A miniature magnetic resonance imager made of diamond

The research team produced a quantum sensor made of synthetic diamond for this purpose. “We enrich the diamond layer, which we provide for the new NMR method, with special nitrogen and carbon atoms already during growth,” explains Dr. Peter Knittel of the Fraunhofer Institute for Applied Solid State Physics (IAF).

After growth, electron irradiation detaches individual carbon atoms from the diamond’s perfect crystal lattice. The resulting defects arrange themselves next to the nitrogen atoms – a so-called nitrogen-vacancy center has been created. Such vacancies have special quantum mechanical properties needed for sensing. “Our processing of the material optimizes the duration of the quantum states, which allows the sensors to measure for longer,” adds Knittel.

The quantum state of the nitrogen-vacancy centers interacts with magnetic fields. “The MRI signal from the sample is then converted into an optical signal which we can detect with a high degree of spatial resolution,” Bucher explains.

In order to test the method, the TUM scientists placed a microchip with microscopic water-filled channels on the diamond quantum sensor. “This allows us to simulate microstructures of a cell,” says Bucher. The researchers were able to successfully analyze the diffusion of water molecules within the microstructure.

In the next step the researchers want to develop the method further to enable the investigation of microstructures in single living cells, tissue sections or the ion mobility of thin-film materials for battery applications. “The ability of NMR and MRI techniques to directly detect the mobility of atoms and molecules makes them absolutely unique compared to other imaging methods,” says Prof. Maxim Zaitsev of the University of Freiburg. “We now have found a way, how their spatial resolution, which is currently often deemed insufficient, can be significantly improved in future.”