Chemotactic steering of bacteria propelled microbeads.

Flagellated bacteria have been embraced by the micro-robotics community as a highly efficient microscale actuation method, capable of converting chemical energy into mechanical actuation for microsystems that require a small payload and high rate of actuation. Along with being highly motile, Serratia marcescens (S. marcescens), our bacterium species of interest, is a highly agile biomotor capable of being steered via chemotaxis. In this paper, we attached S. marcescens bacteria to polystyrene microbeads towards creating biohybrid that can propel themselves towards an attractive chemical source. Using a three-channel microfluidic device, linear chemical gradients are generated to compare the behavior of bacteria-propelled beads in the presence and absence of a chemoattractant, L-aspartate. We tested and compared the behavior of three different bacteria-attached bead sizes (5, 10 and 20 μm diameter) using a visual particle-tracking algorithm, and noted their behavioral differences. The results indicate that in the presence of a chemoattractant, the S. marcescens-attached polystyrene beads exhibit a clear indication of directionality and steering control through the coordination of the bacteria present on each bead. This directionality is observed in all bead size cases, suggesting potential for targeted payload delivery using such a biohybrid micro-robotic approach.