Target-inhibited MCOF-Apt-AuNPs self-assembly for multicolor colorimetric detection of *Salmonella Typhimurium*

Pathogens detection is a crucial measure in the prevention of foodborne diseases. This study developed a novel multicolor colorimetric assay to visually detect Salmonella Typhimurium (S. Typhimurium), by utilizing the etching process of gold nanorods (AuNRs) with TMB2+. The strategy involved the construction of nanozyme by assembling magnetic covalent organic framework (MCOF) with aptamer-conjugated AuNPs (Apt-AuNPs), exhibiting remarkable peroxidase-like activity to catalyze the oxidation of TMB/H2O2 and inducing the etching of AuNRs. The presence of S. Typhimurium could inhibit this process, resulting in the generation of vivid colors. The multicolor colorimetric assay could specifically determine S. Typhimurium from 102 to 108 CFU mL−1 in 60 min with visual detection limit of 102 CFU mL−1, and instrumental detection limit of 2.3 CFU mL−1. Moreover, detecting S. Typhimurium in chicken, milk, pork and lettuce samples has shown promise in practical applications.