SIMS imaging is performed in a vacuum chamber: after the sample is fixed on a target stage, the primary ion beam bombards point by point according to a preset raster; at each coordinate the sputtered secondary ions are collected by the mass analyzer as a frame of full spectrum. The whole process corresponds beam-spot position and spectrum one to one, forming a three-dimensional data cube of 'coordinate—m/z—intensity'.
After imaging, the software projects each pixel's intensity to space by the selected m/z window, obtaining the 2D distribution map of that ion; switching different m/z reconstructs multiple molecular and element distributions on the same data. Because the TOF analyzer records a full spectrum at every pixel, the data is 'acquire once, reconstruct many times', with no need to repeat experiments later.
SIMS is best at spatial distribution of elements and isotopes (such as metal ions in tissue, labeled elements in drugs), small-molecule fragments and some polymers, with outstanding value in materials, semiconductor and biological thin-layer research. For biological tissue, freezing or conductive treatment is often needed to suppress charging and morphological distortion.
For drugs and endogenous metabolites, SIMS mostly detects them as fragments or characteristic adduct ions, needing standards or fragment rules for annotation; layer-by-layer sputtering also enables depth profiling, observing the longitudinal distribution of molecules on a cross-section, a relatively unique capability.
Hard ionization makes SIMS molecular ion signals weak and fragments many, and imaging and annotation of intact large molecules difficult; sputtering consumes the sample and also limits continuous imaging depth. These limits make SIMS complementary to matrix-free ambient sources: the former targets the ultra-fine scale, the latter targets large-scale small-molecule low-background imaging.
In practice, combine by scientific question: use SIMS to probe subcellular elements and ultra-structure, and use Neo-Source LDPI at ambient matrix-free for single-cell-scale small-molecule metabolite distribution; the two complement in scale and molecule type.
| Dimension | SIMS | matrix-free ambient source (such as LDPI) |
|---|---|---|
| Resolution | nanoscale | 2–3 μm (Neo-Source LDPI) |
| Working condition | high vacuum | ambient, matrix-free |
| Strength | elements, isotopes, small-molecule fragments | small-molecule drug/metabolite low background |
| Limit | hard ionization, hard to quantify | focus on small molecules, coarser scale than SIMS |
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).