The functionalization and patterning of biomedical materials with enhanced surface activity is a main objective for the development of high-specificity biosensors. The surfaces of sol-gel condensed aminopropyltriethoxysilane-tetraisopropyl orthotitanate hybrid materials have been studied in order to describe the mechanisms that allow the fixation of amino groups. X-ray photoelectron spectra obtained from these surfaces are compared with those coming from the surfaces of plasma-etched coatings. The results show that aminopropyl radicals remain on the surface after room-temperature condensation and that they are drastically removed after partial etching of the coating in an Ar plasma. This confirms that the functionalization is effectively a surface feature and suggests that amino groups may remain at the surface covalently bonded to the original amorphous Si-O-structure. Further evidence of the surface functionalization efficiency is illustrated with contact angle and zeta-potential measurements. It is complementarily proved by confocal microscopy that masked regions conserve their molecular activity and are not affected by the etching process. These facts suggest that these materials could play an active role when incorporated into biosensor devices. (C) 2004 Elsevier Inc. All rights reserved.