Spectroscopic evaluation of surface functionalization efficiency in the preparation of mercaptopropyltrimethoxysilane self-assembled monolayers on glass

Four synthetic protocols have been examined for the preparation of a self-assembled monolayer of propanethiol functions on glass surfaces, through the wet reaction of mercaptopropyltrimethoxysilane (MPTS) on glass slides, in order to determine an optimal method to obtain dense SH monolayers for further reaction with maleimide-bearing molecules. We have also demonstrated that the surface density of reactive SH groups can be indagated by the coupling reaction with a maleimide-functionalized rhodamine dye and by the examination of the absorption spectra of the glass slides. The reaction of MPTS in dry toluene gives the most dense surface of reactive thiols, among the examined protocols. We have also evidenced that thermal curing of the MPTS functionalized slides induces thiol coupling and SS formation, resulting in a dramatically lowered availability of SH groups.