Photocurrents generated by bacteriorhodopsin adsorbed on nano-black lipid membranes

Purple membranes were adsorbed on freestanding lipid bilayers, termed nano- black lipid membranes ( nano-BLMs), suspending the pores of porous alumina substrates with average pore diameters of 280 nm. Nano- BLMs were obtained by. first coating the upper surface of the highly ordered porous alumina substrates with a thin gold layer followed by chemisorption of 1,2- dipalmitoyl- sn- glycero- 3- phosphothioethanol and subsequent addition of a droplet of 1,2- diphytanoyl- sn- glycero- 3-phosphocholine and octadecylamine dissolved in n- decane onto the hydrophobic submonolayer. By means of impedance spectroscopy, the quality of the nano- BLMs was verified. The electrical parameters confirm the formation of single lipid bilayers with high membrane resistances covering the porous matrix. Adsorption of purple membranes on the nano- BLMs was followed by recording the photocurrents generated by bacteriorhodopsin upon continuous light illumination. The membrane system exhibits a very high long- term stability with the advantage that not only transient but also stationary currents are recordable. By adding the proton ionophore carbonyl cyanide- m- chlorophenylhydrazone the conductivity of the nano- BLMs increases, resulting in a higher stationary current, which proves that proton conductance occurs across the nano- BLMs.