deionized water and placed under a 0.5 mM solution of Tris buffer at pH 7 for AFM
imaging and analysis in fluid tapping mode (Multimode NanoScope IV, Veeco
Metrology, Santa Barbara, CA).
3.2.2 Preparation of DOPC:DOPS:DMPC:DMPS supported lipid membranes
Lyophilized dioleoylphosphatidylserine (DOPS-anionic),dimyristoylphosphatidylserine
(DMPS-anionic), dioleoylphosphatidylcholine (DOPC-Zwitterionic) and
dimyristoylphosphatidylcholine (DMPC-Zwitterionic) obtained from Avanti Polar Lipids,
Alabaster, AL, were dissolved in chloroform and mixed at mole fractions of 1:3 and 1:3
respectively and then these components were also mixed together. The mixture was dried
under nitrogen gas, placed under low vacuum for at least 1.5 h, and then hydrated with
deoxygenated deionized water for a final lipid concentration of ~2 mg∕mL. The lipid
solutions were heated to 50 0C and agitated for 30 minutes and stood overnight in a dark,
room-temperature environment followed by vigorous agitation for at least 1 h. The
resulting Inultilamellar vesicle solutions were refrigerated and stored for up to two weeks.
Supported lipid bilayer membranes for AFM analysis were formed on mica substrates by
vesicle fusion. A multilamellar vesicle solution at a lipid concentration of 20-200 mg∕mL
(diluted from stock in deionized water) was heated to 50 0C and a 100 mL drop was
placed on the mica for 20 min at 35-40 0C. The sample was then rinsed with double
deionized water and placed under a 0.5 mM solution of Tris buffer at pH 7 for AFM
imaging and analysis in fluid tapping mode (Multimode NanoScope IV, Veeco
Metrology, Santa Barbara, CA).
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