Hydrodynamic Co-Localization of Molecules in Supported Lipid Bilayers Detected by Secondary Ion Mass Spectrometry

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Here we report on the use of secondary ion mass spectrometry (SIMS) to study the hydrodynamic co-localization of membrane components in supported lipid bilayers formed by the fusion of multi-component giant unilamellar vesicles to oxidized silicon substrates. In these experiments, hydrodynamic drag forces arising from flow above the supported lipid bilayer (SLB) results in the directed motion of molecules protruding from the SLB. In this particular case, protrusion of the cholera toxin B into the aqueous layer serves as a handle for the directed motion of its natural ligand, ganglioside GM1, and any other molecule (i.e. cholesterol) strongly associated with it. Orthogonal isotopic labeling or fluorination of every lipid bilayer component allowed generation of molecule-specific images, using a nanoSIMS, that map the lateral re-distribution of molecules in a lipid bilayer as a result of hydrodynamic flow. Furthermore, simultaneous detection of up to seven different ion species, including secondary electrons, allowed generation of ion ratio images whose signal intensity values could be correlated to composition through the use of calibration curves from standard samples.