Institute of Physics , École Polytechnique Fédérale de Lausanne , CH-1015 Lausanne , Switzerland.
SWISSto12 SA, 1015 , Lausanne , Switzerland.
Anal Chem. 2018 May 1;90(9):5620-5626. doi: 10.1021/acs.analchem.7b04700. Epub 2018 Apr 11.
Nuclear hyperpolarization in the liquid state by dynamic nuclear polarization (DNP) has been of great interest because of its potential use in NMR spectroscopy of small samples of biological and chemical compounds in aqueous media. Liquid state DNP generally requires microwave resonators in order to generate an alternating magnetic field strong enough to saturate electron spins in the solution. As a consequence, the sample size is limited to dimensions of the order of the wavelength, and this restricts the sample volume to less than 100 nL for DNP at 9 T (∼260 GHz). We show here a new approach that overcomes this sample size limitation. Large saturation of electron spins was obtained with a high-power (∼150 W) gyrotron without microwave resonators. Since high power microwaves can cause serious dielectric heating in polar solutions, we designed a planar probe which effectively alleviates dielectric heating. A thin liquid sample of 100 μm of thickness is placed on a block of high thermal conductivity aluminum nitride, with a gold coating that serves both as a ground plane and as a heat sink. A meander or a coil were used for NMR. We performed H DNP at 9.2 T (∼260 GHz) and at room temperature with 10 μL of water, a volume that is more than 100× larger than reported so far. The H NMR signal is enhanced by a factor of about -10 with 70 W of microwave power. We also demonstrated the liquid state of P DNP in fluorobenzene containing triphenylphosphine and obtained an enhancement of ∼200.
通过动态核极化（DNP）实现的液态核极化在 NMR 光谱学中具有很大的应用潜力，因为它可以用于对水溶液中的生物和化学化合物的小样本进行研究。在液态中进行 DNP 通常需要微波谐振器，以产生足够强的交变磁场来使溶液中的电子自旋饱和。因此，样品尺寸受到限制，尺寸必须与波长相当，这使得在 9 T（约 260 GHz）下的 DNP 样品体积限制在 100 nL 以下。在这里，我们展示了一种克服这种样品尺寸限制的新方法。通过使用无微波谐振器的高功率（约 150 W）回旋管，可以获得电子自旋的高饱和。由于高功率微波会在极性溶液中引起严重的介电加热，因此我们设计了一种平面探头，可以有效缓解介电加热。将厚度为 100 μm 的薄液态样品放置在高热导率的氮化铝块上，并用金涂层作为接地平面和散热器。采用曲折线或线圈进行 NMR。我们在 9.2 T（约 260 GHz）和室温下进行了 H DNP，使用了 10 μL 的水，这一体积比迄今为止报道的体积大 100 倍以上。在 70 W 的微波功率下，H NMR 信号增强了约 10 倍。我们还在含有三苯基膦的氟苯中证明了 P DNP 的液态，并获得了约 200 的增强。
