SINGAPORE – A new Covid-19 rapid test that can detect variants of the virus has been developed in Singapore.
It produces results within 30 minutes and can be used directly on patient samples. It is also about 10 times more accurate than rapid antigen tests (ART) currently in use in the country.
The Variant Nucleotide Guard (VaNGuard) test is the first rapid test here to make use of a gene-editing tool known as CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats).
Developed by scientists from Nanyang Technological University (NTU), the VaNGuard test uses a reaction mix containing a specific enzyme that acts like a pair of “molecular scissors”.
The enzyme targets specific segments of the genetic material of Sars-CoV-2 – the virus responsible for Covid-19 – and snips them off the rest of its viral genome. Successfully snipping off these segments is how the enzyme identifies the presence of the virus.
To ensure that variants are not missed, two short genetic sequences – known as guide RNAs – are used to recognise sequences that are extremely similar between the variants but also unique to the virus.
Associate Professor Tan Meng How, who led the study, said on Monday (March 29): “Should these binding regions mutate, a new test can be redesigned in under a week.”
CRISPR technology is traditionally used in scientific research to alter DNA sequences, giving it the potential to cure – and not just treat – any disease caused by DNA differences.
Currently, ARTs that detect proteins called antigens on the surface of the virus are used in Singapore. Should a mutation affect the viral antigen, some ARTs may be ineffective.
Redesigning an ART takes longer because the test relies on antibodies and the redesigning of an antibody requires more time, Prof Tan added.
Several strains of the Sars-CoV-2 have been identified globally, such as Britain’s B117 strain, the Brazilian P1 variant and South Africa’s B1351 variant.
Prof Tan, who is from NTU’s School of Chemical and Biomedical Engineering, said the new test would likely cost slightly less than a traditional ART when sold in the market.
“Polymerase chain reaction (PCR) tests – the gold standard for testing – can detect extremely low viral loads of around five copies of the viral RNA per reaction. The limit of our test is around 50 RNA copies,” he said.
To make the test easier to use once it has been approved, it has been integrated into a specially treated paper strip that looks similar to a pregnancy test.
The paper strip is then dipped into a swab sample and the reaction mixture. In the presence of the Sars-CoV-2 virus or its variant, two bands will appear. Otherwise, only one band will appear.
Since August 2020, the NTU team has been working with a local hospital to obtain clinical samples that they can use the new test kit on. The scientists hope to obtain more samples to further refine their test and eventually develop a kit that can identify the specific variant and not simply detect the presence of viral strains in general.
The project was started in January 2020 and the team hopes to obtain regulatory approval this year.
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