Nanoscale MRI Devised to Be Similar to an Atomic Force Microscope

German and American scientists have opened the possibility for nanoscale magnetic resonance imaging (MRI) by exploiting the minuscule flaws in diamonds to sense the magnetic resonance properties of molecules.

MRI shows the tiny specifics of living tissues, tumors, diseased organs inside the body without the need for surgery or X-rays. This new technology could potentially visualize down to the level of atoms. Clinicians could make visual diagnoses of an individual’s molecules—examining damage on a strand of DNA, watching molecules misfold, or identifying a cancer cell by the proteins on its surface.

Dr. Carlos Meriles, associate professor of physics at the City College of New York (NY, USA), and an international team of researchers at the University of Stuttgart (Germany) have published their new findings in the February 1, 2013, issue of the journal Science.

“It is bringing MRI to a level comparable to an atomic force microscope,” said Prof. Meriles, referring to the device that tracks the shape of atoms or the pull on a molecule to measure its strength. A nanoscale MRI could display how a molecule moves without touching it. Standard MRI typically gets to a resolution of 100 microns,” about the width of a human hair, said Prof. Meriles. “With extraordinary effort, it can get down to about 10 microns”—the width of a couple of blood cells. Nanoscale MRI would have a resolution 1,000 to 10,000 times better.

To try to capture magnetic resonance on such a small level, the investigators took advantage of the spin of protons in an atom, a characteristic typically used to study quantum computing. Specifically, they used miniscule imperfections in diamonds. Diamonds are crystals comprised of nearly entirely of carbon atoms. When a nitrogen atom stays next to an area where a carbon atom is missing, however, it creates a defect known as a nitrogen-vacancy (NV) center.

“These imperfections turn out to have a spin—like a little compass—and have some remarkable properties,” noted Prof. Meriles. In the last few years, researchers realized that these NV centers could serve as very sensitive sensors. They can pick up the magnetic resonance of nearby atoms in a cell, for example. But unlike the atoms in a cell, the NVs shine when a light is directed at them, signaling what their spin is. If you illuminate it with green light it flashes red back. “It is a form of what is called optically detected magnetic resonance,” he said. Similar to a boat flashing Morse code on the sea, the sensor “sends back flashes to say it is alive and well.”

Prof. Mireles has written on the hypothetic foundations of the research and proposed the project to the scientists, led by Prof. Jörg Wrachtrup, a physicist at the University of Stuttgart, with the help of postdoctoral researcher Friedemann Reinhard and collaborators from the University of Bochum (Germany) and the University of Science and Technology of China (Hefei, Anhui). Prof. Wrachtrup is head of a leading group studying such defects.

“The NV can also be thought of as an atomic magnet. You can manipulate the spin of that atomic magnet just like you do with MRI by applying a radio frequency or radio pulses,” Prof. Meriles explained. The NV responds, such as when one shines a green light at it when the spin is pointing up, it will respond with brighter red light. A down spin gives a dimmer red light.

Tobias Staudacher, a graduate student, and the first author in this study, employed NVs in the laboratory that had been created just below the diamond’s surface by bombarding it with nitrogen atoms. The scientists identified MR within a film of organic substance applied to the surface, just as one might study a thin film of cells or tissue.

“Ultimately,” concluded Prof. Meriles, “One will use a nitrogen-vacancy mounted on the tip of an atomic force microscope—or an array of NVs distributed on the diamond surface—to allow a scanning view of a cell, for example, to probe nuclear spins with a resolution down to a nanometer or perhaps better.”

Related Links:
City College of New York
University of Stuttgart
University of Bochum