Design of Self-Reporting Liquid Crystals for Food-Borne Bacteria

Abstract

Rapid, sensitive, and selective recognition of salmonella that causes food poisoning is necessary for food-safety and prevention of pathogenic infection. However, previous methods (e.g., polymerase chain reaction (PCR)) require laborious process, time-consuming process, and trained personnel. Here, we offer simple and generalizable approach to realize rapid detection of food-borne bacteria (salmonella) by liquid crystals (LCs) based system integrated with organic ionics (OIs). Specifically, OIs are self-assembled at the aqueous-LC interface, causing vertical ordering of LC molecules. However, under the incubation of LCs in the aqueous solution with specific amino acids (glutamic acid (Glu), aspartic acid (Asp)), we observed gradually reoriented LC, leading to formation of macroscopic optical signal within ~3.5 h. Surprisingly, we observed extremely low concentration (10 cfu/mL) of salmonella accelerates self-assembly of specific amino acids into the aqueous-LC interface and the formation of bright domains, which enables rapid and sensitive detection within 1.5 h without any complex procedure. The results in this study show the significant influences of anionic amino acids (Glu, Asp) and salmonella on the optical response of LCs. First, the observations reveal the adsorption of anionic molecules that consist of cell culture media (Luria-Bertani (LB) broth) into interfacial LCs via high affinity between bulky anions and hydrophobic LCs. Second, we suggest that salmonella lipopolysaccharide (LPS) plays an important role in facilitating the self-assembly of Glu and Asp at aqueous-LC interface by crosslinking them. (Fig. 1) Furthermore, we propose simple approaches to enhance functionalities (e.g., sensitivity, selectivity) of LC-based salmonella detection system. First, the findings show that remarkably sensitive LC-based system can be realized by increasing the concentration of salmonella or regulating length of aliphatic tails of OIs at aqueous-LC interface. In addition, LCs in micro-sized droplet geometry enable the system to enhance sensitivity due to their initial elastic deformation. Second, we provide selectivity to target bacteria (salmonella) using antibody-magnetic nanoparticle clusters (Ab-MNCs), which also allow one to concentrate salmonella using magnetic force, leading to rapid detection for salmonella without any time-consuming procedure (e.g., cell culture). Overall, we offer a new strategy based on LCs for recognizing specific bacteria (salmonella) which severely threaten food-safety. This new approach provides the insights into a wide variety of fields including medical fields, biological fields, and food-safety, suggesting further potentials of both fundamental studies and practical applications. This work was supported by NRF (RS-2023-00212739) and Samsung Electronics Co., Ltd (4.0026312).