Development and Application of ToF-SIMS for Clinical and Microbiological Analysis

Abstract: The aim of the work of this thesis was to further the implementation of timeof-flight secondary ion mass spectrometry (ToF-SIMS) in biological analysis and to generate new knowledge from the samples analysed. ToF-SIMS is a chemical analysis technique. It is a surface sensitive technique that generates detailed chemical information with high lateral resolution. ToF-SIMS is versatile in that it is capable of analysing a wide range of samples. This thesis exploited the versatility of ToF-SIMS by applying the technique to two very different areas of medical research by analysing widely different types of biological samples. Furthermore, the thesis included characterisation and implementation of a technical modification to the ion gun which was aimed at improving ToF-SIMS capabilities in analysing biological samples. Bacterial antibiotic resistance is a global health threat that undermines the many improvements in public health and modern medicine that the advent of antibiotics has brought. Spread of mobile DNA coding for antibiotic resistance through conjugation is an instrumental mechanism behind this threat. Part of this thesis has been devoted to the use of ToF-SIMS in characterising molecular changes in the bacterial envelope of Escherichia coli strains genetically altered to inhibit conjugation in an attempt to shed some light on the mechanisms behind conjugation and its inhibition. The rising incidence of skin cancers is another problem of increasing severity, especially in Caucasian populations. Understanding the origin of the tumours and developing treatment methods are therefore of growing importance. ToF-SIMS was used to image entire tissue slices from excised basal cell carcinoma (BCC) tumours, as well as probing the microenvironment of the individual tumour islets comprising the tumour, looking for molecular clues on how the lipid profile differs between healthy and diseased tissue. As with any technique, ToF-SIMS has its drawbacks. One of these has been the lack of generation of intact pseudo-molecular ions above a few hundred Da. This has been the target of the development of gas cluster ion beams (GCIBs). Part of this thesis was dedicated to characterising one of the most recent GCIB advents, the H2O GCIB. The aim of the work was to evaluate the pros and cons of this ion beam in analysis of different types of biological samples as well as developing protocols on how to use the ion beam to gain the best results and in doing so making ToF-SIMS better equipped to analyse biological samples.