The capillary applies high voltage so the outflow forms a Taylor cone and ejects charged droplets; solvent evaporation shrinks droplets and raises charge density, finally releasing the analyte as quasi-molecular ions ([M+H]+, [M-H]-) into the gas phase via Coulomb explosion or ion evaporation. The whole process is low-energy, preserving molecular structure.
Because it directly produces quasi-molecular ions, ESI is ideal for direct molecular identification and is a representative of soft ionization; but it has limited response for hard-to-electrospray, nonpolar, or thermally unstable molecules.
ESI-MSI (electrospray imaging) applies the ESI spray directly to the tissue surface to desorb and ionize molecules, scanning point by point to reconstruct distribution; it is a close relative of DESI. It retains ESI's friendliness to polar large molecules and samples in-situ under ambient, matrix-free conditions.
ESI-MSI, DESI, and Nano-DESI all belong to the electrospray family, differing in spray geometry and desorption method; for tissue imaging, DESI/Nano-DESI are more common, but ESI-MSI unifies liquid-phase ionization and imaging conceptually.
ESI is the absolute main force of LC-MS, supporting most proteomics, metabolomics, and drug quantification; in imaging, it is the precursor and basis of the ESI-MSI/DESI system. Its high resolution with Orbitrap and Q-TOF enables precise molecular assignment.
For matrix-free ambient imaging, sources such as Neo-Source LDPI/DPI can pair with ESI-system analyzers (ambient interfaces) to form high-resolution imaging solutions.
ESI is sensitive to matrix effects (signal suppression in complex extracts) and needs front-end separation for large-volume samples; direct imaging is affected by spray spot and surface, with resolution typically microns to tens of microns. For small nonpolar molecules, APPI/APCI or matrix-free photochemical sources may be better.
Selection advice: for proteins/peptides/polar large molecules and LC-MS, prioritize ESI; for in-situ distribution imaging prioritize imaging sources such as DESI/LDPI/DPI.
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).