Web Release Date: September 2,
Modification of a Supported Lipid Bilayer by Polyelectrolyte Adsorption
Department of Chemistry and Fredrick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
Received April 16, 2004
In Final Form: July 13, 2004
Abstract:
Addition of a weak polyelectrolyte, poly(methacrylic acid) (PMA), to a supported phospholipid bilayer
made from 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) depresses the melting temperature and
alters the morphology of the bilayer in the gel phase. Ellipsometry measurements show that PMA adsorption
lowers the phase transition temperature by 2.4 
C. Atomic force microscopy (AFM) showed no visible
contrast in the fluid phase (above the melting temperature) but a rich morphology in the gel phase. In the
gel phase, adsorption leads to formation of significantly less mobile phospholipid islands and other defects.
One consequence of this lower mobility is a decrease in the implied cooperativity number of the phase
transition, N, when polymer is added. Additionally, AFM images of the gel-phase bilayer show a highly
defected structure that anneals significantly more slowly than in the absence of adsorbed polymer.
Tentatively, we suggest that PMA preferentially decorates island and defect edges of the DMPC bilayer.
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