ORIENTED BACTERIORHODOPSIN POLYCATION MULTILAYERS BY ELECTROSTATIC LAYER-BY-LAYER ASSEMBLY/

The purple membrane (PM) containing bacteriorhodopsin (BR) is a promis ing biomaterial for many potential optical and optoelectronic device a pplications. Organized, heterogeneous assemblies using polycationic po ly(dimethyldiallylammonium chloride) (PDAC) and PM fragments have been successfully constructed by the spontaneous alternating adsorption of PDAC and PM. The fabrication process of the multilayers was followed by UV-vis absorption spectroscopy and ellipsometry. The results indica te that the deposition process is linear and highly reproducible from layer to layer and that a monomolecular film of PM may be obtained in each PDAC/PM bilayer by controlling the adsorption time. Second harmon ic generation measurements from the composite films gave a second-orde r susceptibility chi((2)) of 8.1 X 10(-9) esu and confirm that the PM fragments are arrayed with a high degree of orientation and acentric p olar order in the films. Atomic force microscopy images provided the s urface morphology of sequential layers of PDAC and PM fragments. Relat ive PDAC/PM bilayer thicknesses of 55 Angstrom were observed, and the homogeneity of the layers was found to improve as the number of layers increased.