Matrix assisted laser desorption ionization is a soft ionization technique which enables the detection of high molecular weight molecules like oligo-saccharides, proteins, peptides and polymers. In contrast to ESI ionization, MALDI produces far less multiply charged ions. Typically the dried-droplet method is used to co-crystalize the matrix with the sample. Common matrix compounds are 2,5-dihydroxy benzoic acid (DHB), sinapinic acid (SA), α-cyano-4-hydroxycinnamic acid (HCCA).
MALDI-imaging (MALDI-MSI) is a mass spectrometric imaging technique to localize molecules in tissue sections of organs, plants or any other material of interest. With that, the spatial distribution of for example proteins, peptides, lipids and other small molecules within a thin tissue section can be visualized and helps to identify markers for specific regions.
MALDI-Imaging is a four step process. First the thin tissue section has to be prepared with a cryotome. Second, the matrix has to be applied using the ImagePrep system (Bruker) or by sublimation. Thirdly, the prepared tissue section are measured with the MALDI-TOF and lastly the obtained data is analyzed using FlexImaging or the SCiLS software package.