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Results just published in the journal Nature suggest that wireless, rotating micro-coil NMR could do for spectroscopy what the recently announced WiTricity will do for cable-free power transmission and help overcome the intrinsic weakness of NMR signals. Dimitris Sakellariou and colleagues Gerald Le Goff and Jacques-François Jacquinot of the Commissariat a l'Energie Atomique, Saclay, in Gif-sur-Yvette, France, have developed a novel technique they refer to as magic angle coil spinning, or MACS. The technique exploits inductive coupling between probe pulses and receiver, which means both the sample and the detector coil can be spun very rapidly with no tangles, thus improving sensitivity at the magic angle. "Our technology is promising for the study of very small organic powders and biological samples under high-resolution conditions," Sakellariou told SpectroscopyNOW, "We are essentially transferring wirelessly radio-frequency energy and nuclear spin response from a commercial NMR probe to the detector which is embedded within the sample holder spinning at the magic angle." This novel technique allows the researchers to take NMR measurements characterized by an optimal filling factor, very high radio-frequency field amplitudes and enhanced sensitivity. This, they explain, increases with decreasing sample volume so that signals obtained for nanolitre samples are an order of magnitude larger than with conventional MAS-NMR, or can be acquired two orders of magnitude faster. "The signal to noise ratio increases with the square root of the time one acquires the signal, therefore it takes 100 more time to increase sensitivity by a factor of ten, in other words to acquire a signal with a ten times greater signal to noise ratio," Sakellariou explains. The team says that the approach can be implemented easily on any commercial NMR setup and enabled high sensitivity NMR for samples of limited mass in nanolitre and picolitre quantities. They point out that it could be easily adapted to various solid-state NMR techniques and to high-throughput systems. As miniaturization technology advances and coil and capacitor lithography improves, allowing smaller devices to be made, so MACS will be enhanced further. Variations in resonator geometry (RF shimming) and resonance mode (self-resonance) might also be used to reduce artefacts due to eddy currents, the researchers add. This could "render the implementation more practical especially for smaller and faster spinning rotors," Sakellariou says. In an editorial accompanying the Sakellariou paper, Arthur Edison and Joanna Long of the Department of Biochemistry and Molecular Biology, at the University of Florida, USA, explain how for low-concentration samples, the amount of material will still need to be increased to obtain the optimal NMR spectrum. However, for many applications in chemistry, biology and materials science, they say, this latest magic advance "opens up new opportunities simply by reducing the amount of material required for solid-state NMR studies, without needing to invest substantially in new technologies." Related links: |
 LeGoff, Sakellariou, Jacquinot, working NMR wirelessly  MACS, a kind of magic |
