Highly selective aptasensor for optical detection of whole cell gastrointestinal pathogen Shigella dysenteriae at label-free liquid crystal–aqueous interface.

This article focuses on the development of a label-free liquid crystal (LC)-based biosensor employing a bacteria-specific aptamer for rapid detection of whole-cell *Shigella dysenteriae* at aqueous interfaces. The sensor utilizes the stimuli-responsive orientational changes of LC molecules at the LC–aqueous interface, where the presence of the negatively charged aptamer induces a planar/tilted LC alignment that reverts to homeotropic alignment upon binding with *S. dysenteriae*, producing a detectable bright-to-dark optical change under polarized optical microscopy. The biosensor demonstrated high specificity with a limit of detection of 30 colony-forming units per milliliter (CFU/ml) and was validated against closely related bacterial strains and real food samples, showing comparable performance to conventional diagnostic methods but with faster results and simpler operation. Spectroscopic analyses confirmed aptamer conformational changes upon target binding, supporting the sensor's detection mechanism. This LC-based aptasensor offers a cost-effective, sensitive, and potentially portable platform for point-of-care detection of *S. dysenteriae*, particularly suited for resource-limited settings.