CHAPTER 19: Laser-Ablation Electrospray Ionization Mass Spectrometry (LAESI^®-MS): Ambient Ionization Technology for 2D and 3D Molecular Imaging

Laser ablation electrospray ionization mass spectrometry is an ambient ionization technique applicable to plant and animal tissue imaging, live-cell imaging (bacterial and fungal colonies), and most recently to cell-by-cell imaging. This ambient pressure technique uses a mid-infrared (mid-IR) laser with a wavelength (2.94 µm) that is strongly absorbed by water to ablate samples. The resultant ablation plume contains a population of neutral molecules from the sample. Ionization occurs via coalescence of the sample molecules with an electrospray plume above the sample, and the sample ions pass into a mass spectrometer for detection. This direct analysis of the tissues alleviates the need for sample preparation, such as rinse steps, the application of a surface coating or matrix, or solvent extraction, all of which adds time to the analysis and may result in sample contamination or loss. The use of the natural water content of tissue enables both 2D and 3D imaging of plant and animal tissue sections, cell colonies on agar plates, and contact lenses. This chapter discusses the advancements in LAESI-MS technology for imaging applications, and describes the Protea LAESI DP-1000 Direct Ionization System, the first integrated commercial instrument system using LAESI technology for imaging.