Diamonds are for NMR: Cutting costs

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  • Published: Jun 1, 2018
  • Author: David Bradley
  • Channels: NMR Knowledge Base
thumbnail image: Diamonds are for NMR: Cutting costs

Magnetic charm

A microscopic image of diamond particles with nitrogen-vacancy defects. These samples, which exhibit a truncated octahedral shape, were used in experiments that sought new ways to tune and control an electronic property known as spin polarization. The scale bar at lower right is 200 microns (millionths of a meter). To the human eye, the pinkish diamonds resemble fine red sand. Credit: Berkeley Lab, UC Berkeley

Diamonds are relatively inexpensive when compared to making and sustaining superconducting magnets. As such, new research offers the possibility of a very-low-cost alternative to multimillion-dollar magnetic resonance imaging (MRI) equipment and the costly nuclear magnetic resonance spectrometers used in drug discovery and other areas by using the former to preclude the need for the latter.

Scientists from the Lawrence Berkeley National Laboratory, University California Berkeley, The City College of New York, City University of New York, USA, Peking University, China, and TU Dortmund University in Germany, have discovered that nanoscopic and microscopic defects in powdered diamond can be exploited to boost the sensitivity of magnetic resonance systems.

Spin control

"This has been a longstanding unsolved problem in our field, and we were able to find a way to overcome it and to show that the solution is very simple," explains Berkeley Lab's Ashok Ajoy. "No one has ever done this before. The mechanism that we discovered is completely new." The high surface area of the tiny particles is key in this effort for spin polarization, the team points out, and could be used in rapid and enhanced biological and medical imaging as well as high-resolution spectroscopy. "This important discovery in the hyperpolarization of nano- and micro-scale diamonds has enormous scientific and commercial implications," Ajoy adds, this is especially true given the high cost of building and running state-of-the art systems, which are nevertheless used in modern hospitals and laboratories the world over. Ajoy also points out that avoiding the need for the superconducting magnets and their attendant cryogenic cooling systems could also reduce the size of high-power MRI and NMR machines from almost room-sized to bedside or laboratory bench-top devices.

Until now, scientists had struggled to orientate diamonds to achieve uniform spin polarization. The issue was even worse when using powdered diamond where the particles simply present themselves as a chaotic jumble of orientations. Various approaches to controlling orientation, such as drilling tiny holes in the diamonds had been tried but much simpler and more likely to succeed was a method that utilizes the natural flaws - nitrogen vacancies, for instance, wherein nitrogen atoms have displaced carbon atoms in the diamond lattice. Nitrogen vacancies have been well studied previously in the context of quantum computing applications where taking back control of spin polarization was key to using electrons to transmit and store information.

Polarized opinion

In the new work, the team has shown that a blast of green laser light, exposure to a weak magnetic field, and sweeping across the sample with a microwave source could enhance this controllable spin polarization property in the diamonds by hundreds of times compared with conventional magnetic resonance systems. UC Berkeley's Emanuel Druga devised a tool for measuring, confirming, and fine-tuning the spin polarization properties of the diamond samples. "It allowed us to debug this in about a week," Ajoy said. The tool also allowed the team to focus on the most suitable size of diamond crystal. In early experiments, they worked with 100 micrometre diamonds. However, tests quickly showed that diamonds of 1 to 5 micrometres performed twice as well as the larger crystals. Such diamonds can be made by an economical conversion process from graphite.

The team has already developed a miniaturized system that uses commercially available components to produce the laser light, microwave energy, and magnetic field required to produce the spin polarization in the diamond samples, and they have applied for patents on the technique and the hyperpolarization system. They are now working out how to transfer the polarization to injectable liquids.

Related Links

Sci Adv 2018, 4, eaar5492: "Orientation-independent room temperature optical 13C hyperpolarization in powdered diamond"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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