Fig. 1: Diagnostics of SARS-CoV-2 variants with MARVE.

A double-stranded DNA probe, the TEprobe, is designed to precisely control the net thermodynamic energy of the strand displacement reaction induced by input RNAs by tuning its terminal forward toehold and reverse toehold sequences. Mutated and wild viral RNAs can be distinguished by the strand displacement reaction on the basis of the thermodynamic energy penalty derived from a single-base-pair mismatch. Recognition of viral RNAs leads to the release of a urease inhibitor metal ion, Ag(I), and thus controls the cleavage of urea and the level of NH₄⁺. Key mutation markers of SARS-CoV-2 variants such as Alpha, Beta, Gamma and Delta are identified and visualized using pH indicators. The diagnosis results are determined and presented to users by smartphone.