Six years ago, America’s National Institute of Standards and Technology (NIST) developed miniature sensors that each utilized about 100 billion rubidium atoms in gas form, a low-power infrared laser and optics to detect tiny magnetic fields. Until recently the sensors had been used almost exclusively for physics research, but now NIST has teamed up with the Physikalisch-Technische Bundesanstalt (PTB – the National Metrology Institute of Germany) to successfully use one of the mini-sensors to track a human heartbeat – an accomplishment which could have medical applications down the road.

The experiment was conducted at the PTB’s headquarters in Berlin. The building is said to have the world’s best magnetic shielding, which was necessary in order to block out magnetic fields from the Earth itself and from other sources. A NIST mini-sensor was then placed five millimeters about the left chest of a test subject lying face up in a bed.

The sugar cube-sized sensor was able to detect the weak but regular magnetic pattern of the test subject’s heartbeat. It only registered in picoteslas, or trillionths of a tesla – a tesla being a unit measurement of magnetic field strength. The Earth’s magnetic field, by contrast, is measured in millionths of a tesla.

To make sure that the mini-sensor was picking up the heartbeat accurately, a more commonly used SQUID (superconducting quantum interference device) magnetic sensor was also utilized, and the findings matched. The mini-sensors generate more signal noise than SQUIDs, but require cheaper, less complicated supporting apparatus. They also work fine at room temperature, unlike SQUIDs, which do best at a chilly -269C (-452F).

It is possible that the mini-sensors could one day be used for magnetocardiograms, which could supplement or replace electrocardiograms. They could also be used in magnetorelaxometry, a process used to identify magnetic nanoparticles inserted into biological tissue for applications including targeted drug treatments.