Beyond compact NMR

Since the discovery of NMR over 70 years ago, the overriding goal of instrument developers was to produce magnets with higher field strengths in an effort to gain sensitivity and chemical shift dispersion for NMR spectroscopy. To achieve this goal, the overall magnet size steadily increased while the size of other spectrometer components shrunk following the advances in the development of electronics. Nevertheless, also NMR instruments with permanent magnets have been developed, which are capable of a diverse range of experiments and are small enough to be operated on the table top in the chemistry laboratory and under the fume hood, so that today the number of studies conducted with compact NMR instruments is steadily expanding. For a few years the use of compact NMR spectrometers is being explored for teaching, chemical analysis and reaction monitoring in academia as well as in industry. In the longer run, tabletop instruments are expected to be an intermediate step towards even smaller NMR analyzers, which might find use as web-interfaced health monitors that employ NMR spectroscopy among other analytical methods to analyze body fluids following microfluidic sample preparation. Key elements in such a device are likely to be signal amplifiers that selectively hyperpolarize marker molecules in complex mixtures, and miniature magnets with homogeneous magnetic fields for spectroscopic detection. The current state of the art of compact NMR is summarized in a perspective view of the potential future of miniaturized NMR sensors. (C) 2017 Elsevier Inc. All rights reserved.