Abstract: In this study, a magnetic relaxation immunosensor based on gold core@platinum shell (Au@Pt) nanozyme-mediated paramagnetic ion valence transition was constructed and used for the rapid detection of Salmonella in foods. Pt@Au nanozyme with high stability and good catalytic performance was synthesized by a microwave-assisted hydrothermal (MAH) method, and its catalase-like activity was used to catalyze hydrogen peroxide (H2O2). The remaining H2O2 could convert MnO4- into Mn2+ through a redox reaction. The significant difference in magnetic signals between MnO4? and Mn2+ allowed the quantitative analysis of hydrogen peroxide. In the immunoreaction, the concentration of Salmonella was directly proportional to the content of “detection antibody-Pt@Au”. Au@Pt could regulate the H2O2-mediated MnO4?/Mn2+ conversion system and consequently control the change of magnetic signal, ultimately allowing the quantitative analysis of Salmonella. The detection limit of this method for Salmonella was 50 CFU/mL, and the linear range was 1 × 102–5 × 107 CFU/mL. The results of this method for Salmonella in eggs were in good agreement with those of fluorescence quantitative polymerase chain reaction (PCR). This method has the advantages of high sensitivity, good stability, simple operation and low cost, thus having a good application prospect in the rapid detection of foodborne pathogens.

Key words: Salmonella; platinum shell@gold core nanozyme; paramagnetic ions; magnetic relaxation switching immunosensor; hydrogen peroxide