Phage-based magnetoelastic (ME) biosensors have proven useful in rapidly and inexpensively detecting food surface con- tamination. 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, shell eggs, watermel- ons, and spinach leaves. Since the topography of these produce surfaces are different, and the biosensor must come into direct contact with Salmonella bacteria, food surfaces with large roughness and curvatures (e.g., spinach leaf surfaces) may allow the bacteria to avoid direct contact, thereby avoiding detection. The primary objective of this paper is, hence, to investigate the effects of food surface topography on the detection capabilities of the biosensors. Spinach leaf surfaces were selected as model surfaces, and detection experiments were conducted with differently sized biosensors (2 mm, 0.5 mm, and 150 μm in length). Spinach leaf roughness and curvatures of both adaxial (top) and abaxial (underside) surfaces were measured using a confocal laser scanning microscope. The experimental results showed that in spinach as the sen- sor was made smaller, the physical contact between the biosensors and bacteria were improved. Smaller sensors thereby enhance detection capabilities. When proper numbers of biosensors are used, micron-scale biosensors are anticipated to yield improved limits of detection over previously investigated millimeter-scale biosensors.
This paper presents the concept of self-propelled magnetoelastic (ME) biosentinels that seek out and capture pathogenic
bacteria in stagnant liquids. These biosentinels are composed of a free-standing, asymmetric-shaped ME resonator coated
with a filamentous landscape phage that specifically binds with a pathogen of interest. When a time-varying magnetic pulse
is applied, the ME biosentinels can be placed into mechanical resonance by magnetostriction. The resultant asymmetric
vibration then generates a net force on the surroundings and hence generates autonomous motion in the liquid. As soon
as the biosentinels find and bind with the target pathogen through the phage-based biomolecular recognition, a change
in the biosentinel’s resonant frequency occurs, and thereby the presence of the target pathogen can be detected. In order
to actuate the ME biosentinels into mechanical resonance of a desired mode, modal analysis using the three-dimensional
finite element method was performed. In addition, the design of a magnetic chamber that can control the orientation and/or
translation of a biosentinel is discussed.