In the absence of the target, utilized in the BRET-based assay developed by Cissell et al., the Rluc-probe and the QD-probe hybridize creating a BRET signal. In the presence of the target, there is a competition between the target and the Rluc-probe, decreasing the BRET signal. With kind permission from Springer Science+Business Media: Bioanal Chem, Rapid single-step nucleic acid detection, 319, 2008, 2577, K.A. Cissell, Y. Rahimi, S. Shrestha, E.A. Hunt, and S.K. Deo, fig. 1.