Temperature governs the speed of biochemical reactions, but measuring it at a single point within a cell has long been elusive: sensors were either too bulky or too imprecise. Nanodiamonds with NV centers have long promised to solve this, yet their sensitivity was limited by short coherence times and weak signals. Nearby in the archive are studies on diamond qubits, magnetometry, and magnetic field sensors for the heart, but thermometry with nanodiamonds has lagged behind: the best samples offered only about 130 mK/√Hz. This work stands apart because it transfers the thermal echo protocol, previously limited to bulk diamond, to a single nanodiamond with two NV centers.
A nanodiamond about 280 nanometers in diameter, cut from isotopically pure carbon-12, was placed on a custom chip with a heater and a resistance thermometer. Inside the diamond, two NV centers shared the same orientation, doubling the photon signal without sacrificing coherence. Temperature was measured using a thermal echo protocol: microwave pulses created a superposition of spin states, and the accumulated phase depended on temperature through the shift in transition frequency. The transition frequencies were calibrated against the built-in resistance thermometer, yielding a coefficient of -95.7 kHz/K.
The team achieved a resolution of 682 microkelvin and an experimental sensitivity of 48.2 mK/√Hz under realistic conditions, and 9.6 mK/√Hz at the shot-noise limit, which is two orders of magnitude better than continuous ODMR and comparable to bulk diamond. Laser heating was linear: 337 mK per milliwatt, and at a maximum power of 0.63 mW the temperature rose by 224 mK. Adding 10 microliters of FCCP solution in DMSO to 200 microliters of water caused a temperature jump of 1.5 K, which dissipated over 180 seconds.
This work differs from neighboring archive papers in that it is the first to apply the thermal echo protocol to a single nanodiamond with two NV centers, rather than to an ensemble or bulk sample. This provides nanometer-scale localization with millikelvin precision, which was previously unattainable. Now hypotheses about mitochondrial heating can be tested without solvent artifacts, and the heat output of individual catalytic particles can be studied.
The next step will be to introduce such nanodiamonds into living cells and measure mitochondrial temperature in real time. Sensitivity could be improved with longer dynamical decoupling sequences or by using nanodiamonds with more NV centers. Combining the method with microfluidics also holds promise for studying thermal effects of chemical reactions in flow.
The method will impact cell biology, where local thermometers are needed, and catalysis, where knowing the temperature at a nanoparticle surface is crucial. It may also find use in microelectronics for monitoring local heating.
Test the sensor inside a living cell and compare results with theoretical models of mitochondrial heating. Optimize the protocol for faster measurements.
This work directly addresses the unresolved question of whether intracellular temperature gradients exist due to metabolic activity. The proposed method provides, for the first time, sufficient sensitivity to test theoretical predictions without artifacts from external heating or solvents.
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
In this work, a nanodiamond with two NV centers is used as a thermometer: a thermal echo protocol previously applied in bulk diamond has been transferred to a single particle. The result is a resolution of 682 µK and a sensitivity of 9.6 mK/√Hz in the shot-noise limit. Measurements of laser heating and the exothermic mixing of DMSO with water are demonstrated.
Where its strength is
Transferring the thermal echo protocol to a single nanodiamond with two NV centers delivers nanometer localization at millikelvin precision, which removes the old trade-off between sensor size and sensitivity.
Where it could go next
Worth trying
Why this may matter
The ability to measure temperature with nanometer resolution and millikelvin precision could clarify the role of local heating in cellular processes and catalysis, where previously only indirect estimates existed.
Nearby works in our archive
The archive is sparse around this work: the closest review is only 0.56, against a usual 0.64. It looks like few have drilled nearby.
A nanodiamond with two NV centers offers 30% better sensitivity than one with a single center, simply because there are twice as many photons and coherence is unaffected.