Diamond quantum technology for medical imaging

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The performance of quantum states offers great potential for highly sensitive sensors to measure a range of variables such as magnetism, temperature and electric fields. This potential is limited because the quantum states (manifested as quantum bits or qubits) need to be isolated and cooled to optimize the measurement, which is a challenge for engineers to control. Diamond is a material that, thanks to its unique properties, could be used to solve some of these challenges.

In an interview with the EE Times, Daniel Twitchen, Senior Technologist at Element Six (E6) stated that advances in the company’s chemical vapor deposition (CVD) diamond growth process are paving the way for diamond to realize its potential as a solution.

Element Six, part of the De Beers Group, has been offering an all-purpose quantum quality CVD diamond since June 2020. E6 highlighted that this particular diamond, called DNV-B1, is a suitable starting material for those interested in nitrogen research -Vacancy (NV) ensembles for quantum demonstrations, maser, detection of RF radiation, Gyroscopes, sensing, and other emerging applications ranging from GPS-denied navigation to medical imaging.

“Diamond is an extraordinary material with such diverse properties that it is used in a wide variety of applications, including smartphone processing, high-power lasers for automotive applications, and high-end audio systems. Thanks to continuous technological advances, synthetic diamond materials with engineered qubits consisting of nitrogen vacancies (NV) are paving the way for the next quantum magnetic sensor devices, ”said Twitchen.

High purity single crystal synthetic diamond plates, produced by microwave-assisted chemical vapor deposition. Each diamond is approximately 4 × 4 × 0.5mm (Source: Element Six)

Diamond technology
Progress in the Quantum mechanics have already led to innovations such as lasers and transistors. The next wave of quantum technology will result from the manipulation of quantum properties such as superposition and entanglement.

However, the extreme fragility of qubits creates challenges. Fragility is the fine line of interaction that must be mastered in order to control the occurrence of errors and measurements and take full advantage of this exciting technology. Ideally, quantum states would be isolated from their environment, but measurement requires some degree of external interaction.

For these new applications, various technological solutions are being investigated, such as trapped ions, superconductors, quantum dots, photons and defects in semiconductors. Trapped ions are difficult to integrate, while superconducting circuits only work at cryogenic temperatures. Twitch pointed out that diamond, which is in the solid state, integrates easily, solves some of the quantum challenges, is also biocompatible, and provides high resolution magnetic imaging. In addition, it can be used at room or body temperature, eliminating the need for bulky cooling equipment.

“Scientists and engineers have already faced many of these challenges and made it possible to use these quantum spins effectively as atomic-scale magnetic compasses that measure fields more than 1,000 times lower than those of the earth, with spatial resolution that Can reach nanometers, ”said Twitchen. “Almost every biological system of interest is linked to electrical signals, from firing neurons to heartbeats. These electrical signals have an associated magnetic field that, unlike them, is not shielded by water and skin. Based on this biological premise, diamond’s biocompatibility opens up new applications in pharmaceutical and medical science, from drug development to the early detection of diseases.

“The ability to now produce synthetic diamonds with exceptional purity has unlocked the intrinsic properties that make it the perfect host material for solid-state qubits,” Twitchen continued. He added: “A number of groundbreaking academic studies, initially at the Universities of Stuttgart and Harvard, have shown that NV color centers have a quantum spin that can be manipulated and read at room temperature using simple and inexpensive optical techniques with exceptional quantum properties. NV centers are created by removing two adjacent carbon atoms from a diamond molecule and replacing one of them with a nitrogen atom, leaving a void in the center. “

The NV has an electron spin that is very sensitive to magnetic fields and forms the basis for sensitive magnetometry. The electron spin can be detected and aligned by switching on a green LED on the material and measuring the intensity of the red fluorescence emitted. “It has been shown that NV electron spins can store quantum information for 1s at room temperature,” said Twitchen.

