A study on the development and application of optically polarized materials: Spin hyperpolarization from the nitrogen vacancy center in diamond and hyperpolarized 129Xe NMR biosensors
Optically hyperpolarized electrons can be harnessed to transfer polarization to interacting nuclei. One example of this is the optically hyperpolarized spin state of nitrogen vacancy centers (NV- center) in diamond, which can act as sources of polarization for neighboring 13C nuclei. Spin-exchange optical pumping (SEOP) using circularly polarized light has been used for 129Xe hyperpolarization. Both hyperpolarization techniques provide a means of overcoming the fundamentally low sensitivity that has been a long-existing problem of NMR/MRI. Here, physical properties on polarization transfer from optically hyperpolarized NV- centers to 13C nuclei in diamond are studied as well as the development of several hyperpolarized 129Xe NMR/MRI biosensors.
On the subject of NV- centers in diamond, I studied polarization transfer to nearby 13C in natural abundance 13C diamond. The bulk 13C spin polarization was estimated to be ~6 % at room temperature. Dynamic nuclear polarization and its mechanism were investigated for various diamonds with different 13C concentrations (10, 25, 100%). The diamond with 10% 13C enrichment showed similar polarization enhancement as the natural abundance sample and spin diffusion was considered to be the limiting factor in the polarization transfer mechanism. Optically detected magnetic resonance (ODMR) studies were also carried out on NV- centers in nanodiamond powders. Interestingly, we observed not only broad powder patterns stemming from Δm =1 transitions, but also sharp powder patterns from orientation independent overtone transitions (Δm =2) that were supported by simulation.
On the subject of hyperpolarized 129Xe biosensors, I synthesized a multi-metal ion sensor using hyperpolarized 129Xe NMR, whose chemical shifts in a cryptophane cage gave distinct signals with regard to different metal ions. Also the metal ion concentration dependent signal intensity was found to have potential for quantification applications. A 129Xe NMR/MRI biosensor targeting a folate receptor was developed and its binding on the Hela cell, which overexpresses folate receptors, was investigated by confocal laser scanning microscopy, flow cytometry, and 129Xe hyper-CEST NMR/MRI technique. Furthermore, an estradiol-based biosensor was developed for 129Xe Hyper-CEST detection of the estrogen receptor in breast cancer and a new methodology to detect endocrine distruptors in environmental samples by using 129Xe hyper-CEST NMR was proposed. Lastly, I successfully synthesized a targeted, selective, and highly sensitive 129Xe NMR nanoscale biosensor using a spherical MS2 viral capsid, cryptophane cage, and DNA aptamer.