Researchers at the Renato Archer Information Technology Center (CTI) in Campinas developed two types of portable rapid tests to detect the virus that causes Covid-19 in saliva. The tests use an electrochemical sensor base where a semiconductor material – a zinc oxide nanostructure – detects small fluctuations in electrical signals caused by the presence of Sars-CoV-2.
At the beginning of the pandemic, the group led by Talita Mazon, a researcher at CTI, soon considered adapting the test originally developed for Zika, dengue and other diseases. “We have been working on biosensors with zinc oxide for about five years. We were in the validation phase of the Zika test and thought an adjustment was sufficient. However, we didn’t have the money to buy the antigen and antibodies, and it takes time for companies to be able to produce a monoclonal antibody that leads to tests with the desired specificity, ”explains the researcher.
In the platform used, which is called the immune sensor, antibodies are immobilized in the nanostructure. When they come into contact with virus proteins (antigen), the chemical bond between antibody and antigen creates characteristic changes in electrical signals that are sensed by the semiconductor material and recorded in a graphic on your computer or mobile devices such as cell phones.
However, monoclonal antibodies (produced in the laboratory) have to be imported and result in high costs that are out of reach for researchers at first. Instead of giving up or waiting for the antibodies to arrive, the group took a different route that resulted in an even more interesting, fully national solution that can be stored at room temperature as it does not contain any biological material.
The group developed a test that prints the Sars CoV-2 virus onto a polypropylene base, a polymer that is deposited as a layer on the zinc oxide sensor. The shape and size of the coronavirus are stamped on the polymer, and the material is then washed, which eliminates the virus. When virus particles present in the contaminated saliva fit into this shape, the electrical signals that are detected by zinc oxide also change. It’s as simple as small children’s toys, which require triangles, squares, and circles to be placed in the appropriate places on a plastic base.
“What we measure with a potentiostat connected to a cell phone or laptop is a variation in the electrical signal that, in the absence of the protein or virus, can be larger or smaller than expected. In some diseases, the connection between the antibody and antigen creates a larger electrical current. In Covid tests, this connection and the adaptation of the virus to the polymer have an insulating property that generates less current, ”says Mazon.
Polymer printing was carried out from isolated viruses by the team from the Laboratory for Emerging Viruses at the Campinas State University (LEVE), coordinated by José Luiz Proença Modena. “I met Professor Modena because samples from patients with Zika were donated by LEVE. I saw in a report that he isolated the new coronavirus and asked for the samples in order to try to print the virus on the polymer layer, “recalls Mazon, explaining that there were more searches for the printing of antibodies.
The effectiveness, specificity and sensitivity of the test has already been demonstrated through the use of inactivated viruses. Active virus analyzes must now be carried out in the LEVE facilities with the required level of biosafety. “Although the development of this test is in the early stages, I find the solution very promising in the long run. Not only do they not require refrigeration or import antibodies and antigens, but they can also be very useful with future viruses. In general, one of the first things to do is isolate the virus. As soon as the methodology is established, it is therefore easy to adapt it in the event of a new virus, ”says the head of the research group.
The group also continued development of the immune sensor through a partnership with a startup that imported antigens and antibodies. In this case, the process is further advanced in a phase of validation by checking against the RT-PCR test, which is considered the gold standard for virus detection. This check is carried out on patients in the Hospital das Clínicas de Botucatu. Completion is scheduled for late January and is being forwarded for approval and large-scale production start-up.
The estimated cost for the immune sensor is around R $ 10 per test, which should be even lower for the device with the polymer layer. The studies are carried out in collaboration with the Center for the Development of Functional Materials, supported by the São Paulo Research Foundation (Fapesp).