The development of electrochemical sensors based on the use of different forms of carbon materials

Thesis

This thesis presents experimental work with the main aim of the development of chemical sensors using electroanalytical methods for applications in the food industry and for medical diagnosis. The first chapter introduces the principles and techniques of electrochemistry. Chapter 2 provides information on the experimental procedures and chemical/reagents used in the studies.

In this thesis, carbon based materials such as pyrolytic graphite; carbon nanotubes and carbon fibre have been used for a number of analytical and fundamental investigations. The first research aim of this thesis is to develop sensors for the detection of chemical compounds in ginger and turmeric. Chapter 3 and 4 demonstrate the capability of multiwalled carbon nanotubes modified electrodes for adsorptive stripping voltammetric determination of gingerol and curcumin along with the possibility for commercialisation. An extension of the first project to compare different types of carbon electrode materials including multiwalled carbon nanotubes, carbon black, graphene nanoplatelets, screen-printed carbon electrode and carbon paste electrode for the AdsSV technique is presented in Chapter 5. General principles to offer guidance in the optimal choice of carbon electrodes for AdsSV are established.

Chapter 6 investigates the reaction mechanism of atmospheric oxygen with an edge plane pyrolytic graphite electrode to generate surface quinone functionality. The results presented in Chapter 6 are evidenced as photochemical in nature and to likely involve singlet oxygen.

As a possible biomarker of salivary pH for diseases such as gingivitis and dental caries, the next aim of this thesis is to develop sensors for pH measurement in saliva. Chapter 7 reports the development of a micro-sized pH probe exploiting the pH dependence of surface quinones on micro carbon fibres for pH measurement of saliva. Applications in human saliva without any pre-treatment are highlighted.

In Chapter 8, amperometric pH sensing in samples of sheep’s blood is investigated. At the beginning, surface quinones on graphite electrode are used in the study. However, in terms of signal size and the lack of robustness of the developed electrodes, micro-disc carbon fibre electrodes appeared to be less than optimal to use for study in biological samples with complex matrices such as blood. The investigation and exploitation of metal/metal oxide specifically iridium oxide electrodes for amperometric pH sensing in sheep’s blood are carried out, shown to be superior, and are described in Chapter 8.

Finally, Chapter 9 presents overall conclusions.

Authors: Chaisiwamongkhol, K

• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford