Low density triethoxysilane self-assembled monolayers and its stability under biological media

A novel space-filling trialkoxysilane derivative was synthesized using a two-step strategy from commercially available starting materials to produce the precursor for the formation of low-density self-assembled monolayers. Self-assembled monolayers of the synthesized compound were prepared on three different substrates (Si/SiO$_{2}$, glass and ITO) and characterized using contact angle, ellipsometry and sum-frequency generation spectroscopy. Removal of the space-filling protecting group, (2-chlorophenyl)diphenyl methanol, yields a carboxyl-terminated surface. Correspondingly, the contact angle and film thickness decrease and the SFG spectra clearly indicate an increase in the gauche defect concentration characteristic of a low-density disordered monolayer. The biological stability of the prepared low-density monolayers compared to high-density monolayers of dodecyltriethoxysilane was studied under storage in water, phosphate buffer saline solution and calf serum for two weeks. The contact angle and thickness measurements show that there was no monolayer degradation during the storage time and the surfaces are more favorable for non-specific protein adsorption.