Self-propelling bacteria are a dream of nano-technology. These unicellular organisms are not just capable of living and reproducing, but they can swim very efficiently, sense the environment and look for food, all packaged in a body measuring a few microns. Before such perfect machines could be artificially assembled, researchers are beginning to explore new ways to harness bacteria as propelling units for micro-devices. Proposed strategies require the careful task of aligning and binding bacterial cells on synthetic surfaces in order to have them work cooperatively. Here we show that asymmetric micro-gears can spontaneously rotate when immersed in an active bacterial bath. The propulsion mechanism is provided by the self assembly of motile Escherichia coli cells along the saw-toothed boundaries of a nano-fabricated rotor. Our results highlight the technological implications of active matter's ability to overcome the restrictions imposed by the second law of thermodynamics on equilibrium passive fluids.
@article{arxiv.0910.2899,
title = {A bacterial ratchet motor},
author = {R. Di Leonardo and L. Angelani and G. Ruocco and V. Iebba and M. P. Conte and S. Schippa and F. De Angelis and F. Mecarini and E. Di Fabrizio},
journal= {arXiv preprint arXiv:0910.2899},
year = {2010}
}