A broad effort is underway to improve the sensitivity of NMR through the use of dynamic nuclear polarization. Nitrogen vacancy (NV) centers in diamond offer an appealing platform because these paramagnetic defects can be optically polarized efficiently at room temperature. However, work thus far has been mainly limited to single crystals, because most polarization transfer protocols are sensitive to misalignment between the NV and magnetic field axes. Here we study the spin dynamics of NV−13C pairs in the simultaneous presence of optical excitation and microwave frequency sweeps at low magnetic fields. We show that a subtle interplay between illumination intensity, frequency sweep rate, and hyperfine coupling strength leads to efficient, sweep-direction-dependent13C spin polarization over a broad range of orientations of the magnetic field. In particular, our results strongly suggest that finely tuned, moderately coupled nuclear spins are key to the hyperpolarization process, which makes this mechanism distinct from other known dynamic polarization channels. These findings pave the route to applications where powders are intrinsically advantageous, including the hyperpolarization of target fluids in contact with the diamond surface or the use of hyperpolarized particles as contrast agents for in vivo imaging.
Selective imaging of diamond nanoparticles within complex matrices using magnetically induced fluorescence contrast
The use of fluorescence microscopy to study fate and transport of nanoparticles in the environment can be limited by the presence of confounding background signals such as autofluorescence and scattered light. The unique spin-related luminescence properties of nitrogen vacancy (NV) centers in diamond nanoparticles (NVND) enable new types of imaging modalities such as selective imaging of nanoparticles in the presence of background fluorescence. These techniques make use of the fact that the spin properties, which affect the fluorescence of NV centers, can be modulated using applied magnetic or radio-frequency fields. This work presents the use magnetic fields to modulate the fluorescence of NVND for background-subtracted imaging of nanoparticles ingested by a model organism, C. elegans . With the addition of modest time-modulated magnetic fields from an inexpensive “hobby” electromagnet, the fluorescence of 40 nm NVND can be modulated by 10% in a widefield imaging configuration. Herein, differential magnetic imaging is used to image and to isolate the fluorescence arising from nanodiamond within the gut of the organism C. elegans . This method represents a promising approach to probing the uptake of nanoparticles by organisms and to assessing the movement and interactions of nanoparticles in biological systems.
more »
« less
- Award ID(s):
- 1503408
- NSF-PAR ID:
- 10146113
- Date Published:
- Journal Name:
- Environmental Science: Nano
- Volume:
- 7
- Issue:
- 2
- ISSN:
- 2051-8153
- Page Range / eLocation ID:
- 525 to 534
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
-
High-temperature annealing is a promising but still mainly unexplored method for enhancing spin properties of negatively charged nitrogen-vacancy (NV) centers in diamond particles. After high-energy irradiation, the formation of NV centers in diamond particles is typically accomplished via annealing at temperatures in the range of 800–900 °C for 1–2 h to promote vacancy diffusion. Here, we investigate the effects of conventional annealing (900 °C for 2 h) against annealing at a much higher temperature of 1600 °C for the same annealing duration for particles ranging in size from 100 nm to 15 μm using electron paramagnetic resonance and optical characterization. At this high temperature, the vacancy-assisted diffusion of nitrogen can occur. Previously, the annealing of diamond particles at this temperature was performed over short time scales because of concerns of particle graphitization. Our results demonstrate that particles that survive this prolonged 1600 °C annealing show increased NV T1 and T2 electron spin relaxation times in 1 and 15 μm particles, due to the removal of fast relaxing spins. Additionally, this high-temperature annealing also boosts magnetically induced fluorescence contrast of NV centers for particle sizes ranging from 100 nm to 15 μm. At the same time, the content of NV centers is decreased fewfold and reaches a level of <0.5 ppm. The results provide guidance for future studies and the optimization of high-temperature annealing of fluorescent diamond particles for applications relying on the spin properties of NV centers in the host crystals.more » « less
-
null (Ed.)Multimodal imaging—the ability to acquire images of an object through more than one imaging mode simultaneously—has opened additional perspectives in areas ranging from astronomy to medicine. In this paper, we report progress toward combining optical and magnetic resonance (MR) imaging in such a “dual” imaging mode. They are attractive in combination because they offer complementary advantages of resolution and speed, especially in the context of imaging in scattering environments. Our approach relies on a specific material platform, microdiamond particles hosting nitrogen vacancy (NV) defect centers that fluoresce brightly under optical excitation and simultaneously “hyperpolarize” lattice C 13 nuclei, making them bright under MR imaging. We highlight advantages of dual-mode optical and MR imaging in allowing background-free particle imaging and describe regimes in which either mode can enhance the other. Leveraging the fact that the two imaging modes proceed in Fourier-reciprocal domains (real and k-space), we propose a sampling protocol that accelerates image reconstruction in sparse-imaging scenarios. Our work suggests interesting possibilities for the simultaneous optical and low-field MR imaging of targeted diamond nanoparticles.more » « less
-
Local characterization of the properties and performances of miniaturized magnetic devices is a prerequisite for advancing present on-chip spintronic technologies. Utilizing nitrogen-vacancy (NV) centers in diamond, here we report quantum sensing of spin wave modes and magnetic stray field environment of patterned micrometer-scale Y3Fe5O12 (YIG) disks at the submicrometer length scale. Taking advantage of wide-field magnetometry techniques using NV ensembles, we map the spatially dependent NV electron spin resonances and Rabi oscillations in response to local variations of the stray fields emanating from a proximal YIG pattern. Our experimental data are in excellent agreement with theoretical predictions and micromagnetic simulation results, highlighting the significant opportunities offered by NV centers for probing the local magnetic properties of functional solid-state devices. The presented quantum sensing strategy may also find applications in the development of next-generation spintronic circuits with improved scalability and density.more » « less
-
null (Ed.)Multimodal imaging—the ability to acquire images of an object through more than one imaging mode simultaneously—has opened additional perspectives in areas ranging from astronomy to medicine. In this paper, we report progress toward combining optical and magnetic resonance (MR) imaging in such a “dual” imaging mode. They are attractive in combination because they offer complementary advantages of resolution and speed, espe- cially in the context of imaging in scattering environments. Our approach relies on a specific material platform, microdiamond par- ticles hosting nitrogen vacancy (NV) defect centers that fluoresce brightly under optical excitation and simultaneously “hyperpolar- ize” lattice 13C nuclei, making them bright under MR imaging. We highlight advantages of dual-mode optical and MR imag- ing in allowing background-free particle imaging and describe regimes in which either mode can enhance the other. Leveraging the fact that the two imaging modes proceed in Fourier-reciprocal domains (real and k-space), we propose a sampling protocol that accelerates image reconstruction in sparse-imaging scenar- ios. Our work suggests interesting possibilities for the simulta- neous optical and low-field MR imaging of targeted diamond nanoparticles.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/C9EN01008D
