Dynamic Nuclear Polarization in Solid Samples by Electrical-Discharge-Induced Radicals

Dynamic nuclear polarization (DNP) is a method for enhancing nuclear magnetic resonance (NMR) signals with many potential applications in chemistry and medicine. Traditionally, DNP signal enhancement is achieved through the use of exogenous stable free-radicals mixed in a solution with the molecules of interest, resulting in a process that changes the Boltzmann population of the nuclear spins’ energy levels. Many solid materials, however, cannot tolerate wetting (such as various pharmaceuticals), and thus pose a challenge to current DNP sample preparation protocols. Here we show that proton DNP signal enhancements can be obtained for solid samples without the use of solvent and exogenous free-radicals [1]. This is achieved by the use ionized gas to generate radicals primarily on the surface of a solid sample. These radicals are found suitable for DNP of various solid samples. The plasma-induced radicals are stable under moderate vacuum conditions, yet can be readily eliminated from the sample by introduction of a solvent. The latter property can be of high importance for medical imaging applications, where there is a strong need for generating highly polarized metabolites, without the use of the potentially harmful stable free radicals.

[1] Journal of Magnetic Resonance – 261, (2015) 95-100