Analysis of liposome model systems by time-of-flight secondary ion mass spectrometry

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is an important technique for studying chemical composition of micrometer scale objects due to its high spatial resolution imaging capabilities and chemical specificity. In this work we focus on the application of ToF-SIMS to gain insight into the chemistry of micrometer size liposomes as a potential model for neurotransmitter vesicles. Two models of giant liposomes were analyzed: histamine and aqueous two phase system (ATPS)-containing liposomes. Characterization of the internal structure of single fixed liposomes was done both with the Bi₃⁺ and C₆₀⁺ ion sources. The depth profiling capability of ToF-SIMS was used to investigate the liposome interior.