SYNTHESIS AND MODIFICATION OF METAL OXIDE NANOSTRUCTURES FOR SENSING APPLICATIONS

Abstract

Metal oxide semiconductors have been known as smart and advanced functional materials showing potential applications in various fields such as solar cells, smart windows, photocatalysis, and sensors etc. However, the confinement of dimensions of these materials in the nano range has remarkably tailored their physical and chemical properties making them novel in their characteristics. Based upon this, in recent years, tungsten trioxide (WO3) evolved as one of the most researched materials due to its simple and economic synthesis approach, high chemical stability, and good electro chemical kinetics. WO3 is found to exist in different polymorphs such as orthorhombic, monoclinic, tetragonal, and hexagonal phase which depends on synthesis parameters. These different crystal systems modify the electronic structure of WO3 and thus influence its electronic properties and hence electrochemical kinetics. In the present study, we have focused our attention towards the synthesis of different dimensional WO3 nanostructures existing in different crystal systems. For a facile and cost-effective production, we have employed hydrothermal synthesis process for synthesis of different WO3 nanostructures and composites. These WO3 based nanostructures have found wide range of applications such as optical and electronic based nanodevices, photocatalysis, and biomedical sensing applications. Among all these, applications of WO3 based nanostructures towards the development diagnostic biosensors have aroused much interest. For the biosensing applications, successful immobilization of bio-entities onto the diagnostic platform is crucial. As Ph.D. Thesis (Deepika Sandil) v

interaction of nanostructure with the biological entities get highly influenced by its crystal phase, morphology, electronic properties, surface chemistry and functionalization of the surface. Our study further focuses on investigations of the biosensing applications of different WO3 nanostructures based upon their electro chemical behaviour. Among different biosensing applications, recently, cardiovascular diseases (CVDs) have raised major health burden leading to prime cause of death. Acute myocardial infarction (AMI) is one of the CVDs caused by the necrosis of myocardial tissues due to ischemia. The insufficient fact details regarding the diseases and its classification seems to delay the diagnosis process of the disease in the clinical laboratories. Learning the concentration of cardiac biomarkers plays a significant role in the diagnosis of AMI. Among other cardiac biomarkers, cardiac Troponin I (cTnI) is a highly cardiac specific muscle protein biomarker which shows significant increase in its value with the onset of myocardial necrosis. Hence in this thesis, our main focus is on studying different WO3 nanostructures, characterizations, and functionalization procedures to be used for the diagnosis of the AMI by detecting cardiac biomarker cTnI.