Imaging catalase reactions through interactions between liquid crystals and oil-in-water emulsions

In this study, a simple label-free technique for imaging catalase reactions through interactions between liquid crystals (LCs) and oil-in-water emulsions was developed. We prepared a dodecanal-in-water emulsion, and mixed the emulsion with 4-cyano-4-pentylbi-phenyl (5CB) droplets. In the absence of hydrogen peroxide, a dark image was observed between crossed polarisers because the 5CB and dodecanal droplets coalesced resulting in the formation of a population of droplets comprised of 5CB and dodecanal that are isotropic. In contrast, if hydrogen peroxide was present, a bright appearance was observed, because some fraction of the dodecanal was converted to dodecanoic acid, which prevented coalescence of 5CB and dodecanal, and thus the 5CB droplets retained their nematic order. Since catalase could decompose hydrogen peroxide, we observed a dark image after LC made contact with a dodecanal-hydrogen peroxide mixture that had been pre-incubated with catalase. Control experiments were conducted to confirm the specificity of the enzymatic reaction. The detection limit of catalase in our system was 0.1 g/mL. These results demonstrate that LC with oil-in-water emulsion can be used for the detection of relevant enzymatic reactions.