Liquid crystal aptamer-based sensor with a functionalized amphiphilic block copolymer for the detection of m-hydroxy cocaine

Cocaine detection is crucial for public health and safety, as it plays a vital role in curbing substance abuse, reducing crime, and protecting individuals from its harmful effects. This research utilizes 4-cyano-4ˊ-pentylbiphenyl (5CB) confined in a transmission electron microscopy (TEM) grid and functionalized with a poly(styrene-b-acrylic acid) (PS-b-PAA) monolayer (5CB_PAA). The PS anchors the block-co-polymer in the 5CB, and a cocaine-specific aptamer (CA) is covalently immobilized onto the PAA (5CB_PAA-aptamer) to detect m-hydroxy cocaine in solution and human urine samples. An initial homeotropic alignment of the 5CB is achieved by optimizing the CA concentration, and monitoring m-hydroxy cocaine is enabled via a homeotropic-to-planar orientation change of the 5CB. The 5CB_PAA-aptamer system detects cocaine within the range of 5–50 nM, with a limit of detection of 5 nM. Additionally, successful cocaine detection has been performed in human urine samples by introducing cocaine into the urine after collection. The study also encompasses the evaluation of the 5CB_PAA-aptamer grid's stability for up to 20 days and the conduction of selectivity tests in the presence of other interfering substances. This study establishes the 5CB_PAA-aptamer system as a simple, cost-effective, selective, and sensitive platform for detecting cocaine, with potential applications in resource-limited settings.