Silicon cylinder spiral coil for nuclear magnetic resonance spectroscopy of nanoliter samples

This contribution presents a new high sensitivity microdetector designed for high resolution proton NMR at 750 MHz (17.6 T) of sample volumes ranging from 5 to 40 nl. The desired volume of fluid is placed in a sealed 330/200 mu m outer/inner diameter glass capillary and is then situated in the center of the detection coil. The high quality factor detection coils are fabricated using silicon microtechnology. The materials from which the device is constructed are specially shaped to improve the homogeneity of the static magnetic field within the sample. Adverse effects of the finite, nonspherical sample geometry on the spectral resolution are mitigated by employing sample rotation up to 2.5 kHz at the magic angle. The new detector exhibits linewidths of smaller than 3.0 Hz (0.004 ppm) and a signal-to-noise ratio in the spectral domain of higher than 4,000 per mu mol of water. Results with respect to sensitivity, spectral resolution, and total sample volume are given and put into context with already published microprobes