Relative quantification of cellular sections with molecular depth profiling ToF-SIMS imaging

We report the use of secondary ion mass spectrometry (SIMS) imaging to quantify the relative difference in the amount of lipid between two sections, the plasma membrane and the cytoplasm, of single cells from two different populations. Cells were each labeled with lipophillic dyes, frozen, fractured and analyzed in a ToF-SIMS mass spectrometer equipped with a 40 keV C₆₀⁺ ion source. In addition to identifying cells from separate populations, the lipophilic dyes can be used as a marker for the outer leaflet of the cell membrane and therefore as a depth finder. Here, we show that it is possible to compare the amount of lipids with particular headgroups in the cell membrane of a treated cell to the membrane of a control cell. Following erosion of the cell membranes, the amount of the two specific lipid head groups in the cytoplasm of the treated cell can be compared to those lipids in a control cell. Here we take the first step in this experimental design and display the ability to analyze multiple sections of frozen cells following a single fracture.