Abstract
Bacteriorhodopsin protein (bR)-based systems are one of the simplest known biological energy converters. The robust chemical, thermal and electrochemical properties of bR have made it an attractive material for photoelectric devices. This study demonstrates the photoelectric response of a dry bR layer deposited on a nitrocellulose membrane with indium tin oxide (ITO) electrodes. Light-induced electrical current as well as potential and impedance changes of dried bR film were recorded as the function of illumination. We have also tested bR in solution and found that the electrical properties are strongly dependent on light intensity changing locally proton concentration and thus pH of the solution. Experimental data support the assumption that bR protein on a positively charged nitrocellulose membrane (PNM) can be used as highly sensitive photo- and pH detector. Here the bR layer facilitates proton translocation and acts as an ultrafast optoelectric signal transducer. It is therefore useful in applications related to bioelectronics, biosensors, bio-optics devices and current carrying junction devices.
Highlights
IntroductionFour decades ago Bacteriorhodopsin protein (bR) was extracted from the membrane of Halobacterium salinarum found in high salt water depositions after its original discovery in 1967 [1,2]
Four decades ago Bacteriorhodopsin protein was extracted from the membrane of Halobacterium salinarum found in high salt water depositions after its original discovery in 1967 [1,2].The bR contains the chromophore retinal and this protein is known to be one of the simplest biological energy convertors [3]. bR has an excellent thermal, chemical, photochemical and photoelectrical stability, which makes bR an attractive material in devices for photosignal transduction. bR protein is known as the purple membrane (PM) due to its purple color patches
Due to the negative charges of the cytoplamsic part of bR, bR proteins get aligned with the positive charge of the nitrocellulose membrane, during illumination protons move in the extracellular site direction
Summary
Four decades ago Bacteriorhodopsin protein (bR) was extracted from the membrane of Halobacterium salinarum found in high salt water depositions after its original discovery in 1967 [1,2]. The overall result includes the transfer of protons from the cytoplasmic side of cell membrane to the extracellular environment. It contributes to building up of the proton gradient across the membrane resulting in electrochemical potential and local pH changes [8]. This proton gradient provides the energy required for the H. salinarium cell activities by supporting adenosine triphosphate (ATP) synthesis from adenosine diphosphate (ADP) [9]. Absence of water assures that there is no washing off of bR from the PM It provides a typical light driven bR response by inducing electrical current between electrodes
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