High-resolution, high-sensitivity NMR of nanolitre anisotropic samples by coil spinning

NMR up to speed Nuclear magnetic resonance (NMR) is one of the most powerful and versatile methods for probing the structure and dynamics of liquids and solids, in an entirely noninvasive manner. But it has one big drawback: an intrinsically extremely poor sensitivity, making it unsuitable for really small samples. Enter MACS — magic angle coil spinning. This new technique exploits inductive coupling to facilitate wireless transmission of probe pulses and wireless reception of NMR signals. This in turn allows the NMR detector coil and the sample to be spun together very rapidly, so that NMR measurements can be made with high sensitivity. The method amplifies signals from small samples of organic powders and biological tissue by almost an order of magnitude, and should prove particularly useful for high-throughput chemical and biomedical analysis. Inductive coupling allows wireless transmission of probe pulses and wireless reception of nuclear magnetic resonance (NMR) signals. The method increases the signals obtained for small samples of organic powders and biological tissue by almost one order of magnitude, and is expected to prove particularly useful for high-throughput chemical and biomedical analysis. Nuclear magnetic resonance (NMR) can probe the local structure and dynamic properties of liquids and solids, making it one of the most powerful and versatile analytical methods available today. However, its intrinsically low sensitivity precludes NMR analysis of very small samples—as frequently used when studying isotopically labelled biological molecules or advanced materials, or as preferred when conducting high-throughput screening of biological samples or ‘lab-on-a-chip’ studies. The sensitivity of NMR has been improved by using static micro-coils 1 , alternative detection schemes 2 , 3 and pre-polarization approaches 4 . But these strategies cannot be easily used in NMR experiments involving the fast sample spinning essential for obtaining well-resolved spectra 5 , 6 from non-liquid samples. Here we demonstrate that inductive coupling allows wireless transmission of radio-frequency pulses and the reception of NMR signals under fast spinning of both detector coil and sample. This enables NMR measurements characterized by an optimal filling factor, very high radio-frequency field amplitudes and enhanced sensitivity that increases with decreasing sample volume. Signals obtained for nanolitre-sized samples of organic powders and biological tissue increas