A Remote Magnetoelastic Sensor with Antibody as a Probe to Detect Salmonella Typhimurium

Abstract

Every year millions of people around the globe suffer from foodborne illnesses as a result of the ingestion of food products contaminated with pathogens. Foodborne illnesses not only result in suffering and permanent injury but also loss of productivity due to hospitalization. Traditional methods such as enzyme linked immunosorbent assay (ELISA) and fluorescence methods are widely used in bacterial detection. However these methods are time consuming, expensive and require trained personnel. Hence, it is desirable to develop real-time detection devices that can be used for the identification of contaminated food products.

This study presents the results of an investigation designed to develop a real time wireless biosensor for the detection of Salmonella typhimurium, the bacterial species responsible for Salmonellosis. This new biosensor technology consists of a wireless, magnetoelastic transducer and an immobilized species specific antibody monolayer. A time varying magnetic field was then used to actuate the platform into mechanical resonance and a pickup coil used to measure the resulting resonance frequency. The characteristic resonance frequency of a magnetoelastic sensor is inversely proportional to its length and mass, so the capture of the target organism onto the surface of the sensor causes a mass increase and, hence, a decrease in the fundamental resonance frequency of the magnetoelastic sensor. Different sizes of sensor strips were used in the study, so as to study the effect of size on the sensitivity of the biosensor. The sensor response was studied in liquid media (water, milk and apple juice) containing graded concentrations of S. typhimurium. The dissociation constant, (Kd) and binding valencies were calculated using a Hill Plot. Binding assays of tests conducted in water showed a Kd values of 435± 76 cfu/ml with a binding valency of 2.3 ± 0.02 in a 2×0.4mm dimension sensor, where fat free milk and apple juice samples showed Kd’s of 1389 ± 142 and 310 ± 101 cfu/ml, respectively. The binding valency for fat free milk was found to be 1.9 ± 0.03 and that for apple juice was 2.3 ± 0.02. These similar values of both Kd and the binding valency clearly suggest consistent performance of the sensors even in the presence of different surrounding media. Confirmation of bacterial binding to the sensor antibody was achieved through Scanning Electron Microscopy (SEM) studies of the sensor samples.