Dynamic anchoring transitions at aqueous–liquid crystal interfaces induced by specific and non-specific binding of vesicles to proteins

Abstract

This paper reports on the dynamics of continuous anchoring transitions at interfaces formed between nematic liquid crystals (LCs, 4′-pentyl-4-cyanobiphenyl (5CB)) and immiscible aqueous phases that are induced by either non-specific or specific interactions between phospholipid vesicles and proteins adsorbed at the LC interfaces. By analyzing the dynamic response of LCs to non-specific adsorption of lipids onto bovine serum albumin (BSA)-decorated LC interfaces, we provide evidence that the LC anchoring transitions are slower than diffusion-controlled accumulation of lipid at the interface, consistent with the hypothesis that the LC transition involves lateral reorganization of proteins and lipids at the interface. Significantly, optical measurements of the tilt angle of the LC as a function of the amount of lipid captured at the interface were found to be quantitatively consistent with theoretical predictions of LC anchoring directed by nanoscopic domains of molecules that cause planar (protein) and homeotropic (lipid) anchoring of the LC. Finally, specific binding interactions between the antibody-decorated LC interfaces and vesicles (through antibody-antigen recognition) greatly accelerated the continuous LC anchoring transitions, with dynamics that were measured to scale with the logarithm of the ligand composition of the vesicles (over four orders of magnitude). The latter dynamics were found to be strongly influenced by addition of synthetic surfactants, consistent with our proposal that the rate-limiting step underlying the response of the LC was the transfer of lipids from captured vesicles into the protein-decorated LC interface. Overall, the results presented in this paper provide quantitative insight into the origin of continuous anchoring transitions triggered by vesicles at protein-decorated LC interfaces and, more broadly, guidance for the design of stimuli-responsive LC systems.