Trifluoro alkyl oligo(ethylene glycol)-terminated alkanethiol self-assembled monolayers : synthesis, characterisation, and protein adsorption properties

Abstract

Self-assembled monolayers have been proven to be well-ordered and to give stable ultrathin films. They show a remarkably high diversity with respect to their functionalisation giving rise to many possible applications. This thesis is focused on the potential use of these molecular thin films in life sciences. The reproduction of a membrane-like environment with these tightly packed and organized unimolecular layers has led to important breakthroughs in their nanotechnological application as biomaterials. Their straightforward modification allows the chemical and physical properties of biological interfaces to be altered. In particular, Oligo(ethylene glycol) based alkanethiol self-assembled monolayers were intensively studied as biointerfaces for their ability to resist the non specific adsorption of proteins. The electrostatic repulsion which originates from these monolayers was seen as one of the possible factors causing this protein repulsion. On the other hand proteins adsorb on alkanethiol self-assembled monolayers. This can be partially attributed to an attractive hydrophobic interaction between the biomolecules and the surface. As a result of the understanding of these two driving forces which are relevant for non-specific protein adsorption/repulsion, novel self-assembling molecules were tailored in an attempt to adjust the adsorption of proteins at the SAM-liquid interface. This was conceivable with these newly designed SAMs since they allow a combination of these forces. We have chosen the ionic strength of the liquid environment as the external parameter which could act on the amount of adsorbed proteins because the electrostatic force created by oligo(ethylene glycol) groups depends on it. In addition to the synthesis of six new molecules, the preparation and characterisation of the novel self-assembled monolayers are reported in this thesis. The density of the monolayers was estimated by X-ray photoelectron spectroscopy and ellipsometry, and the wettability properties were studied by measuring the contact angle. The total force acting on proteins from the SAMs was studied with an atomic force microscope, equipped with a tip mimicking proteins, by measuring force-distance curves. An in-situ technique was investigated in order to study the influence of the variation of this total force on the quantity of adsorbed proteins by varying the ionic strength.