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Extremely High-Resolution Magnetic Resonance Detects Single Atom

mri atom diamond

Image credit: Alexander Eichler / ETH Zürich

It has been more than forty years since Magnetic resonance imaging (MRI) was applied for investigation of soft bodily tissues for medical diagnosis.

For the time being, an MRI machine is able to resolve structures down to about 0.1 millimeters, which has been in practice for a quite long time so far.

However, a newly designed small MRI machine could detect a structure which was nearly one million times smaller–a single hydrogen atom. Scientists hoped that they would eventually apply this new machine to determine the specific molecule’s structure. This new technology was developed by Christian Degen and his team of ETH Zurich and their research had been released in Science.

Generally, by using electromagnetic coils, MRI machines could create a magnetic field and give off short bursts of radio waves around a targeted tissue. Such field would then arouse protons in the nucleus of hydrogen atoms so as to allow protons to be aligned. In fact, radio waves released from the machine would make the alignment disrupted. However, when the signal was absent, the atoms would align again and then send out the radio signal of their own, which was detected by the machine and interpreted in cross-sectional images.

According to Degen, as a well-developed technology, the spatial resolution of MRI was basically same as it was ten years ago, because of physical constraints which had prevented the resolution from further increase.

In an effort to greatly increase the resolution, Degen and his colleagues used a diamond sensor chip in a fluorescent microscope instead of previously applied electromagnetic coil. Their machine was targeted on the so-called nitrogen-vacancy center. Primarily, there was small flaw in regard to the diamond which was composed of perfect carbon lattice structure. When one nitrogen atom replaced two carbon atoms, a very small spot would be created, which would be both fluorescent and magnetic.

The diamonds that scientists used had nitrogen-vacancy centers only a few nanometers below the surface. Therefore, the MRI machine was capable of obtaining an optical readout from such spots, which was used by researchers to identify where the individual hydrogen atoms were located. By doing so, the machine could resolve the atoms to about one angstrom compared with a strand of DNA, whose width was nearly 20 Å.

As Degen said, quantum mechanics then could offer an simple proof of whether an individual nucleus, or a cluster of several hydrogen atoms had been detected.

Although working on such a fine scale, a machine would not be enough for patient diagnostics practically, but it did present unbelievably significant implications. It was hoped by Degen’s team that further development of this technology would helpful in resolving small molecules and in the end; it could be used for the study of the proteins’ structure, thus more applications from it could be foreseen, for example, discovering new drugs.

Typically the study of protein molecular structure was carried out by use of x-ray crystallography, but in many cases, it was difficult to crystallize them because of their properties. Since the technique was mainly dependant on billions of the proteins which were being crystallized in a uniform way, this might pose a challenge. But, this new small and almighty MRI could succeed in working out a final solution.

In his conclusion, Degen hoped that what they were doing would be regarded as an important intermediate step in the process of mapping of entire molecules.

Source: ETH Zurich

Journal reference: Loretz, M., et al. “Single-proton spin detection by diamond magnetometry.”Science (2014): 1259464.

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