A novel one-step liquid crystal (LC)-based aptasensor has been developed for on-site detection of trace substances in sewage analysis. The platform utilizes different mechanisms to simultaneously trigger the upper and bottom layers of LC orientation. By employing trace amounts of CTAB in Tris-HCl buffer, the upper layer of LC is aligned, while DNA aptamers modified on a single glass induce the orientation of the bottom layer. When targeting cocaine, the asymmetric single-stranded DNA aptamers transition to a symmetric Y-shape, causing the reorientation of LCs from planar to homeotropic. This results in an optical change from bright to dark in the LC image. The sensing procedure involves adding pre-buffered samples at pH 7.4 to the system in one step. The platform requires only 10 ng of DNA aptamers, which can be kept dry. It enables on-site detection of cocaine in sewage, exhibiting a linear calibration curve from 1 pM to 15 µM in water (R2 = 0.997) with a limit of detection of 0.5 pM. The aptasensor demonstrates quantitative recoveries ranging from 89.6% to 110.9% in sewage samples. This sensitive, robust, and portable LC-based aptasensor shows promise as a tool for on-site detection of trace substances.
