I just read about nitrogen vacancy detection of single proteins with electron paramagnetic resonance, or EPR, in an article that referenced related NMR technology. When nitrogen is implanted in diamond, a charge defect is created. The defect, a “nitrogen vacancy,” or “NV,” creates a strong field that can detect and respond to a single electron spin within about 30 nm under ambient conditions. The spin is detected by laser fluorescence.
In more detail: Using ion implanting, single NVs, consisting of a nitrogen atom and an adjacent lattice vacancy, were created at a depth of about 5 nm below a diamond’s surface. A complex dynamic decoupling pulse sequence facilitated detection of a single electron spin label despite the shallow depth. With this, NMR wizards at Harvard were able to locate individual protons on the diamond surface with Angstrom accuracy.1
This was extended to EPR by a group at the Hefei National Laboratory, University of Science and Technology of China. They chose to study the mitotic arrest deficient-2, which is involved in cell cycle control. After labeling the protein with a single spin label (nitroxyl2), the spectra showed motion of various parts of the protein.3
Using the NV as the spin probe may lead to development of protocols to probe higher-ordered structure, study population/occupancy patterns from post-translational modifications including DNA methylation and possibly analyze the structural details of antibody drug conjugates. Imaging of proteins and complexes seems like a particularly attractive application. Conventional NMR requires the signals from about 1010 atoms, which limits spatial resolution.
Conceivably, one might even want to do chemistry, for example, with protocols for the selective removal of glycans, or for methylating specific sites in DNA or RNA. NMR is already used to study drug‒target binding, but on a much larger scale. Improved detection sensitivity could be useful in studying individual events rather than working on a heterogeneous population of proteins.
I’m eager to see how NV develops. It certainly seems to have the potential to appeal to the mainstream in the new, smaller world.
References
- physics.aps.org/synopsis-for/10.1103/PhysRevLett.113.197601.
- en.wikipedia.org/wiki/Site-directed_spin_labeling.
- Fazhan, S.; Zhang, Q et al. Single-proton spin resonance spectroscopy under ambient conditions. Science Mar 6, 2015, 347(6226), 1135‒8.
Robert L. Stevenson, Ph.D., is Editor Emeritus, American Laboratory/Labcompare; e-mail: [email protected].