Secondary ion MS imaging of lipids in picoliter vials with a buckminsterfullerene ion source

Investigation of the spatial distribution of lipids in cell membranes can lead to an improved understanding of the role of lipids in biological function and disease. Time-of-flight secondary ion mass spectrometry is capable of molecule-specific imaging of biological molecules across single cells and has demonstrated potential for examining the functional segregation of lipids in cell membranes. In this paper, standard SIMS spectra are analyzed for phosphatidylethanolamine, phosphatidylglycerol, phosphatidylserine, phosphatidylinositol, cholesterol, and sulfatide. Importantly, each of the lipids result in signature mass spectral peaks that allow them to be identified. These signature peaks are also useful for imaging experiments and are utilized here to simultaneously image lipids on a micrometer scale in picoliter vials. Because the low secondary ion signal achieved for lipids from an atomic primary ion source makes cell-imaging experiments challenging, improving signal with cluster primary ion sources is of interest. Here, we compare the secondary ion yield for seven lipids using atomic (Ga⁺ or In⁺) ion sources and a buckminsterfullerene (C₆₀⁺) primary ion source. A 40-1000-fold improvement in signal is found with C₆₀ ⁺ relative to the other two ion sources, indicating great promise for future cellular imaging applications using the C₆₀⁺ probe.