A Self-Assembled Flagellated Bacterial Micropump*

Magnetotactic bacteria (MTB) are prokaryotic microorganisms that utilize innate lipid-bound chains of magnetic nanocrystals to orient their swimming direction in the weak (~0.5 Gauss) geomagnetic field. This magnetic guidance mechanism often reduces the search space in their quest for favorable environmental conditions. The present study is directed at developing a novel self-assembled flagellated bacterial micropump based on the response of the swarm dynamics to a sequence of designed magnetic fields. This microbial device is demonstrated on-chip through local constraints of oxygen due to the aerobic respiration of an MTB cluster. The fluid flow characteristics of the pump are modeled based on the cell response to ambient oxygen levels including the magneto-aerotactic polarity reversals and oxygen-dependent swimming speeds. The momentum transfer onto non-magnetic colloidal particles is described by considering the flagellar-driven hydrodynamic interactions, and experimentally verified using non-magnetic fluorescent nanoparticles. These findings, and the dynamics of the system including the role of oxygen diffusion, is numerically modeled.