A new strategy for imaging urease activity using liquid crystal droplet patterns formed on solid surfaces

In this study, we demonstrate a simple and label-free method for imaging urease activity using liquid crystal (LC) droplet patterns on solid surfaces. The LC droplet patterns were spontaneously formed by spreading stearic acid doped-LCs dissolved in organic solvents on glass microscope slides. The LC droplets displayed a bright appearance in urea or urease solution, while dark cross images were exhibited when LC droplets contacted an aqueous mixture of urease and urea, indicating an orientational transition of LC molecules from a planar to a perpendicular state. The enzymatic reaction between urea and urease produced ammonia that could be hydrolyzed into ammonium and hydroxide ions. Due to the increase of pH, the carboxylic acids were deprotonated and self-assembled at the aqueous/LC interface, which induced an orientational transition of LC molecules in the droplet. These results indicate that the surface-anchored LC droplets with dopants show high promise for developing LC pattern-based sensing devices for label-free detection of biological events.