Development of a high sensitivity atmospheric MALDI-2 source for imaging mass spectrometer

Significance of the Topic

The development of atmospheric pressure MALDI-2 addresses inherent MALDI sensitivity limitations by enhancing ionization efficiency for deeper molecular insights.

Objectives and Study Overview

This study upgraded a commercial Shimadzu iMScope QT with a laser-based post-ionization (MALDI-2) module and evaluated its performance on rat liver and heart tissues to detect lipids and small metabolites.

Methodology and Instrumentation

• Instrumental Setup: Shimadzu iMScope QT with 266 nm laser-2 positioned 0.5 mm above the sample for post-ionization; laser parameters: 1 kHz repetition rate, 600 μJ pulse energy, 105 μs delay, 30 shots, 20 μm pixel size.
• Sample Preparation: 8 μm cryosections on ITO slides coated with DHB matrix via iMLayer.
• Data Acquisition and Analysis: Positive mode MSI with and without MALDI-2; processed using IMAGEREVEAL software.

Main Results and Discussion

• Optimal laser-2 alignment within 0.1 mm was critical; delay time optimization less critical.
• MALDI-2 increased diacylglycerol signals (m/z 600) several-fold; overall detected m/z features rose by ~50% vs conventional MALDI.
• Rat liver and heart imaging revealed additional lipids and metabolites not seen with laser-2 off.

Benefits and Practical Applications

• Improved detection of low-abundance lipid and metabolite species in tissue imaging.
• Enhanced chemical signature differentiation for MSI-based research.
• Compatible retrofit for existing atmospheric MALDI platforms.

Future Trends and Utilization

1. Incorporation of higher repetition rate lasers for increased throughput.
2. Extension to diverse analytes including clinical biomarkers and drugs.
3. Integration with high-resolution mass analyzers for deeper molecular mapping.
4. Automation of alignment and parameter optimization for routine workflows.

Conclusion

Atmospheric MALDI-2 on the iMScope QT significantly enhances sensitivity and molecular coverage in MSI, enabling discovery of previously undetected lipids and small molecules through optimized post-ionization.

References

1. Soltwisch J. et al. Science 348, 211–215 (2015)
2. Niehaus M. et al. J Am Soc Mass Spectrom 31, 2287–2295 (2020)
3. Frache G. ASMS Conference Abstract (2024)