High-Performance DESI-MSI using a DESI XS Xevo™ TQ Absolute XR system for Sensitive and Specific Targeted Imaging of Small Molecules in Tissue Sections

Importance of the Topic

Desorption Electrospray Ionization Mass Spectrometry Imaging (DESI-MSI) enables direct, minimal-preparation mapping of small molecules and lipids in tissue sections. High spatial resolution imaging reveals microenvironmental heterogeneity and region-specific metabolic changes that bulk assays overlook. In neuroscience and pathology research, visualizing phospholipids and endogenous metabolites at tens of microns is critical for studying development, disease progression and therapeutic responses.

Objectives and Study Overview

This application note demonstrates a high-performance DESI-MSI workflow combining an ACQUITY µBSM binary pump, DESI High-Performance Sprayer (HPS) and DESI XS source on a Xevo TQ Absolute XR triple quadrupole mass spectrometer. The goals are to:

• Achieve long-term solvent flow and spray stability for multi-hour imaging runs.
• Perform targeted multiple reaction monitoring (MRM) imaging of phospholipids, small endogenous metabolites and isomeric/isobaric species in rodent brain tissue.
• Demonstrate sensitivity and specificity improvements over prior systems.

Methodology and Instrumentation

Consecutive 18 µm cryosections of frozen rodent brain were thaw-mounted on slides and maintained at –80 °C. DESI was conducted at 2 µL/min (98:2 MeOH/H2O) with 15 psi N2 nebulization. A heated transfer line was applied in negative-mode experiments (450 °C) to enhance desorption. Imaging pixel sizes of 25–35 µm were used. Acquisition was in targeted MRM mode at 5 scans/s over 11–13 hours per experiment.

Instrumental Setup

• Mass Spectrometer: Xevo TQ Absolute XR (triple quadrupole)
• Ion Source: DESI XS with High-Performance Sprayer
• Solvent Delivery: ACQUITY µBSM binary pump
• Software: MassLynx v4.2, HDI 1.8 for image reconstruction

Main Results and Discussion

The system maintained stable signal and robust performance across prolonged acquisitions. Targeted MRM imaging resolved phospholipid distributions in positive and negative modes, including isobaric/isomeric pairs (e.g. PC [35:2] vs PC [32:0]). Signal-to-noise ratios for low-abundance lipids and metabolites were significantly improved compared to previous platforms. Extensive panels of amino acids, TCA cycle intermediates, oxylipins and fatty acids were visualized at 25–35 µm resolution. Distinct anatomical localization patterns emerged for neurotransmitters, carnitines and lipid mediators, highlighting the value of targeted DESI-MSI for metabolic mapping.

Benefits and Practical Applications

• High sensitivity and specificity for low-abundance small molecules directly from tissue.
• Robust solvent flow and spray stability enable consistent multi-hour imaging runs.
• Targeted MRM workflows differentiate isomeric/isobaric species via diagnostic product ions.
• Applicable to neuroscience, biomarker discovery, QA/QC and translational research.

Future Trends and Opportunities

Advances in DESI source design, faster scanning electronics and enhanced informatics will drive sub-10 µm spatial resolution and real-time metabolic profiling. Integration with multimodal imaging (e.g. microscopy, fluorescence) and machine learning–based image analysis can further elucidate complex tissue biochemistry. Expanding targeted panels to lipids, peptides and small drug molecules will broaden clinical and pharmaceutical applications.

Conclusion

The combination of ACQUITY µBSM pump, DESI HPS and DESI XS on a Xevo TQ Absolute XR delivers high-performance targeted DESI-MSI. Achieving stable, sensitive and specific imaging of phospholipids and small metabolites over extended runs enables detailed metabolic mapping in tissue sections. This platform represents a robust solution for advanced spatial metabolomics and lipidomics.

Reference

Using Targeted MRM MS Imaging With DESI to Visually Localize Isobaric And/or Low Abundance Lipids, Waters application note, 720008692.