title: Optical magnetic detection of single-neuron action potentials using quantum defects in diamond.
abstract: Magnetic fields from neuronal action potentials (APs) pass largely unperturbed through biological tissue, allowing magnetic measurements of AP dynamics to be performed extracellularly or even outside intact organisms. To date, however, magnetic techniques for sensing neuronal activity have either operated at the macroscale with coarse spatial and/or temporal resolution-e.g., magnetic resonance imaging methods and magnetoencephalography-or been restricted to biophysics studies of excised neurons probed with cryogenic or bulky detectors that do not provide single-neuron spatial resolution and are not scalable to functional networks or intact organisms. Here, we show that AP magnetic sensing can be realized with both single-neuron sensitivity and intact organism applicability using optically probed nitrogen-vacancy (NV) quantum defects in diamond, operated under ambient conditions and with the NV diamond sensor in close proximity (∼10 µm) to the biological sample. We demonstrate this method for excised single neurons from marine worm and squid, and then exterior to intact, optically opaque marine worms for extended periods and with no observed adverse effect on the animal. NV diamond magnetometry is noninvasive and label-free and does not cause photodamage. The method provides precise measurement of AP waveforms from individual neurons, as well as magnetic field correlates of the AP conduction velocity, and directly determines the AP propagation direction through the inherent sensitivity of NVs to the associated AP magnetic field vector.
authors.affiliation: Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138.|Department of Physics, Harvard University, Cambridge, MA 02138.|Center for Brain Science, Harvard University, Cambridge, MA 02138.
authors.forename: John F
authors.initials: JF
authors.lastname: Barry
authors.affiliation: Department of Physics, Harvard University, Cambridge, MA 02138.|Center for Brain Science, Harvard University, Cambridge, MA 02138.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Turner
authors.affiliation: Center for Brain Science, Harvard University, Cambridge, MA 02138.|Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139.
authors.forename: Jennifer M
authors.initials: JM
authors.lastname: Schloss
authors.affiliation: Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138.|Department of Physics, Harvard University, Cambridge, MA 02138.|Center for Brain Science, Harvard University, Cambridge, MA 02138.
authors.forename: David R
authors.initials: DR
authors.lastname: Glenn
authors.affiliation: Marine Biological Laboratory, Woods Hole, MA 02543.|Department of Genetics, Yale School of Medicine, New Haven, CT 06510.|Howard Hughes Medical Institute, Yale School of Medicine, New Haven, CT 06510.|Harvard Program in Therapeutic Science, Department of Systems Biology, Harvard Medical School, Boston, MA 02115.
authors.forename: Yuyu
authors.initials: Y
authors.lastname: Song
authors.affiliation: Department of Physics, Harvard University, Cambridge, MA 02138.
authors.forename: Mikhail D
authors.initials: MD
authors.lastname: Lukin
authors.affiliation: Department of Physics, Harvard University, Cambridge, MA 02138.|Center for Brain Science, Harvard University, Cambridge, MA 02138.|Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138.|Broad Institute of MIT and Harvard, Cambridge, MA 02142.
authors.forename: Hongkun
authors.initials: H
authors.lastname: Park
authors.affiliation: Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138; rwalsworth@cfa.harvard.edu.|Department of Physics, Harvard University, Cambridge, MA 02138.|Center for Brain Science, Harvard University, Cambridge, MA 02138.
authors.forename: Ronald L
authors.initials: RL
authors.lastname: Walsworth
keywords: action potential; magnetometry; neuron; nitrogen-vacancy center