Figure 6.

Fluorescence-based optical aptasensors. Fluorescence intensity-change as increase (A), (signal-on) (B), and decrease (signal-off) (C) formats are shown for fluorescently labeled aptamers. In the intensity-change format, fluorescence depends on target binding to promote conformational changes and subsequent structural reorganization. In “signal-on” and “signal-off” formats (i.e., aptabeacon-based designs), target-induced structural changes dictate liberation/quenching of the fluorescence signal (F: Fluorophore, Q: Quencher).