Colorimetry/fluorescence dual-mode detection of Salmonella typhimurium based on self-assembly of MCOF with Au NPs nanozyme coupled AIEgen

Sensitive, accurate, simple and quick monitoring of Salmonella typhimurium (S. typhimurium) in food is significant for preventing food poisoning, but still remains a challenge. Herein, a colorimetry/fluorescence dual-mode sensing strategy was fabricated to detect S. typhimurium by integrating the self-assembly of magnetic covalent organic framework (MCOF) with gold nanoparticles (Au NPs) as the peroxidase-mimicking nanozyme and aggregation-induced emission luminogen (AIEgen). S. typhimurium could competitive bind to aptamer conjugated Au NPs (Au NPs@apt), inhibit the self-assembly of MCOF with Au NPs, and shield the catalytic activity of AuNPs. After adding H2O2 and TPE-4A, the dark green solution changed to light with increasing S. typhimurium concentration, on the contrary, the fluorescent signals were generated. As a result, in colorimetry/fluorescence modes, S. typhimurium could be detected in the linear ranges of 103-108 CFU mL-1 and 101-107 CFU mL-1, with LODs of 1000 and 10 CFU mL-1, respectively. Importantly, different colors consistent with various S. typhimurium concentrations can be accurately classified by smartphone app and linear discriminant analysis (LDA). The smartphone-assisted data interpretation can generate complementary colorimetry and fluorescence signals without any sophisticated equipment and achieve on-site detection. Moreover, the proposed strategy could be explored for S. typhimurium monitoring in milk with satisfactory recoveries (97.6-100.4 %) in colorimetry and fluorescence mode and good classification and prediction performance in smartphone/LDA system, suggesting the feasibility and potential applications of the sensing platform.