Lipid monolayers were formed using a KSV NIMA KN 2002 (Biolin Scientific, Stockholm, Sweden) Langmuir trough (273 cm 2 ). Whatmann filter paper was used as a Wilhelmy plate to monitor surface pressure. Lipid mixtures dissolved in chloroform were spread on water (>18 MΩ from Milli-Q system) within the clean trough using a glass syringe. The chloroform was left to evaporate for 10 minutes and the barriers were compressed at 10 mm/min until the surface pressure reached 32 mN/m. Plasma cleaned NanoSIMS substrates were glued to a glass slide and pulled through the air-water interface at a rate of 1 mm/min while the surface pressure was maintained at 32 mN/m. Lipid monolayers were not subjected to freezedrying, as unlike SLBs, lipid monolayers are stable in air. Both lipid monolayers and freeze-dried lipid bilayers were stored in a desiccator when not being analyzed via NanoSIMS.