Chemotactic Behavior of Bacteria Propelled Microbeads in Linear Microfluidic Gradients

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 low 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 used a biohybrid system of S. marcescens bacteria attached to polystyrene beads to create microrobots that can propel themselves towards a chemoattractant source. Using a three-channel linear chemical gradient generator, we compared the behaviors of bacteria-propelled beads in the presence and absence of a chemoattractant, L-aspartate. Additionally, we tested and compared the behavior of three different bacteria-attached bead sizes, and noted their behavioral differences. By using a particle tracking algorithm, we analyzed the behavior of each bead: 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. Moreover, this directionality exists in all bead size cases.