Known for its noninvasiveness, NMR has long been a fixture in medicine, structural biology, and many other arenas. In conventional implementations, induction coils are used to detect magnetic signals generated when a sample’s nuclei, polarized by an external magnetic field, are manipulated with RF pulses. (See the article by Clare Grey and Robert Tycko, Physics Today, September 2009, page 44.) But because nuclear spins polarize weakly—at room temperature, even a state-of-the-art magnet pulls only about 1 extra spin per 10 000 into alignment with its field—NMR doesn’t work well on tiny samples. A microliter (1 mm3) or more of material is typically required to produce a detectable signal.
Researchers have long sought to perform NMR spectroscopy at far smaller scales—on single biological cells, single proteins, even single atoms. To do so, they’ve proposed swapping out induction coils for more sensitive instruments: atomic-scale diamond defects known as...
