STUDIES ON CONDUCTING POLYMER-BASED NANOCOMPOSITES FOR PESTICIDE DETECTION

Abstract

The research work reported in the thesis speaks about the development of biosensors that provides quantitative information about pesticide detection by utilizing a bio-component (enzyme) in a direct contact with a transducer. Pesticides are extensively used to enhance productivity in the agriculture field due to their high insecticidal property and potency for pest control. However, their careless use on a large scale can lead to severe health issues, making it a global concern. Pesticides leave behind residues in agricultural resources, soil, and water which can enter the human body and lead to serious health problems, such as Alzheimer's, Parkinson's, cognitive disorders, thyroid problems, etc. Thus, there is an urgent need to develop a sensitive and effective technique for monitoring the concentration of these harmful substances to protect living beings from their injurious effects. Among the various pesticides, organophosphate pesticides (OPs) are commonly used because of their unique characteristics, including high insecticidal activity, low persistence, low bioaccumulation, and rapid degradation in the environment. In the literature, various chromatographic methods are available for detecting the presence of OPs. High-performance liquid chromatography (HPLC) and gas chromatography (GC) are the most popular methods in this domain. Although these methods are reliable, few shortcomings are still there. These methods are time-consuming and usually very rigid to implement. Therefore, we require a new technique that is authentic, possesses a low detection limit, cost-effective, rapid and easy to use. In this context, biosensors can be an attractive alternative to these conventional techniques for the detection of pesticides. Biosensors are analytical devices having biological sensing elements that are attached to a transducer and produce an electronic signal. The acetylcholinesterase (AChE)-based electrochemical biosensors have become increasingly popular for detecting OPs due to their on-site convenience, low-cost instrumentation, excellent selectivity, and rapid analysis. Their sensitivity significantly depends on the efficiency of enzyme immobilization and the electron transfer rate between the enzyme and electrode surface. To address these critical factors, researchers have explored various transducers in their studies. In recent years, conducting polymers (CPs) have been widely used as a supporting material for fabricating effective transducers. CPs contain π-electron backbone responsible for their unusual electronic properties such as electrical conductivity, low energy optical transitions, low ionization potential and high electron affinity. CPs based biosensors are cost-effective, easy to fabricate and offer a direct electrical readout for the detection of biological analytes with high sensitivity and selectivity. Various CPs such as polypyrrole, polythiophene, polyaniline, etc. have been widely used in biosensor fabrication. Apart from the merits, pure CPs have a few shortcomings like low sensitivity and poor selectivity. Nanomaterials based CPs nanocomposites overcome these issues. Nanomaterials have their own characteristics like high conductivity, large surface area, biocompatibility and excellent catalytic activity. Metal oxides (CuO, TiO2, MnO2, ZnO), graphene, carbon nanotube, etc. are some widely used nanomaterials. The incorporation of these nanomaterials effectively enhances the effective specific surface area, density, and catalytic power of nanocomposite. CPs nanocomposites increase electron transfer in an electrochemical reaction which further improves the sensitivity and selectivity of the biosensor.