How is Coronavirus testing done using the RT-PCR method? What did IIT Delhi just create?

Viruses are really, really tiny. And they are different from us. We have 2 strands of DNA. (Our genes are carried by the DNA in the form of a type of protein).

Some viruses, on the other hand, have a single strand of genetic material – RNA. (The D in DNA above stands for Di- meaning two. DNA has 2 strands of protein, RNA has only one).

Let’s understand how testing is done for viruses.

The 2 strands that carry all our genes: DNA

Collection and Transport

We collect a sample from the throat or nose of the person because the virus is very likely to be found here. These samples are then carefully transported to the lab. But they must be tested in a batch

(because each batch must have one test tube where the virus is definitely not there, and one where the virus is definitely there. These are called the ‘controls’. Preparing controls for each sample will increase the cost of testing a lot.)

So, they are stored carefully until a batch is ready for testing. (This batching system also means some delay in getting our results. The actual testing takes only about 4 hours).

Amplifying the sample

Each sample or control to be tested is put in a test tube and amplified (made larger and multiplied many times). This process of amplification takes about 90 minutes. An enzyme (a natural chemical) called reverse-transcriptase (RT for short) is added to the sample. This converts a single RNA to DNA, and another enzyme called polymerase amplifies the DNA with the help of a DNA sequence called a ‘primer’. Primers bind DNA and can amplify it.

Testing

The tube also contains a fluorescent dye that makes the amplified DNA ‘glow’. That’s how we know whether the virus is present or not. After about 4 hours, we compare all the tested samples to the 2 control test tubes. The test tubes that match the ‘definitely there’ test tubes are Covid positive, and the others, as you can guess, are Covid negative.