Molecular Probes Based on Cyanine Dyes for Nucleic Acid Research

Abstract

The development in the last several years of cyanine dyes as fluorescent labels is reviewed. The dyes are covering the spectrum from the blue to the near infrared region. The non-covalently binding labels have no tluorescence of their own, but a strong fluorescence enhancement is observed in the presence of nucleic acids. Monomeric, homodimerle and heterodimeric cyanine dyes with one to four positive charges are discussed. With the increasing number of positive charges in the dye molecule, the affinity to nucleic acids of such non-covalent labels is also increasing. Cyanine dyes (usually tri-, penta-, and heptamethine cyanines) with large molar absorptivity and high fluorescence quantum yield are suitable as covalent labels. Dyes with amine-reactive groups, such as isothiocyanates or succinimidyl esters, are used for covalent labelling of chemically modified nucleic acids. The efficient energy transfer from the donor cyanine dye to the acceptor fluorescent dye(s) by excitation of the single wavelength in donor-acceptor dye systems results in well separated emission maxima with enhanced fluorescence intensity both in the covalently and non-covalently binding nucleic acid labels.