Abstract
A series of organized multilayers have been formed by the alternative adsorption of positively charged poly(dimethyldiallylammonium chloride) (PDAC) and purple membrane (PM) fragments in suspensions at pH = 4-11. Both UV-vis spectrophotometry and quartz crystal micro-balance (QCM) technique were used to monitor the deposition process of PDAC/bacteriorhodopsin (bR) multilayers, suggesting that PM fragments and PDAC are deposited alternatively on the substrate uniformly. Upon illumination, all these multilayers generate photovoltages with defined signs. The negative sign of photovoltage accompanying the formation ofM-state at pH < 7 indicates that the extracellular side of PM fragments is directed toward the substrate; and the positive sign at pH⩾7 indicates that the cytoplasmic side of PM fragments is directed toward the substrate. In addition, the long-lived multipleM-state has been observed in all multilayer films. Moreover,M-state at high pH, which shows the longer lifetime than that at low pH, decays into the ground state (B) completely in 30 min.
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