Quantum Nanosensors: Nanodiamonds (NDs) with nitrogen-vacancy (NV) centers detect physical and chemical changes.
Lower Energy Needs: New NDs need 20 times less microwave power and maintain spin states longer.
Broad Uses: Potential fields include bioimaging, battery diagnostics, and thermal oversight of devices.
Quantum sensing leverages quantum states, such as spin configurations, to measure changes in various systems. Nanodiamonds (NDs) equipped with nitrogen-vacancy (NV) centers are a promising class of sensors, where replacing a carbon atom with nitrogen near a lattice gap yields sensitive points. When illuminated, the NV centers emit fluorescence that shifts under external influences, including magnetism and temperature, enabling detection through optically detected magnetic resonance (ODMR).
Traditionally, nanodiamonds used for bioimaging do not match the spin quality of bulk diamonds. The group at Okayama University tackled this by creating single-crystal diamonds enriched with 99.99% 12C carbon atoms. They introduced controlled quantities of nitrogen (approximately 30–60 parts per million) to form NV centers, then crushed the crystals into NDs averaging 277 nanometers in size.
These newly produced NDs demonstrated strong fluorescence (with photon count rates around 1500 kHz) and stable spin qualities. Compared to commercial NDs, they required significantly less microwave power to obtain ODMR contrast and maintained spin states 6 to 11 times longer. They were suspended in water and showed minimal splitting of magnetic resonance peaks, indicating fewer spin disturbances.
"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."
— Prof. Masazumi Fujiwara, Okayama University
To assess biological relevance, the team introduced the NDs into HeLa cells. Results from ODMR measurements confirmed that the particles remained bright enough to be easily located, even while subject to random motion within cells. They also detected subtle shifts in temperature at around 300 K to 308 K, recording sensitivity of 0.28 K/√Hz—a notable enhancement over conventional type-Ib NDs.
The researchers envision the NDs supporting early disease detection, battery diagnostics, and thermal management for energy-efficient electronics. By offering precise environmental sensing with limited power requirements, they may create added benefits across healthcare, engineering, and sustainability endeavors.
Along with the team’s progress in nanosensor development, lead author Prof. Fujiwara focuses on wide-ranging nanochemistry projects within the Department of Chemistry at Okayama University. Having worked at Osaka City University and the Humboldt University of Berlin, he continues to guide research spanning material design and quantum photonics. The lab’s international collaborations include programs under JST-ASPIRE, with aims of refining functional nanomaterials and developing new quantum-based methods.
