Researchers achieved a breakthrough in nanodiamond sensors with quantum-grade spin properties, ideal for bioimaging and biosensing. These advanced sensors promise transformative applications in medicine and energy technologies.
Quantum sensing is an emerging field that harnesses the unique quantum properties of particles — such as superposition, entanglement, and spin states — to detect changes in physical, chemical, or biological environments. One promising tool in this field is nanodiamonds (NDs) embedded with nitrogen-vacancy (NV) centers. These NV centers are formed when a carbon atom in the diamond lattice is replaced by nitrogen near a vacancy. When illuminated, the NV centers emit photons that preserve stable spin information and respond to external factors such as magnetic fields, electric fields, and temperature.
By using a technique called optically detected magnetic resonance (ODMR), scientists can measure fluorescence changes in the NV centers under microwave radiation, revealing subtle shifts in spin states. Biocompatible and customizable, NDs with NV centers can be engineered to interact with specific biological molecules, making them valuable tools for sensing within biological systems. However, compared to bulk diamonds, NDs used in bioimaging often have lower spin quality, which limits their sensitivity and accuracy in detecting changes.
Breakthrough in Nanodiamond Sensor Technology
In a recent breakthrough, scientists from Okayama University in Japan developed nanodiamond sensors bright enough for bioimaging, with spin properties comparable to those of bulk diamonds. The study, published on December 16, 2024, in ACS Nano, was led by Research Professor Masazumi Fujiwara from Okayama University, in collaboration with Sumitomo Electric Company and the National Institutes for Quantum Science and Technology.
“This is the first demonstration of quantum-grade NDs with exceptionally high-quality spins, a long-awaited breakthrough in the field. These NDs possess properties that have been highly sought after for quantum biosensing and other advanced applications,” says Prof. Fujiwara.
Challenges and Innovations in ND Development
Current ND sensors for bioimaging face two main limitations: high concentrations of spin impurities, which disrupt NV spin states, and surface spin noise, which destabilizes the spin states more rapidly. To overcome these challenges, the researchers focused on producing high-quality diamonds with very few impurities.
They grew single-crystal diamonds enriched with 99.99% 12C carbon atoms and then introduced a controlled amount of nitrogen (30–60 parts per million) to create an NV center with about 1 part per million. The diamonds were crushed into NDs and suspended in water.
Enhanced Performance for Biological Applications
The resulting NDs had a mean size of 277 nanometers and contained 0.6–1.3 parts per million of negatively charged NV centers. They displayed strong fluorescence, achieving a photon count rate of 1500 kHz, making them suitable for bioimaging applications.
These NDs also showed enhanced spin properties compared to commercially available larger NDs. They required 10–20 times less microwave power to achieve a 3% ODMR contrast, had reduced peak splitting, and demonstrated significantly longer spin relaxation times (T1 = 0.68 ms, T2 = 3.2 µs), which were 6 to 11 times longer than those of type-Ib NDs.
These improvements indicate that the NDs possess stable quantum states, which can be accurately detected and measured with low microwave radiation, minimizing the risk of microwave-induced toxicity in cells.
Applications Across Healthcare and Technology
To evaluate their potential for biological sensing, the researchers introduced NDs into HeLa cells and measured the spin properties using ODMR experiments. The NDs were bright enough for clear visibility and produced narrow, reliable spectra despite some impact from Brownian motion (random ND movement within cells).
Furthermore, the NDs were capable of detecting small temperature changes. At temperatures around 300 K and 308 K, the NDs exhibited distinct oscillation frequencies, demonstrating a temperature sensitivity of 0.28 K/√Hz, superior to bare type-Ib NDs.
With these advanced sensing capabilities, the sensor has potential for diverse applications, from biological sensing of cells for early disease detection to monitoring battery health and enhancing thermal management and performance for energy-efficient electronic devices.
“These advancements have the potential to transform healthcare, technology, and environmental management, improving quality of life and providing sustainable solutions for future challenges,” says Prof. Fujiwara.
Reference: “Bright Quantum-Grade Fluorescent Nanodiamonds” by Keisuke Oshimi, Hitoshi Ishiwata, Hiromu Nakashima, Sara Mandić, Hina Kobayashi, Minori Teramoto, Hirokazu Tsuji, Yoshiki Nishibayashi, Yutaka Shikano, Toshu An and Masazumi Fujiwara, 16 December 2024, ACS Nano.
DOI: 10.1021/acsnano.4c03424
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