Magnetoelastic Biosentinels for the Detection of Pathogenic Bacteria in Stagnant Liquids

This paper presents an investigation into magnetoelastic (ME) biosentinels that seek out, capture, and detect target pathogens in stagnant liquids. The ME biosentinels are designed to mimic various types of white blood cells, the main defensive mechanism in the human body against different pathogenic invaders. This nature-inspired ME biosentinel is composed of a freestanding ME resonator coated with a landscape phage that is engineered to bind specifically with the pathogen of interest. When subjected to an externally applied alternating magnetic field, the biosentinel can be placed into mechanical resonance (i.e., bending or longitudinal mode of vibration) by magnetostriction. The resonating biosentinel can then move autonomously through a liquid due to the net acting force and fluid-structure interactions. As soon as the biosentinel finds and binds with the target pathogen, changes in the mass as well as resonant frequency of the biosentinel occur, and thereby the presence of the target pathogen can be detected. Due to the wireless nature of detection, the resonance frequency changes can be measured in real time without any physical connection to a detector (by using a designed electromagnetic coil and a network analyzer operating in the reflection mode). In order to actuate the biosentinel into mechanical resonance of a desired mode, modal analysis using the three-dimensional finite element method was first performed, followed by determination of the resonant frequency. In addition, the net acting force and resultant motion of the biosentinel due to the induced mechanical vibration were calculated. As a model study, this paper presents detection of Bacillus anthracis spores, a Category A bioterrorism agent, under stagnant flow conditions. Both dynamic simulation and experimental results showed that the ME biosentinels can move autonomously through the liquid and actively bind with the target pathogen. This investigation will advance the fundamental scientific theories describing the operation of biosentinels and have broad societal impact by improving human health through earlier detection of pathogens. Potential short-term applications include the capture and detection of pathogenic bacteria in liquid food products such as juices and milk.