Bacteria-Activated Janus Particles Driven by Chemotaxis.

In the development of biocompatible nano-/micromotors for drug and cargo delivery, motile bacteria represent an excellent energy source for biomedical applications. Despite intense research of the fabrication of bacteria-based motors, how to effectively utilize the instinctive responses of bacteria to environmental stimuli in the fabrication process, particularly, chemotaxis, remains an urgent and critical issue. Here, by developing a molecular-dynamics model of bacterial chemotaxis, we present an investigation of the transport of a bacteria-activated Janus particle driven by chemotaxis. Upon increasing the stimuli intensity, we find that the transport of the Janus particle undergoes an intriguing second-order state transition: from a composite random walk, combining power-law-distributed truncated Lévy flights with Brownian jiggling, to an enhanced directional transport with size-dependent reversal of locomotion. A state diagram of Janus-particle transport depending on the stimuli intensity and particle size is presented, which allows approaches to realize controllable and predictable propulsion directions. The physical mechanism of these transport behaviors is revealed by performing a theoretical modeling based on the bacterial noise and Janus geometries. Our findings could provide a fundamental insight into the physics underlying the transport of anisotropic particles driven by microorganisms and highlight stimulus-response techniques and asymmetrical design as a versatile strategy to possess a wide array of potential applications for future biocompatible nano-/microdevices.