Designing of electrocatalysts for the detection of fatal chronic diseases and production of greener energy fuels

Abstract

Preface: The rapid and exponential growth of the global population, anticipated to reach 8.2 billion by 2025, has raised significant concerns about the challenges associated with human health. This issue transcends geographical boundaries and is at the core of numerous public health problems. Acknowledging the gravity of the situation is paramount, as it demands collective efforts to address its multifaceted repercussions. The surge in population has led to an intensification of public health challenges over recent decades, prompting researchers to focus on identifying and implementing new and innovative remedies. Understanding the nuances of the global burden of disease (GBD) has become increasingly crucial in devising effective strategies to combat the health issues arising from overpopulation. In response to the escalating need for comprehensive information on potential future trends in global health, the United Nations has formulated 17 Sustainable Development Goals (SDGs). These goals serve as successors to the Millennium Development Objectives and encompass a broad spectrum of objectives aimed at fostering sustainable development across the globe. The third SDG strives to achieve the objective of promoting the well-being of individuals while ensuring the sustainability of the planet. This goal endeavors to create a balance that safeguards the welfare of current and future generations. This necessitates the development and adoption of innovative healthcare solutions and the establishment of policies that encourage sustainable living practices. In this scenario, faster disease diagnosis in its early stages is crucial for the healthcare sector, playing a life-saving role. There is a pressing need for the development of a highly effective biosensor that holds substantial importance in the betterment of public health. Electrochemical biosensors, equipped to rapidly, sensitively, and selectively detect biological molecules, play a crucial role as essential instruments in driving progress in healthcare, guaranteeing environmental sustainability, and nurturing scientific and technological advancements. The first chapter of this thesis describes a brief introduction to electrochemical biosensors and immunosensors along with their application in the detection of biomarkers for fatal diseases. Another part of the thesis consists of the production of hydrogen as a green energy fuel for the development of a sustainable energy source, leading to less dependence on the usage of fossil fuels. The second chapter describes the details of the materials synthesis, characterization techniques and the discusses the important terms used in the field of electrochemical biosensors. In the third chapter, electrochemical immunosensing of small cell lung cancer (SCLC) biomarkers, Neuron-specific enolase (NSE) and carcinoembryonic antigen (CEA), has been discussed utilizing nitrogen-rich polymeric materials and nitrogen-rich mesoporous carbon as transducing elements. Besides, a cost-effective, paper-based flexible screen printed immunosensor has been explored by simply coating conductive ink over cellulose paper for a point-of-care electrochemical detection of NSE and CEA. Firstly, for this purpose, Polydopamine (PDA) was introduced as a substrate-independent coating material for its excellent bonding characteristics, making it a suitable choice for stabilizing antibodies and antifouling compounds on the surface of an electrode. The electrodeposition of bioinspired low-cost PDA over oxygen-functionalized carbon CNTs-based was utilized for the direct attachment of antibodies. The proposed ePDA/OCNT-based immunosensor displayed a wider detection range in physiological pH (0.1 M PBS) and superior sensitivity. Moving forward, a novel approach focused on the protonation of nitrogen-rich porous organic polymer, polymelamine formaldehyde (PMF), as an efficient substrate material for label-free detection of NSE. Moreover, the protonation induces the electrostatic force of interactions for the efficient immobilization of antibodies. The proposed immunosensor has achieved a wider detection range from 120 fM – 70 nM with the lowest detection limit of 120 fM with a storage stability of 12 days on the homemade screen-printed electrode. Next, the mesoporous nitrogen containing carbon (MNC) as substrate for immobilization of antibodies was used for the label-free detection of CEA. The presence of various sp2 carbon atoms and positively charged ammonium groups (NH4+) facilitated the immobilization an adequate amount of anti-CEA molecules via electrostatic interactions in the physiological