Covid-19 test imbued with nanoparticles promises higher sensitivity

Currently, rapid antigen tests aren’t very sensitive as they can fail to detect early infections with low viral loads.

The new test developed by Newcastle University researchers is more sensitive and works under more extreme conditions than antibody-based tests.

The PCR test remains the “gold standard” for Covid-19 diagnosis but it generally takes 1-2 days to get a result, is expensive and requires special lab equipment and trained personnel.

In contrast, rapid antigen tests are fast (15-30 minutes), and people can take them at home with no training. However, they lack sensitivity, which sometimes results in false negatives.

The tests typically use antibodies against SARS-CoV-2 for detection, which can’t withstand wide ranges of temperature and pH.

The researchers produced nanoMIPs against a small fragment, or peptide, of the SARS-CoV-2 spike protein by creating molecular imprints, or moulds, in the nanoparticles.

These nanoscale binding cavities had a suitable size and shape to recognise and bind the imprinted peptide and, therefore, the entire protein. They attached the nanoparticles that bound most strongly to the peptide to printed electrodes. After showing that the nanoMIPs could bind SARS-CoV-2, they developed a 3D-printed prototype device that detects binding of the virus by measuring changes in temperature.

When the team added samples from seven patient nasopharyngeal swabs to the device, the liquid flowed over the electrode, and the researchers detected a change in temperature for samples that had previously tested positive for Covid-19 via PCR test.

The test required only 15 minutes, and preliminary results indicated that it could detect a 6,000-times lower amount of SARS-CoV-2 than a commercial rapid antigen test.

Unlike antibodies, the nanoMIPs withstood warm temperatures, which could give the test a longer shelf life in hot climates, and acidic pH which might make it useful for monitoring the virus in wastewater and saliva samples.

However, the researchers now need to use their tests on many more patient samples to prove that it has a lower false negative rate than existing rapid antigen tests.

Since the pandemic started, a number of research teams have been focused on developing new forms of diagnostic tests.

Last year, one team of researchers unveiled a less invasive Covid-19 test that uses saliva samples instead of the nasal and throat swabs, while the UK government considered adopting an AI-based test designed to detect the virus via recordings of a user coughing into their smartphone’s microphone.