The fundamental understanding of biochemical processes functioning in living organisms relies on the availability of highly selective and sensitive analytical tools. One of the most powerful techniques in the research of biomolecules is mass spectrometry (MS). Recent developments in MS facilitate the production of ions under atmospheric pressure conditions, enabling the direct investigation of living organisms without disrupting viability. The present work tells my endeavor to introduce a novel methodology for the analysis and molecular imaging of biological tissues.

Chapter 1 introduces ambient mass spectrometry and reviews the reported direct ionization methods based on the leading process of sampling and ion generation. The fundamental aspects of atmospheric-pressure laser desorption/ablation and electrospray postionization are presented.

Chapter 2 briefly reviews the disintegration mechanisms of electrostatic spraying and studies the physical and chemical properties of the generated charged droplets in light of their potential to serve the basis of postionization in the method under development.

Chapter 3 introduces mid-infrared laser ablation electrospray introduction (LAESI) as an ambient ion source for mass spectrometry. The underlying mechanisms of LAESI, analytical figures of merit, and capabilities for molecular spatial profiling and in vivo analyses are discussed.

Chapter 4 presents LAESI MS for the spatial mapping of endogenous metabolites in the leaf tissue of a variegated plant and deliberates on the feasibility of molecular depth profiling with single laser pulses.

Chapter 5 focuses on molecular imaging of animal tissues with the LAESI method. Endogenous distributions of small metabolites and lipids are probed in coronal sections of rat brain without the need for any chemical treatment.

Chapter 6 discusses the combination of depth profiling with lateral molecular imaging in LAESI experiments. Proof-of-principle experiments confirm three-dimensional (3D) molecular imaging under ambient conditions that enables the investigation of biosynthetic pathways. Correlation analysis is introduced to reveal the underlying biochemistry of the tissue sectors.

Chapter 7 deliberates on the current state of ambient mass spectrometry and underlines major challenges this field is likely to experience while it is undergoing scientific evolution. Future directions in LAESI MS research are highlighted and potential applications are mentioned.