Rapid qualitative and quantitative detection ofSalmonella typhimurium(S. typhimurium) takes an important role in ensuring food safety. Herein, a colorimetric assay aptasensor forS. typhimuriumutilizing intrinsic peroxidase-like activity of gold nanoparticles embedded spherical covalent organic framework and the affinity and specificity ofS. typhimurium-aptamer has been explored. This aptasensor can capture theS. typhimuriumvia the selective binding effect of aptamer, and the catalytically active sites were shielded. As a result, the colorimetric signals of the 3,3′,5,5′-tetramethylbenzidine-H₂O₂system were turned off. Under optimum conditions, the aptasensor gave a linear response over the range of 10 to 10⁷CFU/mL forS. typhimurium. The detection limit of 7 CFU/mL was obtained within 45 min and was effectively applied to detectS. typhimuriumin milk and lake water samples with recoveries in the range from 96.4 to 101.0%. More importantly, combined with a self-developed smartphone-based image analysis system, the proposed aptasensor can be used for point-of-care testing applications.