Characterization of amphiphile-induced ordering transitions at aqueous-liquid crystal interfaces.

摘要

The studies described in this thesis were initiated in order to further understand the fundamental mechanisms underlying the amphiphile-driven liquid crystal (LC) anchoring transitions and to advance the development of LC-based analyte detection methodologies. The research reported within is organized into three main parts (described below).;First, the coupling of the LC mesogen with the analyte adsorbed at aqueous-LC interfaces is studied via the Langmuir-Schaefer transfer technique. By utilizing the Langmuir-Schaefer transfer technique, the preparation of a known areal density of self-assembled molecules at aqueous-LC interfaces is facilitated with precision; the proposition that analyte tail interactions with LC mesogens can lead to an LC anchoring transition is demonstrated as a proof of concept. Mixed phospholipid/glycolipid monolayers with known compositions at an aqueous-LC interface were then prepared with the transfer technique and specific binding events between glycolipid GalBeta1-3GalNAcBeta1-4(NeuAcAlpha2-3)GalBeta1-4GlcBeta1-1'-ceramide (GM1) and cholera toxin was amplified by the LC anchoring transition in contact with the self-assembled molecules at the aqueous-LC interface.;Second, nematic-force mediated solid microparticle organization at aqueous-LC interfaces was facilitated via a modified Langmuir-Schaefer transfer technique. The study demonstrated that LC topological defects result in unique microparticle assemblies that are not observed in isotropic fluids. We also report microparticle assemblies at aqueous-LC interfaces that are driven through dynamic and reversible ordering transitions of the LCs via analyte adsorption, which demonstrates the potential utility of microparticles for the amplification of biomolecular interaction at interfaces.;Last, spontaneous analyte adsorption from water to the surface of microdroplets of nematic liquid crystals suspended in water was investigated. We observe the spatially localized regions of the analyte endotoxin (lipopolysaccharide, LPS) at the aqueous-LC droplet interface. The corresponding limit of detection of LPS using this novel technique is in the pg/ml range. Preliminary experimental results regarding the mechanism of LC anchoring transition upon LPS adsorption are also discussed.;The results of the studies reported in this thesis, when combined, provide principles for LC-based label-free monitoring of aqueous streams for biomolecular species without the need for complex instrumentation and expensive reagents.