13 C hyperpolarization with nitrogen-vacancy centers in micro- and nanodiamonds for sensitive magnetic resonance applications
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-02-28 |
| Journal | Science Advances |
| Authors | Rémi Blinder, Yuliya Mindarava, Martin C. Korzeczek, Alastair Marshall, Felix Glöckler |
| Institutions | OmniVision Technologies (Germany), UniversitÀt Ulm |
| Citations | 7 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis analysis summarizes the technical achievements in 13C hyperpolarization (HP) using Nitrogen-Vacancy (NV) centers in diamond nanoparticles for sensitive magnetic resonance applications.
- Core Achievement: Demonstrated efficient, room-temperature 13C hyperpolarization in diamond particles down to 100 nm median size, achieving NMR signal enhancements of 1500x (2 ”m) and 940x (100 nm) over the thermal signal at 0.29 T.
- Material Optimization: A combined surface treatment (Air Oxidation + Triacid Cleaning) was implemented, prolonging the crucial 13C spin-lattice relaxation time (T1) by a factor of 7 (up to 152 s at 7.05 T) in 100 nm particles, mitigating surface magnetic noise.
- DNP Sequence Robustness: The Phase-offset PulsePol sequence was optimized, utilizing the n = 4.5 resonance condition to virtually suppress the adverse effects of the NV-14N hyperfine interaction, resulting in a 70% improvement in polarization transfer efficiency.
- Illumination Enhancement: A 3D-printed microphotonic waveguide structure was used to improve the homogeneity of 532 nm laser illumination, providing an estimated 3.3x gain in NV initialization efficiency.
- Ensemble Utilization: Slow sample rotation (up to 25°/s) was introduced to cycle different subsets of randomly oriented NV centers through the narrow microwave excitation bandwidth, doubling the hyperpolarized signal.
- Application Potential: This work establishes NV-nanodiamonds as non-cryogenic, nanoparticle-based agents for high-sensitivity NMR and Magnetic Resonance Imaging (MRI) tracers.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Particle Median Size (Small) | 100 | nm | Milled HPHT diamond powder |
| Particle Median Size (Large) | 2 | ”m | Milled HPHT diamond powder |
| Polarization Field (Bpol) | 0.29 | T | DNP/HP Experiment |
| NMR Detection Field (Bdet) | 1 | T | Final 13C signal acquisition |
| 13C Enhancement (2 ”m) | 1500 | Times | Over thermal signal (0.29 T) |
| 13C Enhancement (100 nm) | 940 | Times | Over thermal signal (0.29 T) |
| 13C T1 (100 nm, AO+TAC) | 152 ± 12 | s | Measured at 7.05 T |
| NV T1 (100 nm, AO+TAC) | 4.23(7) | ms | Longitudinal relaxation time |
| NV T2,Hahn (100 nm) | 2.7(1) | ”s | Coherence time |
| NV Density (100 nm) | 3.4(2) | ppm | Concentration after treatment |
| Laser Wavelength | 532 | nm | Optical Pumping |
| Laser Pulse Length | 400 | ”s | NV Initialization |
| Maximum Sample Rotation Speed | 25 | °/s | Mechanical rotation during DNP |
| Polarization Buildup Time (Tpol) | 32 to 34 | s | Time to reach maximum HP signal |
| MW Rabi Frequency (Ω1) | (2Ï)10.5 | MHz | NV driving frequency |
| Effective MW Bandwidth (Apol) | (2Ï)15 | MHz | Using composite pulses |
Key Methodologies
Section titled âKey Methodologiesâ- NV Center Creation: HPHT diamond powders were subjected to high-energy electron irradiation (10 MeV, 3 x 1018 cm-2 dose) followed by annealing at 800 °C to convert substitutional nitrogens (P1 centers) into NV centers.
- Surface Cleaning and T1 Optimization:
- Air Oxidation (AO): Annealing at 620 °C for 5 hours in air to remove surface graphite and dangling bonds.
