Direct Detection of Salmonella on Fresh Produce

Phage-immobilized magnetoelastic (ME) biosensors have proven promising in detecting food surface contamination rapidly and inexpensively. These biosensors are wireless, mass-sensitive biosensors and can be placed directly on food surfaces to detect the presence of target pathogens. Previously, millimeter-scale strip-shaped ME biosensors have been used to demonstrate direct detection of Salmonella Typhimurium on various fresh produce surfaces, including tomatoes, apples, shell eggs, and watermelons. Since the biosensor must come into direct contact with Salmonella bacteria, food surfaces with large roughness and curvatures (e.g., leafy green vegetables) may allow the bacteria to avoid direct contact, thereby avoiding detection. Hence, the primary goal of this paper is to investigate the effects of food surface topography and sensor size on the detection capabilities of the biosensors. Spinach leaf surfaces were selected as model surfaces, and detection experiments were conducted with differently sized micron-scale biosensors. Spinach leaf roughness and curvatures of both adaxial (topside) and abaxial (underside) surfaces were measured using a laser confocal microscope. The experimental results showed that in spinach as the sensor is made smaller, the physical contact between the biosensors and bacteria are improved. Smaller sensors thereby enhance detection capabilities. When proper numbers of biosensors were used, micron-scale biosensors were found to yield improved limits of detection over previously investigated millimeter-scale biosensors.