Nitrogen vacancy center defects in diamonds confer remarkably useful properties.
Diamonds may be a girl's best friend, but they will also become increasingly desirable to biological researchers. Diamonds have long served as useful tools in the physical sciences, where, among other applications, they have been used to subject samples to immense pressures. But their value to biological research lies in the remarkable properties of a particular defect in the highly regular carbon lattice that gives diamonds their conventional desirable properties. This defect consists of a single nitrogen atom adjacent to a missing carbon atom. The resulting nitrogen vacancy (NV) center exhibits fluorescence that is insensitive to photobleaching, retains its properties in nanodiamonds as small as 4 nanometers and, being carbon-based, has excellent biocompatibility.
Nanodiamonds are beginning to be used as probes for in vivo imaging and have been demonstrated to allow extraordinarily high-precision localization using super-resolution microscopy. Their use as cellular probes has been limited so far because they are not as easy for biologists to use as genetically encoded probes, but development of functionalization and targeting methods should start to change this. NV centers have been shown to function as highly efficient donors to dye-acceptor molecules during fluorescence resonance energy transfer and could be used to create a new class of sensors.
The most intriguing potential for NV centers, though, results from the properties of the unpaired electronic spin state of the center. This spin state is sensitive to magnetic fields, and the state has a fluorescence signature that can be read out using fluorescence microscopy. Use of a single NV center at the tip of a scanning atomic force microscope allows fine mapping of magnetic fields. Further development could result in a true benchtop miniature nuclear magnetic resonance (NMR) instrument and allow structure determination of a single protein. Alternatively, arrays of these centers could bridge the imaging gap between NMR instruments for molecular structure determination and the kind of magnetic resonance imaging machine used in hospitals for whole-body imaging.
It is too early to say where these bits of flawed diamond will have the greatest impact, but their potential makes them as fascinating to many scientists as ornamental diamonds are to their admirers.
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Evanko, D. Defective (but useful) diamonds. Nat Methods 10, 36 (2013). https://doi.org/10.1038/nmeth.2295