PhD thesis defense in physical sciences by Xavier Delvaux

ToF-SIMS investigation of biological tissues under normal and pathological conditions

Candidate

Xavier Delvaux

Promoter

Prof. Laurent Houssiau, UNamur, Namur Institute of Structured Matter (NISM), Laboratoire Interdisciplinaire de Spectroscopie Electronique

Jury

• Prof. Charles NICAISE (UNamur), président
• Prof. Laurent HOUSSIAU (UNamur), secrétaire
• Prof. Yves POUMAY (UNamur)
• Prof. Anne-Catherine HEUSKIN (UNamur)
• Dr Alain BRUNELLE (CNRS-Sorbonne Université)
• Dr Peter SJÖVALL (Institut RISE, Boras, Suède)

Summary

Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) is a versatile surface characterization technique widely used in materials science for the investigation of the elemental and molecular composition of solids with high chemical specificity and micrometric to sub-micrometric spatial resolution. Owing to its ability to simultaneously detect a broad range of molecular species, the technique has progressively emerged as a valuable tool for the characterization of biological systems. When combined with complementary histological, biochemical and advanced data-processing approaches, ToF-SIMS provides a powerful framework for the investigation of complex biological tissues, enabling the extraction of biologically relevant information from high-dimensional datasets. Additionally, dedicated labeling strategies can expand its analytical capabilities by providing access to molecular information that is not directly accessible through conventional ToF-SIMS analysis. Within this context, the present thesis developed and applied a multimodal analytical workflow through three complementary research projects.

The first work package focused on the characterization of reconstructed human epidermis (RHE) models. ToF-SIMS analyses identified lipid- and metabolite-related molecular signatures associated with the major histological layers of the epidermis, while Principal Component Analysis (PCA) proved effective for extracting biologically meaningful information from complex hyperspectral datasets. This work established the experimental and data-processing methodology used throughout the thesis.

The second work package investigated antibody-conjugated gold nanoparticles as protein probes for ToF-SIMS imaging. Three nanoparticle systems differing in synthesis route, surface chemistry and bioconjugation strategy were evaluated. Poly(allylamine)-functionalized gold nanoparticles showed the best performance, enabling the successful immunolabeling and ToF-SIMS imaging of involucrin in reconstructed human epidermis cross sections. These results demonstrate the feasibility of integrating metallic nanoparticle-based immunolabeling within a ToF-SIMS workflow, allowing the correlation of targeted protein information with the untargeted molecular information provided by the technique.

The final work package investigated molecular alterations following traumatic spinal cord injury. Combining ToF-SIMS imaging with microscopy and multivariate analysis enabled the identification of lipid species associated with white and grey matter, as well as molecular changes occurring around the lesion site at early and late stages after injury. Spectral alterations were also detected in tissue regions remote from the lesion epicenter, suggesting the presence of secondary molecular responses extending beyond the primary injury.

Taken together, these results demonstrate the versatility of ToF-SIMS for the investigation of biological systems, from tissue characterization and targeted protein imaging to the study of pathology-induced molecular remodeling. More broadly, this work highlights the value of combining mass spectrometry imaging with complementary biological approaches to obtain a more comprehensive understanding of complex biological systems.