Adopting architectural elements of naturally occurring riboswitches, fluorescent light-up aptamers such as Spinach can be made responsive to the presence of RNA input molecules and also small molecule ligands such as guanine or adenine. In the absence of input triggers, the FLAPs display a very low background fluorescence, making this approach potentially useful for sensing applications:
T. Wang, F. C. Simmel, Switchable fluorescent light-up aptamers based on riboswitch architectures, Angew. Chem. Int. Ed. e202302858 (2023). https://doi.org/10.1002/anie.202302858