Potential Controls the Interaction of Liposomes with
Octadecanol-Modified Au Electrodes: An in Situ AFM Study
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Abstract
The formation of supported lipid
bilayers using liposomes requires
interaction with the solid surface, rupture of the liposome, and spreading
to cover the surface with a lipid bilayer. This can result in a less-than-uniform
coating of the solid surface. Presented is a method that uses the
electrochemical poration of an adsorbed lipid-like layer on a Au electrode
to control the interaction of 100 nm DOPC liposomes. An octadecanol-coated
Au-on-mica surface was imaged using tapping-mode AFM during the application
of potential in the presence or absence of liposomes. When the substrate
potential was made negative enough, defects formed in the adsorbed
layer and new taller features were observed. More features were observed
and existing features increased in size with time spent at this negative
poration potential. The new features were 1.8β2.0 nm higher
than the octadecanol-coated gold surface, half the thickness of a
DOPC bilayer. These features were not observed in the absence of liposomes
when undergoing the same potential perturbation. In the presence of
liposomes, the application of a poration potential was needed to initiate
the formation of these taller features. Once the applied potential
was removed, the features stopped growing and no new regions were
observed. The size of these new regions was consistent with the footprint
of a flattened 100 nm liposome. It is speculated that the DOPC liposomes
were able to interact with the defects and became soluble in the octadecanol,
creating a taller region that was limited in size to the liposome
that adsorbed and became incorporated. This AFM study confirms previous
in situ fluorescence measurements of the same system and illustrates
the use of a potential perturbation to control the formation of these
regions of increased DOPC content