Quantum Diamond Technologies, Inc (QDTI) is a start-up that emerged from Harvard University to enable point-of-care diagnostics for diseases that require ultra-sensitive detection of early-stage proteins, such as heart disease, cancer and Alzheimer’s. QDTI uses diamond-based quantum systems and uses NV centers as the engine that will drive our novel approach to the detection of biomolecules.

Figure 2: A diamond quantum magnetometer is roughly the size of a large shoebox. (Source: Lockheed Martin Corporation. For more information, visit: https://www.lockheedmartin.com/en-us/news/features/2019-features/tech-thats-cool-as-dark-ice.html)

Medical
Many current medical imaging solutions, such as the superconducting magnets used in magnetic resonance imaging (MRI), require cryogenic cooling systems that are only feasible in the largest research hospitals.

“Diamond magnetometry typically relies on a large ensemble of NV centers to increase magnetic sensitivity and provide higher spatial resolution while operating at room temperature. The reduction in size and the biocompatibility of diamond make it possible to move sensors closer to or in contact with the biological sample (e.g. the patient’s skin). These unique properties are ideal for medical diagnostic techniques such as magnetocardiography (MCG), which measures the magnetic fields created by electrical currents in the heart. Why is that important? Heart disease is the leading cause of death worldwide. Inexpensive and responsive diamond-powered quantum magnetometers could enable healthcare professionals to identify heart disease more quickly and accurately at the point of care, resulting in faster diagnosis and shorter discharge times for patients, ”said Twitchen.

In addition, Twitchen emphasized that when diagnosing diseases in patients, it can be crucial to measure the content of biomarkers such as proteins, nucleic acids and cells in a fluid sample such as blood or saliva. “These immunoassays are currently being analyzed by labeling the biomarker of interest with a tag such as a green fluorescent protein, followed by imaging the sample under a microscope to count the labeled biomarkers. This diverse and successful approach is behind a global market valued at over US $ 18 billion annually. However, fluorescent tag immunoassays suffer from undesirable background autofluorescence from biomolecules, and removing this autofluorescence requires a lengthy washing and sampling process before imaging can be performed. “

Since biological samples have low magnetism, immunoassays can be measured with a magnetic tag instead of a fluorescent tag. “Diamond-containing NV centers (DNV) use this method to provide excellent magnetic images without the need for washing. Single cell resolution was determined by QDTI with wide field DNV magnetic microscopy over a field of view of ~ 1 mm. demonstrated2 with a one minute imaging time used to identify the magnetically labeled cells. This enables new methods for the isolation and enumeration of important biomarkers with high sensitivity in small systems with faster processes, ”said Twitchen.

Figure 3: Single cell magnetic imaging with a quantum diamond microscope, published in Nature Methods, June 22, 2015. (a) Wide field NV diamond magnetic imaging microscope. (b) Electron micrograph of an SKBr3 cell labeled with magnetic nanoparticles (MNPs) conjugated to HER2 antibodies. (c) Diagram of an MNP-labeled target cell above the diamond surface surrounded by unlabeled normal blood cells.

Twitchen emphasized that the main interest of the users is not in the technology itself, but rather in its ease of use and its added value to make everyday life easier and better. The aim is to unlock the potential of diamond quantum sensors for simple and reliable application. “In particular, the efficient and robust integration of diamond sensors with optical excitation, control electronics and readout integrated with the relevant existing technologies must develop further. A major challenge for diamond engineers is to integrate their solution with existing supporting technologies. Technological revolutions often require a change in user behavior, but for that change to take place the benefits involved must be sufficiently significant. It is exciting to see how, in all of the possible applications discussed, the concepts have quickly developed from an idea to a prototype that can now be researched and tested by end users, ”says Twitchen.

Twitch pointed out that many quantum effects startups are working with diamond, including NVision, Qnami, QZabre, QDM.IO, and QDTI.

Another obstacle to device development is the learning curve required to get the most out of the NV defect, which requires specialist knowledge of materials, lasers, microwaves and quanta. The ultimate challenge is to make it available in the most practical markets by optimizing the manufacturing and design processes.



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