May 23 2018
As contradictory as this may sound, diamonds have been considered as the answer to a new method that could deliver a very-low-cost substitute to multimillion-dollar medical imaging and drug-discovery instruments.
Microscopic images 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. (Image credit: Berkeley Lab, UC Berkeley)
An international research team led by the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley discovered how to manipulate defects in nanoscale and microscale diamonds to strongly optimize the sensitivity of magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) systems while removing the need for their expensive and bulky superconducting magnets.
“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,” said Ashok Ajoy, a postdoctoral researcher in the Materials Sciences Division at Berkeley Lab, and the Department of Chemistry at UC Berkeley, who served as the study’s lead author. “No one has ever done this before. The mechanism that we discovered is completely new.”
MRI machines are used to detect cancerous tumors and help in the development of treatment procedures, while NMR machines are employed to inspect the atomic-scale structure and chemistry of drug compounds and other molecules.
The new method, illustrated in the May 18 edition of the Science Advances journal, could result in the direct use of these miniature diamonds for fast and improved biological imaging. The researchers will also try to transfer this special tuning, called spin polarization, to a harmless liquid such as water, and to inject the liquid into a patient for quicker MRI scans. The high surface area of the minute particles is crucial in this effort, the researchers observed.
Improving this spin polarization in the electrons of the diamonds’ atoms can be compared to aligning a few compass needles pointing in a number of different directions in the same direction. A sharper contrast can be provided by these “hyperpolarized” spins for imaging than conventional superconducting magnets.
“This important discovery in the hyperpolarization of nano- and microscale diamonds has enormous scientific and commercial implications,” Ajoy said, as some of the most modern NMR and MRI machines can be extremely expensive and beyond the reach of some hospitals and research institutions.
“This could help expand the market for MRI and NMR,” he said, and could also possibly reduce the size of the devices from room-sized to benchtop-sized, which “has been the dream from the start.” Ajoy is a member of the Alex Pines research lab at UC Berkeley—Pines is a senior faculty scientist in Berkeley Lab’s Materials Sciences Division, and a pioneer in the development of NMR as a research tool.
Researchers had found it tough to overcome a problem in correctly orienting the diamonds to attain a more uniform spin polarization—and this problem was even more distinct in collections of miniature diamonds that presented a disordered clutter of orientations. Previous efforts, for instance, had examined whether drilling minute features into diamond samples could help in manipulating their spin polarization.
The tunable spin properties in diamonds with defects referred to as nitrogen vacancies—in which nitrogen atoms replace carbon atoms in the crystal structure of diamonds—have also been explored for probable use in quantum computing. In those applications, researchers seek to regulate the spin polarization of electrons as a way to convey and store information like the ones and zeros in more conventional magnetic computer data storage.
In the recent study, researchers discovered that by zapping a group of microscale diamonds with green laser light, exposing it to a weak magnetic field, and sweeping across the sample with a microwave source, they could improve this controllable spin polarization property in the diamonds by numerous times compared with conventional NMR and MRI machines.
Emanuel Druga, an electrician in the UC Berkeley College of Chemistry R&D shops, created a large measurement tool for the new method that proved helpful in validating and perfecting the spin polarization properties of the diamond samples.
“It allowed us to debug this in about a week,” Ajoy said.
The device assisted researchers to attain a good size for the diamond crystals. Initially, they were using crystals measuring about 100 microns, or 100 millionths of an inch across. The minute samples of pinkish diamonds look like fine red sand. Following testing, they discovered that diamonds measuring around 1 to 5 microns performed about twice as well.
The minute diamonds can be produced in cost-effective processes by changing graphite into diamond, for instance.
The team of researchers has already built a miniaturized system that uses off-the-shelf components to generate the microwave energy, laser light, and magnetic field required to develop the spin polarization in the diamond samples, and they have applied for patents on the method as well as the hyperpolarization system.
“You could think of retrofitting existing NMR magnets with one of these systems,” said Raffi Nazaryan, who participated in the research as an undergraduate researcher at Berkeley Lab and UC Berkeley. Prototypes of the system cost only several thousand dollars, he observed.
While the spin is brief, scientists said they are looking for ways to continuously polarize the samples, and are also examining how to transfer this polarization to liquids.
Ajoy said, “We could potentially recycle the liquid so it flows in a closed loop, or keep injecting newly polarized liquid.”
Researchers from The City College of New York, Peking University in China, TU Dortmund University in Germany, and the Graduate Center of the City University of New York also participated in the study. This study was supported by the National Science Foundation and the Research Corporation for Science Advancement.