Real-Time Bacterial Detection in Liquid By Using Magnetoelastic Biosensors and a Surface-Scanning Coil Detector

Foodborne illness is a common public health problem because food can be contaminated with pathogens at any point in the farm-to-table continuum. This paper presents a rapid method of detecting foodborne bacteria in a small volume of liquid (1 ml) using magnetoelastic (ME) biosensors and a surface-scanning coil detector. The ME biosensors are mass-sensitive, strip-shaped magnetic particles (1 mm × 0.2 mm × 0.03 mm). Phage was coated on the surface of the biosensors to capture a specific pathogen. The resonant frequency of the biosensors decreases when the specific pathogen is attached to the sensor surface. This decrease in resonant frequency was measured in real time by using a surface-scanning coil detector connected to a network analyzer. In this work, the detection device was comprised of the surface-scanning coil detector and glass capillary tubes with two different diameters (0.5 mm and 0.3 mm). The two capillary tubes were nested each other (i.e., the 3 mm tube inserted into the 5 mm tube) to form a flow channel through which a 1 ml bacteria solution was passed. An ME biosensor was placed inside the flow channel through the 0.5 mm tube and positioned where it meets the tip of the 3 mm tube. The 3 mm tube tip served as a stopper to fix the biosensor position in a liquid stream. The surface-scanning detector was positioned under the biosensor for real-time resonant frequency measurement. The flow channel and surface-scanning detector were embedded and fixed in polydimethylsiloxane (PDMS) to ensure the mechanical stability of the entire device. In order to control and change the flow rate of the bacteria solution, a peristatic pump was used to deliver the solution into the flow channel. The E2 phage was used to specifically capture Salmonella Typhimurium cells in a 1 ml concentrated solution passing through the flow channel. The concentration of Salmonella solutions ranged from 103 cfu/ml to 108 cfu/ml. ME biosensors without E2 phage were used as control sensors, and ones coated with E2 phage were used as measurement sensors. Both groups of sensors were tested by passing the Salmonella solutions, and changes in the resonant frequency of the sensors were recorded. The resonant frequency of the measurement sensors were found to decrease, resulting from specific binding of Salmonella on the biosensors. In addition, the resonant frequency shifts of the measurement sensors were much larger than those of the control sensors for the whole tested range of Salmonella concentrations. The presented method can be combined with surface-sampling of bacterial pathogens by swabbing and used for real-time pathogen detection.