Explained: FELUDA paper strip test for coronavirus

It uses CRISPR-Cas technology for the detection of genes specific to SARS-CoV-2 virus.

In May, CSIR IGIB and TATA Sons signed an MoU for licensing the knowhow related to development of the FELUDA kit.

Union Health Minister Harsh Vardhan said on Sunday that the rollout of the FELUDA paper strip test for coronavirus is expected in the next few weeks.

He said that tests on over 2000 patients during the trials at the CSIR-Institute of Genomics and Integrative Biology (CSIR-IGIB) and in private labs, showed that the test had 96% sensitivity and 98% specificity.

What is FELUDA?

FELUDA is an acronym for FNCAS9 Editor-Limited Uniform Detection Assay. It uses CRISPR-Cas technology for the detection of genes specific to SARS-CoV-2 virus.

In this method, a protein called FnCas9 and a guide RNA(gRNA) which helps in recognising the viral genes is used.

If the patient sample has the viral gene, this gRNA-FnCas9 complex binds to the gene and using a paper strip this binding can be visualised.

How is the test done?

• The nasopharyngeal swab is collected
• RNA is extracted
• A single step RT-PCR is done
• The FELUDA mix is prepared by incubating the dead FnCas9 protein, guide RNA and the amplified viral DNA
• The dip stick is immersed in the FELUDA mix
• Gold nanoparticle on the strip bind to the FELUDA complex
• A protein called Streptavidin on the test line captures this gold nanoparticle bound-FELUDA complex
• Unbound gold particles are captured on the control line
• Colour develops on the test line and/or control line. One line indicates negative and two lines mean positive.
• The test takes about one to two minutes

Is it better than RT-PCR?

RT- PCR equipment and reagents are costly and a technical expertise is needed.

Dr. Debojyoti Chakraborty, Senior Scientist at CSIR-IGIB writes on his webpage that: “With FELUDA, the need for technical expertise is minimal and no requirement of expensive equipment, making it an easy to perform, point of care test. It thus saves space, time and money.” He is one of the authors of the pre-print shared on bioRxiv that describes the development of FELUDA.

Can I test myself at home?

“We are in the process of developing a Do-it-yourself/at-home detection kit, but at the moment the answer is no and you will have to visit your doctor or testing center to get yourself tested,” Dr. Chakraborty writes on his webpage.

Who is making the FELUDA test kits?

In May, CSIR IGIB and TATA Sons signed an MoU for licensing the knowhow related to development of the kit.

“This innovative ‘Feluda’ test uses cutting-edge CRISPR technology for detection of the genomic sequence of the novel coronavirus. It uses a test protocol that is simple to administer and easy to interpret, enabling results to be made available to the medical fraternity in relatively lesser time as compared to other test protocols,” says Banmali Agrawala, president, Infrastructure and Defence and Aerospace, Tata Sons in a release.