Rapid and sensitive magnetoelastic biosensors for the detection of Salmonella typhimurium in a mixed microbial population.

In this article, we report the results of an investigation into the performance of a wireless, magnetoelastic biosensor designed to selectively detect Salmonella typhimurium in a mixed microbial population. The Langmuir-Blodgett (LB) monolayer technique was employed for antibody (specific to Salmonella sp.) immobilization on rectangular shaped strip magnetoelastic sensors (2 x 0.4 x 0.015 mm). Bacterial binding to the antibody on the sensor surface changes the resonance parameters, and these changes were quantified as a shift in the sensor's resonance frequency. Response of the sensors to increasing concentrations (5 x 10(1) to 5 x 10(8) cfu/ml) of S. typhimurium in a mixture of extraneous foodborne pathogens (Escherichia coli O157:H7 and Listeria monocytogenes) was studied. A detection limit of 5 x 10(3) cfu/ml and a sensitivity of 139 Hz/decade were observed for the 2 x 0.4 x 0.015 mm sensors. Binding kinetics studies have shown that the dissociation constant (K(d)) and the binding valencies for water samples spiked with S. typhimurium was 435 cfu/ml and 2.33 respectively. The presence of extraneous microorganisms in the mixture did not produce an appreciable change in the biosensor's dose response behavior.