Detecting covid with the lead of a pencil

A health provider offers a rapid test to a young woman who is walking through Carnaby this Monday in London.FACUNDO ARRIZABALAGA / EFE

César de la Fuente Núñez, the Galician biotechnologist recognized with the last Princess of Girona Foundation Prize for Scientific Research and head of different scientific teams at the University of Pennsylvania, has been warning for months: the control of the pandemic, in addition to vaccines, requires a appropriate social behavior (masks and distance) and "public health interventions to identify contagion": "The important measure to prevent future infections is to know if the person is contagious, not whether or not they are infected with the virus." Its laboratories in the United States have already developed two fast and cheap covid detection devices, elements that a study published in

PLOS Computational Biology

considers fundamental when defending that quantity is better than quality of test to surround the pandemic.

More information

• Covid vaccination of only a part of the population is insufficient to consider the pandemic controlled

• Condemned to PCR

The latest device created by César de la Fuente's teams, collected in the

PNAS

magazine

,

makes it possible to "diagnose covid quickly and cheaply using pencil leads," according to the researcher. The work is based on the urgent need for high-frequency tests to help prevent the spread of covid. To this end, they have developed the Low Cost Advanced Electrochemical Diagnosis (LEAD), a test that detects SARS-CoV-2 in 6.5 minutes and costs one and a half dollars (1.27 euros). ) per unit.

The great advantage of the device is that it uses common materials, available worldwide and easy to assemble, such as modified graphite cables and a plastic vial.

Its sensitivity is comparable to that of devices considered "gold standard", the international reference set by the well-known PCR, and gives results of 100% in saliva samples and close to 90% in nasopharyngeal tests.

After being assembled, it maintains a shelf life of five days when stored at four degrees Celsius.

An investigation concludes that the use of only rapid and cheap tests would allow results similar to those found by PCR in the control of the pandemic if the number of people tested is high enough

It is not the first device created by César de la Fuente's teams in the departments of Bioengineering and Chemical and Biomolecular Engineering at the University of Pennsylvania. They have also patented the

Rapid

method

,

collected in the scientific journal

Matter

and consisting of a "miniaturized, simple, portable and highly sensitive biosensor" that detects SARS-CoV-2 using a cubic millimeter (a drop of water is approximately 50 millimeters cubic) of sample in 240 seconds and with a sensitivity that ranges between 85.3% and 100% depending on the origin of the fluid (nose, pharynx or saliva). The price of each test is $ 4.67 (3.81 euros).

De la Fuente explains that rapid tests are cheap and can be performed at home or in the vicinity of an event that provides for massive participation without waiting days to know the result: "They are the best tool we have to identify the infectious individual and intervene immediately".

Their proposals coincide with those of Philip Cherian and Gautam Menon, from the Indian University of Ashoka, and Sandeep Krishna, from the Center for Biological Sciences in the same country.

From a computational analysis of covid tests, these scientists conclude that, to minimize the number of infections in a population, the number of tests matters more than the sensitivity of the tests that are used.

The results have been presented in

PLOS Computational Biology

.

The three scientists have carried out simulations of how covid spreads based on people's mobility and calculated the total number of infections that would occur in each scenario. The analysis indicates that the use of only rapid and inexpensive tests would allow results similar to those found by PCR in the control of the pandemic if the number of people tested is high enough. This conclusion would facilitate the monitoring of infections by prioritizing the amount over the sensitivity of the test and at a much lower cost. Compared to the 1.27 per test of the last device presented by De la Fuente, a PCR can cost an average of 150 euros.

The conclusion is especially relevant for those countries with fewer resources, as they could achieve optimal results by concentrating on increasing testing with methods that, although less sensitive, provide immediate results.

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