The Fluorophore-Quencher system is a variation on the same idea that the IRES system was predicated on: use an aptamer as a sensing domain, and something else as an expression platform to signal that the aptamer had bound its target. In the case of the fluorophore-quencher, we synthesized a fluorescent molecule (fluorophore) directly onto the 5’ end of the aptamer, and a biotinylated the 3’ end. From there, we ordered an oligo that was complementary to the 5’ end of the aptamer and had a quencher synthesized onto the end of it. When both oligos were allowed to incubate in a streptavidin plate, the result was the complex in Figure 1 part A, where the sensor is attached to a solid surface, and its fluorescence is quenched. When target ligand is introduced, the aptamer undergoes conformational change as it folds around the ligand. This conformational change sterically displaces the quencher oligo and exposes the fluorophore, thus emitting detectable signal.