In a vacuum chamber, a focused primary ion beam (such as Ga+, Bi3+ cluster ions) bombards the sample surface at high energy, giving surface atoms/molecules enough energy to sputter out as charged secondary ions. These secondary ions pass through a mass analyzer (usually TOF) where they are separated and detected by their m/z, and point-by-point scanning yields the spatial distribution map of elements and molecules.
Since the primary beam can be focused to a very small spot, SIMS's spatial resolution is determined by the beam spot size; TOF-SIMS, with cluster ion sources and fine focusing, can reach sub-micron and even nanometer scale. This is why it leads in resolution among the three major imaging sources.
Resolution depends on the focusing capability of the primary ion beam and the control of sputter yield. When the beam spot shrinks to the nanometer scale and each bombardment removes only a very few surface atoms, ultra-fine spatial information can be obtained with almost no destruction of the overall structure. Combined with the high throughput and full-mass acquisition of the TOF analyzer, a single pixel can simultaneously record multiple elements and fragment ions.
Precisely because the beam spot is extremely small, SIMS imaging often has a huge number of pixels and massive data volume, imposing higher requirements on positioning accuracy, charge compensation, and the data system. It is the imaging source that 'sees the finest', but at the cost of a trade-off between throughput and molecular fidelity.
SIMS has outstanding advantages in imaging element distribution, small-molecule drugs, lipids, and surface components. The abundant fragments brought by hard ionization make it good at distinguishing isomers and surface chemical states; it is widely used in materials science, semiconductors, forensics, biological membrane lipid distribution, and drug nanocarrier localization.
| Dimension | SIMS / TOF-SIMS | MALDI | DESI |
|---|---|---|---|
| Resolution | Sub-micron–nanometer | Tens of μm | Tens–hundreds of μm |
| Ionization environment | High vacuum | Vacuum | Ambient |
| Excels at | Elements/small molecules/fragments | Proteins/peptides/lipids | Metabolites/lipids/drugs |
| Ionization type | Hard ionization | Soft ionization | Soft ionization |
SIMS is a hard ionization method with strong molecular fragmentation; the probability of directly giving molecular ions is low, so it is mostly used for information at the element and fragment level, and molecular identification is relatively complex; high-energy bombardment may also cause some damage to the sample and is poorly suited to thermally sensitive or volatile molecules; quantification requires standards and calibration, a cumbersome process. In addition, the vacuum requirement raises the preparation threshold.
Therefore SIMS is often combined with routes such as MALDI, DESI, and LDPI: SIMS tackles nanometer-scale element/small-molecule problems, while other soft ionization sources supplement broad molecular-level coverage. At the single-cell/subcellular level, Neo-Source LDPI (2–3 μm) and SIMS (nanometer scale) respectively cover the different needs of 'cellular scale' and 'subcellular/molecular scale'.
To obtain detailed specifications, compatible models, or a quotation for the MSI LDPI / DPI full series imaging ion sources, visit the Neo-Source official website, or contact the official team for compatibility advice tailored to your mass spectrometer (Agilent / SCIEX / Thermo and other mainstream MS).