Magnetoelastic biosensor for the detection of Salmonella typhimurium in food products

In this article, a magnetoelastic sensor immobilized with polyclonal antibody for the detection of Salmonella typhimurium in food products is described. The remote query nature of magnetoelastic sensors enables the detection of bacterial species in sealed and opaque containers. Bacterial binding to the antibody on the sensor surfaces changed the resonance parameters, and these changes were quantified by the shift in the sensor’s resonance frequency. Response of the sensors to increasing concentrations (5 × 101–5 × 108 cfu/ml) of S. typhimurium in three different food products (water, fat-free milk and apple juice) was studied and similar responses were observed. These results were also further ascertained by Scanning Electron Microscopy (SEM) studies. A detection limit of 5 × 103 cfu/ml, with a sensitivity of 139 Hz/decade was obtained for the sensors tested in water samples, as compared to 129 Hz/decade in apple juice and 127 Hz/decade in fat free milk. A 2 × 0.4 × 0.015 mm sensor was employed in all the investigations. The dissociation constant Kd and the binding valencies for S. typhimurium spiked in water samples was 435 cfu/ml and 2.33 respectively; as compared to 309 cfu/ml and 2.38 for apple juice; and 1389 cfu/ml and 1.85 for fat free milk samples. Bacterial binding was specific and a divalent binding was observed.