Detection of Multiple Pathogens on Fresh Produce Using a Surface-Scanning Coil

Abstract

The wireless phage-based magnetoelastic (ME) biosensor combined with a surface-scanning coil is being developed as a direct pathogen detection method on food surfaces. The biosensor consists of a free-standing ME resonator as the signal transducer that is coated with a genetically engineered phage as the biomolecular-recognition element. Due to the Joule magnetostriction effect, the biosensor can be placed into mechanical resonance when subjected to a time-varying magnetic field alternating at the right frequency. The detection is based on measuring a change in the sensor’s resonant frequency, which is proportional to the number of pathogens bound to the biosensor. This paper investigates the real-time detection of multiple bacterial pathogens, Salmonella Typhimurium and Bacillus anthracis Sterne spores, on apple surfaces using ME biosensors. Measurement biosensors coated respectively with E2 phage (specific for S. Typhimurium) and JRB7 phage (specific for B. anthracis Sterne spores) were prepared and used for detection. Control biosensors (without phage) were also fabricated and used to compensate the effects of environmental changes. Fresh apple surfaces were spiked with S. Typhimurium cells, B. anthracis spores and their mixtures with known concentrations. Both measurement and control sensors were placed directly on the apple surfaces, and these pathogens were detected simultaneously by wirelessly monitoring changes in the biosensors’ resonant frequency in real time in a humid environment. These frequency shifts were measured with a surface-scanning coil detector. The pathogen binding was then confirmed by optical and scanning electron microscopy. The results showed that specific binding of the pathogens on the measurement sensors has occurred. The effects of masking bacteria such as Escherichia coli on the detection performance were also investigated.