Mass spectrometry imaging of untreated wet cell membranes in solution using single-layer graphene

We report a means by which atomic and molecular secondary ions, including cholesterol and fatty acids, can be sputtered through single-layer graphene to enable secondary ion mass spectrometry (SIMS) imaging of untreated wet cell membranes in solution at subcellular spatial resolution. We can observe the intrinsic molecular distribution of lipids, such as cholesterol, phosphoethanolamine and various fatty acids, in untreated wet cell membranes without any labeling. We show that graphene-covered cells prepared on a wet substrate with a cell culture medium reservoir are alive and that their cellular membranes do not disintegrate during SIMS imaging in an ultra-high-vacuum environment. Ab initio molecular dynamics calculations and ion dose-dependence studies suggest that sputtering through single-layer graphene occurs through a transient hole generated in the graphene layer. Cholesterol imaging shows that methyl-beta-cyclodextrin preferentially extracts cholesterol molecules from the cholesterol-enriched regions in cell membranes.

Automated summary

This study demonstrates a method for sputtering atomic and molecular secondary ions through single-layer graphene to enable SIMS imaging of untreated wet cell membranes at subcellular resolution. The findings show that the method allows observation of lipid distribution in cell membranes without labeling, and that cells remain intact during imaging. Additionally, molecular dynamics calculations and ion dose-dependence studies suggest that sputtering through graphene occurs through a transient hole in the graphene layer.