In order to develop an optical immunosensor based on Surface Plasmon Resonance (SPR) and guided waves propagation, the sol-gel process has been used to prepare thin films of amorphous silica, deposited by spin coating on a gold-coated glass slide, and possessing chemically active functional groups (SH, NH2...). After activation of the sol-gel film in aqueous buffers by a bifunctional coupling agent, biological molecules such as antibodies could be covalently bonded on or inside the sol-gel film. Therefore, the behaviour of the functionalized silica thin films in aqueous solutions has been analyzed by SPR and guided waves propagation. The matrix hydrophilicity has been studied with different mixtures of functionalized silicon precursors forming organic-inorganic hybrid films. Immunoassays outline the possibility of obtaining covalent binding of antibodies to the sol-gel matrix with optimal stability and biological activity.