Faculty of Science Faculty of Science

Mass spectrometry imaging

Mass spectrometry imaging is a technique used to visualize the spatial distribution of ionized molecules in a sample. For every XY position on the sample (i.e., a pixel or a voxel), an MS (or MS/MS) spectrum is acquired. The spatial or lateral resolution depends on the ionization technique (e.g., SIMS, MALDI, DESI, etc.) and the mass spectral resolution depends on the mass analyzer (e.g., TOF, orbitrap, etc.). 

There are currently two MS imaging instruments at UniGe: a DESI-HDMS at the CHEMBIO MS - Molecules platform, and a Tof-SIMS on the LTA premises. A brief description of their capabilities is given below.

Sample preparation for MS imaging techniques differs somewhat from traditional morphological visualization methods, particularly in the choice of embedding medium for tissue sectioning. The widely used "optimal cutting temperature" (OCT) embedding medium consists of polymers that ionize well in mass spectrometry, often suppressing the signals of the compounds of interest. Hence, we advise contacting us prior to embedding your tissues to discuss alternative embedding media appropriate for MS imaging experiments.

 

DESI-HDMS

Desorption ElectroSpray Ionisation High Definition Mass Spectrometry (DESI-HDMS) imaging is characterized by its moderate spatial resolution but high spectral resolution with or without ion mobility separation (IMS).

The DESI-XS interface is installed on a Synapt G2-Si HDMS instrument (Waters), and located at lab 3-333 at Science II. The DESI-XS interface was purchased by Pr. Yogeshvar N. Kalia (School of Pharmaceutical Sciences) for his own research, and is generously made available to the CHEMBIO MS - Molecules platform.

Capabilities:

  • Molecular imaging at moderate spatial resolution (50-200 µm)
  • In situ IMS separation and/or MS/MS characterization
  • Suitable for mapping small molecules (metabolites, lipids, pharmaceuticals, etc.) and polymers

 

Tof-SIMS

Time of Flight-Secondary Ion Mass Spectrometry (ToF-SIMS) imaging is characterized by its high spatial resolution for mapping both elements and organic molecules on solid surfaces including tissue and cells.

The nanoTOF II ToF-SIMS instrument (Physical Electronics, inc.) is located at lab-041 at AEM.

Capabilities:

  • Chemical imaging at high spatial resolution (sub-µm)
  • Depth profiling of inorganic ad organic materials
  • In situ MS/MS characterization
  • Suitable for mapping elements, small molecules (metabolites, lipids, pharmaceuticals, etc.), polymers, and tagged macromolecules