Ordering Transitions Triggered by Specific Binding of Vesicles to Protein-Decorated Interfaces of Thermotropic Liquid Crystals

Abstract

We report that specific binding of ligand-functionalized (biotinylated) phospholipid vesicles (diameter = 120 ± 19 nm) to a monolayer of proteins (streptavidin or anti-biotin antibody) adsorbed at an interface between an aqueous phase and an immiscible film of a thermotropic liquid crystal (LC) (nematic 4′-pentyl-4-cyanobiphenyl (5CB)) triggers a continuous orientational ordering transition (continuous change in the tilt) in the LC. Results presented in this paper indicate that, following the capture of the vesicles at the LC interface via the specific binding interaction, phospholipids are transferred from the vesicles onto the LC interface to form a monolayer, reorganizing and partially displacing proteins from the LC interface. The dynamics of this process are accelerated substantially by the specific binding event relative to a protein-decorated interface of a LC that does not bind the ligands presented by vesicles. The observation of the continuous change in the ordering of the LC, when combined with other results presented in this paper, is significant as it is consistent with the presence of sub-optical domains of proteins and phospholipids on the LC interface. An additional significant hypothesis that emerges from the work reported in this paper is that the ordering transition of the LC is strongly influenced by the bound state of the protein adsorbed on the LC interface, as evidenced by the influence on the LC of (i) “crowding” of the protein within a monolayer formed at the LC interface and (ii) aging of the proteins on the LC interface. Overall, these results demonstrate that ordering transitions in LCs can be used to provide fundamental insights into the competitive adsorption of proteins and lipids at oil-water interfaces, and that LC ordering transitions have the potential to be useful for reporting specific binding events involving vesicles and proteins.

Chemical and biological sensing using liquid crystals

“…In additional studies, s pecific capture of ligand-functionalized phospholipid vesicles has been reported at LC-aqueous interfaces that were decorated with a monolayer of adsorbed protein (streptavidin or anti-biotin antibody) (Figure 11A) [66]. The specific binding of the vesicles to the proteins was demonstrated to trigger a continuous anchoring transition (continuous change in the tilt) in the LC, which was quantified by measurement of the optical retardance of the LC (Figure 11B-D).…”

“…(D) Tilt angle of 5CB at the LC-aqueous interfaces corresponding to (B) diamonds and (C) squares. Reproduced with permission [66]. …”

Liquid Crystal Biosensors: New Approaches

“…reported that these changes in optical appearance result from strong coupling between aliphatic tails of the adsorbed amphiphiles and the mesogens of the LC. The advantages of these adsorbed surfaces make them attractive for a number of potential applications involving more complex interfacial phenomena, such as high-throughput screening of enzymatic activity (Park and Abbott, 2008) and molecular binding events (Hu and Jang, 2012;Hartono et al, 2009;Tan et al, 2012;Liu et al, 2013;Hu and Jang, 2012) through LC reorientations driven by chemical or physical events that perturb the organization of the monolayer interfaces. Enthused by the budding utility of LC materials in biological applications (particularly, reporting biological interactions), in this paper we report progress made in our laboratory toward the design of interfaces of LC materials such that desired interactions are realized between the LC materials and biological systems.…”

Design of bio-molecular interfaces using liquid crystals demonstrating endotoxin interactions with bacterial cell wall components

“…32 Briefly, the lipids were dissolved in chloroform (0.5 mL) and dispensed into round bottomed flask. 32 Briefly, the lipids were dissolved in chloroform (0.5 mL) and dispensed into round bottomed flask.…”