A nitrogen vacancy (NV) center is “sort of like a little quasi-molecule that sits in the diamond lattice, and it can trap a certain number of electrons,” explains McCloskey. NVs in diamonds have been exploited as sensors, but typically the magnetic properties of negatively charged NVs were harnessed. “What we are doing is a bit non-standard,” says McCloskey. “We are just exploiting the fact that the color of [the NV’s] fluorescence and the brightness of its fluorescence depend on its charge state.” In their case, they use the switch between orange emission of uncharged NV centers and the absence of emission from positively charged NVs in the presence of voltage changes.
“There had been a lot of theoretical work … looking at the possibility of using the nitrogen vacancies’ magnetic sensing capabilities to image action potential propagation in neurons,” says McCloskey. But the diamond material wasn’t sensitive enough for voltage imaging of neurons. In their work, the researchers managed to achieve a high density of NVs close the surface of the diamond. This technical breakthrough provides a sensitivity that “would be sufficient to record what are called intracellular action potentials,” says McCloskey. With the diamond being extracellular, the recorded signals are, however, much smaller. Still, he thinks it is possible to record action potentials extracellularly with their diamond-based microscope. The researchers are working on this demonstration. And they are developing the diamond material further to increase the sensitivity. It will be exciting to see what is possible with this technology in the biological imaging space.
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