induced by specific and no
Lie Na Tan, Nicholas L. Abbott ⇑
Department of Chemical and Biological Engineering, Un g r a p h i c a l a b s t r a c t bumin (BSA)-decorated LC interfaces, we provide evidence that the LC anchor1. Introduction
Liquid crystalline materials are being investigated in a range of fundamental and technological contexts because the orientational ordering of this class of materials can be highly sensitive to molecular-level events occurring at their interfaces . Specifically, the long-rangeorderingofmoleculeswithin the liquid crystal (LC enables interfacial perturbations to LC anchoring to propaga bulk ordering transitions that are accompanied by measurable changes in optical and electrical properties . For instance, the surface sensitivity of LCs has been demonstrated to permit amplificationof interfacial events involvinga range of biological species – including proteins [3–5], peptides [6,7], cholic acid [8,9], DNA [10–13], polyelectrolytes , viruses  and lipids [16–20] – into optical signals. Amongst these studies, a subset have also ⇑ Corresponding author. Fax: +1 608 262 5434.
E-mail address: email@example.com (N.L. Abbott).
Journal of Colloid and Interface Science 449 (2015) 452–461
Contents lists availab n .cohttp://dx.doi.org/10.1016/j.jcis.2015.01.078 0021-9797/ 2015 Elsevier Inc. All rights reserved.) phase te intotions, 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. 2015 Elsevier Inc. All rights reserved.Keywords:
Protein-binding anchoring transitions
Kinetics ing 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 transi-lipids onto bovine serum ala r t i c l e i n f o
Received 15 November 2014
Accepted 29 January 2015
Available online 7 February 2015n-specific binding of vesicles to proteins iversity of Wisconsin–Madison, 1415 Engineering Drive, Madison, WI 53706, United States a b s t r a c t
This paper reports on the dynamics of continuous anchoring transitions at interfaces formed between nematic liquid crystals (LCs, 40-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 ofDynamic anchoring transitions at aqueous–liquid crystal interfacesJournal of Colloid a www.elsevierle at ScienceDirect d Interface Science m/locate / jc is sitions triggered by specific binding interactions between vesicles and protein-decorated interfaces of LCs. We sought to determine anddemonstrated that it is possible to tailor the chemical functionality of interfaces between LCs and aqueous solutions inways that cause the
LCs to undergo ordering transitions in response to specific interactions between biological molecules [4,7,11,16,17,19]. For example, peptide-based amphiphiles assembled at aqueous–LC interfaces, when recognized andprocessedby a protease, can trigger an anchoring transition in the LC . The fundamental molecular-level mechanisms that couple suchbiomolecular interactions at interfaces into LC ordering transitions, however, remain to be fully understood.
Of particular relevance to the study reported in this paper, we note that a number of past publications have reported that biological lipids (including phospholipids, glycolipids and lipopolysaccharides), when captured at the interface of a thermotropic LC, can promote an orientation of the LC that is perpendicular to the interface (so-called homeotropic orientation) [21,22]. This orientation of the LC is generally believed to be a consequence of interactions (including interdigitation) of the hydrophobic tails of the lipids with the LCs, although other interactions (such as electrostatic interactions) can also influence the ordering of the LC . In contrast, proteins, when adsorbed to the aqueous interfaces of LCs, typically cause the orientation of the LC to be parallel to the interface, thus leading to an optical appearance of the LC that is distinct from that induced by the lipids . Although it is not yet fully understood why thermotropic LCs assume a parallel orientation in the presence of bound proteins, recent studies have reported that the orientations of LC on well-defined dipeptide-decorated surface are strongly influenced by patterns of hydrogen bonds formed between the LC and the dipeptide on the surface . In this paper, we characterize and analyze dynamic LC anchoring transitions that result from the competing influences of phospholipids and proteins assembled at LC–aqueous interfaces to provide insight into the underlying molecular-level processes.