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

Abstract 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 × 10 3 –10 6  CFU/mL, and that the relative standard deviation was below 13.5%. The detection limit of the sensor was 10 3  CFU/mL, which was 20 times lower than that of enzyme-linked immunosorbent assay (ELISA, 2 × 10 4  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.