Cationic covalent organic framework with electrostatic-magnetic synergy for efficient enrichment and immunochromatography assay of Salmonella typhimurium.

BACKGROUND: Conventional lateral flow immunoassays (LFIA) for pathogen detection often suffer from insufficient sensitivity, limited anti-interference capability, and reliance on matched antibody pairs. To address these challenges and advance the concept of integrated enrichment-detection platforms, this work innovatively developed a multifunctional probe based on cationic Fe3O4@COF. By combining magnetic responsiveness with a high-density cationic COF shell, a more efficient enrichment-detection strategy was designed to streamline the LFIA workflow and eliminate the need for paired antibodies.

RESULTS: The cationic Fe3O4@COF nanocomposite serves as both an enrichment platform and a colorimetric label for rapid detection of Salmonella typhimurium, where its intrinsic dark color enables naked-eye visual readout without any additional instrumentation. The material enabled highly efficient bacterial capture via electrostatic and physicochemical interactions, achieving a capture efficiency of up to 98%. Benefiting from its high binding affinity and enrichment capability, the proposed Fe3O4@COF-LFIA achieved a visual detection limit as low as 103 CFU mL-1 within a detection time of 6 min, representing a 100-fold improvement over conventional AuNPs-LFIA. The method also demonstrated high accuracy and reliability in lettuce, shrimp, and apple juice samples, with recoveries ranging from 85.1% to 101.2% and a precision below 8.7% coefficient of variation. The improved anti-interference capability results from the synergistic action of magnetic separation and the cationic COF shell.

SIGNIFICANCE: This study introduced a novel methodology for pathogen detection, shifting from traditional antibody-dependent LFIA to a more integrated, multifunctional probe-based system. The Fe3O4@COF-based enrichment-detection platform not only simplifies the assay architecture but also enhances sensitivity and anti-interference capability, highlighting the potential of functionalized magnetic COF composites in point-of-care diagnostics for food safety surveillance.