Design and Synthesis of Graphene-based Nanocomposites for Sensing and Medical Applications

Abstract

The objective of this thesis is to develop graphene oxide-based nanocomposites for sensing and medical applications. The research in this work involved two main projects: the fabrication of graphene oxide-based sensor materials for the detection of biomolecules using electrochemical methods under various conditions, and the design of biocompatible graphene oxide-based biomaterials for antibacterial applications. Hydroxyproline (Hyp) is a significant amino acid that is present in the connective tissues and extracellular matrices of all animal cells. The quantitative analysis of Hyp plays a vital role as it is a biomarker in lung disease and facilitates the determination of collagen in the biomedical and food industries. In the livestock farming industry, sodium metabisulfite (SMBS) is employed as a feed additive to control the effects of deoxynivalenol (DON), which is a Fusarium mold mycotoxin. The monitoring of SMBS is essential as its over-dosage may induce significant side effects (e.g., stomach upset). In this work, the synthesis of gold nanoparticles and graphene-based nanocomposites and their applications for the detection of Hyp and SMBS are reported. Our studies revealed that gold nanoparticles exhibited high sensitivity (8.5 μA μM-1 cm-2), a low limit of detection (2.6 μM), and a wide linear range for the identification of Hyp in various media. The synthesized gold and fluorine-doped reduced graphene oxide nanocomposites showed high-performance for the detection of SMBS in different digestive fluids (e.g., simulated salivary fluid and gastric fluid). Graphene oxide decorated with silver nanoparticles (GO/AgNPs) was synthesized utilizing different concentrations of AgNPs (GO/Ag-1, GO/Ag-2, GO/Ag-3, and GO/Ag-4) and examined for its antibacterial properties. Spherical AgNPs with average diameters of 5 – 15 nm were evenly distributed across the partially reduced GO surfaces. The nanocomposites exhibited high antibacterial activities, and it was observed that GO/Ag-1 and GO/Ag-2 was less toxic to human epithelial cells. The above investigation led to the synthesis of four types of CS/GO/AgNPs (CS/GO/Ag-1, CS/GO/Ag-2, CS/GO/Ag-3, and CS/GO/Ag-4). The CS/GO/Ag-1 and CS/GO/Ag-2 nanocomposites were examined using electrical stimulation (ES), which produced improved antibacterial activities than the samples without ES. It was concluded that these nanocomposites might be utilized for promising biological applications, including tissue engineering scaffolds, biosensors, and wound healing.