Generation of Multiple Images from a Single Tissue Section with Dual Polarity Desorption Electrospray Ionization Mass Spectrometry

Importance of the Topic

Desorption electrospray ionization imaging is a versatile tool for spatially resolved molecular analysis of tissue sections. By combining surface desorption with electrospray ionization, DESI enables rapid metabolite and lipid profiling without specialized sample preparation.

Objectives and Study Overview

This study aimed to demonstrate the feasibility of performing sequential DESI imaging in both negative and positive ion modes on a single tissue section. The goal was to maximize chemical information from one sample and assess the impact of repeated analysis on signal integrity.

Methodology and Instrumentation

Tissue preparation included cryo sectioning of porcine and human liver samples at 15 micron thickness. Sections were thaw mounted on glass slides and analyzed at room temperature. Imaging was carried out using a SYNAPT G2 Si HDMS mass spectrometer fitted with a 2D DESI source. Spray solvent was a 90 10 methanol water mix delivered at 1.5 microliters per minute under 100 psi of nitrogen. A 5 kilovolt potential was applied for both ion modes. Spatial resolution was set at 150 microns using a raster speed of 0.15 millimeters per second and 0.15 millimeter lateral step size. Data acquisition used one second scan cycles and was processed with HDI Software version 1.3.

Main Results and Discussion

• Repeated imaging of the same tissue region in negative then positive mode yielded comparable high quality spectra with minimal signal loss.
• Key lipid and metabolite distributions were observed across both polarities without significant alteration of chemical signatures.
• Comparative analysis of spectra before and after negative mode imaging confirmed the tissue surface remained chemically intact for subsequent positive mode analysis.
• Application to a tumor containing liver section revealed distinct lipid markers differentiating healthy and tumor areas in each polarity.

Benefits and Practical Applications

• Eliminates the need for multiple adjacent sections, preserving precious or limited samples.
• Provides extended molecular coverage by combining positive and negative ion data from one section.
• Maintains tissue architecture for follow up histological staining or other surface analyses.
• Simplifies workflow by avoiding changes in solvent or hardware between runs.

Future Trends and Opportunities

Advancements in DESI source design and high mass resolution instrumentation may further improve spatial resolution and sensitivity. Integration with other imaging modalities and multimodal data analysis could lead to comprehensive tissue characterization. Application to clinical biopsies and drug distribution studies represents a promising area for translation.

Conclusion

Optimized DESI imaging conditions allow dual polarity analysis on a single tissue section without compromising signal quality or tissue integrity. This approach enhances molecular coverage and preserves sample for additional assays, offering significant advantages for biological and clinical research.

Reference

1. Claude E and Jones E Generation of Multiple Images from a Single Tissue Section with Dual Polarity DESI Imaging Waters Corporation 2015