By using a microscopic diamond and some gold nanoparticles, researchers at Harvard have measured the internal temperature of a living human embryonic cell. This groundbreaking new ‘nanothermometer’ could lead to therapies in which specific cells are treated.


Indeed, while it might seem weird to measure the internal temperature of a living cell, there are some very good reasons for wanting to do so. In addition to targeting and treating diseased cells (e.g. killing cancer while sparing healthy cells), scientists could also use a nanothermometer to manipulate human immune responses and control temperature-induced gene expression. It could also be used to investigate cell behavior.

Techniques to measure cellular temperature do exist, but they can't measure temperature changes inside living cells. And they're not very accurate.


Needless to say, taking the temperature of something as tiny as a cell is a delicate task. You can’t just stick a thermometer into it. But you can throw a tiny diamond at it — a very, very tiny diamond.

Turning Diamonds Into Probes

Nanodiamonds have impurities in their lattice structure that sometimes results in extra electrons. When there’s an impurity, one nitrogen atom, along with an empty spot, sets in to replace two carbon atoms. These states vary with temperature, causing the lattice structure to either expand or contract.

Interestingly, nanodiamonds were originally developed to assist in quantum computing. They do a remarkable job handling quantum information. When deliberately manipulated, they can be used to perform quantum calculations (i.e. by producing digital bits, or quibits).

But as Mikhail Lukin’s team at Harvard discovered, this same attribute can be used to turn these tiny diamonds into veritable thermometers. Because they're so sensitive to temperature, and because their structure can be manipulated and measured, they can be used as probes.


To prove it, the researchers directed microwaves at a living human embryonic fibroblast cell under a microscope.


Image: Nature.

In order to determine the structure of the diamond, and in turn its temperature, the researchers had to record how much energy was required to move an electron to a higher energy level. Once this was done, they could deduce the cell’s temperature at various locations within the cell.


Record Setting Sensitivity

To insert the diamonds, which were a miniscule 100 nanometers across, along with some gold nanoparticles, the scientists used nanowires. Then, by shining a green laser onto the cell, the cell and the gold particles were heated up, causing the nitrogen impurities to fluoresce with red light. This altered the shape of the diamonds — and so too their energy level. Variations in temperature affected the intensity of the red light.


Image: Georg Kucsko.

Variable laser intensities created different, but measurable, light effects, allowing the researchers to determine the cell’s temperature. Basically, the scientists were able to deduce actual temperature by measuring changes in temperature.


And in fact, the technique was so precise that the researchers could detect temperature differences to thousandths of a degree inside the cell — 0.0018 °C to be precise.

Interestingly, the scientists also used the opportunity to determine the precise temperature required to kill the cell.


Read the entire study at Nature: “Nanometre-scale thermometry in a living cell.”