Orientations of liquid crystals on mechanically rubbed films of bovine serum albumin: A possible substrate for biomolecular assays based on liquid crystals

We report the uniform planar anchoring of thermotropic liquid crystals on f ilms of bovine serum albumin (BSA) covalently immobilized on the surface of glass microscope slides and mechanically rubbed using a cloth. The azimuth al orientations of the liquid crystals were measured to be parallel to the direction of rubbing. Following immersion and removal of these rubbed films of BSA from aqueous solutions containing either BSA, fibrinogen, lysozyme, anti-FITC immunoglobulin G (IgG), or anti-streptavidin IgG, we measured li quid crystals placed onto these surfaces to largely retain their uniform al ignment. In contrast, following immersion of a rubbed film of BSA into an a queous solution of anti-BSA IgG, we observed liquid crystals on these surfa ces to assume nonuniform orientations. We conclude that specific binding of anti-BSA IgG to the film of rubbed BSA erased anisotropy induced within th e film of BSA by rubbing. This result suggests that the spatial scale of an isotropy within the rubbed film of BSA is comparable to or smaller than the size of the IgG molecule. Because the anisotropy within a rubbed film of a protein can be erased by specific binding of a second protein, we believe these types of substrates (rubbed films of proteins) have the potential to be useful in a variety of label-free biomolecular assays where specific bin ding of a target species to its ligand can be imaged through observation of the optical appearance of liquid crystal placed onto the surface.