A multifunctional iron catalyst-based colorimetric sensor for rapid bacterial detection in food

Herein, we report an on-site sensing system for detecting the presence of foodborne pathogen, Escherichia coli O157:H7, by using paramagnetic immuno-iron oxide nanoparticles (immuno-IONPs) that possess intrinsic peroxidase-like activity. The surface functionalization of IONPs with dextrin, followed by oxidation to form OxDex-IONPs, significantly improved their colloidal stability and peroxidase-like activity. The catalytic activity of OxDex-IONPs was employed to induce the oxidation of colorless 3,3′,5,5′-tetramethylbenzidine (TMB) to a blue product in the presence of hydrogen peroxide, which was successfully utilized in the development of a colorimetric sensor. The generation of specific signals in response to the target bacteria could be achieved through magnetophoresis, a technique that specifically fractionates the IONPs clustered with the target bacteria based on their faster mobility. The detection system was demonstrated to be compatible with real food samples, exhibiting a detection limit of around 80 CFU/mL. Due to its straightforward procedure and rapid analysis time of under 50 min, the proposed detection system would offer an effective way to monitor bacterial contamination and evaluate the safety of food.