Three-dimensional imaging of metabolites in tissues under ambient conditions by laser ablation electrospray ionization mass spectrometry.

Three-dimensional (3D) imaging of molecular distributions offers insight into the correlation between biochemical processes and the spatial organization of a biological tissue. Simultaneous identification of diverse molecules is a virtue of mass spectrometry (MS) that in combination with ambient ion sources enables the atmospheric pressure investigation of biomolecular distributions and processes. Here, we report on the development of an MS-based technique that allows 3D chemical imaging of tissues under ambient conditions without sample preparation. The method utilizes laser ablation electrospray ionization (LAESI) for direct molecular imaging with lateral and depth resolutions of approximately 300 microm and 30-40 microm, respectively. We demonstrate the feasibility of LAESI 3D imaging MS of metabolites in the leaf tissues of Peace lily (Spathiphyllum lynise) and the variegated Zebra plant (Aphelandra squarrosa). Extensive tandem MS studies help with the structure identification of the metabolites. The 3D distributions are found to exhibit tissue-specific metabolite accumulation patterns that correlate with the biochemical roles of these chemical species in plant defense and photosynthesis. Spatial correlation coefficients between the intensity distributions of different ions help to identify colocalization of metabolites and potentially uncover connections between metabolic pathways.