MSI ion source = general ionization principle + spatially resolved desorption/ionization mechanism. It acts on sample surfaces such as tissue sections point by point according to a raster; each action produces a beam of ions that enters the mass analyzer, and software then colors the intensity of specific m/z by coordinates into an image. In other words, an ordinary ion source answers 'what is in the sample', while an imaging ion source additionally answers 'what is at each position, and how much'.
From a systems perspective, an imaging system = imaging ion source + mass analyzer + sample positioning/scanning platform + imaging software. Among these, the imaging ion source determines the ionization method, whether matrix is required, ambient/vacuum, and the resolution scale; the mass analyzer determines mass accuracy and acquisition speed; the positioning platform determines pixel coordinate accuracy. The three together determine the final imaging quality.
General-purpose ion sources (ESI, MALDI, APCI, etc.) serve liquid/gas phase injection and do not directly provide spatial resolution; but when ESI is modified into DESI/nano-DESI, MALDI is used for section scanning, or post-ionization routes such as LDPI/DPI are introduced, they gain imaging capability. Therefore the 'MS ion source' is the parent technology of the 'MSI ion source'; the two share the same ionization physics but diverge in system configuration.
Understanding this relationship is important: when selecting, if you already have a mainstream mass spectrometer host (such as Agilent/SCIEX/Thermo), you often do not need to replace the entire instrument, but rather extend imaging capability with an external imaging ion source (such as Neo-Source LDPI/DPI, which is compatible by model), which involves lower investment and faster deployment than purchasing a whole imaging system.
MALDI: Matrix-Assisted Laser Desorption/Ionization, operating under vacuum and requiring matrix spraying, with resolution on the order of tens of micrometers, excelling at proteins/peptides/lipids/sugars, and is the most widely used imaging source. DESI: Desorption Electrospray Ionization, ambient open-air and matrix-free, with resolution from tens to hundreds of micrometers, excelling at metabolite/lipid/drug distribution. SIMS: Secondary Ion Mass Spectrometry, bombarding the sample with primary ions under vacuum, with sub-micron to nanometer resolution, hard ionization with many fragments, excelling at elements/small molecules.
| Dimension | MALDI | DESI | SIMS |
|---|---|---|---|
| Ionization environment | Vacuum | Ambient | High vacuum |
| Matrix required | Required | Not required | Not required |
| Resolution scale | Tens of μm | Tens–hundreds of μm | Sub-micron–nanometer |
| Molecules excelled at | Proteins/peptides/lipids | Metabolites/lipids/drugs | Elements/small molecules/fragments |
| Main limitations | Matrix interferes in low-mass region | Polarity bias / ion suppression | Hard ionization, sample damage-prone |
Selection should revolve around four dimensions: spatial resolution (determines whether cells/subcells can be resolved; single-cell requires μm-level), whether matrix is required (matrix-free significantly reduces small-molecule background and simplifies sample preparation), ionization environment (ambient suits in-situ/live analysis; vacuum gives cleaner background), and instrument compatibility (modular external add-on lowers investment). In addition, sensitivity, polarity coverage, scan speed, and the maturity of the data analysis pipeline must also be considered.
Taking recent popular incremental demands as an example: 'matrix-free', 'ambient operation', and 'single-cell resolution' are becoming focal points of R&D interest. Neo-Source MSI LDPI is designed around these three points — matrix-free, ambient, 2–3 μm resolution; MSI DPI offers no polarity bias and high sensitivity (1–4 orders of magnitude higher than traditional DESI), compatible with high-throughput analysis.
Sample preparation differs significantly across sources: MALDI requires matrix spraying and co-crystallization, and section thickness and matrix choice affect results; DESI/LDPI/DPI ambient matrix-free routes have simpler preparation, but require controlling surface flatness and air background; SIMS requires high vacuum and conductive/ultra-thin samples. Regardless of the route, tissue section quality, slide conductivity, and freezing/embedding method all significantly affect the image.
At the data level, imzML has become a cross-platform common format, and software such as SCiLS Lab, MetaboScape, and MSiReader are used for image reconstruction, alignment, and statistical analysis. When selecting, one should also confirm whether the imaging source vendor provides supporting software or standard-format export, to ensure smooth follow-up analysis.
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).