Ultrasensitive RNA biosensors for SARS-CoV-2 detection in a simple color and luminescence assay

Chakravarthy, A.; N, A. K.; George, G.; Ranganathan, S.; Shettigar, N.; U, S.; Palakodeti, D.; Gulyani, A.; Ramesh, A.

The COVID-19 pandemic underlines the need for versatile diagnostic strategies. Here, we have designed and developed toehold RNA-based sensors for direct and ultrasensitive SARS-CoV-2 RNA detection. In our assay, isothermal amplification of a fragment of SARS-CoV-2 RNA coupled with activation of our biosensors leads to a conformational switch in the sensor. This leads to translation of a reporter-protein e.g. LacZ or Nano-lantern that is easily detected using color/luminescence. This response can be visualized by the human eye, or a simple cell phone camera as well as quantified using a spectrophotometer/luminometer. By optimizing RNA-amplification and biosensor-design, we have generated a highly-sensitive diagnostic assay; with sensitivity down to attomolar (100 copies of) SARS-CoV-2 RNA. Finally, the biosensor efficiently detects the presence of viral RNA in human patient samples, with clear distinction from samples designated negative for the virus. The biosensor response correlates well with Ct values from RT-qPCR tests and thus presents a powerful and easily accessible strategy for detecting Covid infection.