A portable smartphone-assisted highly emissive magnetic covalent organic framework-based fluorescence sensor for the detection of Salmonella typhimurium

The core/shell magnetic covalent organic framework doped with gold nanoparticles (MCOF-AuNPs) was prepared by a facile two-step in situ synthesis strategy to achieve high emission. The fluorescence emission was enhanced and overcame the aggregation-induced quenching of COF after the introduction of Fe₃O₄ and AuNPs. Interestingly, the emission can be quenched by Fe³⁺ ions. MCOF-AuNPs combined with a specific aptamer (apt-MCOF-AuNPs) can capture Salmonella typhimurium selectively, and Fe³⁺-induced fluorescence quenching was inhibited based on the competitive binding of Fe³⁺ ions. A fluorescent assay strategy was constructed with excellent specificity and sensitivity. The detection limit is as low as 4 CFU/mL within 33 min. Furthermore, we developed smartphone-based software as an image reader and analyzer to determine S. typhimurium by capturing the change in fluorescence lightness, which can be assisted for point-of-care testing. Collectively, this innovative design showed a promising on-site detection approach for S. typhimurium.