Multimodal MSI in Conjunction with Broad Coverage Spatially Resolved MS² Increases Confidence in Both Molecular Identification and Localization

Abstract

One critical aspect of mass spectrometry imaging (MSI) is the need to confidently identify detected analytes. While orthogonal tandem MS (e.g., LC-MS) experiments from sample extracts can assist in annotating ions, the spatial information about these molecules is lost. Accordingly, this could cause mislead conclusions, especially in cases where isobaric species exhibit different distributions within a sample. In this Technical Note, we employed a multimodal imaging approach, using matrix assisted laser desorption/ionization (MALDI)-MSI and liquid extraction surface analysis (LESA)-MSI, to confidently annotate and localize a broad range of metabolites involved in a tripartite symbiosis system of moss, cyanobacteria, and fungus. We found that the combination of these two imaging modalities generated very congruent ion images, providing the link between highly accurate structural information onfered by LESA and high spatial resolution attainable by MALDI. These results demonstrate how this combined methodology could be very useful in differentiating metabolite routes in complex systems.

Advanced Molecular Techniques Provide New Rigorous Tools for Characterizing Organic Matter Quality in Complex Systems

“…Journal of Geophysical Research: Biogeosciences database against which to identify and quantify compounds; therefore, novel compounds remain a challenge and are best identified via FTICRMS and related emerging techniques (e.g., Veličković et al, 2017).…”

“…By integrating all of these techniques we can gain a more holistic view of the DOM (Figure ). One caveat with both GCMS and NMR is that they require a database against which to identify and quantify compounds; therefore, novel compounds remain a challenge and are best identified via FTICRMS and related emerging techniques (e.g., Veličković et al, ).…”

An approach for visualizing the spatial metabolome of an entire plant root system inspired by the Swiss‐rolling technique

“…We were able to attain spatially explicit MS 2 data from our sample using the LESA approach we described previously (Figure ), which we could correlate to our high mass accuracy MALDI‐MS imaging data. We annotated m/z 156.0421 as [C 5 H 11 NO 2 + K] + (Figures and A), but two other potential pseudomolecular ions with differing molecular formulas are possible within 1.2 ppm of the measured m/z , and they were also annotated in METASPACE (as the same ion image, due to the 3 ppm detection window METASPACE utilizes).…”

“…To demonstrate this, we used Brachypodium distachyon (henceforth Brachypodium) as our plant system, due to its tractability as a model grass system and its extensive characterization . By using this method, we were able to resolve spatial metabolomics information from Brachypodium roots by probing with MALDI and liquid extraction surface analysis (LESA), similar to as we demonstrated previously on the microbiome of Sphagnum . We anticipate that our method will complement current RSA studies by providing spatial mapping of metabolite distribution in roots, which can aid in identifying mechanism of root response to environmental perturbation, such as water deficiency or nutrient limitation conditions.…”

“…LESA‐MS 2 was performed on serial sections relative to those analyzed with MALDI‐MSI using a Triversa Nanomate (Advion) coupled to a Velos Orbitrap Mass Spectrometer (Thermo Scientific), and positive ions were collected and analyzed similar to as we described previously . LESA sampling conditions were as follows: 8.0 μL of 70% MeOH with 0.1% formic acid was aspirated in the pipette tip, then 0.3 μL of this volume was dispensed at a height of 0.2 mm above the sample.…”