A miniature magnetic resonance imager made of diamond

The development of tumors begins with small changes inside the cells of the body. Diffusion of ions at the smallest scales is decisive in the performance of batteries. Until now, the resolution of conventional imaging methods has not been high enough to represent these processes in detail. A research team led by the Technical University of Munich (TUM) has developed diamond quantum sensors that can be used to improve the resolution of magnetic images.

Nuclear Magnetic Resonance (NMR) is an important imaging technique in research that can be used to visualize tissues and structures without damaging them. The technique is better known in the medical field as magnetic resonance imaging (MRI), where the patient is moved into a slot with a large magnet on the table. The MRI machine creates a very strong magnetic field that interacts with the small magnetic fields of the body’s hydrogen nuclei. Because hydrogen atoms are distributed in a certain way between different types of tissue, it becomes possible to distinguish between organs, joints, muscles and blood vessels.

NMR techniques can also be used to visualize the diffusion of water and other elements. Research, for example, often involves looking at the behavior of carbon or lithium to study the structure of enzymes or processes in batteries. “Existing NMR methods give good results, for example, when it comes to recognizing abnormal processes in cell colonies,” says Dominik Bucher, Professor of Quantum Sensing at TUM. “But we need new approaches if we want to explain what happens in the microstructures of single cells.”

Sensors made of diamond

The research team produced a quantum sensor made of synthetic diamond for this purpose. “We enrich the diamond layer that we provide for the new NMR method with specific nitrogen and carbon atoms already during growth,” explains Dr. Peter Nitel from the Fraunhofer Institute for Applied Solid State Physics (IAF). The work is published in a journal The progress of science.

After growth, electron beam separates individual carbon atoms from the perfect crystal lattice of diamond. The resulting defects are arranged next to the nitrogen atom, a so-called vacant nitrogen center is created. Such vacancies have special quantum mechanical properties necessary for sensing. “Our development of the material optimizes the lifetime of the quantum states, allowing the sensors to measure longer,” adds Knittel.

Quantum sensors pass the first test

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

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

In the next step, the researchers want to further develop the method to enable the investigation of the microstructure of single living cells, tissue sections, or the ionic 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 Professor Maxim Zaitsev of the University of Freiburg. “We have now found a way how their spatial resolution, which is currently often considered insufficient, can be significantly improved in the future.”