Understanding the magnetic resonance spectrum of nitrogen vacancy centers in an ensemble of randomly-oriented nanodiamonds

Nanodiamonds containing nitrogen vacancy (NV-) centers show promise for a number of emerging applications including targeted in vivo imaging and generating nuclear spin hyperpolarization for enhanced NMR spectroscopy and imaging. Here, we develop a detailed understanding of the magnetic resonance behavior of NV- centers in an ensemble of nanodiamonds with random crystal orientations. Two-dimensional optically detected magnetic resonance spectroscopy reveals the distribution of energy levels, spin populations, and transition probabilities that give rise to a complex spectrum. We identify overtone transitions that are inherently insensitive to crystal orientation and give well-defined transition frequencies that access the entire nanodiamond ensemble. These transitions may be harnessed for high-resolution imaging and generation of nuclear spin hyperpolarization. The data are well described by numerical simulations from the zero- to high-field regimes, including the intermediate regime of maximum complexity. We evaluate the prospects of nanodiamond ensembles specifically for nuclear hyperpolarization and show that frequency-swept dynamic nuclear polarization may transfer a large amount of the NV- center's hyperpolarization to nuclear spins by sweeping over a small region of its spectrum.Comment: 6 pages, 5 figure

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

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

Assessment of Various Density Functional Theory Methods for Finding Accurate Structures of Actinide Complexes

Density functional theory (DFT) is a widely used computational method for predicting the physical and chemical properties of metals and organometals. As the number of electrons and orbitals in an atom increases, DFT calculations for actinide complexes become more demanding due to increased complexity. Moreover, reasonable levels of theory for calculating the structures of actinide complexes are not extensively studied. In this study, 38 calculations, based on various combinations, were performed on molecules containing two representative actinides to determine the optimal combination for predicting the geometries of actinide complexes. Among the 38 calculations, four optimal combinations were identified and compared with experimental data. The optimal combinations were applied to a more complicated and practical actinide compound, the uranyl complex (UO2(2,2′-(1E,1′E)-(2,2-dimethylpropane-1,3-dyl)bis(azanylylidene)(CH3OH)), for further confirmation. The corresponding optimal calculation combination provides a reasonable level of theory for accurately optimizing the structure of actinide complexes using DFT

Reduced graphene oxide coated cotton e-textile for wearable chemical warfare agent sensors

A facile, safe, and scalable method for fabricating electrically conductive-reduced graphene oxide (rGO) e-fabric using a plasma-assisted coating process has been demonstrated. A wearable sensor based on rGO e-fabric was fabricated and used to detect and distinguish deadly chemical warfare agents (CWAs). The rGO e-fabric-based CWA sensor exhibited consistent responses upon repeated exposure to chemicals, including dimethyl methylphosphonate (DMMP) and soman (GD), which is a nerve agent. A difference in responses of the sensor toward GD and DMMP was observed. Theoretical studies further confirmed the potential of the as-prepared device as an e-fabric sensor for the detection of nerve agents. This novel functional e-fabric holds promise for future applications of wearable chemical agent sensors in smart personal protective suits.</p

Optical Dynamic Nuclear Polarization of 13C Spins in Diamond at a Low Field with Multi-Tone Microwave Irradiation

Majority of dynamic nuclear polarization (DNP) experiments have been requiring helium cryogenics and strong magnetic fields for a high degree of nuclear polarization. In this work, we instead demonstrate an optical hyperpolarization of naturally abundant 13C nuclei in a diamond crystal at a low magnetic field and the room temperature. It exploits continuous laser irradiation for polarizing electronic spins of nitrogen vacancy centers and microwave irradiation for transferring the electronic polarization to 13C nuclear spins. We have studied the dependence of 13C polarization on laser and microwave powers. For the first time, a triplet structure corresponding to the 14N hyperfine splitting has been observed in the 13C polarization spectrum. By simultaneously exciting three microwave frequencies at the peaks of the triplet, we have achieved 13C bulk polarization of 0.113 %, leading to an enhancement of 90,000 over the thermal polarization at 17.6 mT. We believe that the multi-tone irradiation can be extended to further enhance the 13C polarization at a low magnetic field

DFT study on the bonding properties of Pu(III) and Pu(IV) chloro complexes

<p>Understanding of chemical bonding is a fundamentally important topic. Given the importance of bonding studies, we performed quantum calculations on plutonium chloro complexes (PuClx(III) and PuClx(IV)) that are believed to form as molten chloride salts during nuclear waste treatment. The result of these calculations was verified by comparing them to experimental data on a similar actinide chloro complex. Charge and bond order analyses of the complexes provide insight into the electronic properties, bonding, and nuclear magnetic resonance characteristics of the plutonium chloro complexes. The chemical shift of the Pu(III) complexes are found to be negative while those of Pu(IV) are positive.</p

Signal Amplification by Reversible Exchange for COVID-19 Antiviral Drug Candidates

Several drug candidates have been proposed and tested as the latest clinical treatment for the coronavirus pneumonia (COVID-19). Chloroquine, hydroxychloroquine, ritonavir/lopinavir, and favipiravir are proved to be effective after treatment. The hyperpolarization technique presents an ability to further understand the roles of these drugs at the molecular scale and applications in nuclear magnetic resonance/magnetic resonance imaging (NMR/MRI). This technique may provide new opportunities in diagnosis and biomedical research to cope with COVID-19. Signal amplification by reversible exchange (SABRE)-based hyperpolarization studies on large-sized drug candidates were carried out. We observed hyperpolarized proton signals from whole structures, due to the unprecedented long-distance polarization transfer by para-hydrogen. We also found that the optimum magnetic field for the maximum polarization transfer yield was dependent on the molecular structure. Therefore, future research on isotope labelling and polarization transfer on long T1 time nuclei including clinical perspectives can help us overcome this worldwide pandemic.</p