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A diamond-based quantum sensor has been used to measure magnetic signals from the heart of a living animal for the first time. It is a step towards being able to use quantum devices in ordinary medical settings.

The heart鈥檚 magnetic signals are a useful diagnostic for cardiovascular diseases, but they are also very faint 鈥� millions of times weaker than fridge magnets. To detect them, medical professionals must use special sensing equipment that is typically costly, bulky and fragile. One potential solution could be sensitive quantum devices based on diamonds. But so far, using them has required open-chest surgery, says at the University of Science and Technology of China.

He and his colleagues developed a technique that avoids this invasive procedure. Their sensors contained a diamond that was about 100 microns thick, with some of its carbon atoms removed or replaced with nitrogen. These changes affected the quantum states that the diamond鈥檚 electrons could have. When exposed to a laser and microwaves, the modified diamond glowed with different intensities as it detected different magnetic fields. Past studies have demonstrated that this effect can be used to measure, for instance, the magnetic field of mouse brain tissue.

The researchers tested their sensor on a living rat without performing any surgery. To help it pick up the faint heart signals, they employed several sensitivity-enhancement techniques, such as adding some components that become magnetised in the presence of a magnetic field, which then concentrated the magnetic signal around the diamond. Though the sensor lacked precision, the experiment proved that this non-invasive approach can work, says team member Ziyun Yu, also at the University of Science and Technology of China.

鈥淭here were similar demonstrations before, but on more artificial lab-type situations. This is a solid step forward, and certainly inspiring and insightful,鈥� says at the University of Stuttgart in Germany. He says that if the sensitivity of the new sensor were improved, its small size would make it possible to use non-invasively and to affix it to existing medical devices like endoscopes. 鈥淭his would have an impact on day-to-day clinical applications. When I talk to surgeons, they say having such a device would be very helpful,鈥� he says.