Optical and structural characterization of bacterio-rhodopsin films on Si-based materials

Aim of this work is to study biological materials as innovative "smart" materials to implement new functions on Si. We characterized the structural and optical properties of a bacterial protein, the bacterio-rhodopsin (bR), located in the purple membrane (PM) of the Halobacterium salinarium, living in salty waters. When it is irradiated with a light at 570 nm a complex photochemical cycle starts. It consists of intermediate states with different absorption spectra and lifetimes. We prepared water solutions containing the protein and studied both the solution and the films formed after deposition on glass, Si and SiO2 surfaces. The films realized have thickness ranging from 5 to 45 microns and, more important, maintain bR optical properties. Finally, the PM confers a high stability to the bR with respect to thermal degradation. Our measurement show a denaturation temperature strongly dependent on the solution and film characteristics. In particular, bR can be stable up to 100 °C in solution and up to 190 °C in thick films, values much higher than the best literature data.