An illustration depicting a quantum sensor made of nanodiamonds. D3Damon/iStock
Researchers at Japan’s Okayama University have developed nanodiamond sensors that can lead to the development of advanced quantum sensors and bioimaging applications.
Quantum-grade bioimaging will allow doctors to produce highly detailed and accurate images of cells, tissues, and organs — drastically improving detection and treatment of deadly diseases.
On the other hand, quantum sensing will enable scientists to detect the slightest atomic and molecular-scale changes in objects that conventional sensors can’t.
“Both these quantum technologies “have the potential to transform health care, technology, and environmental management, improving quality of life and providing sustainable solutions for future challenges,” Masazumi Fujiwara, one of the researchers and an associate professor at Okayama University, said.
Creating nanodiamonds with NV centers
Whether it is quantum sensing or bioimaging, both rely on harnessing the quantum properties of particles such as spin state, entanglement, and superposition.
Scientists have known that nanodiamonds with nitrogen-vacancy centers have exceptional sensitivity when it comes to detecting tiny changes in the electrical, thermal, and magnetic behavior of objects — making them a promising quantum sensor material.
This is because when a nitrogen atom replaces a carbon atom in the diamond, it leaves a small empty space (a vacancy) next to it. This NV vacancy center gives the nanodiamonds unique properties, like the ability to glow under certain light and detect tiny magnetic or electric fields.
However, producing high-quality nanodiamonds with NV centers has been a big challenge for scientists. Almost every time they attempted to do so, it resulted in diamonds with impurities and unstable spin states.
Fujiwara and his team overcame this challenge with a controlled NV center creation approach. They first grew a diamond crystal with 99.99% 12C atoms. Next they added nitrogen at 30 to 60 parts per million concentration into the crystal. However, since not every nitrogen atom forms a vacancy, so the final NV center concentration in the diamond was one part per million.
The researchers then broke down the crystal into many tiny pieces, mixed it into water, and then dropped it onto glass coverslips that had grid patterns. This process resulted in the creation of numerous nanodiamonds (NDs), each measuring roughly 277 nanometers and having negatively charged NV centers at 0.6 to 1.3 parts per million.
“They displayed strong fluorescence, achieving a photon count rate of 1500 kHz, making them suitable for bioimaging applications. Plus, these NDs also showed enhanced spin properties compared to commercially available larger NDs,” the study authors note.
Deploying NDs for quantum sensing
A photo showing quantum-grade nanodiamonds. Source: Masazumi Fujiwara from Okayama University
The study authors successfully developed quantum-grade bright fluorescent nanodiamonds. Now in order to use them for quantum sensing or bioimaging, one is required to study their spin states using optically detected magnetic resonance (ODMR).
ODMR is a method that combines light and microwaves to examine magnetic fields. Scientists first shine a light on materials like nanodiamonds and then apply microwaves, to see how the material reacts. By studying this interaction, they can detect tiny magnetic signals and understand the material’s magnetic properties such as spin.
To test the capabilities of their nanodiamonds, they introduced them into HeLa cells (human cells widely used by scientists for lab research experiments) and then employed ODMR to examine the spin. The NDs successfully detected slight temperature changes, which are nearly impossible to detect with existing technologies.
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Moreover, “They required 10–20 times less microwave power to achieve a 3 percent 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,” the researchers said.
This is the first time high-quality quantum-grade nanodiamonds have been successfully created and tested. Hopefully, this innovation will boost the creation of advanced quantum biosensing applications.
The study is published in the journal ACS Nano.
