Since the beginning of the development of COVID-19, rapid tests have been a global priority. Different types of tests are used, such as the diagnostic test or the antibody tests. Their sensitivity, specificity as well as their accuracy can vary depending on the test used. To contain the spread of the virus and promote the patient’s isolation, it is critical to delivering the results as quickly as possible. Depending on the technology being used, it can take minutes up to several days to get the results.
Detecting COVID-19: How does-it work?
As of October 16, more than 500 million tests were performed to assess the spread of Covid-19, including more than 120 million in the United-States. Tests are somehow not created equal and come in different flavors, each with their own pros and cons.
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Two families of tests are in use, providing different information and each with their pros and cons.
- Diagnostic tests detect active infection. A positive result will mean that the necessary measures will have to be taken to self-isolate and quarantine. Two types of diagnostic tests are currently in use: the Polymerase Chain reactions (PCR) that detect the virus genetic material and the antigen test targeting specific proteins on the virus’s surface.
- Antibody tests will target the immune system and the antibodies expressed during the infection. It will take several days for the antibodies to be expressed. It explains why these tests can not be used reliably to establish a diagnostic. They are somehow instrumental in determining if people have been in contact with the virus. Reinfection in the future is somehow possible even in the presence of antibodies.
The table below summarizes the different types of tests, their pros, and their limitations as well.
|CHARACTERISTICS||MOLECULAR TESTS||ANTIGEN TEST||ANTIBODY TEST|
|Type||Diagnostic test, viral test, molecular test, nucleic acid amplification test (NAAT), RT-PCR test, LAMP test||Rapid diagnostic test||Serological test, serology, blood test, serology test|
|Site of sampling||- Nasal or throat swab (most tests) - Saliva (a few tests)||- Nasal or throat swab||- Finger stick or blood draw|
|time before result||- Same day (some locations) - Can take or up to a week||- One hour or less||- Same day (many locations) - 1-3 days|
|Need for another test||No||- Positive results are highly accurate - Negative results may need confirmation by molecular test||- May need a second antibody test for confirmation|
|What is detected?||- Active coronavirus||- Active coronavirus||- Previous infection by coronavirus|
|Limitations||- Can not detect a previous infection||- May miss an active infection||- Diagnose active or previous infections|
Even if the PCR tests are the current gold standard, it is known to produce false-negative results, meaning that the virus carriers will have a false sense of safety and continue spreading the virus. On top of that, the sampling using a nasal swab requires trained technicians, and the analyses take time. A rapid, reliable, inexpensive, and ideally telemedicine compatible is then much needed. This is what has been presented by Dr. Wei Gao from Caltech recently: a multiplexed, portable, wireless electrochemical platform to test SARS-Cov-2. The results of the Graphene-Based Multiplex platform for Diagnosis and Monitoring of COVID-19 were recently published in the journal “Matter.”
The future of SARS-CoV-2 testing is now
More than a test, this is a Graphene-Based telemedicine platform able to perform a Multiplex Electrochemical Detection of SARS-CoV-2 in blood and saliva. The device comprises four graphene working electrodes, a reference electrode, and a graphene counter electrode. The cost of the materials to produce such an electrode is evaluated to be under $0.05. When adding the reagents and other chemicals needed, the authors evaluated the cost of around $1.
The electrodes are functionalized with specific markers and provide information regarding the detection of SARS-CoV-2 nucleocapsid protein, antibodies (IgG and IgM), and inflammatory biomarkers (CRP). One of the interesting points about this test is that it works with both saliva or blood, making it very easy to use. The principle is that when the blood or saliva touches the sensor, the virus will be trapped by the antigens or antibodies that cover their surface. An electrochemical reaction will occur, and the test results provided instantly.
The test is also highly sensitive and specific. The array device is connected to an electronic board to transfer the data wirelessly to the user’s device over Bluetooth. The team also envisages integrating the chipset directly in wearables for continuous monitoring.
To date, the device has been tested with samples from 19 COVID-19 patients. The next steps are to test the sensor and supporting chipset in a clinical setting. The road is still long before approval by the food and drug administration and mass production.
This rapid test platform is ideal for home testing, remote monitoring, and telemedicine. The technology has the potential to become a game-changer for the COVID-19 tests and could be very useful will it be public health, at home, or in nursing homes.
Reference: “SARS-CoV-2 RapidPlex: A Graphene-based Multiplexed Telemedicine Platform for Rapid and Low-Cost COVID-19 Diagnosis and Monitoring” by Rebeca M. Torrente-Rodríguez, Heather Lukas, Jiaobing Tu, Jihong Min, Yiran Yang, Changhao Xu, Harry B. Rossiter and Wei Gao, 1 October 2020, Matter.
Funding for the research was provided by the National Institutes of Health; the Tobacco-Related Disease Research Program, a California state agency focused on reducing tobacco use; the Merkin Institute for Translational Research; and the Translational Research Institute for Space Health.