- Triacid Cleaning (TAC): Exposure to a 1:1:1 mixture of HNO3, HClO4, and H2SO4 at 200 °C and 6 bar pressure for approximately 2 hours to remove paramagnetic metallic residues (e.g., iron).
- Illumination Enhancement:
- A viscous fluid mixture of diamond powder and ethyl cinnamate (index matching, n = 1.57) was prepared.
- This mixture was placed within a 3D-printed microphotonic waveguide structure (fabricated via two-photon polymerization) to increase the surface area accessible to the 532 nm laser light, improving illumination homogeneity (3.3x gain).
- Dynamical Nuclear Polarization (DNP) Protocol:
- The Phase-offset PulsePol sequence was employed, consisting of a six-pulse block repeated M=68 times.
- Pulse Shaping: Individual rectangular pulses were replaced by optimized two-sideband composite pulses to increase robustness against frequency detuning and extend the effective MW bandwidth to 15 MHz.
- Resonance Selection: The sequence timing was set to the n = 4.5 resonance condition to minimize polarization loss caused by the NV-14N hyperfine interaction, which is critical for NV oriented at 90° to the magnetic field.
- Mechanical Cycling: The sample was rotated slowly (up to 25°/s) around an axis perpendicular to the magnetic field to ensure that a larger fraction of randomly oriented NV centers passed through the narrow MW excitation bandwidth during the polarization buildup time (Tpol).
- Detection: 13C NMR signal was detected in situ using the radio frequency coil of the ENDOR resonator after ramping the magnetic field up to 1 T.
Commercial Applications
Section titled âCommercial ApplicationsâThe demonstrated technology leverages optimized NV-nanodiamonds for applications requiring highly sensitive magnetic resonance detection at ambient conditions.
- Biomedical MRI Tracers: Nanodiamonds (100 nm size) are candidates for use as non-toxic, hyperpolarized 13C MRI contrast agents, enabling enhanced in vivo imaging of metabolic processes (e.g., tracking 13C-pyruvate).
- Replenishable Polarization Sources: The NV-NDs can act as renewable sources of polarization for external substances (e.g., liquids or solids) via cross-polarization or Nuclear Overhauser Effect (NOE) enhancement, relevant for drug screening and monitoring.
- Sensitive NMR/MRS: Enhancing the signal-to-noise ratio (SNR) in NMR and Magnetic Resonance Spectroscopy by orders of magnitude, benefiting fields like metabolomics, protein studies, and analysis of nano/mesoporous systems.
- Quantum Material Engineering: The established protocols for defect creation (electron irradiation) and surface passivation (AO + TAC) are directly applicable to producing high-quality, low-magnetic-noise nanodiamonds required for advanced quantum sensing platforms.
- Microphotonic Integration: The use of 3D-printed waveguide structures demonstrates a scalable method for efficient optical initialization of color centers in highly scattering powder ensembles, applicable to other solid-state quantum systems (e.g., divacancy in silicon carbide).
View Original Abstract
Nuclear hyperpolarization is a known method to enhance the signal in nuclear magnetic resonance (NMR) by orders of magnitude. The present work addresses the 13 C hyperpolarization in diamond micro- and nanoparticles, using the optically pumped nitrogen-vacancy center (NV) to polarize 13 C spins at room temperature. Consequences of the small particle size are mitigated by using a combination of surface treatment improving the 13 C relaxation ( T 1 ) time, as well as that of NV, and applying a technique for NV illumination based on a microphotonic structure. Adjustments to the dynamical nuclear polarization sequence (PulsePol) are performed, as well as slow sample rotation, to improve the NV- 13 C polarization transfer rate. The hyperpolarized 13 C NMR signal is observed in particles of 2-micrometer and 100-nanometer median sizes, with enhancements over the thermal signal (at 0.29-tesla magnetic field) of 1500 and 940, respectively. The present demonstration of room-temperature hyperpolarization anticipates the development of agents based on nanoparticles for sensitive magnetic resonance applications.