A 'dual click' strategy for the fabrication of bioselective, glycosylated self-assembled monolayers as glycocalyx models.

Solid surfaces decorated with specific saccharide patterns can serve as a model for the chemically and structurally highly complex glycocalyx of eukaryotic cells. Here we present an approach based on self-assembled monolayers on gold, which are built up in a three-step manner to provide a solid basis, a biorepulsive oligoethylene glycol part, and a specific carbohydrate terminus in a modular way. Of the different reaction sequences, the one with two consecutive 'click reactions' (the copper(i)-catalysed 1,3-dipolar cycloaddition of alkynes with azides and the thiourea-bridging of isothiocyanates with amines) directly 'on SAM' results in the densest layers, as demonstrated by infrared absorption reflection spectroscopy and ellipsometry. As a 'real life' test, the surfaces obtained this way were used for bacterial adhesion experiments. Here the biorepulsivity of the middle part of the SAMs as well as specific binding to the carbohydrate termini could be clearly demonstrated.

Bacteria-repulsive polyglycerol surfaces by grafting polymerization onto aminopropylated surfaces.

The formation of hydrogels on surfaces is a frequently used strategy to render these surfaces biorepulsive. Hyperbranched polyglycerol layers are a promising alternative to the frequently used polyethyleneglycol layers. Here, we present a strategy to covalently graft polyglycerol layers onto surfaces by first depositing an aminopropylsiloxane layer, which then acts as initiator layer for the ring-opening polymerization of 2-(hydroxymethyl)oxirane (glycidol). For silicon surfaces, the resulting polyglycerol layers start being biorepulsive for E. coli at a thickness of 2 nm and reach their highest bacterial repulsion (98%) at thicknesses of 7 nm or larger. This deposition strategy promises general applicability because the formation of aminopropylsiloxane layers has already been described for many materials.