Diamond Sparks Single-Protein EPR

Scientists have recently learned how to use diamond crystal lattice defects as nuclear magnetic resonance detectors to extract chemical and structural information from individual biomolecules or nano­scale features of other materials. Expanding on that work, researchers now report using those same defects to get electron paramagnetic resonance (EPR) signals from single proteins (Science 2015, DOI: 10.1126/science.aaa2253). The diamond defects are called NV centers and consist of a nitrogen atom and an adjacent lattice vacancy in place of a pair of adjacent carbon atoms. The fluorescence of the NV center is sensitive to the magnetic dipole interaction between the center and an unpaired spin associated with the protein. In the test case, the researchers used a nitroxide spin label attached to a protein involved in cell duplication. The protein was immobilized in a polylysine layer on the diamond surface, placing the spin label about 10 nm from the diamond defect. The team, led by Jiangfeng Du of the University of Science & Technology of China, was able not only to detect a signal for the spin label but also to extract information about protein motion. Going forward, interactions between the spin label and neighboring protein nuclei, as detected by the diamond NV center, could provide even more structural and dynamical information, the researchers write.