Nature 496, 486–491 (2013)

Credit: © 2013 NPG

The magnetic field created by individual living biological cells — magnetotactic bacteria — has now been successfully mapped using optically detected magnetic resonance imaging. Researchers from Harvard University, MIT and the University of Berkeley in the USA placed a saline solution containing the bacteria on the surface of a diamond chip featuring a 10-nm-deep layer of nitrogen–vacancy centres. The bacteria created internal magnetic nanoparticles that altered the spin states of the nitrogen–vacancy centres, which were then read-out using spin-state-dependent fluorescence in the red part of the spectrum. By making four independent measurements, the researchers were able to determine the vector components of the bacteria's magnetic field with a spatial resolution of 400 nm. They estimate that the magnetic moment of each magnetotactic bacterium is of the order of 10−16 A m−2. By using visible LED illumination and a CMOS camera, the researchers captured high-resolution optical images of the bacteria, allowing the cell positions to be correlated with the magnetic field maps.