Controlling Swimming Magnetotactic Bacteria Through Microfabrication Toward a Non-Destructive Biological Sensor

The development of non-destructive sensors is an important direction to pursue to advance approaches, which are less intrusive in their monitoring. One area where significant advances can be made in this field is through using biological inspiration. In this work, we demonstrate the ability of swimming magnetic bacteria, Magnetospirillum magneticum strain AMB-1, to respond to microfabricated magnetic field concentrators. These magnetic bacteria are envisioned as a potential non-destructive sensor approach for detecting defects in submerged metal structures such as ship hulls and bridges. To accomplish this, a pair of Helmholtz coils was built to magnetize microfabricated permalloy (NiFe) structures of different shapes that mimic defects in metals. The NiFe structures were fabricated through photolithography and depositing a thin film of NiFe on a master mold. The substrate was a thin piece of glass (<170μm) that permitted us to observe the interaction of the magnetic bacteria with the NiFe structures that were positioned at the center of the Helmholtz coils. The response of the bacteria around the structures was quantified through analyzing the images of the bacteria in terms of orientation. The bacteria change orientation as they approach the fabricated structures with concentrated fields due to their geometries. In addition, we used magnetic particles to examine the fields and estimated the local magnetic fields exerted on the particles through calculations involving the forces on the beads. We believe that this work is important in a variety of areas from bacterial mechanics to synthetic biology to aqueous non-destructive sensors.