Fig. 2. Construction of the three component reactions of SENSR.

a, The ligation reaction. The ligation products were amplified with a pair of PCR primers (LigChk_F and LigChk_R in Supplementary Table 7) and analysed using Bioanalyzer. The ligation reaction occurred only when the promoter probe, reporter probe, SplintR ligase and target RNA were all present. A full-length probe combining the promoter and reporter probes was amplified with the same set of PCR primers and used as a size control, as indicated by the red arrow. The full scan of the Bioanalyzer image is provided in Supplementary Fig. 10a. bp, base pairs. b, The transcription reaction. The ligated mixtures were used as a DNA template to validate transcription. The transcript was obtained only in the presence of target RNA and all other components, demonstrating both target-dependent ligation and subsequent transcription. The red arrow points to the correct size of the transcript. The full scan of the Bioanalyzer image is provided in Supplementary Fig. 10b. nt, nucleotides. c, The aptamer–fluorogenic dye binding reaction. After sequential ligation and transcription reactions, the reaction mixture with the correct size of the transcript produced higher fluorescence compared with other conditions that lacked one of the necessary components. Fluorescence tests were performed as four biological replicates (two-tailed Student’s t-test; ****P < 0.0001; bars represent means ± s.d). RFU, relative fluorescence units.