Evanescent wave induced fluorescence microscopy combined with phase contras
t microscopy is applied to study the strong electrostatic adhesion of giant
unilamellar vesicles (GUV) on flat surfaces. This technique gives the shap
e of the adsorbed vesicles and an insight into the dynamics of spreading. I
n addition, it is used to investigate the possible induction of membrane pe
rmeability by adhesion. We show that the vesicle shape on the surface is a
spherical cap and that a three-regime process with characteristic times tau
(1), tau(2) and tau(3) rules the dynamics of spreading. tau(1) is the time
elapsed between the moment when the vesicle reaches the surface and the ins
tant when the vesicle actually adheres. tau(1) stands between 10 s and one
minute and is determined by the drainage of the liquid film between vesicle
and substrate. tau(2) and tau(3) are the characteristic times of the biexp
onential law that fits the curve of the radius of the contact area as a fun
ction of time. tau(2) is about 0.05 s and corresponds to a regime of vesicl
e adhesion at constant volume. During tau(2), the negatively charged lipids
of the outer monolayer of the membrane bilayer flow toward the surface whi
le the excess area of the membrane is resorbed; the vesicle bilayer is then
under tension. The regime ts corresponds to a regime of water permeation t
hrough the membrane. We find that 0.5 s < tau(3) < 5 s according to the exp
erimental conditions. On average, vesicles lose 7% of their inner content t
hrough a process of pore formation along the contact line. The role of para
meters such as vesicle size, medium viscosity, lipid composition, and surfa
ce charge on the adhesion phenomenon is investigated and analyzed.