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