Optical detection of lithocholic acid with liquid crystal emulsions.

The concentration level of bile acids is a clinical biomarker for the diagnosis of intestinal diseases because individuals suffering from intestinal diseases have a sharply increased concentration of bile acids at micromolar levels. Here, we report the detection of lithocholic acid (LCA) in aqueous solution by using surfactant-stabilized 4-n-pentyl-4'-cyanobiphenyl (5CB) liquid crystal droplets as an optical probe. We find that the surfactant adsorbed at the 5CB/water interface can be replaced by LCA, triggering a radial-to-bipolar configuration transition of the 5CB in the droplets. By simply observing the LCA-triggered transition with a polarizing optical microscope, micromolar levels of LCA in aqueous solution can be detected. The detection limit and selectivity of surfactant-stabilized 5CB droplets for LCA depend on the chain length and headgroup of the surfactants used for stabilizing 5CB droplets.