MALDI bombards a sample coated with organic matrix using a laser; the matrix absorbs the energy to desorb and softly ionize the analyte, and this matrix dependence is its defining feature. DESI uses charged droplets to strike the sample surface, desorbing and ionizing molecules by droplet momentum, entirely ambient and matrix-free.
SIMS, by contrast, bombards the sample with a focused primary ion beam (e.g., Ga+, Bi3+), sputtering and ionizing surface molecules; it is a hard ionization, requires no matrix and can operate under ultra-high vacuum. These three mechanisms determine their different trajectories in resolution, background and molecular coverage.
SIMS (especially TOF-SIMS) offers the highest resolution, reaching sub-micrometer or even nanometer scale, and is the only subcellular/nanoscale imaging approach; MALDI is typically several to tens of micrometers, with ambient AP-MALDI slightly lower; DESI is usually tens of micrometers, limited by spray spot size.
The Neo-Source LDPI uses laser desorption plus photoionization to reach 2–3 μm (among the leading in the industry) under matrix-free ambient conditions, filling the gap between 'ambient matrix-free' and 'single-cell resolution'. For nanometer scale, TOF-SIMS is required.
MALDI requires uniformly spraying a small-molecule matrix, a tedious step, and matrix peaks interfere with the low-mass region below m/z<700, so it excels at proteins and peptides (m/z above several thousand); SIMS needs no matrix and has a clean background but is a hard ionization that fragments macromolecules easily, excelling at lipids, metabolites and elements; DESI is matrix-free, ambient and suited to metabolites and lipids.
For small-molecule drug and metabolite imaging, MALDI's matrix background is the main obstacle, whereas the matrix-free routes such as DESI/LDPI/DPI have a cleaner low-mass region. The three can be summarized in one line: MALDI sees macromolecules, SIMS sees nanometers, DESI sees ambient matrix-free metabolism.
Choose MALDI for protein/peptide tissue imaging; choose SIMS for single-cell, subcellular or elemental/lipid nanometer distributions; choose DESI or LDPI/DPI for ambient, matrix-free, rapid tissue metabolism and lipid imaging.
It must be stressed that the three are not mutually exclusive and often complement each other in the same project: use MALDI to see protein distribution, DESI/LDPI to see small-molecule metabolism, and SIMS to see nanometer-scale lipids or elements, then register with H&E to build a multi-scale evidence chain.
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).