Molecular beacons are increasingly being used in many applications involving nucleic acid detection and quantification. The stem.loop structure of molecular beacons provides a competing reaction for probe.target hybridization that serves to increase probe specificity, which is particularly useful when single-base discrimination is desired. To fully realize the potential of molecular beacons, it is necessary to optimize their structure. Here we report a systematic study of the thermodynamic and kinetic parameters that describe the molecular beacon structure.function relationship. Both probe and stem lengths are shown to have a significant impact on the binding specificity and hybridization kinetic rates of molecular beacons. Specifically, molecular beacons with longer stem lengths have an improved ability to discriminate between targets over a broader range of temperatures. However, this is accompanied by a decrease in the rate of molecular beacon.target hybridization. Molecular beacons with longer probe lengths tend to have lower dissociation constants, increased kinetic rate constants, and decreased specificity. Molecular beacons with very short stems have a lower signal-to-background ratio than molecular beacons with longer stems. These features have significant implications for the design of molecular beacons for various applications.

Reference: Tsourkas et al., "Hybridization kinetics and thermodynamics of molecular beacons", NAR 2003, 31(4): 1319-1330.

The paper is available at http://nar.oupjournals.org/cgi/reprint/31/4/1319

Other interesting papers on the topic can be found at: http://www.molecular-beacons.org