Up-converting radio: NMR sees the light

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  • Published: Oct 1, 2018
  • Author: David Bradley
  • Channels: NMR Knowledge Base
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International signals

Dr. Kazuyuki Takeda (left) and Dr. Koji Usami (right) with their experimental system (Kyoto University / Kazuyuki Takeda)

Up-converting radio-frequency signals to the optical range opens up a new , more sensitive way to use nuclear magnetic resonance (NMR) spectroscopy, according to an international team led by Kazuyuki Takeda of Kyoto University and Koji Usami of the University of Tokyo. The approach is based on a high-stress, elastic silicon nitride membrane that couples electrical detection with an optical cavity.

The team of Takeda, Usami and their colleagues Kentaro Nagasaka, Atsushi Noguchi, Rekishu Yamazaki, Yasunobu Nakamura, Eiji Iwase, Jacob Taylor in Kyoto and Tokyo and at RIKEN in Saitama, Wakeda University, NIST and the University of Maryland provide details of their new detection method in the journal Optica. They suggest that the approach has the potential to provide a more sensitive analysis compared with conventional NMR spectroscopy and might also expand the abilities of magnetic resonance imaging, MRI.

Powerful techniques

"NMR is a very powerful tool, but its measurements rely on amplification of electrical signals at radio frequencies," explains Takeda. "That pulls in extra noise and limits the sensitivity of [the] measurements," he adds. "We developed an experimental NMR system from scratch that converts radio-frequency signals into optical ones." The "up-conversion" exploits a novel hybrid quantum conversion technology that the team has now integrated into an NMR system.

"We constructed a capacitor by vacuum-depositing a metal layer on to the silicon nitride membrane," explains team member Usami. Using this with an inductor, the team could then build a resonator to detect the signals from the NMR spectrometer and constructed an optical cavity using the metal layer as a mirror to bring the two together. "The incoming electric NMR signal shakes the membrane, causing motion that is detected by an optical interferometer," Usami adds.

Finding EMO

The researchers suggest that the success of this optical detection method for NMR spectroscopy could push the technique forward. They hope that it will not only increase sensitivity but accuracy of detection and ultimately the characterization of compounds, perhaps specifically the more convoluted macromolecules that are not necessarily amenable to conventional NMR spectroscopy. The technique could have implications across a wide range of disciplines from chemistry, materials science, and the biomedical and molecular biology fields.

"Various methods for optical NMR detection have been reported, and while some are highly sensitive, they have so far lacked widespread applicability," Takeda says. "Our new scheme has proven to be both versatile and applicable to a wide range of materials." In addition, the approach could be of benefit in laser cooling techniques applied to nuclear spins, the team reports. For those readers wondering about the putative acronym for this technique, it is EMO - electro-mechano-optical NMR!

Related Links

Optica 2018, online: "Electro-mechano-optical detection of nuclear magnetic resonance"

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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