Liquid crystal-based aptasensor to detect ractopamine hydrochloride at a femtomolar level

Abstract

We developed a liquid crystal (LC)-based aptasensor to detect ractopamine hydrochloride (RAC) at the femtomolar level by analyzing the optical texture of LCs. The LC-based sensor comprises an aptamer that reacts with cetrimonium bromide (CTAB) and RAC at the interface between the aqueous phase and the LCs. The self-assembled CTAB causes the LCs to anchor perpendicularly at the aqueous/LC interface. The ordering of the LCs at the interface between the CTAB-packed aqueous phase and LCs depends on the concentration of RAC. When the specific binding events between the aptamers and RAC were superior to the electrostatic interactions of the aptamers with CTAB, the ordering of the LCs remained in the homeotropic orientation. When the electrostatic interaction became relatively dominant, it perturbed the orientation of the LCs, changing their anchoring from homeotropic to tilted or planar. We monitored the optical response of the LCs, which depends on their ordering transitions. RAC levels as low as approximately 0.697 fg/mL (2.323fM) in phosphate-buffered saline and 0.840 pg/mL (2.813 pM) in pig urine could be detected using this aptasensor. The change in the optical texture of the LCs was quantitatively interpreted by comparing the averaged grayscale intensity data of the LC optical images. Our results indicate that this LC-based aptasensor has highly sensitivity and selectivity and can be reused.