Self-assembly of amino-terminated monolayers depending on the chemical structure

Amino-terminated self-assembled monolayers (SAMs) are widely used to functionalize silica surfaces as a primary layer in the field of biosensors. The use of commercial aminosilanes suffers from a lack of control of molecular organization due to the multiple interactions of the amine end group of the silylated coupling agent with polar groups available on the surface and from the possible hydrolytic degradation of the layer. In this study, we report the successful preparation of well-defined amino-terminated monolayers using a direct grafting strategy with phthalimide as a protecting amino group to prevent undesirable non-covalent interactions. Three phthalimide-terminated silanes were synthesized for this purpose. Their grafting was achieved using the classic immersion method and the spin coating process. Polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS) was used to study the grafting efficiency and the phthalimide-terminated SAM organization. After the total conversion of the phthalimide into amine groups, the reactivity of the resulting amino-terminated monolayers was evaluated using a coumarin derivative as a fluorescent probe. PM-IRRAS and fluorescence measurements confirmed the reactivity of amino-terminated SAMs. Preparation of well-defined amino-terminated monolayers using a direct grafting strategy with phthalimide as a protecting amino group.