Many ionization methods (MALDI, laser ablation, LAESI, etc.) mainly perform the first step of transferring molecules into the gas phase, while only a portion actually becomes charged. Post-ionization separates the step of charging molecules and applies a second ionization field in the gas-phase plume, thereby increasing the overall ion yield.
This decoupling brings methodological flexibility: the primary step can focus on gentle desorption to preserve molecular structure, and the post-ionization step focuses on improving ionization efficiency; the two parameters can be optimized separately without interfering with each other.
By energy source, post-ionization can be divided into laser-induced post-ionization (using a second laser to photoionize neutral molecules), plasma/corona discharge-assisted ionization, and electron-beam-mediated ionization, among others. MALDI-2 is a typical implementation of laser-induced post-ionization in tissue imaging; LDPI and DPI achieve similar gain goals through photoionization in a matrix-free context.
Different post-ionization methods differ in applicable molecules and background characteristics: laser-induced is sensitive to wavelength and timing, while discharge-assisted is more friendly to ambient environments. Selection needs to integrate sample preparation (whether matrix is used) and the host platform.
The most intuitive value of post-ionization is to expand the types of detectable molecules and improve the signal-to-noise ratio of low-abundance species, especially significant in lipid and metabolite imaging. It does not change pixel resolution, so it can be overlaid with high-resolution imaging sources.
The cost is an additional parameter space (energy, timing, position) and method-development cost; improper settings will simultaneously amplify background and matrix signals. Post-ionization is generally a complementary acquisition mode rather than an independent replacement.
Neo-Source LDPI (laser desorption photoionization) and DPI (dual photoionization) belong conceptually to the same approach of enhancing the ionization of weak-signal molecules, but are implemented in a matrix-free, ambient manner, eliminating matrix spraying and sample preparation. Post-ionization (such as MALDI-2) is mostly built on a matrix desorption system.
For users who do not want matrix interference and require in-situ ambient conditions, LDPI/DPI can be prioritized; for users with existing MALDI platforms who want low-cost expansion of weak-signal coverage, MALDI-2-type post-ionization modules are more direct.
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).