Fabrication and Characterization of Polyaniline- Carbon Modified
Total Page:16
File Type:pdf, Size:1020Kb
UNIVERSITY OF NAIROBI FABRICATION AND CHARACTERIZATION OF POLYANILINE- CARBON MODIFIED ELECTRODE (CME) BIOSENSOR FOR ANALYSIS OF BISPHENOL A BY LUCIA. K. KIIO. I56/74297/2014. A Thesis Submitted for Examination in Partial Fulfillment of the Requirements for Award of the Degree of Master of science in Environmental Chemistry of the University of Nairobi. 2017. DECLARATION I declare that this thesis is my original work and has not been submitted elsewhere for examination, award of degree or publication. Where other people’s work or my own work has been used, this has properly been acknowledged and referenced in accordance with the University of Nairobi’s requirements. SIGNATURE DATE: LUCIA.K. KIIO I56/74297/2014 Department of Chemistry …………………………… ……..………… School of Physical Sciences University of Nairobi This thesis is submitted for examination with our approval as research supervisors: SIGNATURE DATE DR. DAMARIS MBUI Department of Chemistry School of Physical Sciences …………………………… ……..………… University of Nairobi P.O Box 30197-00100 Nairobi Kenya [email protected] DR. IMMACULATE MICHIRA Department of Chemistry University of Nairobi …………………………… ……..………… P.O Box 30197-00100 Nairobi Kenya [email protected] PROF. HELEN NJENGA Department of Chemistry University of Nairobi …………………………… ……..………… P.O Box 30197-00100 Nairobi Kenya [email protected] i DEDICATION I dedicate this thesis to my mum Domitilla Muthio, my dad Richard Munyao and family members for their steadfast support, financially and morally and their encouragement throughout my studies. ii ACKNOWLEDGEMENTS First and foremost I would like to thank the Almighty God for his guidance, protection and giving me strength, good health, knowledge and patience during my studies. Second, I would like to thank my parents for their everlasting love, encouragement, patience, support and motivation in my whole life. Greatest thanks to my supervisor Dr. Damaris Mbui, for her tireless and continuous support and encouragement for the entire period of my Masters degree studies, Dr. Immaculate Michira and Prof. Helen Njenga for giving me an opportunity to complete my Masters degree under their excellent supervision, support and encouragement during this period. I would also like to appreciate all my lecturers and technical staff in the Departments of, Chemistry, Physics, School of Biological sciences, Biochemistry, the university, mentors, sponsors, colleagues and all who have contributed to my progress during the entire period of this study. Many thanks to Kianda School for giving me an opportunity to pursue my master’s degree, their encouragement and support. Many special thanks to all my friends who encouraged me and supported me during the entire period of my study. I would also like to acknowledge the National Commission for Science, Technology and Innovation (NACOSTI) for generously funding this study. iii ABSTRACT In this work, a biosensor to qualitatively and quantitatively determine the amount of BPA was fabricated, with the aim of analyzing levels of BPA in the environment. It was observed that most drinking bottles in the Kenyan market have a substantial amount of BPA that leaches into drinking water. Monitoring BPA is difficult as various known analytical methods may not be available in a developing country like Kenya. A more versatile and cheaper method is urgently required so as to assess the levels of BPA that the average Kenyan is exposed to with the intention of minimizing the BPA concentration in the environment. The biosensor for determination of Bisphenol A was developed from a bentonite-modified carbon electrode, polyaniline, SLS surfactant and Tyrosinase enzyme. The biosensor obtained was used to determine Bisphenol A in plastic water bottles and feeding baby bottles. Electrochemical methods, including cyclic voltammetry, DPV and square wave voltammetry were used in characterization of the biosensor. Other methods used were UV-VIS and Raman spectroscopy. The pH of the experiments was maintained using a phosphate buffer, and the optimal pH for the operation of the biosensor was obtained as 7.2. An elaborate peak signaling the presence of BPA was found at +0.5V for reduction potential and +0.2V oxidation potential. Under optimized conditions, the detection limit for BPA using the developed biosensor was found to be 2.1 x 10-9M within a concentration range of 0.02-0.2 mM where the response time reached 95% within 15 seconds. The concentrations of BPA in the water from the plastic bottles were found to be 0.030mM, 0.021 mM and 0.035mM for green, pink and blue drinking water bottles respectively and 0.030mM and 0.019mM green and pink feeding baby bottles respectively. We would like to sensitize the government and the people of Kenya against using plastics that have BPA because of the risks associated with the chemical compound. We would also like to recommend that the amount of BPA in other substances like CDs, DVDs, thermal paper and the various medical implements that are known to be manufactured using BPA be established and that the public be likewise alerted on using these substances. iv TABLE OF CONTENTS DECLARATION....................................................................................................................... i DEDICATION.......................................................................................................................... ii ACKNOWLEDGEMENTS .................................................................................................. iii ABSTRACT ............................................................................................................................. iv LIST OF TABLES ............................................................................................................... viii LIST OF FIGURES ................................................................................................................ ix LIST OF SCHEMES ............................................................................................................. xii ABBREVIATIONS AND ACRONYMS ............................................................................ xiii CHAPTER 1: INTRODUCTION ........................................................................................... 1 1.1 Background .................................................................................................................... 1 1.2 Problem Statement ......................................................................................................... 4 1.3 Overall objective ........................................................................................................... 5 1.4 Specific Objectives ........................................................................................................ 5 1.5 Research Justification .................................................................................................... 6 1.6 Significance of the Study ............................................................................................... 7 CHAPTER 2: LITERATURE REVIEW .............................................................................. 8 2.1 Introduction .................................................................................................................... 8 2.2 Endocrine Disrupting Compounds ................................................................................. 8 2.3 Bisphenol A ................................................................................................................. 10 2.4 Scholarly Knowledge on BPA ..................................................................................... 13 2.4.1 Studies on reproductive health effects of BPA .................................................. 15 2.4.2 Non-reproductive health effects of BPA Studies ............................................... 16 2.5 Actions taken by various states due to issues concerning BPA .................................. 18 2.6 Studies on Bisphenol Substitute (BPS) ........................................................................ 20 2.7 Biosensors ................................................................................................................... 20 2.8 Types of Biosensors ..................................................................................................... 22 2.8.1 Electrochemical biosensors ................................................................................ 22 2.8.2 Amperometric biosensor .................................................................................... 22 2.8.3 Potentiometric biosensor ................................................................................... 22 2.8.4. Conductimetric Biosensors ................................................................................... 23 2.8.5 Biosensors used in health care .............................................................................. 23 2.8.6 Enzyme Immobilization ........................................................................................ 25 2.8.7 Tyrosinase Enzyme ............................................................................................... 26 2.8.8: Catalytic cycle of Tyrosinase ................................................................................... 28 2.9 Historical background of conducting Polymers .......................................................... 30 v 2.9.1 Polyaniline ....................................................................................................... 32