Matrix-assisted laser desorption/ionization mass spectrometry and Raman spectroscopy: An interesting complementary approach for lipid detection in biological tissues

Recently, matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) has emerged as a powerful technique to study the distribution of lipids. However, quantification still remains a challenge because the MALDI signal is strongly affected by ion suppression effects. On the contrary, Raman spectroscopy is recognized as a non-destructive analysis method and spectral images can also be acquired. The combination of these two techniques was applied for lipids detection in tissue sections. In MALDI, two lipids families (glycerophosphocholine, PC; gycerophosphoethanolamine, PE), three MALDI matrices (1,5-diaminonapthalene, 1,5-DAN; 2,5-dihydroxybenzoic acid, 2,5-DHB; alpha-4-hydroxicinammic acid, CHCA), and various mixtures of lipids were investigated. The nature of the lipid, as well as the nature of the matrix and the composition of the sample influences the signal of a given lipid. In Raman, despite a strong overlap with the spectrum of the native tissue, an intensity profile constructed along the diameter of the section clearly shows that the signature of one given lipid (a glycerophosphocholine) can be detected on a doped biological sample. Practical applications: This study highlights some important factors that should be considered in future lipids analyses by MALDI MSI and Raman spectroscopy. Ultimately, a combined approach of these two techniques will give information for instance about the alteration of the lipid metabolism associated with specific diseases.