Microscale Liquid Crystal Droplet-Embedded Hydrogel Film for Ultrasensitive Optical Detection of Bacterial Endotoxins

This study presents a novel approach that involves the development of micrometer-sized liquid crystal (LC) droplet-embedded chitosan (CS) hydrogel film, referred to as the CSLC gel-film, for ultrasensitive and selective detection of bacterial lipopolysaccharide (endotoxin). The hydrogel matrix effectively restricts the mobility of the embedded LC droplets, preventing coalescence and sedimentation, while maintaining a long-term structural integrity. The fiber-like structure of the hydrogel network facilitates the transport of aqueous analytes, allowing endotoxins to reach the LC-water interface and induce a bipolar-to-radial configurational transition. The sensing performances of the CSLC hydrogel film are systematically evaluated for LPS extracted from Escherichia coli (E. coli.), Pseudomonas aeruginosa (P. aeruginosa), and Salmonella typhosa at different pH conditions using a polarized optical microscope (POM). Notably, the prepared gel-film exhibits an exceptional selectivity for LPS, despite the presence of commonly known interferents, including surfactants, chelating agents, divalent cations, and structurally similar biomolecules. The gel-film is capable of detecting endotoxins directly from live bacterial sources, as evidenced by its response to living E. coli. cells. Overall, the results highlight the potential of CSLC hydrogel film as a simple, cost-effective, and scalable platform for the rapid and reliable detection of bacterial endotoxins in biomedical and environmental settings.