Proc. Natl Acad. Sci. USA 110, 8417–8421 (2013)

In fluorescence thermometry, temperature is measured by monitoring the variation in the intensity of light emitted by a fluorophore. Nitrogen–vacancy (NV) centres in diamond nanocrystals — defects that consist of a nitrogen impurity linked to a carbon vacancy — are promising for fluorescence thermometry, particularly in biological environments, because of the small size of the crystals and the relative inertness of diamond.

David Awschalom and colleagues at the University of California, Santa Barbara, Ames Laboratory and the University of Chicago have now shown that the electron spin associated with a NV centre can be used to achieve a record sensitivity, seven times better than previously attained. The long coherence time of NV centres allows coherent control of the electron spin state population through excitation with optical pulses. This results in oscillations of the fluorescence intensity with a frequency that is dependent on temperature.

With the approach, the researchers are able to achieve a sensitivity approaching 10 mK Hz−1/2 at room temperature, which suggests that it could be useful in a variety of biological settings.