[en] Thin films of silica functionalized with NH₂ groups were prepared by the sol-gel technique from tetraethoxysilane (TEOS) and (3-aminopropyl)-triethoxysilane (APTES) precursors. Selected proteins labeled with isothiocyanate fuorescein (FTIC) were covalently attached to their surfaces via the NH2 groups. The presence of the functional groups was confirmed by infrared absorption and Raman spectra measurements. The obtained films were immersed in a buffer and polarized emission spectra were measured. Next, the samples were incubated with selected bacterial endotoxin and the emission spectra were collected again. The influence of the endotoxin binding on the luminescence depolarization has been proven. The system based on this effect is suggested as an optical biosensor for the endotoxin recognition