Coronavirus: fast, cheap and reliable alternative to the PCR test

You feel limp, your throat starts to scratch. Have you just caught a cold, got infected with the flu or have you contracted Corona? To clarify this, a Fraunhofer research group has developed a test chip called the “Pathogen Analyzer,” which combines the speed of antigen testing and the accuracy of PCR testing, reportedly providing reliable results within an hour.

Antigen testing is the fastest way to detect a corona infection so far. You can do it at home or at the citizen testing center. However, these test kits only respond to large amounts of virus proteins and thus only work in advanced infections. They are also more prone to false positive results. PCR tests, on the other hand, are more accurate and have an earlier effect because they can detect already small amounts of genetic material. Their disadvantage, on the other hand, is that they are more expensive and last longer, as it can take up to three days for the result to be available.

The alliance of the Fraunhofer Institute for Production Technology (IPT), the Fraunhofer Institute for Interfacial Engineering and Biotechnology (IGB) and the Fraunhofer Center for Manufacturing Innovation in Boston wants to change that. Similar to PCR testing, their “Pathogen Analyzer,” which they will be showcasing at the Medica fair in mid-November, multiplies the viral genetic material present in the samples for detection.




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However, unlike the PCR, the sample does not need to be heated and then cooled several times in succession. In the so-called LAMP assay, the test is heated up to 62 degrees Celsius only once in a mobile analysis instrument and kept at this temperature. A buffer solution and the high temperature expose the genetic material of the virus and multiply the nucleic acids. “The result is then already available after 20 to 40 minutes,” says Daniel Reibert, project manager and scientist at the Fraunhofer IPT.

To do this, the researchers improved an existing measurement method that was previously flawed. “LAMP has been known for a few years and it has already been used in commercial infection tests,” explains Reibert. With the Abbott ID NOW, there is already a rapid Covid-19 test with this method. However, LAMP assays have often been hypersensitive to date and have too easily given false positive results.

“We were able to solve this problem with a multiplex approach. Instead of running just one or two tests, where a false positive signal naturally introduces a corresponding inaccuracy, we have thousands of points per sample, each of which is considered a individual test work. And so we have a statistically more accurate result,” explains Reibert.

The multiplexing process works in detail as follows: Numerous small hydrogel droplets are printed on the test cassette, which are comparable in size to an antigen rapid test. Experts speak of signal points. The sample is applied to these points, which, as with previous tests, is obtained from a nose and throat swab and transferred to a buffer solution. “Each signal point contains capture molecules that, when irradiated with light, emit fluorescent radiation of a different wavelength once they have captured the correct pathogen,” explains Reibert. The final result is later sent directly to the subjects’ smartphone app.



The test chip is placed in the analyzer after sample application. Here it is heated to 62 degrees Celsius so that the reaction can take place.

(Image: Fraunhofer IPT)

The exact sensitivity and selectivity values ​​for the new test are not yet available, Reibert says. This data indicates what proportion of samples the chip can identify as correct positive and correct negative. That will be published.

The multiplex approach not only increases reliability, but also makes it possible to detect up to twelve different virus types simultaneously with one sample and one chip. “Because we developed the system as a modular system, it can be quickly adapted to new pathogens,” says Reibert. So far, the researchers have implemented four virus detections: for Sars-CoV-2, flu strains A and B, and for a rhinoceros virus, which is a cold virus.

The researchers are already helping to develop the fabrication processes for the test, as mass production would be much cheaper than the cost of PCR tests. The goal is no more than one euro. Depending on the provider, PCR tests cost between 40 and 60 euros. At the peak of the pandemic, this amounted to 90 euros, Reibert says.



Mobile analyzer. Here the rapid test is heated and evaluated, after which the result is made available to the test persons via an app.

(Image: Fraunhofer IPT)

For the test kits themselves, the researchers therefore rely on the existing roll-to-roll method. The individual sample points can then be printed via 3D printing or the established screen printing process.

Another goal is that the test also has to do without an analyzer and must work completely via the smartphone: the light source and camera are already present in the mobile phone and the heating element can be integrated into the test itself. Next, the developers hope that the test can not only be evaluated in central locations such as medical practices or stadiums, but also detect a large number of pathogens at home.




(vsz)

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