patterns for analytes, the classification of each analyte as A or B, and the uniqueness of each sensor was investigated to ascertain that the chemical variation of these sensors occurred. Pattern recognition algorithms involving techniques such as principal component analysis and linear discriminant analysis were relevant to relate the measured resistance responses in the form of data clusters or numerical separation of clusters to differentiate patterns as a function of sensor-analyte interactions. This created the needed discrimination, as the resolving power of the multi-sensor arrays was investigated with linear discriminant analysis as a function of analytes or sensors. A decision boundary provided through this analysis shows the uniqueness of each chemically diverse sensor in the array. An ensemble of all homopolymer, copolymer and conducting polymer composites created in this research resulted in broadly responsive, partially selective arrays which progressively tend towards realizing the number of olfactory receptors (450 unique receptors in humans) utilized by the mammalian olfactory system in performing odor discriminatory function. To determine the efficacy of the modifications applied to vary the sensing films, spectroscopic methods were used III to monitor the various changes in their chemical composition. A real world application of these arrays as ‘fuel sensor’ has been investigated and is included in this thesis. Note: Some details of Chapters 2, 3, 4 and 5 are based on the publications: Iyogun, A. A.; Kumar, M. R.; Freund, M. S. Sens. Actuators, B 2015, 215, 510-517. Iyogun, A. A.; Buchanan, D. A.; Freund, M. S. RSC. Adv., 2015, 6(39), 32549-32559. Reproduced with written permission from Elseivier pulisher, 2015 and 2016 respectively. IV Acknowledgement I give God all the glory for the wisdom and strength through the difficult times in the course of this scientific adventure. My deepest gratitude and thanks go to my Ph. D. advisor, Dr. M. S. Freund for giving me the opportunity to study and work under his instructions. His timely support and willingness to help, even at the shortest notice is well appreciated. I sincerely thank my co-advisor, Dr. G. Tomy for his moral support and advice. Thanks also to the other members of my committee, Dr. D. A. Buchanan, Dr. Helen Perreault and Dr. Schreckenbach, for your accessibility and guidance. I also appreciate the efforts that will be committed by the external examiner who will eventually review this thesis. Many thanks go to members of the Freund group; Kelvin McEleney, Michael McDonald, Shaun Ryman, Patrick Giesbrietcht, Jared Bruce, Onkar Sign Kang, Sophia Schreckenbach, Ehsan Tahmasebian and Jenifer Low McEleney, you are the best. I am also indebted to Ramesh Kumar, who was helpful in getting me started on the project. To Denise McInnes, your kindness is appreciated. Thank you to all the academic and non-academic staff of the Chemistry Department, the University of Manitoba. To my friend Emmanuel Ariyo, the times we spent during lunch hours were very useful in bringing calm when the research became very tense. Thanks also go to Ifeoluwa Idowu. My heartfelt thanks go to my wife, Ololade, and children, Samuel and Deborah Iyogun. Your support was incredible throughout the years spent in this study. I greatly appreciate my parents for the tremendous work of raising me to be who I am. V Dedicated to Lola (wife), Sam (son) and Debby (daughter). VI Table of Contents Title page --------------------------------------------------------------------------------------------- I Abstract ---------------------------------------------------------------------------------------------- II Acknowledgement --------------------------------------------------------------------------------- V Dedication ----------------------------------------------------------------------------------------- VI Table of Contents -------------------------------------------------------------------------------- VII List of Figures -------------------------------------------------------------------------------------- X List of Tables ------------------------------------------------------------------------------------ XVI List of Schemes -------------------------------------------------------------------------------- XVII List of Abbreviations ------------------------------------------------------------------------- XVIII Chapter 1: Introduction ------------------------------------------------------------------------ 1 1.1 Overview of the Mammalian Versus Artificial Olfaction ------------------------------- 1 1.2 Olfaction ---------------------------------------------------------------------------------------- 3 1.3 Chemical Diversity and Sensor Arrays ----------------------------------------------------- 7 1.4 Conducting polymers ------------------------------------------------------------------------ 15 1.4.1 Doping of Conducting Polymer -------------------------------------------------18 1.4.2 Classification of Conducting Polymers ---------------------------------------- 23 1.4.2.1 Homopolymers ------------------------------------------------------------------ 23 1.4.2.1.1 Polypyrrole -------------------------------------------------------------------- 24 1.4.2.1.2 Polyaniline --------------------------------------------------------------------- 25 1.4.2.2 Copolymers ---------------------------------------------------------------------- 26 1.4.3 Synthesis of Conducting Polymer Sensor Films ------------------------------ 28 1.4.3.1 Chemical Synthesis ------------------------------------------------------------- 29 1.4.3.2 Electrochemical Synthesis ----------------------------------------------------- 30 1.5 Interaction Between Conducting Polymers Sensors and Analytes --------------------- 35 1.5.1 Chemiresistor Array for Analytes Detection -------------------------------------------- 38 1.6 Instrumentation -------------------------------------------------------------------------------- 40 1.6.1 Electrodes --------------------------------------------------------------------------- 40 1.6.1.1 Gold Electrode (Working Electrode) ----------------------------------------- 40 1.6.1.2 Interdigitated Array Electrodes ------------------------------------------------ 42 1.6.1.3 Indium Tin Oxide --------------------------------------------------------------- 43 1.6.2 Experimental Techniques -------------------------------------------------------- 44 1.6.2.1 Cyclic Voltammetry ------------------------------------------------------------ 44 1.6.2.2 Potentiostat ----------------------------------------------------------------------- 47 1.7 Sensors Fabrication and Characterization -------------------------------------------------
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