Quantum physics: The human body is controlled by electrical impulses, including the brain, the heart and nervous system. These electrical signals create tiny magnetic fields, which doctors could use to diagnose various diseases of the brain or heart in young foetuses. Researchers from the Niels Bohr Institute have now succeeded in developing a method for extremely precise measurements of such ultra-small magnetic fields with an optical magnetic field sensor. The results are published in the scientific journal, Scientific Reports.

Small magnetic fields from the human body can usually only be picked up by very sensitive superconducting magnetic field sensors that have to be cooled by liquid helium to near absolute zero (which is -273° C). But now researchers from the Niels Bohr Institute at the University of Copenhagen have developed a much cheaper and more practical optical magnetic field sensor that even works at room temperature or at body temperature.

Ultra sensitive magnetic field sensor

The researchers at the Niels Bohr Institute have been developing the sensitive magnetic field sensor for several years in the Quantum research group laboratories. The magnetic field sensor itself consists of a glass container, which has a channel that is approximately 1 cm long and 1 mm wide. At the bottom of the glass container is caesium metal. Caesium evaporates into gas at room temperature and the gas atoms rise up into the small channel in the sensor head. Each caesium atom rotates around itself and the axis is like a tiny bar magnet. Now the sensor is held close to a nerve, which emits an electrical nerve pulse. The electrical pulse has a magnetic field that causes a change in the tilt of the axes of the caesium atoms and by sending a laser beam through the gas, you can read the ultra-small magnetic fields of the nerve signals.

The laboratory tests, which were carried out in collaboration with researchers from the Faculty of Health and Medical Sciences, have shown that you can use the magnetic field sensor to detect the magnetic fields from the electrical impulses from the nervous system. The tests were done on the sciatic nerve from a frog, which in many ways resemble the nerves in the human body. For practical reasons, the nerve was removed from the frog before the tests, but it is also possible to pick up electrical impulses from live frogs or from humans.

The magnetic field sensor is made up of a glass container embedded with caesium metal. The caesium evaporates into gas at room temperature and the gas atoms rise up into the small channel in the sensor head. Each caesium atom is like a tiny bar magnet. The sensor is held close to a nerve, which emits an electrical nerve pulse. The electrical pulse has a magnetic field that causes a change in the tilt of the axes of the caesium atoms and by sending a laser beam through the gas, you can read the ultra-small magnetic fields of the nerve signals.

Measures without contact

The advantage of the optical sensor is that the magnetic fields and electrical impulses can be safely and easily picked up at a distance of a few millimeters or centimeters without the sensor coming into contact with the body.

Eugene Polzik explains that you can calculate the speed at which the nerve impulses are moving from the measured signals. There are a large number of diseases where the nerves are damaged, like multiple scleroses, where the nerve impulses move more slowly than in people who are not ill. Other issues could be various eye diseases where a diagnosis can be made without having to put electrodes on the eye, or Alzheimer’s, where you will be able to measure the electrical signals in specific nerve pathways.

Niels Bohr Institute
nbi.ku.dk