environment. The proposed immunosensor has achieved two linear ranges from 100 pM - 1 nM and 2 nM - 50 nM which covers the clinically relevant concentration region. of Food analysis is a critical aspect of understanding the nutritional composition, safety, and quality of food products, and it has direct implications for human health. The relationship between food analysis and health encompasses various aspects, including nutritional content, contaminants, allergens, and overall food safety. Therefore, Chapter 4 focuses on the detection of Capsaicin, an important phytochemical present in peppers. It is recognized for its diverse health-promoting properties, encompassing anti-cancer properties along with protective effects against cholesterol and obesity. Herein, PMF in combination with OCNTs as PMF/OCNT composite was used for selective determination of capsaicin due to the π-π affinity between PMF and OCNTs facilitating the electron transfer at electrode/electrolyte interface. Moreover, huge number of amine functional groups of PMF in hybridization with OCNTs enhances the sorption capacity of PMF. The proposed sensor has shown outstanding physicochemical stability in highly acidic media (pH 1) along with high selectivity towards capsaicin with a detection of wide detection range of 0.1-500 µM and lowest detection limit (LOD) of 71.5 nM. In Chapter 5, taking into consideration the properties of PMF, it was explored for highly sensitive determination of creatinine by conjugation with Cu nanoparticles. Creatinine (CRE), a nitrogenous by product of amino acid metabolism, is expelled from the body during blood purification by filtering through the kidneys and its measurement is helpful in taking care of patients with renal malfunctioning. Besides this, serum creatinine level also plays a vital role in the diagnosis of muscular diseases as well as post-surgery renal functions. Its detection is important to identify the adequacy of kidney function as well as early-stage diagnosis and progression of kidney diseases. Herein, electrodeposition of Cu nanoparticles over the surface of PMF was utilized where PMF provides numerous nitrogen-containing active sites for creatinine binding, and Cu metal forms a complex with creatinine facilitating its sensing. The developed eCu-PMF composite-based non-enzymatic electrochemical creatinine sensor exhibited excellent stability under physiological conditions (pH 7.4) with a wider detection range of 100 fM-60 mM having a LOD of 13.2 pM and a low response time of two minutes with storage stability of 15 days. A rise in environmental concerns and global energy crises caused by the overconsumption of fossil fuels has motivated researchers to take into consideration alternate energy sources. As a sustainable substitute, biomass conversion is an encouraging technique to curb this major energy crisis. Glucose, an important biomolecule, can be converted to useful commodities such as glucaric acid, gluconic acid, and 5-hydroxymethylfurfural. Glucaric acid (GRA) is defined as a “top value-added chemical” by the US Department of Energy (DOE) because of its utilization in chemical, food, pharmaceutical, and therapeutic fields. Additionally, hydrogen (H2) is obtained as a product of the counter-reaction of glucose oxidation. Currently, the hydrogen economy is gaining interest from both industry and academia owing to its high energy density (142 MJ kg-1), high efficiency, renewable production, and environmentally friendly nature of hydrogen. Nickel manganese oxide (NiMn(x:y)On/OCNT) composite with oxygen functionalized carbon nanotubes (OCNTs) as an efficient electrocatalyst for selective oxidation of glucose to glucaric acid along with the production of value-added fuel, H2. Besides the enhancement in the H2 evolution rate (from 0.05 mL min-1 in water electrolyzer to 0.16 mL min-1 in glucose electrolyzer) and the production of glucaric acid as a selective product of glucose oxidation was achieved with an F.E. of 62.8 % at 1.3 V vs. RHE. Furthermore, NiMnOn/OCNT was used for glycerol oxidation reaction (GlOR). It shows potential applications viz. production of value-added products such as glyceric acid, dihydroxyacetone, tartronic acid, glyceraldehyde, formic acid, lactic acid, and hydropyruvic acid, hydrogen production at a lower overpotential making the process more efficient and reducing the environmental impact of glycerol waste disposal by converting it into useful products and reducing the carbon footprint associated with its disposal. Herein, oxalic acid was produced as a value-added product at the anode and hydrogen as a fuel on the cathode. The last emphasizes chapter the conclusions of this thesis and the possible future directions in the related field.