Short answer: Nitrogen-vacancy (NV) defects in diamond change their optical and spin properties with temperature, so diamond particles as small as tens of nanometres can act as nanoscale thermometers. Papers from 2013 and 2015 reported temperature noise floors of 130 mK per root hertz in doped nanodiamonds and 0.3 K in an all-optical probe, and a 2021 review surveys the field. These are laboratory sensing demonstrations.
Why diamond thermometry?
The 2021 review in Nanotechnology says diamond quantum thermometry exploits the optical and electrical spin properties of colour defect centres and acts as a quantum sensing method with high precision and robustness. Compared with existing luminescent nanothermometry techniques, the review says a diamond thermometer can operate over a wide temperature range and with sensor sizes from nanometres to micrometres. It names applications in electronics and biology, and covers operating principles for spin-based and all-optical methods, diamond material development and application examples in electrical and biological systems.
What did the 2013 spin-based work show?
The 2013 Nano Letters paper demonstrates a nanoscale temperature sensing technique based on optically detected electron spin resonance in single atomic defects in diamond, with sensor sizes from a micrometre down to a few tens of nanometres. The authors report a temperature noise floor of 5 mK per root hertz for single defects in bulk sensors. Using doped nanodiamonds, the noise floor is 130 mK per root hertz, with accuracies down to 1 mK for nanocrystal sizes of a few tens of nanometres. They say this combination of precision and position resolution, along with sensor photostability, should allow measurement of heat produced by chemical interactions involving a few or single molecules, even in heterogeneous environments like cells. That is a stated prospect and no such measurement is reported in the abstract.
What did the 2015 all-optical probe show?
A 2015 Nanotechnology paper demonstrates a temperature noise floor of 0.3 K and long-term stability better than 0.6 K peak-to-peak, using a single diamond crystal smaller than 50 nm across containing about 100 NV centres. The authors compare this with other single-particle sensors and say it is one of the best ratiometric all-optical nano-probes of temperature to date. The introduction lists cellular biology, nano-electronics and hot-spot localization in integrated circuits as motivating problems.
How to read this
The 2013 and 2015 figures use different methods, spin resonance versus all-optical ratiometric readout, and different noise-floor units, so they are not directly comparable. All claims are the authors' own. The topic name mentions levitated particles, but none of the readable abstracts is about levitation, so this post does not cover it. This post is based on abstracts and visible summary text and full texts were not checked. It makes no claim about products.
FAQ
How does an NV thermometer work?
It reads temperature from the optical or spin properties of NV defects, which depend on temperature, as the 2021 review describes.
How small can the sensor be?
Tens of nanometres in the 2013 work, and under 50 nm containing about 100 NV centres in 2015.
How precise was it?
A noise floor of 130 mK per root hertz in doped nanodiamonds for spin readout, and 0.3 K for the all-optical probe.
Has it been used in living cells?
The abstracts name cells as a possible application. They do not report a cell measurement.
All field notes