STUDIES ON CONDUCTING POLYMER-BASED NANOCOMPOSITES FOR XANTHINE DETECTION

Abstract

The research work reported in the thesis focuses on the development of biosensors that provide quantitative information about Xanthine (Xn) detection by utilizing a bio-component (enzyme) in direct contact with a transducer. Xn is a purine base, derived from guanine and adenosine-3-phosphate (ATP) which is catabolized in the animal muscle tissues, and its accumulation may result in several physiological disorders. Abnormal Xn levels in human plasma and urine may contribute to deregulation of Xn metabolism, and an excess amount of Xn acquired through spoiled food with an unpleasant smell could eventually lead to physiological problems such as gout, xanthinuria, hyperuricemia, and preeclampsia. Therefore, Xn not only acts as a biomarker for the above diseases but also acts as an indicator for fish and meat spoilage and freshness determination. The analytical methods commonly used for Xn determination are based on spectrophotometric and chromatographic techniques which contain limitations such as long time for sample preparation, requiring skilled personnel to operate highly specialized equipment, impossibility of onsite detection, complex sample pre treatment, etc. To overcome the limitations of existing techniques, we require a new method that is authentic, possesses a low detection limit, and is cost-effective, rapid and easy to use. Biosensors are analytical devices having biological sensing elements that are attached to a transducer and produce an electronic signal. The electrochemical-based biosensors have become increasingly popular for detecting Xn due to their on-site vii 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 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. CP nanocomposites increase electron transfer in an electrochemical reaction which further improves the sensitivity and selectivity of the biosensor. Consequently, my research employs a variety of electrochemical biosensors to detect xanthine selectively. These biosensors demonstrated the electrical, structural, morphological, compositional, and electrochemical properties of conducting polymers viii and their nanocomposites with TiO2, as well as their application potential in biosensing. Fish freshness indication can now be detected using a highly sensitive label-free electrochemical biosensor. The nanocomposite, which exhibits outstanding electrochemical characteristics, and selectivity, and functions as a suitable sensing layer, was created using a sustainable method.