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Light-Addressable Transducer Bacteriorhodopsin Based

Victor Erokhin, Sergio Paddeu and Claudio Nicolini*

El.B.A. Foundation, Rome (Italy) and
Institute of Biophysics, University of Genoa (Italy)

This is an abstract for a talk to be given at the Fifth Foresight Conference on Molecular Nanotechnology. The full paper is available here.

Bacteriorhodopsin is the object of numerous studies due to its unique ability to act as a light-driven proton pump and to its optical properties. Moreover, due to its high stability [1,2] it can be considered a promising candidate for protein-based optoelectronics [2,3]. In order to utilize its proton pumping properties it is necessary to have a technique, allowing to make very thin and oriented films of it. Langmuir-Blodgett technique corresponds to the first demand, allowing to deposit films with molecular resolution in thickness. However, it is not so easy to provide the same orientation of molecules in the layer, due to the nature of the protein. Spreading solutions usually contain fragments of purple membranes (about 80% of bacteriorhodpsin). Thus, they are rather big systems with a thickness of about 5 nm. Due to such structure they form a layer in the air/water interface, where individual fragments are oriented with practically equal probability in opposite directions. Therefore, at a macroscopic level the film is isotropic and both photopotential and proton photocurrent are compensated.

In this study the films of bacteriorhodopsin were formed by injecting the solution of membrane fragments into the condensed salt solution over which rather large flat electrode was placed. Platinum plate was immersed into the liquid subphase to act as second electrode. Voltage of different value and polarity was applied to these electrodes, whereby the movement of the fragments to the surface from the inner volume was estimated by the increase in the surface pressure. It was found that the effective formation of the layer took place when the upper electrode was biased positively. The films were deposited onto solid substrates covered with transparent electrode and onto porous membranes. As a result of the above procedure, measurements of the photovoltage allows to conclude that the orientation of bacteriorhodopsin fragments appears highly improved with respect to films being deposited by the standard Langmuir - Blodgett technique.

Based upon this proof-of-principle work is in progress towards the implementation of light-addressable potentiometric transducers and sensors of new design and unique performance with respect to the existing one silicon based [4,5].

[1] Yi. Shen, C.R. Safinya, et al., Nature, 366, 48-50 (1993).
[2] Nicolini, C., Biosensor and Bioelectronics, 10, 105-111 (1995)
[3] Nicolini, C., "Molecular Bioelectronics", World Scientific Publ (1996)
[4] Sartore, M. et al., Review Scient Instr, (1996)
[5] Hafemann, D.G. et al., Science, 240, 1182-1186 (1988)

*Corresponding Address:
Claudio Nicolini, Fondazione EL.B.A., Via Medaglie d'Oro 305 - 00136 Rome, Italy, ph: +39 6 35410728, fax: +39 6 35451637, email:
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