AP-SMALDI uses a pulsed laser to irradiate the matrix-analyte co-crystallized surface at ambient pressure; the matrix absorbs energy to trigger desorption and primary ionization, and the resulting ions are captured in the ambient plume by ion-optical components (such as a capillary or electrode focusing) and directed into the mass analyzer located in a reduced-pressure region. The key is the ion transmission efficiency from ambient pressure to vacuum, which determines overall sensitivity.
Compared with vacuum MALDI, the target surface of AP-SMALDI is exposed to ambient air or inert atmosphere, and the sample can be irradiated without entering the vacuum chamber, enabling point-by-point scanning in an open environment; matrix spraying, section loading, and other sample preparations are also more flexible.
Vacuum MALDI and transmission-mode MALDI (t-MALDI) complete desorption inside the vacuum chamber, and the ions are directly received by the analyzer with more controllable background; AP-SMALDI sacrifices some vacuum cleanliness for the convenience of ambient operation. All three share the physical basis of matrix-assisted desorption, differing mainly in pressure environment and ion transmission architecture.
In imaging scenarios, AP-SMALDI suits users who need frequent sample changes, samples with size limitations, or emphasize in-situ operation; transmission-mode MALDI still has advantages in ion yield and resolution. Selection should weigh resolution requirements, sample throughput, and sample preparation workflow.
AP-SMALDI can image peptides, proteins, and lipids on tissue sections such as brain, liver, and tumors; spatial resolution is limited by the laser focal spot and scan step, typically on the order of tens of micrometers. Its ambient nature facilitates coupling with optical microscopy for morphology-molecular comparison within the same field of view.
Samples require sample preparation such as matrix spraying; for heat-sensitive or easily oxidized molecules, the ambient air environment may introduce additional oxidation background, and operation under inert atmosphere or humidity-controlled conditions can be used to suppress interference when necessary.
AP-SMALDI can serve as an ambient complement to MALDI imaging platforms, working with analyzers such as Orbitrap and TOF. For laboratories that want to obtain MALDI imaging capability at a lower vacuum-retrofit cost, it is one of the alternative paths to vacuum MALDI.
If the project emphasizes matrix-free, no-sample-preparation, or ambient in-situ live sampling, Neo-Source LDPI, DPI, and other matrix-free ambient imaging sources can also be compared, selected according to the analyte polarity and acceptance of sample preparation.
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).