Biomolecular Interactions at Phospholipid-Decorated Surfaces of Liquid Crystals

Abstract

The spontaneous assembly of phospholipids at planar interfaces between thermotropic liquid crystals and aqueous phases gives rise to patterned orientations of the liquid crystals that reflect the spatial and temporal organization of the phospholipids. Strong and weak specific-binding events involving proteins at these interfaces drive the reorganization of the phospholipids and trigger orientational transitions in the liquid crystals. Because these interfaces are fluid, processes involving the lateral organization of proteins (such as the formation of protein- and phospholipid-rich domains) are also readily imaged by the orientational response of the liquid crystal, as are stereospecific enzymatic events. These results provide principles for label-free monitoring of aqueous streams for molecular and biomolecular species without the need for complex instrumentation.

Chemoresponsive assemblies of microparticles at liquid crystalline interfaces

“…Past studies have demonstrated that nematic 5CB adopts an orientation at a flat interface to water that is parallel to the interface (socalled planar anchoring of the LC; Fig. 2A) (11). When an isolated microparticle was observed at this interface (crossed polars, with one polarizer aligned parallel to the far-field orientation of the LC; Fig.…”

“…We used silica microparticles (diameters of 2.3 μm) functionalized with the silane dimethyloctadecyl [3-(trimethoxysilyl) propyl]ammonium chloride (DMOAP; Acros). Particles functionalized with DMOAP cause 5CB to assume a perpendicular orientation at the particle surface (2), and the covalent attachment of the DMOAP to the particle surface ensures that desorption of DMOAP from the particle surface (and potentially onto the LC-aqueous interface) does not take place (9,11).…”

“…1A). Although the microparticles were hydrophobic, with sonication and stirring, the microparticles could be singly dispersed in water and then introduced as a droplet (diameter of ∼5 mm) into an aqueous phase overlying a 20-μm-thick film of nematic 5CB supported within a metal specimen grid on top of an octyltrichlorosilane (OTS) functionalized glass microscope slide (11). The individual sections of the metal specimen grid measured 280 × 280 μm 2 , which was large compared to the size of the microparticles but small compared to the size of the droplet used to deliver the microparticles into the aqueous phase overlying the grid (the latter condition ensures that relatively uniform densities of microparticles were deposited within each grid).…”

“…At high surfactant concentrations, the 5CB assumes an orientation at the 5CB-aqueous interface that is perpendicular to the interface (so-called homeotropic anchoring; Fig. 2F) (11). We sought to determine the influence of such surfactant-induced LC ordering transitions on the ordering of 5CB near microparticles located at the 5CB-aqueous interface.…”

“…We sought to determine the influence of such surfactant-induced LC ordering transitions on the ordering of 5CB near microparticles located at the 5CB-aqueous interface. In our initial experiment, the anionic surfactant SDS was added to the aqueous phase to a final concentration of 1,300 μM, which is above the threshold concentration required to change the orientation of the 5CB at the 5CB-aqueous interface from planar to homeotropic (11). Inspection of the polarized (Fig.…”