Design of tethered bilayer lipid membranes, using wet chemistry via aryldiazonium sulfonic acid spontaneous grafting on silicon and chrome

Abstract

We describe a bottom-up surface functionalization to design hybrid molecular coatings that tether biomembranes using wet chemistry. First, a monolayer was formed by immersion in a NH₂-Ar-SO₃H solution, allowing aryldiazonium salt radicals to spontaneously bind to it via strong C bonding. After formation of the air-stable and dense molecular monolayer (-Ar-SO₃H), a subsequent activation was used to form highly reactive -Ar-SO₂Cl groups nearly perpendicular to the monolayer. These can bind commercial surfactants, PEGylated oligomers and other inexpensive molecules via their -OH, -COOH, or -NH₂ chain end-moieties, to build hybrid coatings. Metal and oxidized chromium, semi-conductor n-doped silicon (111), are the substrates tested for this protocol and the aromatic organic monolayers formed at their surface are characterized by X-ray photoelectron spectroscopy (XPS). XPS reveals unambiguously the presence of C-Cr and C-Si bonds, ensuring robustness of the coatings. Functional sulfur groups (-SO₃H) cover up to 6.5×10^-10 mol cm^-2 of the silicon interface and 4.7×10^-10 mol cm^-2 of the oxidized chromium interface. These surface concentrations are comparable to the classic values obtained when the prefunctionalisation is driven by electrochemistry on conductors. Tethered lipid membranes formed on these coatings were analyzed by neutron reflectivity at the interface of functionalized n-doped silicon substrates after immersion in a solution of lipid vesicles and subsequent fusion. Results indicate a rather compact hybrid coating of Brij anchor-harpoon molecules that maintain a single lipid bilayer above the substrate, on top of a hydrated PEO cushion.

Keywords: Anchor-Harpoon hybrid coatings to stabilize hydrated and fluid membranes; Covalent polymer ultra-thin films and surfactants molecular coatings; Planar membrane sensors; Solid supported tethered single lipid bilayer; Surface functionalization by covalent wet chemistry and spontaneous grafting of aryldiazonium sulfonic acid.