Cu2O@CeO2 heterostructure nanozyme with synergistic amplification effect-enhanced immunoassay for sensitive detection of Salmonella in food.

Colorimetric immunoassays based on nanozyme labelling offer promising solution to rapid detect pathogenic bacteria for ensuring food safety. However, sluggish electron transfer kinetics and finite active sites of nanozyme result in unsatisfactory catalytic activity, achieving sensitive detection remains a challenge. Here, we report a Cu2O@CeO2 heterostructure nanozyme with synergistic amplification effect integrating rapid charge transfer kinetics and abundant active sites to enhance the colorimetric immunoassay for sensitive detection of pathogenic bacteria. Highly active CeO2 nanoparticles (NPs) are uniformly and firmly anchored onto stable Cu2O nanocubes to form Cu2O@CeO2 core-shell heterostructure, which effectively alleviates the aggregation of NPs and achieves extremely exposure of catalytic active sites. Density functional theory (DFT) calculations reveal that electron transfer at the heterointerface induces a strong built-in electric field, along with abundant density and high affinity for H2O2, thus enhancing the reaction kinetics and catalytic activity of the nanozyme. Benefiting from these advantages, the Cu2O@CeO2 heterostructure nanozyme exhibits excellent peroxidase-like activity, which could effectively catalyze the substrate 3,3',5,5'-tetramethylbenzidine (TMB) to generate blue oxidized TMB. More importantly, the colorimetric immunoassay utilizing Cu2O@CeO2 nanozyme as labeling probe achieves sensitive detection of Salmonella with a low limit of detection (LOD) of 26 CFU/mL and presents high specificity and stable applicability in spiked food samples. This work provides scientific insights for developing high-activity heterostructure nanozyme and advancing the exploitation of fast bacteria detection technologies to ensure food safety.