TABLE 1.
Differences between matrix-assisted laser desorption/ionization (MALDI), secondary ion mass spectrometry (SIMS), and desorption electrospray ionization (DESI) (Svatos, 2010; Yang et al., 2020).
| MALDI | SIMS | DESI | |
|---|---|---|---|
| Beam source | Primary ion | Secondary ion | Primary ion |
| Ionization method | UV-laser | primary charged particles (Cs+, SF5 +, Au, and Sb clusters, C60 +) eject and ionize material from surface | Modified ESI source spraying solvent using high-pressure gas flow on the sample surface |
| Sample preparation | Freezing microtome section and matrix application is needed | Freezing microtome section is needed, then directly analyzed | Directly analyzed |
| Matrix | Needed | None | None |
| Environment | Vacuum | Vacuum/low pressure | Atmosphere |
| Space resolution | 10–100 µm | 100 nm∼1 µm | 40–200 µm |
| Sample damaging level | High | Low | Low |
| Detected object | All kinds of biological samples, no limitation of molecular weight | Hydrophobic compounds with molecular weight not exceeding 1,000 Da | Compounds with molecular weight not exceeding 2,000 Da |