Fabrication of nanoisland surfaces by self-assembling monolayers and intact liposome arraying
Lipid supported membranes are essential for the studies of membrane-bound proteins and membrane-mediated processes. The general method to spread planer lipid on surface is from lipid vesicle (liposome) fusion where the liposome vesicles unravel and break up to lipid layers. This process is undesired for many other studies such as biosensor and drug delivery system in which the complete conformation of lipid membrane with the natural mobility is required. The individually localized liposome on surfaces with intact structure is an ideal lipid model system for those applications. In this research we proposed a general machinery to array the intact liposomes on chemically patterned surface.
Submicrometer-sized patterns have been produced by using self-assembling monolayers (SAMs) on silicon surfaces. Binary SAM systems with different chain lengths and desired terminal groups have been phase separated to form the nanoisland patterned surfaces, in which the island domain promotes the liposome bonding via electrostatic interaction and the surrounded inert matrix resists their adsorption. The contrasting properties of island domains and the matrix barrier, along with the recessed nanoisland structure of the comparable size to the adsorbed liposomes could facilitate the liposome arraying on the island sites and maintain their intact structure as well.
The liposome adsorption behaviors on various monolayer surfaces have been firstly investigated to determine the adhesive and resistive functionality for the nanoisland patterns. The hydrophobic alkyl terminated surface (like Octadecyl trichlorosilane, OTS), hydrophilic amine terminated surface (like Amino phenyl trimethoxysilane, APhMS) and Polyethylene glycol (PEG) grafted monolayers have been studied by AFM, ATR-FTIR, Goniometry, Ellipsometry and indicate that, the hydrophobic OTS surface and hydrophilic APhMS surface adsorb liposomes irreversibly whereas the PEG surface resists their adsorption under aqueous solution.
Thus the PEG/APhMS binary SAMs have been focused to fabricate the nanoisland patterns for liposome immobilization. In this work we have developed two approaches of self-assembling monolayers to fabricate nanoisland patterns. In the mixed adsorption approach two self-assembling amphiphiles with distinct chain length are adsorbed concurrently on surfaces while in the sequential adsorption approach two amphiphiles are adsorbed successively. Various strategies have been utilized to control the partial adsorption of monolayers on surfaces.
Finally, the liposome vesicles have been displayed on the PEG/APhMS nanoisland patterned surfaces. The PEG nanoisland after backfilled with APhMS silane could effectively capture the liposomes and maintain their intact structure. The dependence of liposome adsorption on the lipid extrusion temperature and liposome concentration further confirmed the selective immobilization of the nanoisland patterns. So the nanoisland patterns provide a unique alternative model system for exploring biosensor and drug delivery studies under spatially well-defined environments.
0794: Materials science