A novel approach to testing for the presence of the virus that causes
COVID-19 may lead to tests that are faster, less expensive, and potentially
less prone to erroneous results than existing detection methods. Though the
work, based on quantum effects, is still theoretical, these detectors could
potentially be adapted to detect virtually any virus, the researchers say.
The new approach is described in a paper published Thursday in the journal
Nano Letters, by Changhao Li, an MIT doctoral student; Paola Cappellaro, a
professor of nuclear science and engineering and of physics; and Rouholla
Soleyman and Mohammad Kohandel of the University of Waterloo.
Existing tests for the SARS-CoV-2 virus include rapid tests that detect
specific viral proteins, and polymerase chain reaction (PCR) tests that take
several hours to process. Neither of these tests can quantify the amount of
virus present with high accuracy. Even the gold-standard PCR tests might
have false-negative rates of more than 25 percent. In contrast, the team's
analysis shows the new test could have false negative rates below 1 percent.
The test could also be sensitive enough to detect just a few hundred strands
of the viral RNA, within just a second.
The new approach makes use of atomic-scale defects in tiny bits of diamond,
known as nitrogen vacancy (NV) centers. These tiny defects are extremely
sensitive to minute perturbations, thanks to quantum effects taking place in
the diamond's crystal lattice, and are being explored for a wide variety of
sensing devices that require high sensitivity.
The new method would involve coating the nanodiamonds containing these NV
centers with a material that is magnetically coupled to them and has been
treated to bond only with the specific RNA sequence of the virus. When the
virus RNA is present and bonds to this material, it disrupts the magnetic
connection and causes changes in the diamond's fluorescence that are easily
detected with a laser-based optical sensor.
The sensor uses only low-cost materials (the diamonds involved are smaller
than specks of dust), and the devices could be scaled up to analyze a whole
batch of samples at once, the researchers say. The gadolinium-based coating
with its RNA-tuned organic molecules can be produced using common chemical
processes and materials, and the lasers used to read out the results are
comparable to cheap, widely available commercial green laser pointers.
While this initial work was based on detailed mathematical simulations that
proved the system can work in principle, the team is continuing to work on
translating that into a working lab-scale device to confirm the predictions.
"We don't know how long it will take to do the final demonstration," Li
says. Their plan is first to do a basic proof-of-principle lab test, and
then to work on ways to optimize the system to make it work on real virus
diagnosis applications.
The multidisciplinary process requires a combination of expertise in quantum
physics and engineering, for producing the detectors themselves, and in
chemistry and biology, for developing the molecules that bind with the viral
RNA and for finding ways to bond these to the diamond surfaces.
Even if complications arise in translating the theoretical analysis into a
working device, Cappellaro says, there is such a large margin of lower false
negatives predicted from this work that it will likely still have a strong
advantage over standard PCR tests in that regard. And even if the accuracy
were the same, this method would still have a major advantage in producing
its results with a matter of minutes, rather than requiring several hours,
she says.
The basic method can be adapted to any virus, she says, including any new
ones that may arise, simply by adapting the compounds that are attached to
the nanodiamond sensors to match the generic material of the specific target
virus.
"The proposed approach is appealing both for its generality and its
technological simplicity," says David Glenn, senior research scientist at
Quantum Diamond Technologies Inc., who was not associated with this work.
"In particular, the sensitive, all-optical detection technique described
here requires minimal instrumentation compared to other methods that employ
nitrogen vacancy centers," he says.
He adds that for his company, "we're very excited about using diamond-based
quantum sensors to build powerful tools for biomedical diagnostics. Needless
to say, we will be following along with great interest as the ideas
presented in this work are translated to the lab."
Reference:
Changhao Li et al, SARS-CoV-2 Quantum Sensor Based on Nitrogen-Vacancy
Centers in Diamond, Nano Letters (2021).
DOI: 10.1021/acs.nanolett.1c02868
No comments:
Post a Comment