Full Spectrum Molecular Imaging on the SYNAPT XS: Combined Imaging Techniques Yield Comprehensive Results

Significance of the Topic

Full Spectrum Molecular Imaging (FSMI) integrates complementary mass spectrometry techniques to deliver holistic spatial mapping of biomolecules. By combining DESI, MALDI, and ion mobility separations on a single platform, it enables detailed visualization of metabolites, lipids, peptides, and proteins without labels, facilitating insights into disease mechanisms, drug distribution, and tissue heterogeneity.

Study Objectives and Overview

This work demonstrates the enhanced capabilities of the Waters FSMI solution on the SYNAPT XS system equipped with the new DESI XS source. Objectives include:

• Showcasing the complementary information from DESI and MALDI imaging.
• Evaluating detection limits, sensitivity, and spatial resolution across multiple analyte classes.
• Validating the integrated workflow using tissue models and pharmaceutical standards.

Methodology and Instrumentation

Tissue sections (10–15 µm) were prepared via cryostat followed by optional H&E staining. Imaging was performed sequentially with:

• DESI XS source under ambient conditions, requiring minimal sample prep.
• MALDI imaging after matrix application in intermediate vacuum.
• Ion mobility separations (HDMS E and SONAR) on the SYNAPT XS high-resolution mass spectrometer.
• Data alignment, processing, and visualization using Waters HDI software and MassLynx.

Key Results and Discussion

Comparative imaging of kidney cortex versus medulla highlighted distinct lipid distributions detected preferentially by DESI for small molecules and by MALDI for larger species. A panel of 24 pharmaceutical compounds was screened, revealing:

• DESI provided lower-limit detection for many small drugs with no matrix background.
• MALDI excelled for analytes benefiting from matrix ionization.
• Combined use increased overall molecular coverage beyond either technique alone.

Benefits and Practical Applications

• Label-free mapping of endogenous and exogenous compounds in tissue.
• High spatial resolution (5–20 µm) for detailed histological correlation.
• Rapid data acquisition and processing for large datasets.
• Flexibility to perform multiple imaging modalities on the same sample.

Future Trends and Opportunities

Advances may include higher throughput via automated slide loading, sub-micron spatial resolution, integration with other omics platforms, and AI-driven image analysis. Expanded applications in clinical research, drug development, and biomarker discovery are anticipated.

Conclusion

The FSMI solution on SYNAPT XS with DESI XS and enhanced HDI software offers a versatile, sensitive, and comprehensive tool for molecular imaging. Its multi-modal approach significantly extends analytical capabilities for research in disease mechanisms and pharmaceutical distribution.

References

1. Anal. Chem. 2018, 90, 9, 5637–5645. Exploring Ion Suppression in Mass Spectrometry Imaging of a Heterogeneous Tissue.
2. Waters Application Note 720005947en. DESI-Mass Spectrometry Imaging Investigation of Discrete and Cassette Drug Dosed Tissues.
3. Evaluation of the Ionization Efficiency Between MALDI and DESI MSI for the Analysis of Pharmaceutical Compounds, 2018 poster. Claude & Towers.