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Phase evolution in cholesterol/DPPC monolayers: atomic force microscopy and near field scanning optical microscopy studies
Author(s) -
Yuan C.,
Johnston L. J.
Publication year - 2002
Publication title -
journal of microscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.569
H-Index - 111
eISSN - 1365-2818
pISSN - 0022-2720
DOI - 10.1046/j.0022-2720.2001.00982.x
Subject(s) - dipalmitoylphosphatidylcholine , monolayer , microscopy , fluorescence microscope , optical microscope , fluorescence , chemistry , cholesterol , phase (matter) , analytical chemistry (journal) , materials science , chromatography , membrane , scanning electron microscope , optics , organic chemistry , biochemistry , phospholipid , physics , phosphatidylcholine , composite material
Summary A combination of atomic force microscopy (AFM) and near field scanning optical microscopy has been used to study domain formation in dipalmitoylphosphatidylcholine (DPPC)/cholesterol monolayers with cholesterol concentrations ranging from 0 to 50%. The results show a clear evolution from a mixture of liquid expanded and liquid condensed phases for cholesterol concentrations < 10% to a mixture of liquid expanded and two cholesterol‐containing phases at intermediate concentrations, and finally to a single homogeneous liquid ordered phase for 33% cholesterol. Mixtures of the various phases are clearly identified by height differences in AFM and in some cases by fluorescence imaging for samples containing 0.5% BODIPY dye, which localizes preferentially in the more fluid phase. Note that fluorescence imaging, at least with the dye used here, is unable to distinguish between the cholesterol‐rich and cholesterol‐poor phases detected at intermediate cholesterol concentrations. The combination of fluorescence and AFM imaging provides a more complete picture of the phase evolution for cholesterol/DPPC monolayers than could be obtained by either technique alone, and presents substantial advantages over conventional fluorescence microscopy in that submicrometre‐sized domains can be readily detected.