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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]