With proof of principle established, we moved on to the development of probes that would allow measurements in the presence of nucleolytic enzymes in cells and cell lysates (Table ). 2'-OMe modifications were introduced into the backbone. In most cases, the resulting RNA FIT probes provided even higher brightness and higher extents of hybridization-induced fluorescence enhancements than the DNA FIT probes (Table ). To explore the generality of the light harvesting approach we also prepared RNA FIT probes based on thiazole orange nucleotides, which emit in the green spectral region. TO and its recently discovered tricyclic analogue TOtric were combined with AF488 dyes. The excitation maxima of AF488 are blue-shifted by 15-20 nm relative to TO and TOtric. Again, with brightness values up to 99,000 M -1 •cm -1 the presence of the auxiliary dyes ensured high emission intensity of target-bound probes while TO and TOtric retained the ability to quench the emission in the single stranded state. The next step was to investigate the properties of the probes for the detection of small amounts of the target RNA. Increasing amounts of target RNA were added to probes C7-2AF568-QB-OMe and C7-QB-OMe in PBS and the incremental fluorescence increase F-F0 (F0, F, fluorescence intensity at 600 nm in absence and presence of target, respectively) determined. Light-harvesting probe C7-2AF568-QB-OMe afforded a 40 pM limit of detection (LOD) compared to 4 nM with the traditional FIT probe C7-QB-OMe (Fig. ). Next, we evaluated the probes in undiluted cell lysates, which is a challenging matrix due to its high autofluorescence. Plotting the incremental fluorescence increase F-F0 against target concentration showed a larger slope for the light-harvesting FIT probe (Fig. ), which indicates a higher Table : 2'-OMe gapmer FIT-probes in the red (QB) and green (TO, TOtric) fluorescence channels targeted against RNA