Laser Activated Electron Tunneling-Based Mass Spectrometric Imaging (LAET-MSI) of Molecular Architectures of Mouse Brain Reveals Regional Specific Lipids.

A comprehensive description of overall brain architecture at the molecular level is essential for understanding behavioral and cognitive processes in health and diseases. Although fluorescent labeling of target proteins has been successfully established to visualize a brain connectome, the molecular basis for diverse neurophysiological phenomena remains largely unknown. Here we report a brain-wide, molecular-level, and microscale imaging of endogenous metabolites, in particular, lipids of mouse brain by using laser activated electron tunneling (LAET) and mass spectrometry. In this approach, atomic electron emission along with finely tuned laser beam size provides high resolution that can be down to the sub-micrometer level to display spatial distribution of lipids in mouse brain slices. Electron-directed soft ionization has been achieved through exothermal capture of tunneling photoelectrons as well as unpaired electron-initiated chemical bond cleavages. Regionally specific lipids including saturated, mono-unsaturated, and poly-unsaturated fatty acids as well as other lipids, which may be implicated in neurological signaling pathways, have been discovered by using this laser activated electron tunneling based mass spectrometric imaging (LAET-MSI) technique.