Phase evolution in cholesterol/DPPC monolayers: atomic force microscopy and near field scanning optical microscopy studies.
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.
Yuan
C
C
Steacie Institute for Molecular Sciences, National Research Council Canada, Ottawa, ON K1A 0R6 Canada.
Johnston
L J
LJ
D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry*; D001896:Boron Compounds; D002784:Cholesterol / Q000737:chemistry*; D005456:Fluorescent Dyes; D008051:Lipid Bilayers / Q000737:chemistry; D018625:Microscopy, Atomic Force / Q000295:instrumentation / Q000379:methods; D008856:Microscopy, Fluorescence / Q000295:instrumentation / Q000379:methods
C095489:4,4-difluoro-4-bora-3a,4a-diaza-s-indacene; D001896:Boron Compounds; D005456:Fluorescent Dyes; D008051:Lipid Bilayers; D015060:1,2-Dipalmitoylphosphatidylcholine; D002784:Cholesterol