Soltwisch, J. et al. Science 348, 211–215 (2015).

Matrix-assisted laser desorption/ionization (MALDI)-based mass spectrometry imaging is used to image the distribution of various biological molecules in tissue slices, thus providing both spatial and molecular information. A limiting factor, however, has been the low sensitivity of the technology, a result of poor ionization; on average, just 1 out of 1,000 biomolecules that is desorbed is ionized. Soltwisch et al. report a strategy called MALDI-2, which improves the sensitivity of MALDI imaging by up to two orders of magnitude. In MALDI-2, a wavelength-tunable positionization laser initiates a secondary ionization process in the gas phase. This allowed the authors to identify many more biomolecules—including various lipid species, fat-soluble vitamins, oligosaccharides and glycosides—imaged in both plant and animal tissue, with a very high lateral resolution of 5 micrometers.