Zhu, Yujiang; (2025) Synthesis of Copper Oxide Nanostructures and Their Application in Non-Enzymatic Glucose Sensors. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Diabetes is a chronic disease prevalent all over the world, characterised by high blood sugar levels in human blood caused by absolute or relative insulin deficiency or resistance. According to the International Diabetes Federation (IDF), diabetes prevalence in 20 to 79 year olds in 2021 was estimated to be 10.5% (536.6 million people), rising to 12.2% (783.2 million) in 2045. In addition to the harm caused by diabetes itself, it is also associated with many different kinds of complications or even leads to death. Unfortunately, no cure for diabetes currently exists, therefore, testing the blood glucose concentration in body fluids is an effective way to diagnose diabetes at an early stage and prevent the further deterioration of the condition in diabetic patients. Glucose sensors are crucial for this and the first three generations of glucose sensors are all enzyme-based. Limited by enzymes, traditional enzymatic sensors are gradually being replaced by their non-enzymatic counterparts (the fourth generation). They rely on the direct redox reaction of glucose on the surface of a metal, metal oxide, or alloy electrode, which eliminates the environmental restrictions associated with the use of enzymes and makes the reaction more efficient. Among many potential materials, cupric oxide (CuO), especially in nanostructural form, is a promising choice, due to its remarkable size and shapedependent advantages, and electrochemical properties. However, extensive work performed to date shows that CuO nanostructures can be synthesised in diverse morphology and small variations in synthesis conditions may change the nanostructure and physical and chemical properties of the final product, thereby leading to different performance in glucose detection. It is essential to understand the impact of each synthesis parameter, such as temperature, precursor, and pH, on the final nanostructures, in hope of eventually correlating these with sensor performance, and ultimately offering further development in copper oxide-based glucose sensors. This work addresses this issue by synthesising copper oxide nanostructures via a wet chemical precipitation method, while modifying the environmental conditions during synthesis, such as the use of various precursors, solution pH value, and synthesis temperature. As-prepared CuO nanostructures are characterised to obtain information about morphology, structure, composition, chemical environments, and electronic structure via scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and ultraviolet-visible (UV-vis) spectroscopy. To explore the glucose sensing capability of the prepared samples, electrochemical testing including such as cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) are employed to characterise sensitivity, detection limit, linear range, and selectivity.

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