Sensitive detection of di-(2-ethylhexyl) phthalate using a liquid crystal-based aptasensor

We report a di-(2-ethylhexyl) phthalate (DEHP) aptasensor based on liquid crystal (LC), 4-cyano-4 '-pentylbiphenyl (5CB). This optical sensor is made up of an aptamer that interacts with DEHP and cetrimonium bromide (CTAB) at the aqueous/LCs interface. The cationic surfactants, CTAB, trigger the homeotropic state of 5CB and control its local anchoring depending on the extent to which they interact with the aptamers. When the aptamers are electrostatically attracted to CTAB, the orientation of 5CB is disturbed. The conformational changes of the aptamers contribute to a change in the ordering of 5CB from a tilted to homeotropic state due to the formation of the DEHP-aptamer complexes. The ordering of the LCs is influenced by the biomolecular interactions at the CTAB-filled aqueous/5CB interface. We analysed the orientational ordering of 5CB according to the DEHP concentrations. An orientational transition from homeotropic to tilted alignment was observed with decreasing DEHP concentration. We determined the detection limit to be approximately 0.651 pg/mL in phosphate-buffered saline. We interpreted the greyscale intensity data that measured the intensity of polarised light, which penetrated the LCs, to quantify the polarised image. Our results demonstrate the potential method for simply monitoring the DEHP levels in various environmental parameters.