Abstract
The study of biological specimens by mass spectrometry imaging (MSI) has had a profound influence in the various forms of spatial-omics over the past two decades including applications for the identification of clinical biomarker analysis; the metabolic fingerprinting of disease states; treatment with therapeutics; and the profiling of lipids, peptides and proteins. No singular approach is able to globally map all biomolecular classes simultaneously. This led to the development of many complementary multimodal imaging approaches to solve analytical problems: fusing multiple ionization techniques, imaging microscopy or spectroscopy, or local extractions into robust multimodal imaging methods. However, each fusion typically requires the melding of analytical information from multiple commercial platforms, and the tandem utilization of multiple commercial or third-party software platforms—even in some cases requiring computer coding. Herein, we report the use of matrix-assisted laser desorption/ionization (MALDI) in tandem with desorption electrospray ionization (DESI) imaging in the positive ion mode on a singular commercial orthogonal dual-source Fourier transform ion cyclotron resonance (FT-ICR) instrument for the complementary detection of multiple analyte classes by MSI from tissue. The DESI source was 3D printed and the commercial Bruker Daltonics software suite was used to generate mass spectrometry images in tandem with the commercial MALDI source. This approach allows for the generation of multiple modes of mass spectrometry images without the need for third-party software and a customizable platform for ambient ionization imaging. Highlighted is the streamlined workflow needed to obtain phospholipid profiles, as well as increased depth of coverage of both annotated phospholipid, cardiolipin, and ganglioside species from rat brain with both high spatial and mass resolution.
Highlights
Mass spectrometry imaging (MSI) has seen widespread use in the world of clinical mass spectrometry (MS) in part due to the flexibility of the label-free nature of the analysis, with applications ranging from biomarker discovery, studying metabolic pathways for pharmaceutical drugs, and spatial profiling of biomolecules [1,2,3,4]
This has been shown by desorption electrospray ionization (DESI)-mass spectrometry imaging (MSI) of lipids and subsequent matrix-assisted laser desorption/ionization (MALDI)-MSI on the same tissue section for proteins, as well as increased coverage of lipids and gangliosides when utilized in tandem [26,27]
A meandering pattern, which has been demonstrated to acquire line scans in the positive and negative direction, has been utilized in many other lab-built DESI-MSI sources [37]. This imaging pattern could not be utilized in this workflow due to the requirement of coordinating DESI scans with pixel coordinates in MALDI-MSI FlexImaging sequences of serial sections, which employs a fly back pattern, and is utilized for DESI-MSI image generation
Summary
Mass spectrometry imaging (MSI) has seen widespread use in the world of clinical mass spectrometry (MS) in part due to the flexibility of the label-free nature of the analysis, with applications ranging from biomarker discovery, studying metabolic pathways for pharmaceutical drugs, and spatial profiling of biomolecules [1,2,3,4]. Many have identified the tandem utility of comprehensive mapping of biomolecules from MSI, with targeted assays having incorporated multiple ionization sources or MSI methods [7,8,9,10], combination of MSI with microscopy and spectroscopy [11,12,13,14,15,16], and subsequent microdissection and extraction for liquid chromatography [17,18] In light of these developments, two techniques of MSI have become predominant in the field, matrix-assisted laser desorption/ionization (MALDI) and desorption electrospray ionization (DESI), both of which are morphologically compatible [7,19]. This has been shown by DESI-MSI of lipids and subsequent MALDI-MSI on the same tissue section for proteins, as well as increased coverage of lipids and gangliosides when utilized in tandem [26,27]
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