Epifluorescence micrographs of a lipid monolayer containing 31%
egg-SM, 31% DMPC, 7% GM1, 30% DChol, and 1% F-DHPE at a surface
pressure of 6 mN/m. (The phase diagram of this mixture is shown
in Fig. 1D, where the “+” symbol denotes the
pressure-composition conditions used here.) The subphase contains
Alexa-labeled CT-B. (A) View of the monolayer when
observed with a F-DHPE-specific filter that excludes Alexa emission.
(B) View of the same monolayer region when observed with
an Alexa specific filter that excludes F-DHPE emission. When this
monolayer is pressurized, all of the domains go through a critical
phase transition at roughly the same pressure, suggestive of proximity
to a tricritical point. The probe distribution demonstrates three
coexisting phases.