Test strips in diamonds

Quantum nanodiamonds may help detect disease earlier

Anna Yudina, "Scientific Russia"

According to a study conducted by UCL researchers, the quantum abilities of nanodiamonds can be used to increase the sensitivity of paper diagnostic tests, potentially allowing early detection of diseases such as HIV, writes a press release Quantum nanodiamonds may help detect disease earlier.

Article by Miller et al. Spin-enhanced nanodiamond biosensing for ultrasensitive diagnostics is published in the journal Nature – VM.

Side–flow paper tests work the same way as a pregnancy test, in the sense that a strip of paper is soaked with a sample of liquid, and a color change – or a fluorescent signal - indicates a positive result and the detection of viral proteins or DNA. They are widely used to detect viruses from HIV to SARS-CoV-2 (side-flow tests for Covid-19 are currently being tested throughout England) and can provide a quick diagnosis, since the results do not need to be processed in the laboratory.

A new study has shown that inexpensive nanodiamonds can be used to signal the presence of an HIV disease marker with sensitivity many thousands of times higher than the sensitivity of gold nanoparticles widely used in these tests.

This increased sensitivity makes it possible to detect lower viral loads, which means that the test can detect the disease at an earlier stage, which is crucial for reducing the risk of transmission and for effective treatment of diseases such as HIV.

The research team is working on adapting the new technology to test for COVID-19 and other diseases in the coming months. The next key step is to develop a portable device that can "read" the results, as this method has been demonstrated using a microscope in the laboratory. Further clinical evaluation studies are also planned.

Lead author, Professor Rachel McKendry, professor of biomedical nanotechnology at UCL and director of the i-sense EPSRC IRC, said: "Our experimental study shows how quantum technologies can be used to detect ultra-low levels of virus in a patient's sample, allowing for much earlier diagnosis. We have focused on HIV detection, but our approach is very flexible and can be easily adapted to other diseases and types of biomarkers. We are working on adapting our approach to COVID-19. We believe that this revolutionary new technology will benefit patients and protect the population from infectious diseases."

The researchers used the quantum properties of nanodiamonds manufactured with precise imperfection. This defect in the very regular diamond structure creates a so-called nitrogen vacancy (NV) center. NV centers have many potential applications, from fluorescent biomarkers for use in hypersensitive imaging to information processing qubits in quantum computing.

NV centers can signal the presence of an antigen or other target molecule by emitting bright fluorescent light. In the past, fluorescent markers were limited to the background fluorescence of a sample or test strip, making it difficult to detect low concentrations of viral proteins or DNA that would indicate a positive test result. However, the quantum properties of fluorescent nanodiamonds make it possible to selectively modulate their radiation, which means that the signal can be fixed at a given frequency using a microwave field and can be effectively separated from background fluorescence, eliminating this limitation.

The optical results showed an improvement in sensitivity by five orders of magnitude (100,000 times) compared to gold nanoparticles (that is, a much smaller number of nanoparticles was required to generate the detected signal). Thanks to the inclusion of a short 10-minute amplification stage at a constant temperature, at which copies of the RNA were multiplied, the researchers were able to detect HIV RNA at the level of one molecule in the model sample.

The work has been demonstrated in laboratory conditions, but the team hopes to develop tests so that the results can be read using a smartphone or a portable fluorescent reader. This means that in the future the test can be carried out in conditions of lack of resources, which will make it more accessible to users.

First author Dr. Ben Miller (i-sense doctoral research fellow at the London Center for Nanotechnology at UCL) said: "Paper cross-flow tests with gold nanoparticles do not require laboratory analysis, which makes them particularly useful in resource-limited settings and when access to healthcare is limited. They are cheap, portable and easy to use. However, these tests currently lack the sensitivity to detect very low levels of biomarkers. By replacing commonly used gold nanoparticles with fluorescent nanodiamonds in this new design and selectively modulating their (already bright) light emission, we were able to separate the signal from the unwanted background fluorescence of the test strip, dramatically improving sensitivity."

Co-author, Professor John Morton, director of UCL's Institute of Quantum Science and Technology (UCLQ), said: "This interdisciplinary collaboration between UCLQ and the i-sense team at LCN is a fantastic illustration of fundamental work on quantum systems, such as the NV Center at Diamond can evolve from a laboratory and play a crucial role in real-world applications in the field of sensing and diagnostics. Researchers at UCLQ are studying and tapping into the impact of these and other quantum technologies, working with industrial and other academic research groups."

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