The magnetic fields of neuronal action potentials readily pass through biological tissue and allow for extracellular and noninvasive measurements of action potential dynamics in organisms. However, magnetic techniques used to detect neuronal activity operate at the macroscale or at a level not scalable to functional networks or intact organisms.

Researchers used a magnetic field sensor consisting of a crystal diamond chip and a surface layer of atomic-scale nitrogen-vacancy (NV) quantum defects to study the magnetic detection of single neuron action potentials in intact organisms. In marine worms and squid, the authors demonstrated that the approach delivered high temporal resolution by providing precise time-resolved measurements of action potentials from individual neurons, correlating magnetic field signals with intracellular voltage measurements, and determining the direction of action potential propagation.

The approach worked under ambient conditions and with the NV diamond sensor positioned within 10 micrometers of the biological sample. In the marine worms, extended periods of exposure to the sensor did not induce photodamage or other adverse effects. 

According to the authors, the technique could have applications in the development of micrometer-scale magnetic imaging for the measurement of functional dynamics in various neuronal processes.

http://www.pnas.org/content/early/2016/11/21/1601513113