Molecular beacons are stem-loop hairpin-structured fluorescence probes with a fluorescent dye at 5' end and a fluorescence quencher at 3' end. When a target complementary sequence is absent, the molecular beacons do not fluoresce, because the formation of the hairpin structure brings the quencher and fluorophore into close proximity, whereby fluorescence is quenched with high efficiency. When a target molecule is present, the hybridization between the target and the loop sequence of the molecular beacon results in the spatial separation of the fluorophore and quencher, which opens the stem-loop structure of molecular beacons to emit fluorescence. Locked nucleic acid is a nucleic acid analogue containing one or more LNA nucleotide monomers with a bicyclic furanose unit locked in an RNA mimicking sugar conformation. It possesses excellent binding affinity to nucleic acid, high biostability and resists to nuclease degradation. Due to the excellent sensitivity and high specificity, the combination of the molecular beacons and locked nucleic acid has aroused wide concern. In this review, we intensively summarize the structure, function, design essentials, current research topics and some important progress. In addition, we also discuss the applications, potential problems and perspective of locked nucleic acid molecular beacons in molecular recognition and bioanalysis.

Contents
1 Introduction
2 Structure and function of molecular beacons
3 Structure and properties of locked nucleic acid
4 Application of LNA in molecular recognition and biomedicine
4.1 LNA antisense
4.2 LNA-modified siRNA (siLNA)
4.3 LNA-modified DNAzyme (LNAzymes)
5 LNA in biotechnology
5.1 LNA primers and PCR
5.2 LNA probes and hybridization
5.3 LNA modification in aptamers
5.4 LNA molecular beacons
6 Design of locked nucleic acid molecular beacons
6.1 Selection of the reporter and quencher
6.2 Hermodynamic aspects
6.3 Balance between selectivity and hybridization rate
6.4 Modification of LNA
7 Applications of LNA-MB in molecular recognition and bioanalysis
7.1 Real time PCR
7.2 mRNA imaging in living cells
7.3 Targeted recognition of microRNA
7.4 Single nucleotide polymorphisms
7.5 Detection of circulating DNA using LNA-MB
8 Conclusion