Real-time monitoring of the enzymatic reaction of urease by using whispering gallery mode lasing

A new strategy is reported here to monitor the enzymatic reactions in real time by using whispering gallery mode (WGM) lasing. The optical microcavity is formed via the self-assembly of an ultraviolet (UV)-treated nematic liquid crystal (LC) 4-cyano-4'-pentylbiphenyl (5CB). The single UV-treated 5CB microdroplet serves as both optical resonator and sensing reactor. The microdroplet configuration transitions induced wavelength shift in the WGM lasing spectra can be used as an indicator for the enzymatic reaction. The proposed sensor has a sub-microgram detection limit of urease (∼0.5 µg/ml), which is lower than the detection limit of currently available urease sensor based on LC materials. Our experimental results demonstrate that WGM lasing has unique advantages in the real-time monitoring of enzymatic reactions compared, for instance, with observation of the optical appearance under a polarized optical microscope.