RECTIFIED PHOTOCURRENTS FROM PURPLE MEMBRANE LANGMUIR-BLODGETT-FILMS AT THE ELECTRODE-ELECTROLYTE INTERFACE

Langmuir-Blodgett (LB) films of the halobacterial purple membrane (PM) were formed on an SnO2 electrode. A photoelectrochemical cell was constructed in which the PM-coated SnO2 electrode in contact with an aqueous electrolyte contributes to light-to-current conversion under regulation of the electrode potential. Visible light irradiation to the PM electrode caused rectified cathodic photocurrents with the action spectrum coinciding with the optical absorption of bacteriorhodopsin (bR). The photocurrent significantly depended on the electrode potential and pH of the electrolyte. The response time of the photocurrent (less than 300-mu-s) agrees with the rate of the proton transfer in the photochemical cycle of bR. The electrochemical investigation showed that charge displacement (or proton transfer) in the bR molecules accommodated in an aqueous electrolyte can be effectively converted to electric currents under potentiostatic regulation of PM electrode.