  Supported Lipid Bilayers (SLBs) are model membranes formed at solid substrate
surfaces. This architecture renders the membrane experimentally accessible to
surface sensitive techniques used to study their properties, including Atomic
Force Microscopy (AFM), optical fluorescence microscopy, Quartz Crystal
Microbalance (QCM) and X-Ray/Neutron Reflectometry, and allows integration with
technology for potential biotechnological applications such as drug screening
devices. The experimental technique often dictates substrate choice or
treatment, and it is anecdotally recognised that certain substrates are
suitable for the particular experiment, but the exact influence of the
substrate has not been comprehensively investigated. Here, we study the
behavior of a simple model bilayer, phase separating on a variety of commonly
used substrates, including glass, mica, silicon and quartz, with drastically
different results. The distinct micron scale domains observed on mica,
identical to those seen in free-floating Giant Unilamellar Vesicles (GUVs), are
reduced to nanometer scale domains on glass and quartz. The mechanism for the
arrest of domain formation is investigated, and the most likely candidate is
nanoscale surface roughness, acting as a drag on the hydrodynamic motion of
small domains during phase separation. Evidence was found that the
physico-chemical properties of the surface have a mediating effect, most likely
due to changes in the lubricating interstitial water layer between surface and
bilayer.
