Molecular Beacons 

Molecular beacons
Molecular beacons are the single stranded oligonucleotide probe attached with fluorescence molecule and a quencher. The 15 nucleotides in the middle are complementary to the target sequence where as the sequence towards 5' and 3' end are complementary to one another. When the molecular beacon is free the fluorescence reporter is close to the quencher, as a result the fluorescence is quenched and there is no fluorescence. When molecular beacon binds the target sequence the fluorescence reporter is now free as it moves away from the quencher. Hence the reporter gives fluorescence, indicating binding with the target sequence.