Gold-diamond duo takes temperature of single cell

TALK about bling. Miniature diamonds more usually found in quantum computers, combined with fragments of gold, can be used to measure the temperature of individual cells. That could lead to a more accurate way to kill cancers while sparing healthy tissue ? and a new way to explore cell behaviour.

There are already ways to take a cell's temperature, using glowing proteins or carbon nanotubes. However, these lack sensitivity and accuracy because their components can react with substances inside the cell.

So Mikhail Lukin at Harvard University and colleagues turned to nanodiamonds, which have defects in their structure that mean they sometimes contain extra electrons. The tendency of these electrons to exist in many states at once, a superposition, makes nanodiamonds promising as the bits, or qubits, of a quantum computer, where superposition enables multiple calculations in parallel. However, these states vary with temperature, which is troublesome for computing.

Lukin's team wondered if this temperature dependence could instead be exploited to build a thermometer, particularly as diamonds are inert, so wouldn't interfere with a cell's chemistry.

The team used nanowires to insert diamonds about 100 nanometres across, along with gold nanoparticles, into a human cell in a dish. Shining a laser onto the cell heats it and the gold particles. The diamond, in turn, changes shape, squeezing the defect electrons and rearranging their energy levels.

Shining a different type of laser on the cell causes the electrons to absorb and then emit light with a brightness that depends on the new energy-level arrangement. The team used this light to deduce the cell's temperature.

They found they could detect temperature differences of just o.oo18 ?C inside the cell, a sensitivity record. And when they placed two diamonds in the cell, they could detect temperature variations between them, caused by their varying closeness to the gold. This should be possible even when the diamonds are just 200 nanometres apart.

The team also used the set-up to heat a cell enough to kill it, and recorded a temperature upon death. Lukin presented the work on 22 July at the Second International Conference on Quantum Technologies in Moscow, Russia, and this week in Nature (DOI: 10.1038/nature12373).

If such thermometers can be used in the body, they might improve cancer therapy, says Lukin's colleague Norman Yao. The temperatures of cancerous cells and their healthy neighbours could be monitored, and just enough heat applied to kill the cancer but not the healthy cells.

"In certain cases, particularly near critical structures such as great vessels, arteries or nerve bundles, an accurate read-out of local cellular temperature would be advantageous in the sparing of those structures," says Glenn Goodrich of Nanospectra Biosciences in Houston, Texas, a company carrying out human trials of cancer therapy based on gold nanoparticles.

Diamond thermometers could also explore cellular mysteries. "If a cell is unhappy, if it's in contact with a virus, a chemical reaction starts and it locally starts producing heat," says Lukin. "How this occurs no one understands in detail. Perhaps we can answer this question."

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