Detection using a dye and a dye modifier

A reagent composition comprising:

• (a) a light-emitting dye capable of switching from a first conformation to a second conformation, and
• (b) a light-emitting dye modifier that interacts with said dye,
• wherein the first conformation represents a first complex formed between said dye and a nucleic acid, and the second conformation represents a second complex formed between said dye and said light-emitting dye modifier, and
• wherein said light-emitting dye modifier is not covalently bonded to said light-emitting dye, and
• wherein the first complex is optically detectable at a fluorescence emission wavelength in a range from 350 nm to 1200 nm, and the second complex is substantially undetectable at said wavelength, and further wherein the light-emitting dye is substantially non-fluorescent when uncomplexed with said nucleic acid in the absence of said light-emitting dye modifier.