The technologies use accessible, low-cost materials with high sensitivity and precision
The graphite used in mechanical pencils and conventional cotton swabs are the raw materials for two new rapid test technologies for diagnosing Covid-19. Protected by patents developed in partnership between Unicamp and the University of Pennsylvania (UPenn-USA), they have in common the use of gold nanoparticles covered with the ACE-2 receptor enzyme, the same one that the coronavirus uses to enter the human body . The kits have high sensitivity and use affordable materials, which can facilitate mass, high-frequency testing. They will be useful, above all, in countries with limited resources.
One of the technologies is a electrochemical sensor which uses conventional graphite as a conductive circuit and indicates the presence of the virus by varying electrical current. The other uses the colorimetric technique, in which the color of the cotton swab is changed when the saliva or nasal secretion sample contains SARS-CoV-2 or its variants. “The numbers have shown a decreasing trend in the transmission of the disease, but there is great concern about the emergence of new variants. Our sensors continue to respond to mutations, as the mechanism for the virus to enter the body continues to be the enzyme we use to functionalize the devices”, explains William Reis de Araújo, professor at the Institute of Chemistry at Unicamp, researcher at the Laboratory of Portable Chemical Sensors and Project's coordenador.
The graffiti test for Covid-19
The researchers used 0,7 millimeter mechanical pencil leads in the prototype. Widely used in industry, the material was dipped into a plastic bottle used to collect the sample. The graphite was polished to anchor the gold nanoparticles functionalized with the ACE-2 enzyme. The device showed high sensitivity to the protein spike of the virus, with accuracy equivalent to that of the RT-PCR test. “When the virus interacts with the modified surface of the graphite, it causes a partial obstruction of the sensor, which induces a decrease in the electrical current value. This decrease in electrical signal can be observed both in conventional laboratory equipment and in association with a portable analyzer coupled to a cell phone”, says Araújo.
In an analysis of 100 patients, carried out in partnership with the University of Pennsylvania, the sensor recorded a performance of 100% in saliva samples and 87,4% in samples of secretion from the nose and throat. The device also detected low concentrations of viral load, being able to identify the disease before symptoms appear.
The technology also diagnosed the Alpha variant, identified in the United Kingdom, and did not react to other types of coronavirus not linked to Covid-19, or to the Influenza virus, which causes the flu, indicating selectivity. The estimated cost of the laboratory-scale prototype was 1,5 dollars (about 9 reais), a value that could decrease with large-scale manufacturing by partner companies. The test result is ready in six minutes.
Cotton swab detects the virus by changing color
The other device developed by the Brazilian team in partnership with the UPenn group detects SARS-CoV-2 using a technique known as colorimetric, which does not require any other analysis equipment. This detection test offers results in up to five minutes, with even more attractive features, such as portability and the possibility of application by the patient themselves. “In the colorimetric test, the only instrument used is a cotton swab. It is already prepared for collection with two tubes, one containing the solution of functionalized gold nanoparticles, and the other a rinsing solution. After collecting the sample and dipping the swab in the containers containing the nanoparticles modified by the ACE-2 enzyme, visualization is almost instantaneous and the detector is the human eye itself.” If the virus is present in the sample, it will adhere to the swab modified with ACE-2 enzymes. When immersing it in the solution of nanoparticles functionalized with the same protein, the ACE-2 in the container will also bind to the virus, causing the swab to change color. The final rinsing step prevents false positives. If the individual does not have the virus, the swab will remain white.
For people with visual disorders or difficulties in seeing color tones, the comparison between before and after can be made using cell phone photos, with the colors analyzed using free applications.
William explains that the idea of the diagnostic kit is to indicate whether or not the person is infected in an easy, quick and cheap way, so that they can take prevention and isolation measures as soon as possible. Other information, such as viral load, requires the use of a smartphone with comparative analyzes based on applications downloaded to the device.
The performance of the colorimetric test was 90% in the samples analyzed, equivalent to that of rapid tests sold in pharmacies. The estimated cost of materials used in bench tests was 15 cents (less than one real) per device. More studies will be needed to evaluate the effectiveness in detecting and discriminating the main SARS-CoV-2 variants. If the results are positive, the kits will allow early detection of the virus, which is essential to reduce the spread and transmission of new variants.
To reach the market, diagnostic sensors Graphite CoV e Color CoV they need to undergo new tests required by the FDA, in the United States, and by Anvisa, in Brazil. The process is carried out in partnership between universities and companies or public institutions interested in producing and commercializing the technologies. At Unicamp, the Inova Unicamp Innovation Agency is responsible for this connection between the academic universe and the market.
Original article published on the Inova Unicamp Innovation Agency website.
Image caption: The technologies for Covid-19 diagnostic kits were developed in a new partnership between Unicamp and the University of Pennsylvania and use accessible, low-cost materials with high sensitivity and precision
