MALDI-MS imaging of lipids and small molecules in rat brain tissue based on graphene oxide film pre-coated matrix

In the study, single-layer graphene oxide (SLGO) was adsorbed on a conductive glass surface to prepare a uniform thin film. We used this film as the pre-coated matrix in matrix-assisted laser desorption ionization–mass spectrometry (MALDI-MS) imaging to avoid the need of a matrix cover. We investigated the effects of the uniformity and matrix amount required to prepare the pre-coated matrix film for the MALDI-MS experiment. The SLGO water-dispersed suspension was centrifuged to remove the suspended particles and improve the film uniformity. We adopted the SLGO (0.75 mg) and a laser energy of 65%. The MALDI-MS experiment based on the pre-coated SLGO thin film presented repeatabilities (relative standard deviation) of less than 4% for four kinds of chemical samples. Through the MALDI-MS imaging based on the pre-coated matrix, we detected more than 60 kinds of lipids and small molecules, including phospholipids, cyclic adenosine monophosphate, inosine, and cholesterol, in a rat brain tissue slice. We further demonstrated the spatial distribution of the detected compounds in the rat brain tissue by imaging. The conductive glass covered with the SLGO thin film could be stored for more than one month and used directly in MALDI-MS imaging, which eliminated the need for a matrix cover and simplified the MALDI-MS imaging experimental process. • Graphene oxide thin film was applied in MALDI–MS imaging as pre-coated matrix. • The graphene oxide thin film pre-coated matrix can be stored for more than one month and can be used directly in MALDI–MS imaging. • More than 60 lipids and small molecules were detected by using the pre-coated matrix.