Chiral cholesteric molecular tweezer 7d was synthesized and its influences on changes in the ultraviolet (UV) and fluorescence spectra of various anions were investigated. The results displayed that molecular tweezer 7d selectively recognized F⁻ ions in dimethyl sulfoxide with a detection limit of 5.14 μmol/L, while other anions had little interference. On this basis, a method for the rapid detection of F⁻ ions by host molecular tweezer 7d was established, and the naked-eye detection of F⁻ was realized through the unique yellow color of the complex solution. According to the determination of F⁻ ions in real food samples, it was proved that the established method had good application prospects in F⁻ ion detection.

Chiral cholesteric molecular tweezer 7a was synthesized, and its recognition properties for Ag⁺, Al³⁺, Ca²⁺ etc., were investigated by UV and fluorescence spectra. The results showed that in ethanol/Tris (1/1, v/v, pH 7.0) buffer solution, the host molecular tweezer 7a had a specific recognition ability for Ag⁺, the detection limit was up to 1 × 10⁻⁶ mol/L, and other metal ions had little effect on Ag⁺ recognition. At the same time, the naked-eye detection of Ag⁺ was realized by the light red color of the complex solution. Furthermore, the mechanism of recognition of Ag⁺ by molecular tweezer 7a was studied by a nuclear magnetic titration test and computer molecular simulation, and a rapid detection method of Ag⁺ using host molecular tweezer 7a was established. Through the determination of Ag⁺ in milk powder, quinoa and other food samples, it was proved that this novel method had a good application prospect for the detection of Ag⁺ in food.

Postbiotics derived from Bacillus species are recognized as promising natural antimicrobial agents. This study aimed to systematically evaluate the inhibitory activity of postbiotics derived from B. velezensis 906 against L. monocytogenes, elucidate the underlying antibacterial mechanisms using agar diffusion assays, broth microdilution, growth kinetics, flow cytometry, phospholipid competition assays, whole-genome mining, and non-targeted metabolomics, and characterize the bioactive metabolites responsible for their antibacterial effects. The postbiotics exhibited significant antagonistic activity against Gram-positive bacteria, Gram-negative bacteria, and fungi. They also inhibited pathogens such as Salmonella and Enterobacter sakazakii. Against L. monocytogenes, the minimum inhibitory concentration was 0.0083 mg/mL. At 1× MIC, the OD600 after 24 h remained at approximately 0.8, compared with 1.3–1.4 in the untreated control, whereas treatment at 4× MIC almost completely inhibited bacterial growth. Mechanistic analyses suggested that the postbiotics interact with membrane phospholipids, resulting in membrane disruption, increased intracellular reactive oxygen species accumulation, and enhanced membrane permeability. Integrated genome mining and non-targeted metabolomics indicated that the antibacterial activity was associated with a coordinated antimicrobial network involving lipopeptides, polyketides, bacteriocin-related compounds, and siderophore-associated metabolites. These findings provide insight into the antibacterial basis of B. velezensis 906 postbiotics and support their potential application in food safety control.