Fluorescence Transduction of Liquid Crystal Ordering Transitions for Biosensing

Liquid crystal (LC) ordering transitions are exquisitely sensitive to molecular interactions at aqueous interfaces and have long served as the basis for optical biosensors. However, the readout of these transitions has almost exclusively relied on polarized-light optical microscopy, which limits quantification and hinders practical deployment. Here, we report a fluorescence-based transduction scheme that converts LC ordering transitions to quantitative optical outputs. Our strategy employs amphiphilic block copolymers bearing aggregation-induced emission (AIE) motifs that undergo dynamic covalent conjugation with IgG antibodies through reversible imine chemistry. In complex LC emulsions, polymer surfactants localize differently depending on droplet LC configuration: accumulation at monopolar defects concentrates AIE units to generate a bright ON state, whereas redistribution along the LC/water interface in the radial configuration suppresses emission to yield an OFF state. Recognition of <i>Salmonella enterica</i> serovar Typhimurium─one of the most prevalent foodborne pathogens─reversibly perturbs this equilibrium, producing rapid (∼1 h) ON/OFF fluorescence responses with detection limits down to 10² cells/mL. Incorporation of a ratiometric reference dye further enhances robustness against experimental variability. This work establishes the fluorescence transduction of LC ordering transitions as a generalizable and portable sensing paradigm, bridging soft matter design with real-world diagnostics.