Preparation of Polypeptide-Dye Multilayers by an Electrostatic Assembly Process

ABSTRACTTo develop novel optical thin films, we have prepared self-assembled polypeptide films by an electrostatic process. The films were placed on a glass slide previously silanized by an amino silane and given a positive charge by immersion in aqueous acid. Subsequent immersion of the slide in aqueous anionic solutions of either poly(L-glutamic acid), congo red, copper phthalocyanine tetrasulfonic acid or p-nitroaniline-modified poly(L-glutamic acid) resulted in deposition of the anions on the surface. Following anionic immersion, the slides were dipped into a cationic poly(L-lysine) solution. Alternate dipping into anionic and cationic solutions yielded multilayers. The thin films were characterized by optical absorption and circular dichroism. The optical density increased with dipping cycles. Circular dichroism measurements of the thin films showed induced dichroism of the congo red and phthalocyanine-containing films, suggesting formation of a locally ordered dye-polypeptide complex. Solution circular dichroism measurements of the polypeptides indicated a coil conformation, while poly(Lglutamic acid)/poly(L-lysine) complexes showed circular dichroism spectrum characteristic of a β-sheet.