STUDIES ON GRAPHENE BASED NANOCOMPOSITES FOR BIOSENSING APPLICATIONS

Abstract

The research work reported in this thesis speaks about the design of a biosensor which provides quantitative information by utilizing a biological recognition element/ biochemical receptor in direct spatial contact with a transducer. As we know that the biosensors are made up of two main parts, namely, the bio-element as well as the sensing element. An enzyme, antibody, DNA, or other bio-element can be used for the detection of a specific analyte. While the transducer section turns the biological signal into an observable electrical signal. Biosensors used in clinical diagnostic and therapeutic applications have a lot of room for innovations employing many multi-disciplinary aspects of science and technology. Recently, a new generation biosensor is designed to assist in combining biological molecules with biocompatible nanotechnology conducting frameworks. The massive expansion in the world's population and rise in habits increases the risk of developing cancer which has long been regarded as the leading cause of death globally. The number of new cases of cancer rapidly increases day by day. The cell development mechanism in a healthy adult is a steady, consistent process that keeps the ideal amount of cells in a different part of the tissue. However, the cells abnormally divide and expand out of control, leading to the development of cancer, which emerges in most of the cases as a swelling mass known as a malignant tumor. Benign tumors, such as moles and warts, are typically not hazardous/ harmful. Further, in case of malignant tumor, the cells invade neighboring tissue through blood arteries and delivered to nearby organs. They divide and develop again in this region, ultimately producing a new tumor in the affected organ. Metastasis is the process by which cancer spreads to the multiple body organs. Cancer sufferer death rates in poor nations are most likely due to both delayed diagnosis and restricted access to early and conventional treatment. Conventional detection approaches,

such as radiography and physical testing, have been observed to take many hours or, in some circumstances, few weeks to produce the conclusions. However, these traditional procedures are highly expensive, require specialized apparatus, take a long time, and are less sensitive. As a result, there is an urgent need to develop reliable, sensitive, specific, fast, and user-friendly devices for detecting the cancer biomarkers. As a result, the efforts have been made on expanding portable biosensors with relatively high sensitivity and specificity. Graphene oxide (GO) has recently attracted much attention in biosensor applications. This is owing to its distinct electrical features, high surface area, superior conductivity, excellent charge transfer capability, flexibility of functionalization, and biocompatibility. Furthermore, due to its high electrocatalytic activity, and potential to exhibit direct electron transfer property for particular protein, GO has been actively investigated as a sensitive platform in electrochemical biosensors. The incorporation of nanomaterials such as metal oxides and metal sulfides has sparked considerable attention due to the possibility of tailoring the specific features of each component into a single material. Additional synergistic effects of these materials have influenced the biosensor performance, resulting in the better sensitivity and selectivity. Thus, the present study focuses on the synthesis, characterization, and use of rGO, rGO nanocomposites with TiO2 and MoS2, in the development of efficient electrochemical biosensors for the sensitive and selective detection of cancer biomarker (EpCAM). A thin coating of rGO and its nanocomposites was electrophoretically deposited over the ITO coated glass electrode and metallic ions and anti-biomarkers were coupled via the functional groups in GO (-OH and -COOH). Thus, a biosensor with better performance for detecting the cancer biomarkers (EpCAM) in buffer and spiked human serum samples has been designed and found fit and promising for biosensing applications.