Molecular beacon probes are a sequence of nucleotides (the building blocks of DNA and RNA) that can be used to fluorescently detect the presence of a specific sequence of DNA or RNA. The molecular beacon is designed so that a small number of nucleotide bases (between 5 and 7) at the sequence terminals are complementary to each other and get paired forming what is called the stem. The formation of the stem creates a loop of the unpaired bases, which is termed the stem-loop or hairpin loop. Finally, at one end of the nucleotide sequence there is a covalently attached fluorophore and a fluorescence quencher at the other end of the sequence.