Fully automated chemical imaging with LA-REIMS

Significance of the Topic

Mass spectrometry chemical imaging enables spatially resolved metabolic profiling of tissue sections without extensive sample preparation. This capability is highly valuable in histological assessment, drug monitoring, and biomedical research where preserving sample integrity and achieving high spatial resolution are critical.

Objectives and Overview of the Study

This work aimed to design, implement, and validate a fully automated imaging platform based on Laser Assisted–Rapid Evaporative Ionization Mass Spectrometry (LA-REIMS). The performance of the LA-REIMS system was benchmarked against Desorption Electrospray Ionization (DESI) imaging to assess spectral differences and imaging quality.

Methodology and Instrumentation

The system integrates a 2940 nm Opolette 2940 laser with a Pannoramic Scan II automatic slide sorter and a Xevo G2 QTof mass spectrometer equipped with a REIMS interface. Custom, MassLynx-compatible software controls ROI selection, laser firing, and data acquisition. Key setup elements include:

• ZnSe aspheric lens (f = 12.7 mm) and CaF2 beamsplitter for optimized laser focus
• Motorized linear translation stages for precise slide movement
• Neutral density filters and alignment plates to ensure round spot size
• Negative ion mode operation in sensitivity settings for lipid-rich tissue analysis

Main Results and Discussion

Proof-of-concept experiments demonstrated successful generation of chemical images at 50 µm resolution on diverse tissue types, such as cancerous dog testicle sections. Comparative studies revealed that LA-REIMS spectra were enriched in phosphatidylethanolamines (with ammonia loss), whereas DESI spectra showed higher phosphatidylinositol content. Multivariate analysis (PCA) and supervised classification (LDA) achieved accurate discrimination of mouse brain regions, confirming the system’s capability for tissue phenotyping.

Benefits and Practical Applications

The automated LA-REIMS platform offers several advantages:

• High throughput processing of up to 150 slides with minimal user intervention
• Ambient, preparation-free imaging that preserves native tissue chemistry
• Micro-scale spatial resolution supporting detailed metabolic mapping in research and clinical workflows

Future Trends and Opportunities

Potential developments include:

• Integration with machine learning algorithms for real-time tissue classification
• Combining LA-REIMS with optical imaging modalities for multimodal analysis
• Application in personalized medicine for in situ metabolic profiling and biomarker discovery

Conclusion

An integrated, fully automated LA-REIMS imaging system has been established, delivering high-resolution (50 µm) chemical images with robust classification performance. This approach offers a complementary alternative to DESI and holds promise for expansive use in analytical and clinical laboratories.

Instrumentation

• Opotek Opolette 2940 laser (2940 nm)
• Pannoramic Scan II automatic slide sorter (3DHISTECH)
• Waters Xevo G2 QTof mass spectrometer with REIMS interface
• Custom MassLynx-compatible control software
• ZnSe aspheric lens, CaF2 beamsplitter, motorized linear stages