Chemical fabrication of ZnO nanostructures and their emission properties: Cholesterol biosensing applications utilizing ZnO and Graphene

Abstract: Zinc oxide (ZnO) is an inorganic compound, owing to wide band gap and large binding energy, and holds promising potential in the fields of semiconducting as well as piezoelectric applications with excellent stability and reliability. In addition, ZnO has a plenteous number of nanoscale structures containing unique physical, chemical, electrical, sensing and optical properties. These properties of nanostructures are being unrevealed extensively since last two decades and have become a prominent field of research in nanoscience and nanotechnology.More specifically, the present dissertation deals with the low temperature synthesis of ZnO nanostructures (nanorods, nanotubes, nanodisks and nanowalls) on a variety of substrates such as silicon, gallium nitride, zinc foil, silver and aluminum; structural characterization and study of their luminescence properties. In paper 1 we investigated the synthesis mechanism of chemically fashioned ZnO nanotubes and their superior emission capability compared to ZnO nanorods with significant enhancements in ultraviolet and visible regions has been studied. These chemically synthesized ZnO nanotubes are further utilized to fabricate a heterostructure with p-GaN thin film in order to achieve white emission (Paper 2). The aim of Paper 3 is to understand the synthesis of ZnO nanorods and their transition into ZnO nanodisks at 55 °C along with temperature dependent micro-photoluminescence studies. However, the second half of the dissertation is devoted to the fabrication of potentiometric cholesterol biosensors through the conjugation of ZnO nanostructures and graphene nanosheets with a thin film of cholesterol oxidase. Paper 4 contains the fabrication of cholesterol biosensor by the deposition of ZnO nanorods on thin silver wire followed by their functionalization under the physical adsorption method. The specificity, reproducibility and stability of the biosensor have been investigated with good linearity slope curve of ~35 mV/ decade. The purpose of papers 5 and 6 is to enhance the sensitivity of the cholesterol biosensor by using ZnO nanowalls and graphene nanosheets as a matrix where the sensitivity of the slope curve is achieved as ~53 and ~82 mV/ decade, respectively.