Thin films of photosensitive proteins for light conversion applications

Cristina Paternolli1, Alberto Leotti2, Victor Erokhin3, Sergio Paddeu3, Paola Ghisellini1, Ilaria Chiossone3, Claudio Serracane4, Sergio Zannella4, Claudio Nicolini1
 
1Institute of Biophysics, University of Genova, Corso Europa 30, 16132 Genova, Italy
2Polo Nazionale Bioelettronica, via Roma 28, 57030, Marciana (Li), Italy
3Fondazione El.B.A., Corso Europa 30, 16132 Genova, Italy
4Edison Termoelettrica S.p.A., Foro Bonaparte 32, 20121 Milano, Italy
 
Biological systems provide the conversion of light energy into the chemical one with extremely high efficiency, much more than man-made devices. Therefore, the study of these processes of the light conversion can increase not only our basic knowledge about living systems, but also open alternative ways for the design of light-to-electricity converting elements. The size of the sensitive unit (protein) in this case is in a nanometer range. Therefore, they can be incorporated into functional systems, in which the resolution at a nanometer level can be reached.

 The aim of this study is the formation of thin layers of light-sensitive proteins, the study of their structure, properties and light energy conversion efficiency.

 The study was carried out on two kind of proteins: photosynthetic reaction centers from Rhodobacter sphaeroides (RC) and bacteriorhodopsin (BR).

 RC provides a light-induced transmembrane electron transport [1], while BR act as light-driven proton pump [2]. Therefore, being properly organized in oriented films, these proteins can provide both photopotentials and photocurrents. Thermal stability of these proteins in thin films [3-5] suggests an additional reason for considering them seriously for the technical applications.

 Thin films of these proteins were deposited with different methods, such as Langmuir-Blodgett technique (with and without application of external electric field), polyelectrolyte self-assembling, electrosedimentation. In some cases complex layers were deposited. Light sensitive proteins were mixed with chromophores in these layers. Chromophore molecules played a role of antenna complexes in them. These films were coupled with electrodes from ITO, evaporated metals, conductive polymers, polycrystal semiconductor layers.

 Surface potential measurements at the air/water interface in dark and light conditions allowed one to determine the functionality of the proteins and to optimize the conditions of the monolayer formation.

 The structure of the layers was studied by X-ray diffraction technique. Rheology of the realized structures was investigated by Brewster angle microscopy.

 Photoelectric measurements were carried out with specially constructed set-up allowing one to measure simultaneously photoresponses and optical absorbance. Proteins were found to be active in all realized structures.

 

References

 

1. D. Tiede, Biochim. Biophys. Acta, 811, 357 (1985).

 2. D. Oesterhelt, C. Bräuchle, and N. Hampp, Quarterly Rev. Biophys., 24, 425 (1991).

 3. C. Nicolini, V. Erokhin, F. Antolini, P. Catasti, and P. Facci, Biochim. Biophys. Acta, 1158, 273 (1993).

 4. Y. Shen, C.R. Safinya, K.S. Liang, A.F. Rupert, and K.J. Rothshild, Nature, 336, 48 (1993).

 5. V. Erokhin, P. Facci, A. Kononenko, G. Radicchi, and C. Nicolini, Thin Solid Films, 284-285, 805 (1996).