Fig. 1.

a The changes in the fluorescence signal of 115 different fluorogenic substrates presence of 10⁸ pfu/mL at 37 °C. b The FRET substrates with significant increase in the fluorescence signal upon incubation with 10⁸ pfu/mL of Covid-19 viral particles at 37 °C. The dotted line represents the threshold fluorescence. The samples were excited at 485 nm and the fluorescence was observed at 535 nm