Detection of Bacillus anthracis spores in liquid using phage-based magnetoelastic micro-resonators

This paper presents the results of an investigation to detect Bacillus anthracis spores in liquids using microfabricated magnetoelastic particles (MEP). Free standing, magnetoelastic resonating particles, as small as 500 μm × 100 μm × 4 μm, have been made using microelectronics fabrication techniques. These magnetoelastic resonators feature wireless signal transmission and are suitable for use in air and liquids. Affinity-selected filamentous bacteriophage was employed as the bio-molecular recognition agent and was immobilized onto all surfaces of the resonators. This phage was selected from a landscape phage library specifically for binding B. anthracis spores, the causative agent for the disease anthrax. The biosensors were tested in B. anthracis spore solutions with concentrations from 103 to 108 cfu/ml. A detection limit of 103 cfu/ml, with a sensitivity of 6.5 kHz/decade was observed. Scanning electron microscopy (SEM) micrographs of the tested sensors were used for visual correlation of the sensors’ responses. To investigate specificity, the biosensors were exposed to mixed spore solutions containing B. anthracis Sterne, Bacillus cereus and Bacillusmegaterium spore strains. The phage-coated biosensors were proven to have better binding preference to B. anthracis spores than other strains. The study on the binding kinetics have shown that the dissociation constant (Kd) and the binding valency for the sensor in B. anthracis spores solutions are 193 cfu/ml and 2.32.