We report on a new technique which was used to detect single Escherichia coli that is based on the changes in the nonlinear rotation of a magnetic microsphere driven by an external magnetic field. The presence of one Escherichia Coli bacterium on the surface of a 2.0 micron magnetic microsphere caused an easily measurable change in the drag of the system and, therefore, in the nonlinear rotation rate. The straight-forward measurement uses standard microscopy techniques and the observed average shift in the nonlinear rotation rate changed by a factor of ~3.8.
@article{arxiv.physics/0610144,
title = {Dynamic detection of a single bacterium: nonlinear rotation rate shifts of driven magnetic microsphere stages},
author = {Brandon H. McNaughton and Rodney R. Agayan and Raoul Kopelman},
journal= {arXiv preprint arXiv:physics/0610144},
year = {2007}
}