Metal-assisted laser desorption ionization imaging mass spectrometry for biological and forensic applications

Abstract

Traditionally, matrix-assisted laser desorption ionization (MALDI) imaging mass spectrometry (IMS) requires the homogenous deposition of an organic matrix prior to analysis. However, organic matrices often generate high background noise in the low mass range (below ∼800 Da) that often prevents the detection and identification of lower molecular weight compounds, especially if these are present in low abundance. Laser desorption ionization (LDI) allows for selective ionization of targeted species with very low background in the low mass range. In this article, the advantages and disadvantages of both solvent free and wet deposition of metals as LDI matrices developed in our laboratory are presented and discussed in the context of IMS analyses. Through several original examples, we highlight the power of silver and gold-based metal-assisted LDI to analyze selected low molecular weight molecules from tissue sections by IMS, including intact cholesterol, triacylglycerols, fatty acids, and phospholipids, as well as numerous other endogenous substances embedded within fingermarks.