Air-Water Interface Assembly Of Protein Nanofibrils Promoted By Hydrophobic Additives

Herein we demonstrate a novel way of modifying the colloidal stability of proteins by the presence of hydrophobic molecules. A protein capable of self-assembly into protein nanofibrils (PNFs) is milled with a hydrophobic molecular material. Upon dissolution in acidic water followed by heating, the proteins are converted into PNFs containing hydrophobic dyes. When aqueous dispersions of such PNFs are heated, films are formed at the air-water interface. The films contain ordered, optically anisotropic domains, and the shape of the reaction vessel can influence the PNF packing. We demonstrate the generality of the process by employing PNFs derived from the three proteins bovine insulin (INS), beta-lactoglobulin (BLG), and hen egg white lysozyme (HEWL) in combination with the dyes alpha-sexithiophene (6T) and 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM). As individual dye molecules are oriented along the long PNF axis, whole ensembles of dyes become aligned and, as a result, display emission of polarized light. Moreover, in the case of PNFs stained with DCM, stimulated emission is demonstrated.