Luminescence depolarization effects in protein-modified SiO2–TiO2 films doped with organic luminophores

Thin SiO2–TiO2 films functionalized with –SH groups were prepared by the sol–gel technique from tetraethoxysilane and (3mercaptopropyl)trimethoxysilane, or –NH2 groups from (3-aminopropyl)-triethoxysilane precursors. Labeled with fluorescein isothiocyanate (FITC), proteins, capable of selective bacterial endotoxins binding, were covalently attached to the films surfaces (via the –NH2 and –SH groups) in a way retaining their rotational freedom. The samples were incubated with selected bacterial endotoxins which bound to the immobilized, FITC-labeled proteins decreasing their rotational freedom. This effect has been detected as a change in the luminescence depolarization. The system based on this effect is proposed as a luminescence biosensor for the endotoxins recognition.