Electron and Nuclear Spins as Sensors and Detectors

Engineering Dynamic Nuclear Polarization

What is Dynamic Nuclear Polarization or DNP ?
Nucleus and Electrons in an atom behave like small "spinning" magnets, also called nuclear spin or electron spin. The elctron spin has higher gyromagnetic moment and therefore more sensitive. DNP enahncement is achieved by transferring the high sentistivity of the "electron spin" to the "nuclear spin". Classically this is analogous to transfer of heat between a cold and hot object when brought in close contact. DNP is an add-on technique to improve sensitivity of magnetic resoance spectropy (NMR) and imaging (MRI).   DNP has revolutionized NMR by improving its sensitivity by orders of magnitude, thereby dramatically reducing the experimental time. Rapid advances in DNP instrumentation, methods, and theory have dramatically enhanced the sensitivity and hence the scope of NMR spectroscopy. This has enabled the study of systems previously inaccessible to NMR, such as low-γ or low natural-abundant (dilute) NMR active nuclei. A few non-exhaustive examples include transient intermediates of amyloid fibrils, mixed states of membrane proteins present at low concentration, surface species in metal organic framework, and catalyst support surfaces.

Despite a massive surge in DNP research in the last few years, there remains innumerable untapped potential, as well as unsolved problems.
DNP signal enhancement factors are still one or two orders of magnitude lower than the theoretical limits, especially at high magnetic fields and for magic-angle spinning (MAS) solid-state samples.  The optimization of DNP enhancement is typically conducted empirically. Mechanistic details about the electron spin couplings (e.g., electron-electron dipolar and exchange coupling, number of spins involved, hyperfine coupling) and spin dynamics (e.g., electron spin T1 relaxation, coherence lifetime, hyperfine fluctuations) that give rise to various DNP mechanisms remain unclear. We aim to further develop dynamic nuclear polarization for solid-state samples, making it a more efficient and ubiquitous technique for bio-solids and materials involving challenging/insensitive nuclei like 17O, 29Si, 37Cl and 43Ca. We also target utilizing the endogenous paramagnetic centers (e.g. metalloproteins, heterogeneous catalyst and photoinduced EPR active states) for polarization enhancement and spin coupling network elucidation.

Specific Projects
1. Development of solid-state MAS DNP using multi-electron spin system

2. Controlling & understanding DNP polarization transfer pathway