Magnetic relaxation switch immunosensor for the rapid detection of the foodborne pathogen Salmonella enterica in milk samples

• Salmonella enterica in milk samples were detected by a rapid and sensitive magnetic relaxation switch (MRS) immunosensor.
• The limit of detection of the sensor was 20 times lower than that of enzyme-linked immunosorbent assay.
• It is sensitive, specific, fast and easy to operate.
• This detection platform is more sensitive in detecting S. enterica from real milk samples.

We present a rapid and sensitive magnetic relaxation switch (MRS) immunosensor based on superparamagnetic nanoparticles (SMNs) for detecting the foodborne pathogen Salmonella enterica in milk samples. The MRS immunosensor employed target-induced aggregation (or disaggregation) of SMNs in immunoreaction, which could modulate the spin–spin relaxation time of the neighboring water molecule. Results showed that the linear range of the MRS immunosensor for detecting S. enterica was 5 × 103–106 CFU/mL, and that the relative standard deviation was below 13.5%. The detection limit of the sensor was 103 CFU/mL, which was 20 times lower than that of enzyme-linked immunosorbent assay (ELISA, 2 × 104 CFU/mL). The analysis time of the sensor (30 min) was also shorter than that of ELISA (2–4 h). This sensor was successfully applied to detect S. enterica in 20 real milk samples, and its accuracy was better than that of ELISA. Therefore, the MRS immunosensor provides a promising platform for the determination of foodborne pathogenic bacteria because of its high sensitivity, simplicity, rapidness, and low cost.