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In this study, we demonstrate a real-time and sensitive strategy for monitoring of lipase activity using liquid crystal (LC) droplets with micrometre scales supported on solid surfaces. The LC droplet pattern was formed by evaporating a solution of nematic LC, 4-cyano-4′-pentylbiphenyl (5CB) dissolved in heptane. The surface-anchored LC droplets displayed a bright fan-shaped appearance in buffer solution, while they exhibited a dark cross appearance when they were in contact with an aqueous mixture of glycerol trioleate (GT) and lipase. Due to adsorption of the released oleic acid generated from the enzymatic reaction between GT and lipase, LCs adopted a perpendicular orientation instead of planar orientation at the aqueous/LC droplet interface, resulting in contrasting optical response. Using this approach, the presence of 0.1 μg/mL lipase in the aqueous solution could be detected within 6 min. When compared to previously reported LC-based sensors for the detection of lipase, this simple and convenient method has the advantage of real-time monitoring of lipase activity with high sensitivity. In addition, this strategy also has high potential for application of the LC droplet pattern for sensing applications. [ABSTRACT FROM AUTHOR]

In this study, we employed a simple liquid crystal (LC)-based system to dynamically image enzymatic events at the aqueous/LC interface decorated with polyelectrolyte-disrupted phospholipid membranes. Since polyelectrolytes were shown to disrupt the arrangement of the self-assembled phospholipid monolayer and induced a dark-to-bright shift in the optical response of LCs that support the phospholipid membrane, we observed that the transfer of an aqueous solution of protease onto the polyelectrolyte-disrupted phospholipid membrane resulted in a gradual recovery of the optical response of LCs from bright to dark appearance. Due to the enzymatic event that occurs at the aqueous/LC interface, the generated polyelectrolyte fragments desorbed from the interface to the bulk solution. This led to the restoration of the disrupted phospholipid monolayer, which resulted in recovery of the optical response. These results suggest that the polyelectrolyte-decorated membrane-supported LCs could be potentially used to examine a range of biological interactions that involve polyelectrolytes. Furthermore, the LC-based system holds great promise for label-free and real-time investigation and detection of biomolecular interactions coupled to membrane disruption and restoration, which might have potential utility in the clinical diagnosis and treatment of membrane-associated disease. [ABSTRACT FROM AUTHOR]

In this study, we examined the anchoring behaviour of the ultraviolet (UV)-tailored nematic liquid crystal (LC) 4-cyano-4'-pentylbiphenyl (5CB) at the aqueous/LC interface. A range of photochemical reaction products are generated when 5CB is exposed to UV light, including the main product 4-cyano-4'-biphenylcarboxylic acid (CBA). When UV-treated 5CB is in contact with an aqueous sodium hydroxide or sodium chloride solution, the optical appearance of the LC undergoes a bright-to-dark shift, which indicates an orientational transition in the 5CB from a planar to homeotropic (perpendicular to the surface) state. Moreover, when the photochemically degraded 5CB was immersed in an aqueous mixture of hydroxide ions and electrolytes, the optical response was even more sensitive, which was associated with the deprotonation of CBA and the screening of electrostatic repulsion between the carboxylate head groups at the interface. In this study, the competitive orientational behaviour of LC in relation to biomolecular conjugation and ionic interaction at the interface was examined. When biomacromolecules, such as urease, were conjugated to a mixed monolayer of tetra(ethylene glycol)-terminated lipid and carboxylic acid-terminated lipid at the interface, UV-treated 5CB exhibited an ordering transition from a homeotropic to planar state. However, when a sodium hydroxide solution was in contact to the urease-decorated interface, the LC reverted back to its homeotropic state. By exploiting the orientational behaviour of the UV-treated 5CB at the aqueous/LC interface, we concluded that the acid-doped LC could potentially be used for the sensitive screening of pathogens and biomolecules. [ABSTRACT FROM AUTHOR]

In this study, we demonstrate a new strategy to image biomolecular events through interactions between liquid crystals (LCs) and oil-in-water emulsions. The optical response had a dark appearance when a nematic LC, 4-cyano-4'-pentylbiphenyl (5CB), is in contact with emulsion droplets of glyceryl trioleate (GT). In contrast, the optical response had a bright appearance when 5CB is in contact with GT emulsions decorated with surfactants such as sodium oleate. Since lipase can hydrolyze GT and produce oleic acid, the optical response also displays a bright appearance after 5CB has been in contact with a mixture of lipase and GT emulsions. These results indicate the feasibility of monitoring biomolecular events through interactions between LCs and oil-in-water emulsions.

In this study, we developed a new type of liquid crystal (LC)-based sensor for the real-time and label-free monitoring of enzymatic activity through changes in the orientation of LCs coupled to the interactions between polyelectrolyte and phospholipid. The LCs changed from dark to bright after an aqueous solution of poly-l-lysine (PLL) was transferred onto a self-assembled monolayer of the phospholipid, dioleoyl-sn-glycero-3-phospho-rac-(1-glycerol) sodium salt (DOPG), at the aqueous/LC interface. Interactions between the positively charged PLL and the negatively charged DOPG drove the reorganization of the phospholipid membrane, which induced an orientational transition in the LCs from a homeotropic to planar state. Since the serine endopeptidase trypsin can enzymatically catalyze the hydrolysis of PLL, the dark-to-bright shift in the optical response was not observed after transferring a mixed solution of PLL and trypsin onto the DOPG-decorated LC interface, indicating that no orientational transitions in the LCs occurred. However, the optical response from dark to bright was observed when the mixture in the optical cell was replaced by an aqueous solution of PLL. Control experiments with trypsin or an aqueous mixture of PLL and deactivated trypsin further confirmed the feasibility of this approach. The detection limit of trypsin was determined to be ~1 μg/mL. This approach holds great promise for use in the development of LC-based sensors for the detection of enzymatic reactions in cases where the biological polyelectrolyte substrates of enzymes could disrupt the organization of the membrane and induce orientational transitions of LCs at the aqueous/LC interface., (© 2012 American Chemical Society)

In this study, we develop a novel method for label-free and real-time imaging of molecular interactions between cationic antimicrobial peptides and lipid membranes using liquid crystals (LCs). The optical appearance of LCs changes from bright to dark after transferring phospholipids onto the aqueous/LC interface, representing an orientational transition of LCs from planar to homeotropic state. Bright domains are observed when an antimicrobial agent is in contact with the LC interface decorated with a lipid monolayer of negatively charged phospholipids, while, there is no change in the optical response when the antimicrobial agent is in contact with the LC interface decorated with neutral phospholipids. This approach holds great promise for studying membrane disruption or permeabilization caused by antimicrobial agents.