Constructing difunctional histidine-modified magnetic hybrid nanozymes as capture probes and signal amplifiers for the sensitive colorimetric detection of Salmonella Typhimurium in food

Nanozyme-based detection methods have gained increasing attention in the field of food safety. However, the effect of the food matrix on the nanozyme activity requires tedious sample pre-treatment for nanozyme-based detection. Therefore, a difunctional histidine-modified magnetic hybrid nanozymes (His-Fe3O4@Cu) was used as capture probes and signal amplifiers to develop a simple colorimetric aptasensor for Salmonella Typhimurium detection. The prepared His-Fe3O4@Cu nanozymes demonstrated a 5.0-fold increase in peroxidase-like activity compared to Fe3O4 nanozymes and exhibited superparamagnetism with saturation magnetization values of 63.5 emu/g. By virtue of the strong superparamagnetism of the His-Fe3O4@Cu nanozymes, aptamer-conjugated His-Fe3O4@Cu nanozymes first enriched and separated S. Typhimurium from food matrix. Then, aptamer-conjugated His-Fe3O4@Cu nanozymes employed an etching solution to generate a detection signal via the peroxidase-like activity. In optimal conditions, this proposed colorimetric aptasensor successfully detected S. Typhimurium with a limit of detection (LOD) of 8 CFU/mL in a linear range of 1.2 × 101 to 1.2 × 106 CFU/mL. Finally, the proposed aptasensor was further validated in three actual samples, with a capture efficiency ranging from 88.6 % to 96.5 % and recoveries between 88.2 % and 104 %. These results revealed the significant potential of this method for S. Typhimurium detection in food samples.