A Caged In‐Source Laser‐Cleavable MALDI Matrix with High Vacuum Stability for Extended MALDI‐MS Imaging

Abstract Insufficient vacuum stability of matrix chemicals is a major limitation in matrix‐assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) of large tissue sample cohorts. Here, we designed and synthesized the photo‐cleavable caged molecule 4,5‐dimethoxy‐2‐nitrobenzyl‐2,5‐dihydroxyacetophenone (DMNB‐2,5‐DHAP) and employed it for lipid MALDI‐MSI of mouse brain tissue sections. DMNB‐2,5‐DHAP is vacuum‐stable in a high vacuum MALDI ion source for at least 72 h. Investigation of the uncaging process suggested that the built‐in laser (355 nm) in the MALDI ion source promoted the in situ generation of 2,5‐DHAP. A caging group is used for the first time in designing a MALDI matrix that is vacuum‐stable, uncaged upon laser irradiation during the measurement process, and that boosts lipid ion intensity with MALDI‐2 laser‐induced postionization.