Molecular beacons are single-stranded oligonucleotide hybridization probes that form a stem-and-loop structure. The loop contains a probe sequence that is complementary to a target sequence, and the stem is formed by the annealing of complementary arm sequences that are located on either side of the probe sequence. A fluorophore is covalently linked to the end of one arm and a quencher is covalently linked to the end of the other arm. Molecular beacons do not fluoresce when they are free in solution. However, when they hybridize to a nucleic acid strand containing a target sequence they undergo a conformational change that enables them to fluoresce brightly.
In the absence of targets, the probe is dark, because the stem places the fluorophore so close to the nonfluorescent quencher that they transiently share electrons, eliminating the ability of the fluorophore to fluoresce. When the probe encounters a target molecule, it forms a probe-target hybrid that is longer and more stable than the stem hybrid. The rigidity and length of the probe-target hybrid precludes the simultaneous existence of the stem hybrid. Consequently, the molecular beacon undergoes a spontaneous conformational reorganization that forces the stem hybrid to dissociate and the fluorophore and the quencher to move away from each other, restoring fluorescence.
click here to read more on molecular beacons
Marras SAE, Tyagi S, Antson D, and Kramer FR (2019) Color-coded molecular beacons for multiplex PCR screening assays. PLoS One 14: e0213906
Vargas DY, Marras SAE, Tyagi S, and Kramer FR (2018) Suppression of Wild-Type Amplification by Selectivity Enhancing Agents in PCR Assays That Utilize SuperSelective Primers for the Detection of Rare Somatic Mutations. The Journal of Molecular Diagnostics, 20, 415-427
Schlachter S, Chan K, Marras SAE, and Parveen N (2017) Detection and differentiation of lyme spirochetes and other tick-borne pathogens from blood using real-time PCR with molecular beacons. Methods in Molecular Biology 1616: 155-170.
Catrina IE, Bayer LV, Yanez G, McLaughlin JM, Malaczek K, Bagaeva E, Marras SAE, and Bratu DP (2016) The temporally controlled expression of Drongo, the fruit fly homolog of AGFG1, is achieved in female germline cells via P-bodies and its localization requires functional Rab11. RNA Biol 13: 1117-1132.